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20192274 | Functional characterization and high-throughput proteomic analysis of interrupted genes in the archaeon Sulfolobus solfataricus. | Sequenced genomes often reveal interrupted coding sequences plicate the annotation process and the subsequent functional characterization of the genes. In the past, interrupted genes were generally considered to be the result of sequencing errors or pseudogenes, that is, gene remnants with little or no biological importance. However, recent lines of evidence support the hypothesis that these coding sequences can be functional; thus, it is crucial to understand whether interrupted genes are expressed in vivo. We addressed this issue by experimentally demonstrating the existence of functional disrupted genes in archaeal genomes. We discovered previously unknown disrupted genes that have interrupted homologues in distantly related species of archaea. bination of a RT-PCR strategy with shotgun proteomics demonstrates that interrupted genes in the archaeon Sulfolobus solfataricus are expressed in vivo. In addition, the sequence of the peptides determined by LCMSMS and experiments of in vitro translation allows us to identify a gene expressed by programmed -1 frameshifting. Our findings will enable an accurate reinterpretation of archaeal interrupted genes shedding light on their function and on archaeal genome evolution. |
20192271 | Characterization of recombinant lysyl oxidase propeptide. | Lysyl oxidase enzyme activity is critical for the biosynthesis of mature and functional collagens and elastin. In addition, lysyl oxidase has tumor suppressor activity that has been shown to depend on the propeptide region (LOX-PP) derived from pro-lysyl oxidase (Pro-LOX) and not on lysyl oxidase enzyme activity. Pro-LOX is secreted as a 50 kDa proenzyme and then undergoes biosynthetic proteolytic processing to active approximately 30 kDa LOX enzyme and LOX-PP. The present study reports the efficient binant expression and purification of rat LOX-PP. Moreover, using enzymatic deglycosylation and DTT bined with mass spectrometry technologies, it is shown for the first time that rLOX-PP and naturally occurring LOX-PP contain both N- and O-linked carbohydrates. Structure predictions furthermore suggest that LOX-PP is a mostly disordered protein, which was experimentally confirmed in circular dichroism studies. Due to its high isoelectric point and its disordered structure, we propose that LOX-PP can associate with extracellular and intracellular binding partners to affect its known biological activities as a tumor suppressor and inhibitor of cell proliferation. |
20192276 | Effect of phosphorylation in the motor domain of human myosin IIIA on its ATP hydrolysis cycle. | Previous findings suggested that the motor activity of human myosin IIIA (HM3A) is influenced by phosphorylation [Kambara, T., et al. (2006) J. Biol. Chem. 281, 37291-37301]; however, how phosphorylation controls the motor activity of HM3A is obscure. In this study, we clarify the kinetic basis of the effect of phosphorylation on the ATP hydrolysis cycle of the motor domain of HM3A (huM3AMD). The affinity of human myosin IIIA for filamentous actin in the presence of ATP is more than 100-fold decreased by phosphorylation, while the maximum rate of ATP turnover is virtually unchanged. The rate of release of ADP from acto-phosphorylated huM3AMD is 6-fold greater than the overall cycle rate, and thus not a rate-determining step. The rate constant of the ATP hydrolysis step of the actin-dissociated form is markedly increased by phosphorylation by 30-fold. The dissociation constant for dissociation of the ATP-bound form of huM3AMD from actin is greatly increased by phosphorylation, and this result agrees well with the significant increase in the K(actin) value of the steady-state ATPase reaction. The rate constant of the P(i) off step is greater than 60 s(-1), suggesting that this step does not limit the overall ATP hydrolysis cycle rate. Our kinetic model indicates that phosphorylation induces the dissociation of huM3AMD from actin during the ATP hydrolysis cycle, and this is due to the phosphorylation-dependent marked decrease in the affinity of huM3AMD.ATP for actin and the increase in the ATP hydrolysis rate of huM3AMD in the actin-dissociated state. These results suggest that the phosphorylation of myosin IIIA significantly lowers the duty ratio, which may influence the cargo transporting ability of the native form of myosin IIIA that contains the ATP-independent actin binding site in the tail. |
20192277 | Molecular diversification of peptide toxins from the tarantula Haplopelma hainanum (Ornithoctonus hainana) venom based on transcriptomic, peptidomic, and genomic analyses. | The tarantula Haplopelma hainanum (Ornithoctonus hainana) is a very venomous spider found widely in the hilly areas of Hainan province in southern China. Its venom contains a variety of ponents with different pharmacological properties. In the present study, we used a venomic strategy for high-throughput identification of tarantula-venom peptides from H. hainanum. This strategy includes three different approaches: (i) transcriptomics, that is, EST-based cloning and PCR-based cloning plus DNA sequencing; (ii) peptidomics, that is, off-line multiple dimensional liquid chromatography coupled with mass spectrometry (MDLC-MS) plus peptide sequencing (direct Edman sequencing and bottom-up mass spectrometric sequencing); (iii) genomics, that is, genomic DNA cloning plus DNA sequencing. About 420 peptide toxins were detected by mass spectrometry, and 272 peptide precursors were deduced from cDNA and genomic DNA sequences. After redundancy removal, 192 mature sequences were identified by three approaches. This is the largest number of peptide toxin sequences identified from a spider species so far. On the basis of precursor sequence identity, peptide toxins from the tarantula H. hainanum venom can be classified into 11 superfamilies (and related families). Our results revealed that gene duplication and focal hypermutation may be responsible for the enormous molecular diversity in spider peptide toxins. The current work is an initial overview for the study of tarantula-venom peptides in parallel transcriptomic, peptidomic, and genomic analyses. It is hoped that this work will also provide an effective guide for high-throughput identification of peptide toxins from other spider species, especially tarantula species. |
20192275 | The synthesis of a c(RGDyK) targeted SN38 prodrug with an indolequinone structure for bioreductive drug release. | Preparation of a novel c(RGDyK) targeted SN38 prodrug incorporating an indolequinone structure for bioreductively triggered drug release is described. This design yields a prodrug that targets surface molecules on tumor cells (alpha(v)beta(3) integrins) and releases drug under bioreductive conditions. There are three moieties in the prodrug design, namely a therapeutic drug SN38, an indolequinone structure serving as a drug releasing trigger, and an alpha(v)beta(3) integrin targeting peptide c(RGDyK). Preliminary studies showed that SN38 is released in the presence of a bioreductive enzyme (DT-diaphorase). |
20192281 | Communications: A nonperturbative quantum master equation approach to charge carrier transport in organic molecular crystals. | We present a nonperturbative quantum master equation to investigate charge carrier transport in organic molecular crystals based on the Liouville space hierarchical equations of motion method, which extends the previous stochastic Liouville equation and generalized master equation methods to a full quantum treatment of the electron-phonon coupling. Diffusive motion of charge carriers in a one-dimensional model in the presence of nonlocal electron-phonon coupling was studied, and two different charge carrier diffusion mechanisms are observed for large and small average intermolecular couplings. The new method can also find applications in calculating spectra and energy transfer in various types of quantum aggregates where the perturbative treatments fail. |
20192280 | Pharmacokinetics, safety and tolerability of single and multiple oral doses of aliskiren in healthy Chinese subjects: a randomized, single-blind, parallel-group, placebo-controlled study. | Aliskiren is the first oral direct renin inhibitor to be approved for the treatment of hypertension. The pharmacokinetic and pharmacodynamic profile of aliskiren has been extensively characterized in Caucasian individuals; however, drug disposition, treatment response and tolerability can vary among ethnic groups, and these variations are difficult to predict. |
20192282 | Communications: Adsorption of element 112 on the gold surface: many-body wave function versus density functional theory. | The applicability of the relativistic density functional theory (RDFT) with conventional generalized gradient and hybrid exchange-correlation functionals to the description of the interactions of element 112 (Cn) and its lighter homolog Hg with a gold surface is assessed. parison of Cn-Au (Hg-Au) bond properties for two simple models of plexes on Au(111) surface obtained by RDFT and accurate many-body calculations indicates a strong underestimation of binding energies by conventional RDFT schemes. This effect provides a possible explanation of the discrepancies between the RDFT-based theoretical and experimental data concerning the thermochromatographic registration of the alpha-decay chain element 114-->Cn. |
20192279 | Agomelatine in the treatment of major depressive disorder: potential for clinical effectiveness. | To demonstrate the clinical effectiveness of an antidepressant drug requires evidence beyond short- and long-term efficacy, including a favourable adverse-effect profile and sustained treatment adherence. Under these conditions, patients should experience enhanced social and functional es. The novel antidepressant agomelatine, a melatonergic MT(1)/MT(2) receptor agonist with serotonin 5-HT(2C) receptor antagonist activity, displays antidepressant efficacy with a favourable adverse-effect profile that is associated with good patient adherence. Specifically, agomelatine has demonstrated significant short-term (6-8 weeks) and sustained (6 months) antidepressant efficacy relative to placebo, as well as evidence of relapse prevention (up to 10 months). In parative studies with venlafaxine and sertraline, there was evidence of early (at 1-2 weeks) and sustained (at 6 months) advantages for agomelatine. In addition to evidence of early efficacy, agomelatine also restored disturbed sleep-wake patterns early in treatment. There was no evidence of antidepressant-induced sexual dysfunction, weight gain or discontinuation-emergent symptoms. Agomelatine has demonstrated a range of properties that suggest it could offer advantages over current treatments for major depressive disorder, although parative trials are still required, as is evidence from real-world clinical practice. |
20192284 | Efficient computation of free energy of crystal phases due to external potentials by error-biased Bennett acceptance ratio method. | Free energy of crystal phases monly evaluated by thermodynamic integration along a reversible path that involves an external potential. However, this method suffers from the hysteresis caused by the differences in the center of mass position of the crystal phase in the presence and absence of the external potential. To alleviate this hysteresis, a constraint on the translational degrees of freedom of the crystal phase is imposed along the path and subsequently a correction term is added to the free energy to account for such a constraint. The estimation of the correction term is putationally expensive. In this work, we propose a new methodology, termed as error-biased Bennett acceptance ratio method, which effectively solves this problem without the need to impose any constraint. This method is simple to implement and it does not require any modification to the path. We show the applicability of this method in putation of crystal-melt interfacial energy by cleaving wall method [R. L. Davidchack and B. B. Laird, J. Chem. Phys. 118, 7651 (2003)] and bulk crystal-melt free energy difference by constrained fluid lambda-integration method [G. Grochola, J. Chem. Phys. 120, 2122 (2004)] for a model potential of silicon. |
20192285 | Electronic excitation energies in solution at equation of motion CCSD level within a state specific polarizable continuum model approach. | We present a study of excitation energies in solution at the equation of motion coupled cluster singles and doubles (EOM-CCSD) level of theory. The solvent effect is introduced with a state specific polarizable continuum model (PCM), where the solute-solvent interaction is specific for the state of interest. Three definitions of the excited state one-particle density matrix (1PDM) are tested in order to gain information for the development of an integrated EOM-CCSD/PCM method. The calculations show the accuracy of this approach for putation of such property in solution. Solvent shifts between nonpolar and polar solvents are in good agreement with experiment for the test cases. pletely unrelaxed 1PDM is shown to be a balanced choice putational effort and accuracy for vertical excitation energies, whereas the response of the ground state CCSD amplitudes and of the molecular orbitals is important for other properties, as for instance the dipole moment. |
20192283 | Communications: Development and characterization of a source of rotationally cold, enriched para-H3+. | In an effort to develop a source of H(3)(+) that is almost entirely in a single quantum state (J=K=1), we have successfully generated a plasma that is enriched to approximately 83% in para-H(3)(+) at a rotational temperature of 80 K. This enrichment is a result of the nuclear spin selection rules at work in hydrogenic plasmas, which dictate that only para-H(3)(+) will form from para-H(2), and that para-H(3)(+) can be converted to ortho-H(3)(+) by subsequent reaction with H(2). This is the first experimental study in which the H(2) and H(3) (+) nuclear spin selection rules have been observed at cold temperatures. The ions were produced from a pulsed solenoid valve source, cooled by supersonic expansion, and interrogated via continuous-wave cavity ringdown spectroscopy. |
20192286 | Quantum dynamics of the H+CH4-->H2+CH3 reaction in curvilinear coordinates: full-dimensional and reduced dimensional calculations of reaction rates. | Full-dimensional quantum dynamics calculations for the H+CH(4)-->H(2)+CH(3) reaction using curvilinear coordinates are presented. A curvilinear coordinate system to describe reactions of the type X+YCH(3)-->XY+CH(3) is developed which facilitates efficient calculations using the multiconfigurational time-dependent Hartree (MCTDH) approach. To describe the bending motion of the X and Y atoms relative to the axis defined by the CH(3) fragment, coordinates based on stereographic projection are introduced. These coordinates yield a kinetic energy operator free of singularities within the dynamically relevant region. Employing this curvilinear coordinate system, full-dimensional and reduced dimensional MCTDH calculations study the cumulative reaction probability (for J=0) and the thermal rate constant for the H+CH(4) reaction on the Jordan-Gilbert potential energy surface [J. Chem. Phys. 102, 5669 (1995)]. The full-dimensional results agree very well with previous full-dimensional MCTDH results which used transition state based normal coordinates. The results of our eight-dimensional (8D) calculations are in reasonable agreement with the full-dimensional ones. They deviate significantly from older 8D results of Zhang et al. [J. Chem. Phys. 127, 234213 (2007)] but agree well with more recent results from the same group. |
20192287 | Identifying and correcting non-Markov states in peptide conformational dynamics. | Conformational transitions in proteins define their biological activity and can be investigated in detail using the Markov state model. The fundamental assumption on the transitions between the states, their Markov property, is critical in this framework. We test this assumption by analyzing the transitions obtained directly from the dynamics of a molecular dynamics simulated peptide valine-proline-alanine-leucine and states defined phenomenologically using clustering in dihedral space. We find that the transitions are Markovian at the time scale of approximately 50 ps and longer. However, at the time scale of 30-40 ps the dynamics loses its Markov property. Our methodology reveals the mechanism that leads to non-Markov behavior. It also provides a way of regrouping the conformations into new states that now possess the required Markov property of their dynamics. |
20192288 | Size consistency of explicit functionals of the natural orbitals in reduced density matrix functional theory. | We report a size-inconsistency problem for several functionals within reduced density matrix functional theory. Being explicit functionals of the natural orbitals and occupation numbers, instead of the one-body reduced density matrix, many of the approximate functionals are not invariant under unitary transformations in the subspace of degenerate occupation numbers. One such transformation mixes the degenerate natural orbitals of identical independent subsystems, delocalizing them. Noninvariance under this transformation results in size inconsistency for some of the approximations while others avoid this pathology by favoring orbital localization. |
20192289 | Møller-Plesset perturbation theory gradient in the generalized hybrid orbital quantum mechanical and molecular mechanical method. | An analytic gradient expression is formulated and implemented for the second-order Møller-Plesset perturbation theory (MP2) based on the generalized hybrid orbital QM/MM method. The method enables us to obtain an accurate geometry at a putational cost. The performance of the method is assessed for various isomers of alanine dipepetide. We pare the optimized structures of fumaramide-derived [2]rotaxane and cAMP-dependent protein kinase with experiment. |
20192291 | Statistics of tethered self-avoiding chains under spherical confinement and an external force. | pute the partition function of self-avoiding chains tethered inside a confining sphere using Monte Carlo simulations on a three-dimensional lattice. Two cases are considered: (i) single-tethered chains with one end anchored and one end free and (ii) double-tethered chains where both ends are tethered at a distance equal to the diameter of the sphere. The self-avoidance, confinement, and tethering constraints dramatically decrease the number of allowed configurations pared with an unconstrained random coil, thereby affecting the sampling method used in the Monte Carlo procedure. The effect of an external applied force and the bias it introduces in the partition function are also investigated. Our method involves a position of the partition function into the product of several terms that can be evaluated independently. For short chains, we demonstrate the validity of our approach through a direct evaluation of the partition function using an exact enumeration of the appropriate paths on the lattice. In the case of long chains, scaling laws for the behavior of the partition function are identified. |
20192292 | Gradient-based multiconfiguration Shepard interpolation for generating potential energy surfaces for polyatomic reactions. | This paper describes and illustrates a way to construct multidimensional representations of reactive potential energy surfaces (PESs) by a multiconfiguration Shepard interpolation (MCSI) method based only on gradient information, that is, without using any Hessian information from electronic structure calculations. MCSI, which is called multiconfiguration molecular mechanics (MCMM) in previous articles, is a semiautomated method designed for constructing full-dimensional PESs for subsequent dynamics calculations (classical trajectories, full quantum dynamics, or variational transition state theory with multidimensional tunneling). The MCSI method is based on Shepard interpolation of Taylor series expansions of the coupling term of a 2 x 2 electronically diabatic Hamiltonian matrix with the diagonal elements representing nonreactive analytical PESs for reactants and products. In contrast to the previously developed method, these expansions are truncated in the present version at the first order, and, therefore, no input of electronic structure Hessians is required. The accuracy of the interpolated energies is evaluated for two test reactions, namely, the reaction OH+H(2)-->H(2)O+H and the hydrogen atom abstraction from a model of alpha-tocopherol by methyl radical. The latter reaction involves 38 atoms and a 108-dimensional PES. The mean unsigned errors averaged over a wide range of representative nuclear configurations (corresponding to an energy range of 19.5 kcal/mol in the former case and 32 kcal/mol in the latter) are found to be within 1 kcal/mol for both reactions, based on 13 gradients in one case and 11 in the other. The gradient-based MCMM method can be applied for efficient representations of multidimensional PESs in cases where analytical electronic structure Hessians are too expensive or unavailable, and it provides new opportunities to employ high-level electronic structure calculations for dynamics at an affordable cost. |
20192290 | A smoothing monotonic convergent optimal control algorithm for nuclear magnetic resonance pulse sequence design. | The past decade has demonstrated increasing interests in using optimal control based methods within coherent quantum controllable systems. The versatility of such methods has been demonstrated with particular elegance within nuclear magnetic resonance (NMR) where natural separation between coherent and dissipative spin dynamics processes has enabled coherent quantum control over long periods of time to shape the experiment to almost ideal adoption to the spin system and external manipulations. This has led to new design principles as well as powerful new experimental methods within magnetic resonance imaging, liquid-state and solid-state NMR spectroscopy. For this development to continue and expand, it is crucially important to constantly improve the underlying numerical algorithms to provide numerical solutions which are patible with implementation on current instrumentation and at same time are numerically stable and offer fast monotonic convergence toward the target. Addressing such aims, we here present a smoothing monotonically convergent algorithm for pulse sequence design in magnetic resonance which with improved optimization stability lead to smooth pulse sequence easier to implement experimentally and potentially understand within the analytical framework of modern NMR spectroscopy. |
20192293 | Localized Hartree product treatment of multiple protons in the nuclear-electronic orbital framework. | An approximation for treating multiple quantum nuclei within the nuclear-electronic orbital (NEO) framework for molecular systems is presented. In the approximation to NEO-Hartree-Fock, the nuclear wave function is represented by a Hartree product rather than a Slater determinant, corresponding to the neglect of the nuclear exchange interactions. In the approximation to NEO-density functional theory, the nuclear exchange-correlation functional is chosen to be the diagonal nuclear exchange interaction terms, thereby eliminating the nuclear self-interaction terms. To further enhance the simplicity putational efficiency, the nuclear molecular orbitals or Kohn-Sham orbitals are expanded in terms of localized nuclear basis sets. These approximations are valid because of the inherent localization of the nuclear orbitals and the numerical insignificance of the nuclear exchange interactions in molecular systems. Moreover, these approximations lead to putational savings due to the reduction in both the number of integrals that must be calculated and the size of the matrices that must be diagonalized. These nuclear Hartree product approximation (HPA) methods scale linearly with the number of quantum protons and are highly parallelizable. Applications to a water hexamer, glycine dimer, and 32-water cluster, where all hydrogen nuclei are treated quantum mechanically, illustrate the accuracy putational efficiency of the nuclear HPA methods. These strategies will facilitate the implementation of explicitly correlated NEO methods for molecular systems with multiple quantum protons. |
20192294 | Compatibility between shape equation and boundary conditions of lipid membranes with free edges. | Only some special open surfaces satisfying the shape equation of lipid membranes can patible with the boundary conditions. As a result of patibility, the first integral of the shape equation should vanish for axisymmetric lipid membranes, from which two theorems of nonexistence are verified: (i) there is no axisymmetric open membrane being a part of torus satisfying the shape equation; (ii) there is no axisymmetric open membrane being a part of a biconcave discodal surface satisfying the shape equation. Additionally, the shape equation is reduced to a second-order differential equation while the boundary conditions are reduced to two equations due to patibility. Numerical solutions to the reduced shape equation and boundary conditions agree well with the experimental data [A. Saitoh et al., Proc. Natl. Acad. Sci. U.S.A. 95, 1026 (1998)]. |
20192295 | Extraction of state-to-state reactive scattering attributes from wave packet in reactant Jacobi coordinates. | The S-matrix for a scattering system provides the most detailed information about the dynamics. In this work, we discuss the calculation of S-matrix elements for the A+BC-->AB+C, AC+B type reaction. Two methods for extracting S-matrix elements from a single wave packet in reactant Jacobi coordinates are reviewed pared. Both methods are capable of extracting the state-to-state attributes for both product channels from a single wave packet propagation. It is shown through the examples of H+HD, Cl+H(2), and H+HCl reactions that such reactant coordinate based methods are easy to implement, numerically efficient, and accurate. Additional efficiency can be gained by the use of a L-shaped grid with two-dimensional fast Fourier transform. |
20192296 | Search for Br* production in the D+DBr reaction. | Deuterium bromide (DBr) is expanded from a pulsed jet into a vacuum and a synchronized pulsed laser causes photodissociation of some of the DBr molecules to produce primarily (approximately 85%) ground-state bromine atoms ((2)P(3/2)) and fast D atoms. The latter collide with the cold DBr molecules and react to produce molecular deuterium (D(2)) via two possible channels, the adiabatic channel D(2)+Br((2)P(3/2)) and the nonadiabatic channel D(2)+Br*((2)P(1/2)), which are asymptotically separated in energy by the spin-orbit splitting (0.457 eV) of the bromine atom. Ion images are recorded for D(2)(v'=1, J'=16, 18-21), D(2)(v'=2, J'=6,7, 10-12, 14-16), and D(2)(v'=3, J'=2-5) for various collision energies. For the nonadiabatic production of spin-orbit-excited Br* in the D+DBr reaction for the conditions studied we estimate that this channel contributes 1% or less. |
20192297 | Valence ionized states of iron pentacarbonyl and eta5-cyclopentadienyl cobalt dicarbonyl studied by symmetry-adapted cluster-configuration interaction calculation and collision-energy resolved Penning ionization electron spectroscopy. | Valence ionized states of iron pentacarbonyl Fe(CO)(5) and eta(5)-cyclopentadienyl cobalt dicarbonyl Co(eta(5)-C(5)H(5))(CO)(2) have been studied by ultraviolet photoelectron spectroscopy, two-dimensional Penning ionization electron spectroscopy (2D-PIES), and symmetry-adapted cluster-configuration interaction calculations. Theory provided reliable assignments for plex ionization spectra of these molecules, which have metal-carbonyl bonds. Theoretical ionization energies agreed well with experimental observations and the calculated wave functions could explain the relative intensities of PIES spectra. The collision-energy dependence of partial ionization cross sections (CEDPICS) was obtained by 2D-PIES. To interpret these CEDPICS, the interaction potentials between the molecules and a Li atom were examined in several coordinates by calculations. The relation between the slope of the CEDPICS and the electronic structure of the ionized states, such as molecular symmetry and the spatial distribution of ionizing orbitals, was analyzed. In Fe(CO)(5), an attractive interaction was obtained for the equatorial CO, while the interaction for the axial CO direction was repulsive. For Co(eta(5)-C(5)H(5))(CO)(2), the interaction potential in the direction of both Co-C-O and Co-Cp ring was attractive. These anisotropic interactions and ionizing orbital distributions consistently explain the relative slopes of the CEDPICS. |
20192278 | The safety and tolerability of newer antiepileptic drugs in children and adolescents. | The newer antiepileptic drugs (AEDs) provide more therapeutic options and overall improved safety and tolerability for patients. To provide the best care, physicians must be familiar with the latest tolerability and safety data. This is particularly true in children, given there are relatively fewer studies examining the effects of AEDs in pared with adults. Since we now have significant paediatric literature on each of these agents, we provide prehensive and current literature review of the newer AEDs, focusing on safety and tolerability data in children and adolescents. Because the safety profiles in children differ from those in adults, familiarity with this literature is important for child neurologists and other paediatric caregivers. We have organized the data by organ system for each AED for easier reference. |
20192298 | On the nature of B-Ccarbene bonding in a stable neutral diborene. | We report the bonding interactions within [R(H)B=B(H)] and [R] (R=:C(NHCH)(2)) as a ligand in a newly synthesized stable neutral diborene. By using theoretical analyses, we have found the nature of the B-C(carbene) bonding, and, more importantly, the key to realize multiple bonds for chemical elements. With character of almost equal covalency and ionicity, the stabilizing orbital interaction term, DeltaE(orb), of B-C(carbene), is mainly given by sigma-symmetry orbital interactions; the donor-acceptor interaction is weak and contributes small to DeltaE(orb). In the weak donor-acceptor interaction, the B-->C(carbene) pi backdonation is stronger than the B<--C(carbene) sigma donation. Thus, in effect, the bond emerges in the B(delta+)-C(carbene)(delta-) dipole. Inspection of the correlation lines of the orbital correlation diagram for the B-C(carbene) bonding indicates that the strength of the bonding orbitals in the central BB unit is weakened due to the coordination of the carbenes, and the center is unstabilized by the carbene ligand. This is contrary to the conventional view on the mechanism of coordination and the Dewar-Chatt-Duncanson model. However this unstabilizing effect should be responsible for the stability of the B=B double bond in the stable neutral diborene. This is because the very short bond lengths arising from multiple bonds will lead to a very strong Pauli repulsion, and, ultimately, destruction of chemical bonds. It can therefore be concluded that, actually, to prevent the very short bond lengths is the true reason for the successful realization of multiple bonds for main-group elements such as boron. |
20192299 | The HOOH UV spectrum: importance of the transition dipole moment and torsional motion from semiclassical calculations on an ab initio potential energy surface. | The absorption cross section of HOOH, a starting point for larger ROOH, was calculated using the "Wigner method." Calculations use the Wigner transform of ground state wave functions and classical approximations for excited state wave functions. Potential energy and transition dipole moment surfaces were calculated using the equation-of-motion coupled-cluster singles and doubles method over an extended Franck-Condon region. The first two O-O stretches and the first five HOOH torsional levels are included. This study also addresses two fundamental questions about ROOH photodissociation. The long wavelength A(1)A:B(1)B excited state preference has been measured from dynamics experiments, but a Franck-Condon overlap explanation has not been directly verified. A moderate barrier to HOOH torsional motion and excited state dynamics affect the temperature dependence in the UV spectrum. Based on these initial findings for HOOH, photodissociation of large ROOH cannot be eliminated as an important factor for ozone and particulate matter production seen in both ambient and laboratory studies. |
20192300 | Seven-degree-of-freedom, quantum scattering dynamics study of the H2D+ + H2 reaction. | A quantum scattering dynamics, time-dependent wavepacket propagation method is applied to study the reaction of H(2)D(+)+H(2)-->H(3)(+)+HD on the Xie-Braams-Bowman potential energy surface. The reduced-dimensional, seven-degree-of-freedom approach is employed in this calculation by fixing one Jacobi and one torsion angle related to H(2)D(+) at the lowest saddle point geometry of D(2d) on the potential energy surface. Initial state selected reaction probabilities are presented for various initial rovibrational states. The ground state reaction probability shows no threshold for this reaction, in other words, this reaction can occur without an activation barrier. The vibrational excitation shows that the stretching motion of H(+)-HD only has a small effect on the reaction probability; the vibrational excitation of HD in H(2)D(+) hinders the reactivity. By contrast, rotational excitation of H(+)-HD greatly enhances the reactivity with the reaction probability increased double or triple at high rotational pared to the ground state. Reactive resonances, seen in all the initial state selected reaction probabilities, are also found in the integral cross section for the ground state of H(2)D(+) and H(2). The thermal rate coefficient is also calculated and is found to be in semiquantitative agreement with experiment; however, quantum scattering approaches including more degrees of freedom, especially including all the angles, are necessary to study this reaction in the future. |
20192301 | Probing the oxygen environment in UO(2)(2+) by solid-state 17O nuclear magnetic resonance spectroscopy and relativistic density functional calculations. | bined theoretical and solid-state (17)O nuclear magnetic resonance (NMR) study of the electronic structure of the uranyl ion UO(2)(2+) in (NH(4))(4)UO(2)(CO(3))(3) and rutherfordine (UO(2)CO(3)) is presented, the former representing a system with a hydrogen-bonding environment around the uranyl oxygens and the latter exemplifying a uranyl environment without hydrogens. Relativistic density functional calculations reveal unique features of the U-O covalent bond, including the finding of (17)O chemical shift anisotropies that are among the largest for oxygen ever reported (>1200 ppm). Computational results for the oxygen electric field gradient tensor are found to be consistently larger in magnitude than experimental solid-state (17)O NMR measurements in a 7.05 T magnetic field indicate. A modified version of the Solomon theory of the two-spin echo amplitude for a spin-5/2 nucleus is developed and applied to the analysis of the (17)O echo signal of U (17)O(2)(2+). |
20192303 | Matrix isolation and computational study of isodifluorodibromomethane (F2CBr-Br): a route to Br2 formation in CF2Br2 photolysis. | The photolysis products of dibromodifluoromethane (CF(2)Br(2)) were characterized by matrix isolation infrared and UV/Visible spectroscopy, supported by ab initio calculations. Photolysis at wavelengths of 240 and 266 nm of CF(2)Br(2):Ar samples (approximately 1:5000) held at approximately 5 K yielded iso-CF(2)Br(2) (F(2)CBrBr), a weakly bound isomer of CF(2)Br(2), which is characterized here for the first time. The observed infrared and UV/Visible absorptions of iso-CF(2)Br(2) are in excellent agreement putational predictions at the B3LYP/aug-cc-pVTZ level. Single point energy calculations at the CCSD(T)/aug-cc-pVDZ level on the B3LYP optimized geometries suggest that the isoform is a minimum on the CF(2)Br(2) potential energy surface, lying some 55 kcal/mol above the CF(2)Br(2) ground state. The energies of various stationary points on the CF(2)Br(2) potential energy surface were putationally; taken with our experimental results, these show that iso-CF(2)Br(2) is an intermediate in the Br+CF(2)Br-->CF(2)+Br(2) reaction. The photochemistry of the isoform was also investigated; excitation into the intense 359 nm absorption band resulted in isomerization to CF(2)Br(2). Our results are discussed in view of the rich literature on the gas-phase photochemistry of CF(2)Br(2), particularly with respect to the existence of a roaming atom pathway leading to molecular products. |
20192302 | Mesoscopic nonequilibrium thermodynamics approach to non-Debye dielectric relaxation. | Mesoscopic nonequilibrium thermodynamics is used to formulate a model describing nonhomogeneous and non-Debye dielectric relaxation. The model is presented in terms of a Fokker-Planck equation for the probability distribution of noninteracting polar molecules in contact with a heat bath and in the presence of an external time-dependent electric field. Memory effects are introduced in the Fokker-Planck description through integral relations containing memory kernels, which in turn are used to establish a connection with fractional Fokker-Planck descriptions. The model is developed in terms of the evolution equations for the first two moments of the distribution function. These equations are solved by following a perturbative method from which the expressions for plex susceptibilities are obtained as a function of the frequency and the wave number. Different memory kernels are considered and used pare with experiments of dielectric relaxation in glassy systems. For the case of Cole-Cole relaxation, we infer the distribution of relaxation times and its relation with an effective distribution of dipolar moments that can be attributed to different segmental motions of the polymer chains in a melt. |
20192304 | Plasticization and antiplasticization of polymer melts diluted by low molar mass species. | An analysis of glass formation for polymer melts that are diluted by structured molecular additives is derived by using the generalized entropy theory, which involves bination of the Adam-Gibbs model and the putation of the configurational entropy based on a lattice model of polymer melts that includes monomer structural effects. putations indicate that the plasticization and antiplasticization of polymer melts depend on the molecular properties of the additive. Antiplasticization is panied by a "toughening" of the glass mixture relative to the pure polymer, and this effect is found to occur when the diluents are small species with strongly attractive interactions with the polymer matrix. Plasticization leads to a decreased glass transition temperature T(g) and a "softening" of the fragile host polymer in the glass state. Plasticization is prompted by small additives with weakly attractive interactions with the polymer matrix. However, the latter situation can lead to phase separation if the attractive interactions are sufficiently strong. The shifts in T(g) of polystyrene diluted by fully flexible short oligomers (up to 20% mass of diluent) are evaluated from putations, along with the relative changes in the pressibility at T(g) (a softening or toughening effect) to characterize the extent to which the additives act as antiplasticizers or plasticizers. The theory predicts that a decreased fragility can pany both antiplasticization and plasticization of the glass by molecular additives. The general reduction in the T(g) of polymers by molecular additives is rationalized by analyzing the influence of the diluent's properties (cohesive energy, chain length, and stiffness) on glass formation in fluid mixtures and the variation of fragility is discussed in relation to changes in the molecular packing in diluted polymer melts. Our description of constant temperature glass formation upon increasing the diluent concentration directly leads to the Angell equation (tau(alpha) approximately A exp{B/(phi(0,p)-phi(p))}) for the structural relaxation time as function of the polymer concentration, where the extrapolated "zero mobility concentration" phi(0,p) calculated from the theory scales linearly with the inverse polymerization index N. |
20192305 | Quantum hydrodynamics of electron gases. | Electron gases in metals are described as quantum charged Newtonian viscous fluids experiencing Ohmic Darcy friction on the solid lattice ions as well. The dispersion relation of the electron acoustic waves is derived, which shows the existence of new quantum diffusion processes. The electric double layer near a metal surface is studied, which exhibits a new quantum oscillatory-decaying behavior different from the Friedel oscillations. |
20192306 | Simulation and reference interaction site model theory of methanol and carbon tetrachloride mixtures. | We report molecular dynamics and reference interaction site model (RISM) theory of methanol and carbon tetrachloride mixtures. Our study passes the whole concentration range, by including the ponent limits. We majorly focus on an analysis of partial, total, and concentration-concentration structure factors, and examine in detail the k-->0 limits of these functions. Simulation results confirm the tendency of methanol to self-associate with the formation of ring structures in the high dilution regime of this species, in agreement with experimental studies and with previous simulations by other authors. This behavior emerges as strongly related to the high nonideality of the mixture, a quantitative estimate of which is provided in terms of concentration fluctuation correlations, through the structure factors examined. The interaggregate correlation distance is also thereby estimated. Finally, pressibility of the mixture is found in good agreement with experimental data. The RISM predictions are throughout assessed against simulation; the theory describes better the apolar solvent than the alcohol properties. Self-association of methanol is qualitatively reproduced, though this trend is much less marked parison with simulation results. |
20192308 | Two-center potential correlations and its use to determine effective ion-ion interactions and dielectric permittivities in dipolar solvents. | General expressions for two-center electrostatic potential correlations and its use to determine (i) the effective interaction between simple ions in a dipolar solvent and (ii) the dielectric permittivity of the solvent are proposed. Such two-center potential correlations were determined from Monte Carlo simulations of spherically confined dipolar particles embedded in a dielectric medium described by using an image charge approximation. The deduced dielectric permittivities increased with increasing dipolar moment, and at large dipole moments the effective interaction displayed an attractive first minimum. |
20192307 | Thermodynamic pressures for hard spheres and closed-virial equation-of-state. | Hard-sphere molecular dynamics (MD) simulation results, with six-figure accuracy in the thermodynamic equilibrium pressure, are reported and used to test a closed-virial equation-of-state. This latest equation, with no adjustable parameters except known virial coefficients, parable in accuracy both to Padé approximants, and to numerical parameterizations of MD data. There is no evidence of nonconvergence at stable fluid densities. The virial pressure begins to deviate significantly from the thermodynamic fluid pressure at or near the freezing density, suggesting that the passage from stable fluid to metastable fluid is associated with a higher-order phase transition; an observation consistent with some previous experimental results. Revised parameters for the crystal equation-of-state [R. J. Speedy, J. Phys.: Condens. Matter 10, 4387 (1998)] are also reported. |
20192309 | Multiscale modeling of interaction of alane clusters on Al(111) surfaces: a reactive force field and infrared absorption spectroscopy approach. | We have used reactive force field (ReaxFF) to investigate the mechanism of interaction of alanes on Al(111) surface. Our simulations show that, on the Al(111) surface, alanes oligomerize into larger alanes. In addition, from our simulations, adsorption of atomic hydrogen on Al(111) surface leads to the formation of alanes via H-induced etching of aluminum atoms from the surface. The alanes then agglomerate at the step edges forming stringlike conformations. The identification of these stringlike intermediates as a precursor to the bulk hydride phase allows us to explain the loss of resolution in surface IR experiments with increasing hydrogen coverage on single crystal Al(111) surface. This is in excellent agreement with the experimental works of Go et al. [E. Go, K. Thuermer, and J. E. Reutt-Robey, Surf. Sci. 437, 377 (1999)]. The mobility of alanes molecules has been studied using molecular dynamics and it is found that the migration energy barrier of Al(2)H(6) is 2.99 kcal/mol while the prefactor is D(0)=2.82 x 10(-3) cm(2)/s. We further investigated the interaction between an alane and an aluminum vacancy using classical molecular dynamics simulations. We found that a vacancy acts as a trap for alane, and eventually fractionates/annihilates it. These results show that ReaxFF can be used, in conjunction with ab initio methods, to plex reactions on surfaces at both ambient and elevated temperature conditions. |
20192310 | Analysis of femtosecond stimulated Raman spectroscopy of excited-state evolution in bacteriorhodopsin. | The dispersive lines observed in time-resolved femtosecond stimulated Raman spectroscopy (FSRS), using a pair of 809 nm, 3 ps Raman pump, and 840-960 nm ultrashort probe pulse, for the first 500 fs photoisomerization dynamics in the excited state of bacteriorhodopsin, BR* (S(1)), created by a prior 500 nm, 35 fs actinic pump pulse, have previously been attributed to Raman initiated by nonlinear emission (RINE). We used four-wave mixing energy level diagrams to describe the FSRS process, which include RINE as a subset, and a 29-mode harmonic oscillator model for BR(568) in the calculations. Our calculations showed that FSRS of BR* effectively occurs from the ground vibrational state of each of the observed 800-1800 cm(-1) modes of S(1). The lifetime on S(1) determines the linewidth and decay of the dispersive lines, and is estimated to be approximately 600 parable to the stimulated emission decay time. The FSRS dipole couplings are from the ground vibrational state of S(1) to high energy vibrational states on BR (S(0)), and we place a fast decay lifetime of approximately 100 fs on S(0) which can be attributed to the correlation function from the many unobserved low frequency modes. The FSRS dispersive lines are shown to be due to the inverse Raman scattering term with mid |0><1| vibrational coherence on the S(1) surface, and are not due to RINE with vibrational coherence on the S(0) surface. Our calculations show that the RINE process gives rise to broad featureless spectra. |
20192311 | Simulations of heteroaggregation in a suspension of alumina and silica particles: effect of dilution. | The influence of dilution on the aggregation process of posed of two kinds of oxide particles (alumina positively charged particles d(1)=400 nm and silica negatively charged particles d(2)=250 nm) has been studied puter simulations. Two kinds of simulations have been performed: Brownian dynamics simulations to study the aggregation process and its kinetics and global minimization searches to find the most stable configurations of aggregates. We show that the rate of dilution has a strong influence on the structure and on the shape of aggregates in Brownian dynamics simulations. By confronting these aggregates with the stable aggregates found by global minimization, we demonstrate that they are metastable and their shape is explained by petition between the kinetics of aggregate coalescence and the kinetics of aggregate reorganization into more stable configurations. |
20192312 | Simulation study of the disjoining pressure profile through a three-phase contact line. | Computer simulations are performed to measure the disjoining pressure profile Pi(y) across the three-phase contact line formed by a liquid-vapor interface intersecting a planar substrate wall lying in the xy plane. The method makes use of an exact expression for the disjoining pressure in terms of the density profile and the wall-fluid interaction. Pi(y) is reported for three distinct values of the wall-fluid attractive potential, representing differing levels of partial wetting by macroscopic adsorbed drops. Mechanical force-balance normal to the substrate is confirmed by direct evaluation of the required analog to Young's equation. For the model system under study, the disjoining pressure profiles are well-fitted by inverted Gaussians. The fitted results are used with an extension (to large values of Young's contact angle theta) of the interface Hamiltonian theory of Indekeu, thereby enabling us to report the line tension tau(theta). |
20192313 | X-ray absorption and photoemission spectroscopy of zinc protoporphyrin adsorbed on rutile TiO2(110) prepared by in situ electrospray deposition. | Zinc-protoporphyrin, adsorbed on the rutile TiO(2)(110) surface, has been studied using photoemission spectroscopy and near-edge absorption fine structure spectroscopy to deduce the nature of the molecule-surface bonding and the chemical environment of the central metal atom. To e the difficulties associated with sublimation of the porphyrin molecules, samples were prepared in situ using ultrahigh vacuum electrospray deposition, a technique which facilitates the deposition of nonvolatile and fragile molecules. Monolayers of Zn protoporphyrin are found to bond to the surface via the oxygen atoms of the deprotonated carboxyl groups. The molecules initially lie largely parallel to the surface, reorienting to an upright geometry as the coverage is increased up to a monolayer. For those molecules directly chemisorbed to the surface, the interaction is sufficiently strong to pull the central metal atom out of the molecule. |
20192314 | Charge regularization in phase separating polyelectrolyte solutions. | Theoretical investigations of phase separation in polyelectrolyte solutions have so far assumed that the effective charge of the polyelectrolyte chains is fixed. The ability of the polyelectrolyte chains to self-regulate their effective charge due to the self-consistent coupling between ionization equilibrium and polymer conformations, depending on the dielectric constant, temperature, and polymer concentration, affects the critical phenomena and phase transitions drastically. By considering salt-free polyelectrolyte solutions, we show that the daughter phases have different polymer charges from that of the mother phase. The critical point is also altered significantly by the charge self-regularization of the polymer chains. This work extends the progress made so far in the theory of phase separation of strong polyelectrolyte solutions to a higher level of understanding by considering chains which can self-regulate their charge. |
20192315 | Spreading of colloid clusters in a quasi-one-dimensional channel. | The effect of hydrodynamic interactions on the spreading of clusters of colloid particles in a quasi-one-dimensional channel is analyzed both experimentally and theoretically. An n-particle cluster spreading diffusion coefficient is defined, in terms of the displacement Deltax(t) in time t, by D(n)[triple bond]<[Sigma(i=1)(n)Deltax(i)(t)](2)>/2nt, where the average is taken over all groups of n adjacent particles. Our study focuses on the n-dependence of D(n) with some attention to the dependence of D(n) on colloid packing fraction. We find that the ratio of D(n) to the infinite dilution self-diffusion coefficient D(S)(0) increases as n increases, eventually saturating for large n. The observed dependence of D(n) on n is in satisfactory agreement with the predictions obtained from both Stokesian dynamics simulations and hydrodynamic calculations using the method of reflections. |
20192316 | Empirical model of residue contact probabilities for polypeptides. | An empirical theory for the probability of formation of intrachain contacts in denatured polypeptides is presented. Contact probabilities for arbitrary sequences are modeled position-weighted averages of the homopolypeptides contact probabilities. Homopolypeptide probabilities are obtained for each one of the 20 amino acids by Monte Carlo simulations. A multipower law model for the homopolypeptides fits very precisely the contact probabilities after optimization. Its asymptotic behavior for large contact loop lengths consist of three different exponents depending on where the contacts are located along the chain in general agreement with other theoretical models. The model for the heteropolypeptide contact probabilities is also able to reproduce the simulated probabilities of a set of denatured proteins but with less accuracy. Contact probabilities for heteropolypeptides are significantly similar, in particular for loop lengths above 20 residues, and the model does not have enough resolution to clearly distinguish between different proteins. Sequence order information seems necessary to increase the precision. Overall, contacts with loop lengths above 33 residues behave as those from random flight chains. One exception are polyproline chains for which this length seems to be much higher. |
20192317 | Unique magnetic signatures of mismatched base pairs in DNA. | Magnetic properties of DNA containing mispairs, such as different conformations of the GA mispair, or a GT mispair inserted into the DNA chain, have been theoretically investigated. The essential ingredients for these studies, the charge transfer integrals, were evaluated from the DNA sequences containing the mispair and optimized in the solvent. We find that the magnetic susceptibilities of the host DNA chain containing a large number of Watson-Crick base pairs are significantly altered in the presence of the mispairs, and the effects depend on the choice of mispairs. In particular, insertion of even a single GA mispair changes the nature of magnetization (sign of the susceptibility) of the host DNA. We propose that measurement of the magnetic properties of DNA might provide a direct route to detection and identification of those mispairs. |
20192320 | The third generation superconducting 28 GHz electron cyclotron resonance ion source VENUS (invited). | VENUS is a third generation electron cyclotron resonance (ECR) ion source, which incorporates a high field superconducting NbTi magnet structure, a 28 GHz gryotron microwave source and a state of the art closed cycle cryosystem. During the decade from initial concept to regular operation, it has demonstrated both the feasibility and the performance levels of this new generation of ECR ion sources and required innovation on magnet construction, plasma chamber design, and beam transport. In this paper, the development, performance, and major innovations are described as well as a look to the potential to construct a fourth generation ECR ion source. |
20192318 | Protein elasticity probed with two synchrotron-based techniques. | Compressibility characterizes three interconnecting properties of a protein: dynamics, structure, and function. pressibility values for the electron-carrying protein cytochrome c and for other proteins, as well, available in the literature vary considerably. Here, we apply two synchrotron-based techniques--nuclear resonance vibrational spectroscopy and inelastic x-ray scattering--to measure the pressibility of this protein. This is the first report of pressibility of any material measured with this method. Unlike the methods previously used, this novel approach probes the protein globally, at ambient pressure, does not require the separation of protein and solvent contributions to the pressibility, and uses samples that contain the heme iron, as in the native state. We show, paring our results with molecular dynamics predictions, that pressibility is almost independent of temperature. We discuss potential applications of this method to other materials beyond proteins. |
20192321 | New development of advanced superconducting electron cyclotron resonance ion source SECRAL (invited). | Superconducting electron cyclotron resonance ion source with advance design in Lanzhou (SECRAL) is an 18-28 GHz fully superconducting electron cyclotron resonance (ECR) ion source dedicated for highly charged heavy ion beam production. SECRAL, with an innovative superconducting magnet structure of solenoid-inside-sextupole and at lower frequency and lower rf power operation, may open a new way for pact and reliable high performance superconducting ECR ion source. One of the recent highlights achieved at SECRAL is that some new record beam currents for very high charge states were produced by 18 GHz or 18+14.5 GHz double frequency heating, such as 1 e microA of (129)Xe(43+), 22 e microA of (209)Bi(41+), and 1.5 e microA of (209)Bi(50+). To further enhance the performance of SECRAL, a 24 GHz/7 kW gyrotron microwave generator was installed and SECRAL was tested at 24 GHz. Some promising and exciting results at 24 GHz with new record highly charged ion beam intensities were produced, such as 455 e microA of (129)Xe(27+) and 152 e microA of (129)Xe(30+), although missioning time was limited within 3-4 weeks and rf power only 3-4 kW. Bremsstrahlung measurements at 24 GHz show that x-ray is much stronger with higher rf frequency, higher rf power. and higher minimum mirror magnetic field (minimum B). Preliminary emittance measurements indicate that SECRAL emittance at 24 GHz is slightly higher that at 18 GHz. SECRAL has been put into routine operation at 18 GHz for heavy ion research facility in Lanzhou (HIRFL) plex since May 2007. The total operation beam time from SECRAL for HIRFL accelerator has been more than 2000 h, and (129)Xe(27+), (78)Kr(19+), (209)Bi(31+), and (58)Ni(19+) beams were delivered. All of these new developments, the latest results, and long-term operation for the accelerator have again demonstrated that SECRAL is one of the best in the performance of ECR ion source for highly charged heavy ion beam production. Finally the future development of SECRAL will be presented. |
20192322 | Simulation of parameter scaling in electron cyclotron resonance ion source plasmas using the GEM code. | Although heating power and gas pressure are two of the two of primary experimental "knobs" available to users of electron cyclotron resonance ion sources, there is still no clear understanding of how they interact in order to provide optimal plasma conditions. FAR-TECH, Inc. has performed a series of simulations with its generalized electron cyclotron resonance ion source model in which the power and pressure were varied over a wide range. Analysis of the numerical data produces scaling laws that predict the plasma parameters as a function of the power and pressure. These scaling laws are in general agreement with experimental data. |
20192324 | The role of seed electrons on the plasma breakdown and preglow of electron cyclotron resonance ion source. | The 14 GHz Electron Cyclotron Resonance Ion Source at University of Jyväskylä, Department of Physics (JYFL) has been operated in pulsed mode in order to study the plasma breakdown and preglow effect. It was observed that the plasma breakdown time and preglow characteristics are affected by seed electrons provided by a continuous low power microwave signal at secondary frequency. Sustaining low density plasma during the off-period of high power microwave pulses at the primary frequency shifts the charge state distribution of the preglow transient toward higher charge states. This could be exploited for applications requiring fast and efficient ionization of radioactive elements as proposed for the Beta Beam project within the EURISOL design study, for example. In this article we present results measured with helium and neon. |
20192325 | Simulation of charge breeding of rubidium using Monte Carlo charge breeding code and generalized ECRIS model. | A Monte Carlo charge breeding code (MCBC) is being developed by FAR-TECH, Inc. to model the capture and charge breeding of 1+ ion beam in an electron cyclotron resonance ion source (ECRIS) device. The ECRIS plasma is simulated using the generalized ECRIS model which has two choices of boundary settings, free boundary condition and Bohm condition. The charge state distribution of the extracted beam ions is calculated by solving the steady state ion continuity equations where the profiles of the captured ions are used as source terms. MCBC simulations of the charge breeding of Rb+ showed good agreement with recent charge breeding experiments at Argonne National Laboratory (ANL). MCBC correctly predicted the peak of highly charged ion state outputs under free boundary condition and similar charge state distribution width but a lower peak charge state under the Bohm condition. parisons between the simulation results and ANL experimental measurements are presented and discussed. |
20192323 | The effect of rf pulse pattern on bremsstrahlung and ion current time evolution of an ECRIS. | Time-resolved helium ion production and bremsstrahlung emission from JYFL 14 GHz ECRIS is presented with different radio frequency pulse lengths. rf on times are varied from 5 to 50 ms and rf off times from 10 to 1000 ms between different measurement sets. It is observed that the plasma breakdown occurs a few milliseconds after launching the rf power into the plasma chamber, and in the beginning of the rf pulses a preglow transient is seen. During this transient the ion beam currents are increased by several pared to a steady state situation. By adjusting the rf pulse separation the maximum ion beam currents can be maintained during the so-called preglow regime while the amount of bremsstrahlung radiation is significantly decreased. |
20192327 | Bio-Nano ECRIS: an electron cyclotron resonance ion source for new materials production. | We developed an electron cyclotron resonance ion source (ECRIS) for new materials production on nanoscale. Our main target is the endohedral fullerenes, which have potential in medical care, biotechnology, and nanotechnology. In particular, iron-encapsulated fullerene can be applied as a contrast material for magnetic resonance imaging or microwave heat therapy. Thus, our new ECRIS is named the Bio-Nano ECRIS. In this article, the recent progress of the development of the Bio-Nano ECRIS is reported: (i) iron ion beam production using induction heating oven and (ii) optimization of singly charged C(60) ion beam production. |
20192326 | Glow plasma trigger for electron cyclotron resonance ion sources. | Electron cyclotron resonance ion sources (ECRISs) are particularly useful for nuclear, atomic, and high energy physics, as unique high current generators of multicharged ion beams. Plasmas of gas discharges in an open magnetic trap heated by pulsed (100 micros and longer) high power (100 kW and higher) high-frequency (greater than 37.5 GHz) microwaves of gyrotrons is promising in the field of research in the development of electron cyclotron resonance sources for high charge state ion beams. Reaching high ion charge states requires a decrease in gas pressure in the magnetic trap, but this method leads to increases in time, in which the microwave discharge develops. The gas breakdown and microwave discharge duration es greater than or equal to the microwave pulse duration when the pressure is decreased. This makes reaching the critical plasma density initiate an electron cyclotron resonance (ECR) discharge during pulse of microwave gyrotron radiation with gas pressure lower than a certain threshold. In order to reduce losses of microwave power, it is necessary to shorten the time of development of the ECR discharge. For fast triggering of ECR discharge under low pressure in an ECRIS, we initially propose to fill the magnetic trap with the plasmas of auxiliary pulsed discharges in crossed ExB fields. The glow plasma trigger of ECR based on a Penning or magnetron discharge has made it possible not only to fill the trap with plasma with density of 10(12) cm(-3), required for a rapid increase in plasma density and finally for ECR discharge ignition, but also to initially heat the plasma electrons to T(e) approximately = 20 eV. |
20192328 | Three-dimensional simulations of ion dynamics in an Electron Cyclotron Resonance Ion Source. | We present a three-dimensional simulation of the ion dynamics in an electron cyclotron resonance ion source. Ion trajectories in the min-B field of the source are calculated taking ion-ion and electron-ion collisions into account. The electrons are not tracked but considered as a neutralizing background with a Maxwell-Boltzmann velocity distribution. Some applications of the code are discussed, e.g., the calculated charge-state and phase-space distributions of extracted ion beams and the ionization dynamics in the plasma. |
20192329 | Measurement of radial and axial high energy x-ray spectra in electron cyclotron resonance ion source plasmas. | Radial and axial x-ray measurements of electron cyclotron resonance ion sources operating at microwave frequencies of 6.4 and 14 GHz are presented. Results indicate a greater detected photon energy in the radial direction than the axial direction for both the 6.4 GHz source and the 14 GHz source. It is also seen that the 14 GHz source produces x-rays with higher energies, pared to the 6.4 GHz source, in both radial and axial directions. |
20192330 | Nb3Sn superconducting magnets for electron cyclotron resonance ion sources. | Electron cyclotron resonance (ECR) ion sources are an ponent of heavy-ion accelerators. Over the past few decades advances in magnet technology and an improved understanding of the ECR ion source plasma physics have led to remarkable performance improvements of ECR ion sources. Currently third generation high field superconducting ECR ion sources operating at frequencies around 28 GHz are the state of the art ion injectors and several devices are either missioning or under design around the world. At the same time, the demand for increased intensities of highly charged heavy ions continues to grow, which makes the development of even higher performance ECR ion sources a necessity. To extend ECR ion sources to frequencies well above 28 GHz, new magnet technology will be needed in order to operate at higher field and force levels. The superconducting magnet program at LBNL has been developing high field superconducting magnets for particle accelerators based on Nb(3)Sn superconducting technology for several years. At the moment, Nb(3)Sn is the only practical conductor capable of operating at the 15 T field level in the relevant configurations. Recent design studies have been focused on the possibility of using Nb(3)Sn in the next generation of ECR ion sources. In the past, LBNL has worked on the VENUS ECR, a 28 GHz source with solenoids and a sextupole made with NbTi operating at fields of 6-7 T. VENUS has now been operating since 2004. We present in this paper the design of a Nb(3)Sn ECR ion source optimized to operate at an rf frequency of 56 GHz with conductor peak fields of 13-15 T. Because of the brittleness and strain sensitivity of Nb(3)Sn, particular care is required in the design of the magnet support structure, which must be capable of providing support to the coils without overstressing the conductor. In this paper, we present the main features of the support structure, featuring an external aluminum shell pretensioned with water-pressurized bladders, and we analyze the expected coil stresses with a two-dimensional finite element mechanical model. |
20192331 | Plasma potential and energy spread determination using ion beams extracted from an electron cyclotron resonance source. | We have obtained estimates of plasma potentials and energy spreads characterizing an electron cyclotron resonance ion source plasma under different source conditions. Our estimates are obtained from analysis of ion beams extracted from the ion source at 10 kV that are subsequently decelerated into a floating surface scattering chamber where their current intensity incident on a solid sample is measured as function of retardation voltage. The deceleration occurs outside the measurement chamber, permitting beam current measurements in a field-free region. Absence of grids in the deceleration section avoids potential issues of field penetration. The behavior of our deceleration optics was modeled with SIMION. The simulation indicated a linear beam attenuation dependence close to full retardation where the beam current goes to zero. Deviations from this linear dependence observed close to zero beam energy give information on the initial energy spread of the ions extracted from the source. Our decelerated beams measurements pared with recent in situ probe results and external beams results based on magnetic analysis. |
20192332 | Progress in ion source injector development at the ion beam therapy center (Heidelberg Ion Beam Therapy Center). | Radiotherapy with heavy ions is an ing cancer treatment method with to date unachieved precision. It associates higher control rates particularly for radio-resistant tumor species with reduced adverse pared to conventional photon therapy. At Heidelberg Ion Beam Therapy Center two 14.5 GHz electron cyclotron resonance ion sources are routinely used to produce a variety of ion beams from protons up to oxygen. The operating time is 330 days per year; our experience after 3 yr of continuous operation will be presented, with special emphasis on stability and breakdowns ponents. In addition, the latest enhancement and the results for the operation will be shown. |
20192334 | Production of electron cyclotron resonance plasma by using multifrequencies microwaves and active beam profile control on a large bore electron cyclotron resonance ion source with permanent magnets. | A new concept on magnetic field with all magnets on plasma production and confinement has been proposed to enhance efficiency of an electron cyclotron resonance (ECR) plasma for broad and dense ion beam source under the low pressure. The magnetic field configuration is constructed by a pair of magnets assembly, b-shaped magnet which cylindrically surrounds the plasma chamber. The resonance zones corresponding to the fundamental ECR for 2.45 GHz and 11-13 GHz frequencies are constructed at different positions. The profiles of the plasma parameters in the ECR ion source are different from each frequency of microwave. Large bore extractor is set at the opposite side against the microwave feeds. It is found that differences of their profiles also appear at those of ion beam profiles. We conducted to launch simultaneously multiplex frequencies microwaves controlled individually, and tried to control the profiles of the plasma parameters and then those of extracted ion beam. |
20192333 | Stability study of all-permanent-magnet electron cyclotron resonance ion source. | Beam intensity fluctuation was investigated using an electron cyclotron resonance ion source of an all-permanent-magnet type under development for highly stable beam intensity. While the source achieved a stability of better than 3.2% by strict regulation of the coolant temperature change within +/-0.1 degrees C, the intensity varies strongly with intentional changes in the temperature of the plasma chamber coolant. The influence of the temperature on chamber expansion, magnetic field strength, and vacuum was measured or estimated in detail. The result shows that a slight change in vacuum and magnetic field strength has considerable influence on the intensity fluctuation. |
20192335 | Design and construction of a compact microwave proton source for a proton linac. | A 100 MeV, 20 mA proton linear accelerator is being developed by the Proton Engineering Frontier Project at the Korea Atomic Energy Research Institute. 20 MeV acceleration system using radio frequency quadrupole and drift tube linac was already developed and has been tested. To operate this acceleration system with a long time, more reliable proton source is needed. pact microwave proton source was proposed and has been designed and constructed as a prototype ion source for the 100 MeV proton linear accelerator. The design of microwave power injection system is based on the microwave proton injector at LANL and CEA. The wave power from a 2.45 GHz, 2 kW magnetron source is introduced into pact plasma chamber with 7 cm diameter and 5 cm length through a standard tapered, double-ridged waveguide (WRD250) and a quartz window. The microwave power supply is installed on high voltage platform. Axial magnetic fields up to 1 kG can be provided with a water-cooled solenoid coil. A single-hole three electrode extraction system is designed for an extraction current up to 30 mA at a 50 kV extraction voltage. The design and initial operations of the proton source are presented. |
20192336 | First beams from the new electron cyclotron resonance source LEGIS (LEGnaro ecrIS) at INFN-LNL. | From April 2008 the PIAVE injector for the ALPI booster was involved in the upgrade of the high voltage platform housing an electron cyclotron resonance (ECR) source. A 14.5 GHz SUPERNANOGAN type ECR replaced the existing source ALICE; at the same time, the whole platform beam line was redesigned and beam shaping and diagnostic system were installed. The source and the platform were ready to be put into operation in January 2009. missioning was started from late March pleted in May 2009 using an argon beam. A description of the upgrade will be given in the following; beam quality leading to an improved transmission through the injector will be shown. Results on first gaseous and metallic beams produced will also be given. |
20192337 | Status report of the heavy ions source research and development for Spiral2. | The physics background requiring a very intense multicharged heavy ion source for Spiral2 is explained. The new Spiral2 low energy beam line dedicated to the heavy ions production and equipped with PHOENIX V2 ECRIS is presented. A status of the missioning at 18 GHz is summarized. A new hybrid ECRIS concept with a cryogenic permanent magnet hexapole is proposed as an improvement of A-PHOENIX technology. |
20192338 | Fabrication of an optimized hexapole magnet for a 14.5 GHz electron cyclotron resonance ion source. | A hexapole magnet for a 14.5 GHz electron cyclotron resonance (ECR) ion source, where the maximum radial field on the wall of the plasma chamber is higher than 1.1 T, has been designed and fabricated. The size of the outer diameter and the number of the sector of the hexapole are optimized for a 14.5 GHz ECR ion source with the help of a three-dimensional field calculation code. Moreover, to make a strong and long-life magnet against the demagnetic field on the hexapole multilayered structure in radial and axial directions is considered in the design. The distributions of the demagnetic fields are estimated by the calculation of the radial field in a hexapole magnet and the axial field from the solenoid coils. Proper grades of magnetic materials depending on the strength of the demagnetic field are applied for the different layers. The magnetic fields of the measured and calculated ones have pared. |
20192339 | Production of highly charged ion beams with SECRAL. | Superconducting electron cyclotron resonance ion source with advanced design in Lanzhou (SECRAL) is an all-superconducting-magnet electron cyclotron resonance ion source (ECRIS) for the production of intense highly charged ion beams to meet the requirements of the Heavy Ion Research Facility in Lanzhou (HIRFL). To further enhance the performance of SECRAL, an aluminum chamber has been installed inside a 1.5 mm thick Ta liner used for the reduction of x-ray irradiation at the high voltage insulator. With double-frequency (18+14.5 GHz) heating and at maximum total microwave power of 2.0 kW, SECRAL has successfully produced quite a few very highly charged Xe ion beams, such as 10 e microA of Xe(37+), 1 e microA of Xe(43+), and 0.16 e microA of Ne-like Xe(44+). To further explore the capability of the SECRAL in the production of highly charged heavy metal ion beams, a first test run on bismuth has been carried out recently. The main goal is to produce an intense Bi(31+) beam for HIRFL accelerator and to have a feel how well the SECRAL can do in the production of very highly charged Bi beams. During the test, though at microwave power less than 3 kW, more than 150 e microA of Bi(31+), 22 e microA of Bi(41+), and 1.5 e microA of Bi(50+) have been produced. All of these results have again demonstrated the great capability of the SECRAL source. This article will present the detailed results and brief discussions to the production of highly charged ion beams with SECRAL. |
20192341 | First results from the new RIKEN superconducting electron cyclotron resonance ion source (invited). | The next generation heavy ion accelerator facility, such as the RIKEN radio isotope (RI) beam factory, requires an intense beam of high charged heavy ions. In the past decade, performance of the electron cyclotron resonance (ECR) ion sources has been dramatically improved with increasing the magnetic field and rf frequency to enhance the density and confinement time of plasma. Furthermore, the effects of the key parameters (magnetic field configuration, gas pressure, etc.) on the ECR plasma have been revealed. Such basic studies give us how to optimize the ion source structure. Based on these studies and modern superconducting (SC) technology, we successfully constructed the new 28 GHz SC-ECRIS, which has a flexible magnetic field configuration to enlarge the ECR zone and to optimize the field gradient at ECR point. Using it, we investigated the effect of ECR zone size, magnetic field configuration, and biased disk on the beam intensity of the highly charged heavy ions with 18 GHz microwaves. In this article, we present the structure of the ion source and first experimental results with 18 GHz microwave in detail. |
20192340 | Effect of electron cyclotron resonance ion source frequency tuning on ion beam intensity and quality at Department of Physics, University of Jyväskylä. | Ion beam intensity and quality have a crucial effect on the operation efficiency of the accelerator facilities. This paper presents the investigations on the ion beam intensity and quality after the mass separation performed with the Department of Physics, University of Jyväskylä 14 GHz electron cyclotron resonance ion source by sweeping the microwave in the 14.05-14.13 GHz range. In many cases a clear variation in the ion beam intensity and quality as a function of the frequency was observed. The effect of frequency tuning increased with the charge state. In addition, clear changes in the beam structure seen with the beam viewer were observed. The results confirmed that frequency tuning can have a remarkable effect on ion beam intensity and quality especially in the case of highly charged ion beams. The examples presented here represent the typical charge state behavior observed during the measurements. |
20192342 | Design of a compact, permanent magnet electron cyclotron resonance ion source for proton and H2(+) beam production. | A 2.45 GHz microwave ion source was developed at China Institute of Atomic Energy (CIAE) for proton beam production of over 60 mA [B.-Q. Cui, Y.-W. Bao, L.-Q. Li, W.-S. Jiang, and R.-W. Wang, Proceedings of the High Current Electron Cyclotron Resonance (ECR) Ion Source for Proton Accelerator, APAC-2001, 2001 (unpublished)]. For various proton beam applications, another 2.45 GHz microwave ion source with pact structure is designed and will be built at CIAE as well for high current proton beam production. It is also considered to be used for the test of H(2)(+) beam, which could be injected into the central region model cyclotron at CIAE, and accelerated to 5 MeV before extraction by stripping. The required ECR magnetic field is supplied by all the permanent magnets rather than electrical solenoids and six poles. The magnetic field distribution provided by this permanent magnets configuration is a large and uniformly volume of ECR zone, with central magnetic field of a magnitude of approximately 875 Gs [T. Taylor and J. S. C. Wills, Nucl. Instrum. Methods Phys. Res. A 309, 37 (1991)]. The field adjustment at the extraction end can be implemented by moving the position of the magnet blocks. The results of plasma, coupling with 2.45 GHz microwave in the ECR zone inside the ion source are simulated by particle-in-cell code to optimize the density by adjusting the magnetic field distribution. The design configuration of the ion source will be summarized in the paper. |
20192344 | The effect of the dc bias voltage on the x-ray bremsstrahlung and beam intensities of medium and highly charged ions of argon. | X-ray bremsstrahlung measurements from the 18 GHz High Temperature Superconducting Electron Cyclotron Resonance Ion Source, Pantechnik-Delhi Ion Source were measured as a function of negative dc bias voltage, keeping all other source operating parameters fixed and the extraction voltage in the off condition. The optimization of medium and highly charged ions of argon with similar source operating parameters is described. It is observed that the high ponent of the electron is altered significantly with the help of bias voltage, and the electron population has to be maximized for obtaining higher current. |
20192345 | SEISM: a 60 GHz cusp electron cyclotron resonance ion source. | LPSC has been involved for several years in a challenging research and development program on the production of pulsed ions beams with high ionization efficiency primarily dedicated to radioactive ion beams. The generation of the high magnetic field requires the use of helix techniques developed at Laboratoire National des Champs Magnétiques Intenses. As a first approach, a cusp structure has been chosen. 3D simulations were used to define the geometry of the helices. puter aided design of the mechanical parts of the magnetic structure has been performed at LPSC and was optimized to decrease the total volume of the source. The first 60 GHz magnetic structure (helices coils in their tanks, electrical, and water cooling environment) should be available before the end of 2009. |
20192343 | Induction heating pure vapor source of high temperature melting point materials on electron cyclotron resonance ion source. | Multicharged ions that are needed are produced from solid pure material with high melting point in an electron cyclotron resonance ion source. We develop an evaporator by using induction heating (IH) with multilayer induction coil, which is made from bare molybdenum or tungsten wire without water cooling and surrounding the pure vaporized material. We optimize the shapes of induction coil and vaporized materials and operation of rf power supply. We conduct experiment to investigate the reproducibility and stability in the operation and heating efficiency. IH evaporator produces pure material vapor because materials directly heated by eddy currents have no contact with insulated materials, which are usually impurity gas sources. The power and the frequency of the induction currents range from 100 to 900 W and from 48 to 23 kHz, respectively. The working pressure is about 10(-4)-10(-3) Pa. We measure the temperature of the vaporized materials with different shapes, pare them with the result of modeling. We estimate the efficiency of the IH vapor source. We are aiming at the evaporator's higher melting point material than that of iron. |
20192346 | Pulse modulated microwave operation on large bore electron cyclotron resonance ion source with cylindrically comb-shaped magnetic fields configuration. | In order to enhance efficiency of an electron cyclotron resonance (ECR) plasma for broad and dense ion beam source under the low pressure, the magnetic field configuration is constructed by a pair b-shaped magnet which has opposite polarity each other, and which cylindrically surrounds the plasma chamber. By using the pulse microwave mode operation, we aim at generation of plasma with parameters that cannot be achieved at the continuous microwave (cw) mode. The maximum beam current is obtained in the experimental condition of the pulse width 100-200 micros at the duty ratio 40%-50%. According to probe measurements of the ECR plasma, it is found the electron density in the pulse mode is larger than that in the cw mode, while the electron temperatures in the pulse mode were lower than that in the cw mode. These indirect evidences cause to enhance ion beams in the pulse mode operation, and then suggest a spread of operation windows for plasma parameters suitable to production of molecular or cluster ions. |
20192347 | Metal-dielectric structures for high power electron cyclotron resonance ion source. | Metal-dielectric (MD)-structures in electron cyclotron resonance ion source (ECRIS) devices (partially) restore the plasma ambipolarity and supply cold electrons to the plasma. Both effects lead to an enhancement of the plasma electron density and temperature and significantly increase the performance of this type of ion source. At the same time, MD-structures are well suited to reduce the heat load on cold masses by Bremsstrahlung radiation. Here, we report on experiments at high microwave powers to test the practical use of MD-structures for new, high performance ECRISs with their much higher power densities. paratively long conditioning times can be shortened by covering only those parts of the source with MD-structures, which are essential for the improvement. |
20192351 | Enhanced confinement in electron cyclotron resonance ion source plasma. | Power loss by plasma-wall interactions may e a limitation for the performance of ECR and fusion plasma devices. Based on our research to optimize the performance of electron cyclotron resonance ion source (ECRIS) devices by the use of metal-dielectric (MD) structures, the development of the method presented here, allows to significantly improve the confinement of plasma electrons and hence to reduce losses. Dedicated measurements were performed at the Frankfurt 14 GHz ECRIS using argon and helium as working gas and high temperature resistive material for the MD structures. The analyzed charge state distributions and bremsstrahlung radiation spectra (corrected for background) also clearly verify the anticipated increase in the plasma-electron density and hence demonstrate the advantage by the MD-method. |
20192349 | Ion sources for MedAustron. | The MedAustron Ion therapy center will be constructed in Wiener Neustadt (Austria) in the vicinity of Vienna. Its plex consists of four ion sources, a linear accelerator, a synchrotron, and a beam delivery system to the three medical treatment rooms and to the research irradiation room. The ion sources shall deliver beams of H(3)(1+), C(4+), and light ions with utmost reliability and stability. This paper describes the features of the ion sources presently planned for the MedAustron facility, such as ion source main parameters, gas injection, temperature control, and cooling systems. A dedicated beam diagnostics technique is proposed in order to characterize electron cyclotron resonance (ECR) ion beams; in the first drift region after the ion source, a fraction of the mixed beam is selected via moveable aperture. With standard beam diagnostics, we then aim to produce position-dependant observables such as ion-current density, beam energy distribution, and emittance for each charge states to pared to simulations of ECR e-heating, plasma simulation, beam formation, and transport. |
20192350 | MIVOC method with temperature control. | The Heavy Ion Medical Accelerator in Chiba at the National Institute of Radiological Sciences has been used for cancer therapy, physics, and biology experiments since 1994. Its ion sources produce carbon ion for cancer therapy. They also produce various ions (H(+)-Xe(21+)) for physics and biology experiments. Most ion species are produced from gases by an 18 GHz electron cyclotron resonance ion source. However, some of ion species is difficult to produce from stable and secure gases. Such ion species are produced by the sputtering method. However, it is necessary to reduce material consumption rate as much as possible in the case of rare and expensive stable isotopes. We have selected "metal ions from pounds method" as a means to solve this problem. We tested a variety pounds. Since pound has a suitable temperature to obtain the optimum vapor pressure, we have developed an accurate temperature control system. We have produced ions such as (58)Fe(9+), Co(9+), Mg(5+), Ti(10+), Si(5+), and Ge(12+) with the temperature control. |
20192348 | The compact electron cyclotron resonance ion source KeiGM for the carbon ion therapy facility at Gunma University. | A high-energy carbon-ion radiotherapy facility is under construction at Gunma University Heavy Ion Medical Centre (GHMC). Its design was based on a study of the heavy ion radiotherapy at the National Institute of Radiological Sciences (NIRS) in order to reduce the size and construction cost of the facility. pact electron cyclotron resonance ion source (ECRIS) for Gunma University, called KeiGM, was installed in 2008. It is almost a copy of the prototype ECRIS Kei2 which was developed by NIRS; meanwhile this prototype produced over 1 e mA of C(4+) using C(2)H(2) gas (660 W and 40 kV). The beam intensity of C(4+) was 600 e microA with CH(4) gas (250 W and 30 kV). The beam intensity satisfies the required value of 300 e microA. |
20192352 | A multicharge ion source (Supernanogan) for the OLIS facility at ISAC/TRIUMF. | The Off-Line Ion Source (OLIS) [K. Jayamanna, D. Yuan, T. Kuo, M. MacDonald, P. Schmor, and G. Dutto, Rev. Sci. Instrum. 67, 1061 (1996); K. Jayamanna, Rev. Sci. Instrum. 79, 02711 (2008)] facility consists of a high voltage terminal containing a microwave cusp ion source, either a surface ion source or a hybrid surface-arc discharge ion source [K. Jayamanna and C. Vockenhuber, Rev. Sci. Instrum. 79, 02C712 (2008)], and an electrostatic switch that allows the selection of any one of the sources without mechanical intervention. These sources provide a variety of +1 beams up to mass 30 for Isotope Separator and ACcelerator (ISAC) [R. E. Laxdal, Nucl. Instrum. Methods Phys. Res. B 204, 400 (2003)] missioning the accelerators, setting up the radioactive experiments, and for tuning the beam lines. The radio frequency quadrupole (RFQ) [M. Marchetto, Z. T. Ang, K. Jayamanna, R. E. Laxdal, A. Mitra, and V. Zvyagintsev, Eur. Phys. J. Spec. Top. 150, 241 (2005)] injector accelerator is a constant velocity machine designed to accept only 2 keV/u and the source extraction energy is limited to 60 kV. Further stripping is then needed downstream of the RFQ to inject the beam into the drift tube linac [M. Marchetto, Z. T. Ang, K. Jayamanna, R. E. Laxdal, A. Mitra, and V. Zvyagintsev, Eur. Phys. J. Spec. Top. 150, 241 (2005)] accelerator that requires A/q up to 6. Base on this constraints a multicharge ion source capable to deliver beams above mass 30 with A/q up to 6 was needed in order to reach full capability of the ISAC facility. A Supernanogan [C. Bieth et al., Nucleonika 48, S93 (2003)] multicharge ion source was then purchased from Pantechnik and was installed in the OLIS terminal. Commissioning and performance of the Supernanogan with some results such as emittance dependence of the charge states as well as charge state efficiencies are presented. |
20192353 | Production of highly charged heavy ions by 18 GHz superconducting electron cyclotron resonance at Research Center for Nuclear Physics. | An 18 GHz superconducting electron cyclotron resonance ion source has been installed as a subject of the azimuthally varying field cyclotron upgrade project (K. Hatanaka et al., in Proceedings of the 17th International Conference on Cyclotrons and Their Applications, Tokyo, Japan, 18-22 October 2004, pp. 115-117), in order to increase beam currents and to extend the variety of ions. The production development of several ions has been performed since 2006 and some of them have already been used for user experiments [T. Yorita et al., Rev. Sci. Instrum. 79, 02A311 (2008)]. Further optimizations for ponent such as the material of plasma electrode, material, and shape of bias probe and mirror field have been continued and more intense ion beams have been obtained for O, N, and Ar. For the purpose of obtaining highly charged Xe with several microamperes, the optimization of position and shape of plasma electrode and bias disk has also been done and highly charged Xe(32+) beam has been obtained successfully. |
20192354 | Microwave to plasma coupling in electron cyclotron resonance and microwave ion sources (invited). | Coupling improvements between microwaves and plasmas are a key factor to design more powerful electron cyclotron resonance and microwave ion sources. On this purpose different activities have been undertaken by the INFN-LNS ion source team and a new approach was developed. Recent experiments confirmed the simulations, demonstrating that even in presence of a dense plasma, resonant modes are excited inside the cavity and the plasma dynamics depends on their structure. An overview of the coupling issues on microwave ion sources is also given along with a discussion on alternative coupling techniques. |
20192356 | Generation of multicomponent ion beams by a vacuum arc ion source with compound cathode. | This paper presents the results of time-of-flight mass spectrometry studies of the elemental and mass-to-charge positions of metal ion beams produced by a vacuum arc ion source pound cathode (WC-Co(0.5), Cu-Cr(0.25), Ti-Cu(0.1)). We found that the ion position agrees well with the position of the cathode material from which the beam is derived, and the maximum ion charge state of the different ponents is determined by the ionization capability of electrons within the cathode spot plasma, which mon to ponents. The beam mass-to-charge state spectrum from pound cathode features a greater fraction of multiply charged ions for those materials with lower electron temperature in the vacuum arc cathode spot, and a smaller fraction for those with higher electron temperature within the spot. We propose a potential diagram method for determination of attainable ion charge states for ponents of pound cathodes. |
20192355 | Plasma ion dynamics and beam formation in electron cyclotron resonance ion sources. | In electron cyclotron resonance ion sources it has been demonstrated that plasma heating may be improved by means of different microwave to plasma coupling mechanisms, including the "frequency tuning" and the "two frequency heating." These techniques affect evidently the electron dynamics, but the relationship with the ion dynamics has not been investigated in details up to now. Here we will try to outline these relations: through the study of ion dynamics we may try to understand how to optimize the electron cyclotron resonance ion sources brightness. A simple model of the ion confinement and beam formation will be presented, based on particle-in-cell and single particle simulations. |
20192358 | The NSCL electron beam ion trap for the reacceleration of rare isotopes coming to life: first extraction tests with a high-current electron gun. | NSCL is currently constructing the ReA3 reaccelerator, which will accelerate rare isotopes obtained from gas stopping of fast-fragment beams to energies of up to 3 MeV/u for uranium and higher for lighter ions. A high-current charge breeder, based on an electron beam ion trap (EBIT), has been chosen as the first step in the acceleration process, as it has the potential to efficiently produce highly charged ions in a single charge state. These ions are fed into pact linear accelerator consisting of a radio frequency quadrupole structure and superconducting cavities. The NSCL EBIT has been fully designed with most of the parts constructed. The design concept of the EBIT and results from missioning tests of the electron gun and collector with a temporary 0.4 T magnet are presented. |
20192357 | Laser ion source: a direct plasma injection scheme for two-beam type interdigital-H radio frequency quadrupole linac. | We developed a laser ion source using a direct plasma injection scheme (DPIS) as an injection system for a two-beam type radio frequency quadrupole (RFQ) linac with an interdigital-H (IH) type cavity. The laser ion source in the DPIS is directly connected to the RFQ cavity without the low energy beam transport system. We achieved a high current C(2+) beam above 60 mA per beam channel from the ion source. The beam will be injected to the two-beam type IH-RFQ linac, and the linac will generate a beam current of approximately 44 mA per beam channel. |
20192359 | Generation of high currents of carbon ions with the use of subnanosecond near-infrared laser pulses. | Emission of carbon currents reaching values up to 2 A/cm(2) at a distance of 1 m from the laser ion source driven by the subnanosecond Prague Asterix Laser System operated at a fundamental wavelength of 1315 nm is reported. Graphite targets were exposed to intensities up to 5x10(16) W/cm(2) varying both the laser energy and the position of the laser beam focus with respect to the target surface. The maximum energy gain of carbon ions was approximately = 1 MeV/u. At high laser intensities the shape of time-of-flight spectra is also formed by plasma outbursts, whose growth correlates with the oscillatory self-focusing of the laser beam. |
20192360 | Time profile of ion pulses produced in a hot-cavity laser ion source. | The time spreads of Mn ions produced by three-photon resonant ionization in a hot-cavity laser ion source are measured. A one-dimensional ion-transport model is developed to simulate the observed ion time structures. Assuming ions are generated with a Maxwellian velocity distribution and are guided by an axial electric field, the predictions of the model agree reasonably well with the experimental data and suggest that the ions are radially confined in the ion source and a substantial fraction of the ions in the transport tube are extracted. |
20192361 | Measurements of the highest acceleration gradient for ions produced with a long laser pulse. | Ultrafast plasma light ion streams have been produced using the 300 ps, kJ-class iodine laser, operating at PALS Centre in Prague. Ion detection was performed through standard ion collectors (IC) in time-of-flight configuration (TOF), shielded by thin metallic absorbers. This new diagnostics technique has been theoretically studied and experimentally tested in order to cut the long photopeak contribution and to analyze the ultrafast particle signal. Processing the obtained experimental IC-TOF data, including deconvolution processes of the TOF signals, UV/soft-x-ray photopeak absorption, and ion transmission calculations for different metallic filters, is shown. Mainly amorphous carbon (graphite) targets have been irradiated in order to limit the maximum number of ion charge states and to focus our study on demonstrating the validity of the proposed investigation technique. Maximum ion energy and acceleration gradient estimations as a function of the laser energy and focal spot diameter are reported. |
20192362 | Short time ion pulse extraction from the Dresden electron beam ion trap. | We present measurements of the extraction of short time pulses of highly charged ions (4 keV, Ar(16+)) from the Dresden electron beam ion trap. Thereby the dependence of the extractable ionic charge on the extraction regime was investigated. The ion extraction time was varied between 20 ns and 1 micros. Furthermore the production of carbon ions and the influence of the extraction regime on the pulse widths was investigated to obtain information about the suitability of the Dresden EBIS-A in synchrotron based particle therapy facilities. |
20192363 | Recent results of the laser ion source facility at INFN-LNS and applications to nuclear and applied research. | A pulsed neodymium-doped yttrium aluminum garnet laser ion source has been used as proton beams generator. The laser wavelength is 1064 nm, the pulse duration is 9 ns and the intensity reaches 10(10) W/cm(2). Laser irradiates hydrogenated polymers targets located in a chamber at 10(-7) mbar. The ions are post-accelerated in a suitable chamber by 30 kV of voltage between the target, positively biased, and the following ground electrode. The extracted beams is characterized through a time-of-flight technique. Possible applications to the field of nuclear physics, such as nuclear excitation and de-excitations, nuclear reactions and nuclear fusion, will be presented and discussed. |
20192365 | Magnetic plasma confinement for laser ion source. | A laser ion source (LIS) can easily provide a high current beam. However, it has been difficult to obtain a longer beam pulse while keeping a high current. On occasion, longer beam pulses are required by certain applications. For example, more than 10 micros of beam pulse is required for injecting highly charged beams to a large sized synchrotron. To extend beam pulse width, a solenoid field was applied at the drift space of the LIS at Brookhaven National Laboratory. The solenoid field suppressed the diverging angle of the expanding plasma and the beam pulse was widened. Also, it was observed that the plasma state was conserved after passing through a few hundred gauss of the 480 mm length solenoid field. |
20192364 | The Brookhaven National Laboratory electron beam ion source for RHIC. | As part of a new heavy ion preinjector that will supply beams for the Relativistic Heavy Ion Collider and the National Aeronautics and Space Administration Space Radiation Laboratory, construction of a new electron beam ion source (EBIS) is now pleted. This source, based on the successful prototype Brookhaven National Laboratory Test EBIS, is designed to produce milliampere level currents of all ion species, with q/m=(1/6)-(1/2). Among the ponents of this source are a 5 T, 2-m-long, 204 mm diameter warm bore superconducting solenoid, an electron gun designed to operate at a nominal current of 10 A, and an electron collector designed to dissipate approximately 300 kW of peak power. Careful attention has been paid to the design of the vacuum system, since a pressure of 10(-10) Torr is required in the trap region. The source includes several differential pumping stages, the trap can be baked to 400 C, and there are non-evaporable getter strips in the trap region. Power supplies include a 15 A, 15 kV electron collector power supply, and fast switchable power supplies for most of the 16 electrodes used for varying the trap potential distribution for ion injection, confinement, and extraction. The EBIS source and all EBIS power supplies sit on an isolated platform, which is pulsed up to a maximum of 100 kV during ion extraction. The EBIS is now fully assembled, and operation will be beginning following final vacuum and power supply tests. Details of the ponents are presented. |
20192366 | Design study of primary ion provider for relativistic heavy ion collider electron beam ion source. | Brookhaven National Laboratory has developed the new preinjector system, electron beam ion source (EBIS) for relativistic heavy ion collider (RHIC) and National Aeronautics and Space Administration Space Radiation Laboratory. Design of primary ion provider is an essential problem since it is required to supply beams with different ion species to multiple users simultaneously. The laser ion source with a defocused laser can provide a low charge state and low emittance ion beam, and is a candidate for the primary ion source for RHIC-EBIS. We show a suitable design with appropriate drift length and solenoid, which helps to keep sufficient total charge number with longer pulse length. The whole design of primary ion source, as well as optics arrangement, solid targets configuration and heating about target, is presented. |
20192368 | Electron beam ion source and electron beam ion trap (invited). | The electron beam ion source (EBIS) and its trap variant [electron beam ion trap (EBIT)] celebrated their 40th and 20th anniversary, respectively, at the EBIS/T Symposium 2007 in Heidelberg. These technologically challenging sources of highly charged ions have seen a broad development in many countries over the last decades. In contrast to most other ion sources the recipe of improvement was not "sorcery" but a clear understanding of the physical laws and obeying the technological constraints. This review will report important achievements of the past as well as promising developments in the future. |
20192367 | Status report of the Dresden EBIS/EBIT developments. | We give an overview about latest developments and measurements with the Dresden electron beam ion source family pact and economically working table-top sources of highly charged ions. The ion sources are potential tools for various applications such as for use bination with accelerators in medical particle therapy, as charge breeder or ion trap injector, as ion sources for a new generation of focused ion beam devices and for applications together with time-of-flight secondary mass spectrometers. |
20192370 | The laser ion source trap for highest isobaric selectivity in online exotic isotope production. | The improvement in the performance of a conventional laser ion source in the laser ion source and trap (LIST) project is presented, which envisages installation of a repeller electrode and a linear Paul trap/ion guide structure. This approach promises highest isobaric purity and optimum temporal and spatial control of the radioactive ion beam produced at an online isotope separator facility. The functionality of the LIST was explored at the offline test separators of University of Mainz (UMz) and ISOLDE/CERN, using the UMz solid state laser system. Ionization efficiency and selectivity as well as time structure and transversal emittance of the produced ion beam was determined. Next step plete characterization is the construction and installation of the radiation-hard final trap structure and its first online application. |
20192369 | Ion production from solid state laser ion sources. | Laser ion sources based on resonant excitation and ionization of atoms are well-established tools for selective and efficient production of radioactive ion beams. Recent developments are focused on the use of the state-of-the-art all solid-state laser systems. To date, 35 elements of the periodic table are available from laser ion sources based on tunable Ti:sapphire lasers. Recent progress in this field regarding the establishment of suitable optical excitation schemes for Ti:sapphire lasers are reported. |
20192372 | Enhanced surface production in H- ion sources by introducing a negatively biased secondary electrode. | A transformer coupled plasma negative hydrogen ion source with an external rf antenna has been developed at SNU, which is capable of continuous operation with long lifetime. A positively biased plasma electrode (PE) has been successfully used for the optimization of H(-) extraction. With molybdenum-coated stainless steel PE, the enhancement of H(-) production at the electrode surface was observed at the bias voltage lower than the plasma potential. However, the low bias voltage is unfavorable to H(-) beam extraction since the negative ions are repelled. A second electrode is inserted in front of the PE to enhance H(-) production at the electrode surface without impeding beam extraction. By biasing the secondary electrode (SE) more negatively, H(-) production is clearly enhanced although the SE itself reduces H(-) beam currents because of suppressed electron transport in front of the PE. In this configuration enhancement of surface productions is most pronounced in tantalum electrode among various electrode materials. |
20192371 | A high-current light-ion injector for tandem accelerators. | A dual-source injector for tandem accelerators to produce negative ion currents of H, D, and He has been developed and built. The system consists of a central vacuum enclosure that modates two multicusp ion sources. Beam currents of several mA of H(-) and D(-) have been obtained by direct negative extraction of one of the multicusp ion sources. The yield for He(-) was optimized applying differentially pumped vacuum sections that support pensation in the He(+) transport section a well as low neutralization loss of He(-) after charge exchange. In addition, an optimized extraction geometry and beam transport system enabled in excess of 10 mA He(+) within the low acceptance of the charge exchange canal. Early measurements yielded approximately 50 microA for He(-) using Li as a charge exchange medium, but currents over 100 microA are anticipated if Na would be used. |
20192374 | Study on transport of negative ion plasma using dc laser photodetachment method. | Transport of negative ion containing plasma was studied in a hydrogen plasma by injecting a semiconductor laser to make an electron density perturbation by photodetachment of negative ions. Change due to laser irradiation on electron saturation current to a Langmuir probe and that on electron current extracted through an orifice biased at the anode potential were measured phase sensitively by a lock-in-amplifier. The measured transport velocity of the negative ion containing plasma was about 1.4x10(5) cm/s for both cases. The photodetachment signal measured through the orifice had given a larger ratio of negative ion density to electron density. Change in transport of negative ion containing plasma around the Langmuir probe has been also investigated by detecting photodetachment signal onto electron current extracted through an orifice. |
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