bluuebunny/crossref_metadata_2025 huggingface dataset:
Iper-ideal kinetic constraints in continuum mechanics
Authors: Vignolo Stefano , Bruno Danilo
Published: July 2002

A geometrical approach to Lagrangian formulation of continuum mechanics in the language of jet-bundles theory is proposed. The resulting environment allows one to deal with a particular class of kinetic constraints, through a suitable implementation of Gauss’ principle. A variational formulation of systems subject to such constraints is also outlined. Two explicit examples are given.
A planar Runge–Lenz vector
Authors: Kamath S. G.
Published: July 2002

Following Dahl’s method an exact Runge–Lenz vector M with two components M1 and M2 is obtained as a constant of motion for a two particle system with charges e1 and e2 whose electromagnetic interaction is based on Chern–Simons electrodynamics. The Poisson bracket {M1,M2}≠Lz but is modified by the appearance of the product e1e2 as central charges.
Effect of the monomer structure on the dynamics of semidilute polyalkylmethacrylate solutions: A quasielastic light and neutron scattering investigation
Authors: Magazù S. , Villari V. , Faraone A. , Maisano G. , Janssen S.
Published: July 2002

The study of the microscopic origin of the slow relaxation modes in the autocorrelation functions of some entangled polymer solutions has recently given rise to much experimental and theoretical work. The aim is to highlight the role of concentration, molecular weight, and temperature on the slow modes and to what extent the entanglement phenomena are responsible for their appearance. The present work reports on the comparison between the dynamics of homologous polymers with different side unit lengths, by use of quasi-elastic light and neutron scattering. The investigation, carried out on both mesoscopic and microscopic scales, with different concentrations and chain lengths, evidenced different dynamical properties in the three polymer solutions. In particular, longer side chains give rise to a bigger volume excluded to the other segments, obstructing the entanglements responsible for the slow relaxation modes and favoring the mobility of segments.
Supersymmetric spin networks
Authors: Ling Yi
Published: July 2002

In this article we study the construction of supersymmetric spin networks, which has a direct interpretation in context of the representation theory of the superalgebra. In particular we analyze a special kind of spin network associated with superalgebra Osp(1|2n). It turns out that the set of corresponding spin network states forms an orthogonal basis of the Hilbert space L2(A/G), and this argument holds even in the q-deformed case. The Osp(n|2) spin networks are also discussed briefly. We expect they could provide useful techniques to quantum supergravity and gauge field theories from the point of nonperturbative view.
Center-of-mass distribution of a polymer near a repulsive wall
Authors: Eisenriegler E. , Maassen R.
Published: July 2002

An exact analytic expression is obtained for the center-of-mass density profile of free ideal polymer chains in a half-space bounded by a hard planar wall. The result differs qualitatively from the monomer density profile and the density profiles of chain ends or midpoints.
Continuum percolation in athermal mixtures of flexible and rigid macromolecules
Authors: Wang Xiaoling , Chatterjee Avik P.
Published: July 2002

An integral equation treatment of connectedness percolation in macromolecular fluids is extended to athermal mixtures of semiflexible and rodlike polymers. The percolation threshold for formation of a geometrically connected network of rodlike particles dispersed in a medium of flexible polymers is investigated as a function of the particle aspect ratio. Results are also presented for a one-component model of identical rodlike particles in the absence of a matrix. The dependence of critical volume fraction on rod aspect ratio is strikingly similar in both instances, and close to that predicted by an analytic thread-chain approximation. The primary effect of explicitly including the athermal, flexible, matrix polymer molecules is a reduction of the critical volume fraction by a factor which depends only weakly on the aspect ratio of the rodlike particles.
An optical-optical double resonance study of the d3sσg(1Πg) Rydberg state of O2 using b(1Σg+) as the resonant intermediate state
Authors: Ridley Trevor , Lawley Kenneth , Sheard Howard , Donovan Robert
Published: July 2002

The v=0 level of the d3sσg(1Πg) Rydberg state of O2 has been excited in a two-color optical-optical double resonance (OODR) multiphoton ionization experiment via b(1Σg+: v=0,J=0–16). Rotational term values are reported for J=1–18. A 1+(1+1′) OODR scheme was used, followed by ionization with one more probe photon and detection in the O2+ channel. There are several power-dependent features of the spectra, notably accidental resonant enhancement of the ionization step with an additional pump photon, which indicate that the b state could be a useful resonant intermediate for accessing both higher gerade and ungerade states of O2.
Foundations for relativistic quantum theory. I. Feynman’s operator calculus and the Dyson conjectures
Authors: Gill Tepper L. , Zachary W. W.
Published: July 2002

In this paper, we provide a representation theory for the Feynman operator calculus. This allows us to solve the general initial-value problem and construct the Dyson series. We show that the series is asymptotic, thus proving Dyson’s second conjecture for quantum electrodynamics. In addition, we show that the expansion may be considered exact to any finite order by producing the remainder term. This implies that every nonperturbative solution has a perturbative expansion. Using a physical analysis of information from experiment versus that implied by our models, we reformulate our theory as a sum over paths. This allows us to relate our theory to Feynman’s path integral, and to prove Dyson’s first conjecture that the divergences are in part due to a violation of Heisenberg’s uncertainly relations.
One-dimensional potential barrier model of protein folding with intermediates
Authors: Jun Bokkyoo , Weaver David L.
Published: July 2002

Protein folding is modeled as one-dimensional diffusion in a potential with square wells representing folding species and square barriers representing transitions among the species. Within the context of the model, one or more intermediate species can either speed up or slow down folding, depending on their energy and on the potential barrier(s) to the final folded state. Intermediate species in deep potential wells may reduce the probability in the final state, as well as slowing the overall folding process. The potential barrier model is consistent with protein folding taking place by diffusion, collision and coalescence of marginally stable subunits of the protein in a sequential but, in principle, arbitrary order, as in the diffusion-collision model. Using parameters taken from the structures of three-helix bundle proteins the potential barrier model gives folding rates consistent with recent experiments on these proteins.
Near ultraviolet photodissociation of allene and propyne
Authors: Qadiri Rafay H. , Feltham Emma J. , Cottrill Emily E. H. , Taniguchi Nori , Ashfold Michael N. R.
Published: July 2002

The fragmentation dynamics of allene and propyne molecules following photoexcitation at 203.3, 209.0 and 213.3 nm have been investigated by H (Rydberg) atom photofragment translational spectroscopy methods. Contrary to conclusions reached in previous photochemical studies of these molecules, at a photolysis wavelength of 193 nm, we find the translational energy spectra associated with the H atom product forming channel in both molecules to be essentially identical, and to have a form that is reproduced well by an approximate statistical model that assumes population of all possible vibrational states of the H2CCCH partner. Such behavior can be most readily accommodated by assuming that, for both molecules, at the excitation energies used in the present work, internal conversion to, and isomerization on, the ground state potential energy surface precedes fragmentation.
Water confined in silica gel and in vycor glass at low and room temperature, x-ray diffraction study
Authors: Fouzri Afif , Dorbez-Sridi Rachida , Oumezzine Mohamed
Published: July 2002

X-ray diffraction experiments on water confined in silica gel powder hydrated at 22% and 50% and in vycor glass hydrated at 25% are presented and analyzed at room temperature and down to 77 K. At room temperature, the molecular packing at the level of the first neighbors is found similar to that in bulk water, but a distortion is observed at the level of the second neighbors. At low temperature, the intensity of water confined in silica gel powder show evidence for the simultaneous presence of cubic ice and uncrystallized water.
Molecular dynamics simulation study of the high frequency sound waves in the fragile glass former orthoterphenyl
Authors: Mossa S. , Monaco G. , Ruocco G. , Sampoli M. , Sette F.
Published: July 2002

Using a realistic flexible molecule model of the fragile glass former orthoterphenyl, we calculate via molecular dynamics simulation the collective dynamic structure factor S(Q,ω), recently measured in this system by inelastic x-ray scattering. The comparison of the simulated and measured dynamic structure factor, and the study of the S(Q,ω) in an extended momentum (Q), frequency (ω), and temperature (T) range allows us (i) to conclude that the utilized molecular model gives rise to S(Q,ω) in agreement with the experimental data, for those thermodynamic states and Q values where the latter are available; (ii) to confirm the existence of a slope discontinuity on the T dependence of the sound velocity that, at finite Q’s, takes place at a temperature Tx higher than the calorimetric glass transition temperature Tg; (iii) to find that the value of Tx is Q-dependent and that its Q→0 limit is consistent with Tg. The latter finding is interpreted within the framework of the current description of the dynamics of supercooled liquids in terms of exploration of the potential energy landscape.
Electron cyclotron resonance ion source one-dimensional fluid modeling
Authors: Edgell Dana H. , Kim Jin-Soo , Bogatu Ioan N. , Pardo Richard C. , Vondrasek Richard C.
Published: July 2002

A one-dimensional (1D) fluid computer model for multiple ion species in an electron cyclotron resonance ion source (ECRIS) plasma has been developed. The ions species are assumed to be highly collisionally coupled and are treated using 1D fluid equations. The non-Maxwellian anisotropic electron distribution function is modeled by a 1D bounce-averaged Fokker–Planck code. ECR heating is included in the model as a quasilinear rf-diffusion term including relativistic detuning, rf pitch-angle scattering, and multiple resonance frequencies/locations. In a typical ECRIS, the electrons are very noncollisional and confined magnetically. The ions follow this electron confinement via the electrostatic potential. The 1D axial electrostatic potential profile predicted by the model shows an ion confining core electrostatic well as expected in ECRIS plasmas. Modeling results for the Argonne National Laboratory ECR-I ECRIS configuration are presented along with a discussion of the difficulties in benchmarking the model with Faraday cup measurements.
Collision physics in ECR and EBIS/T
Authors: Becker Reinard
Published: July 2002

Today’s most common ion sources for the production of highly charged ions, the electron cyclotron resonance (ECR) source and the electron-beam ion source and trap (EBIS/T) differ very much in their construction, while the basic physical processes are the same in both sources. In both sources highly charged ions are created by electron impact in a stepwise ionization process and trapped in an electrostatic potential well. As a consequence, heating of ions by small angle Coulomb collisions with fast electrons takes place in a similar way for both sources. A controversy of the past on the physical nature of the benefit of gas mixing in ECR now has disappeared, explaining the gas mixing effect as mainly due to ion cooling by ion–ion collisions, which has been observed in EBIT and called “evaporative cooling.” In spite of all these common processes, the resulting charge state spectra look very different for both source types, typically narrow for EBIS and wide for EBIT and ECR. This is a result of radiative recombination and charge exchange, limiting the buildup of higher charge states under steady state conditions in ECR ion sources and in EBIT.
Reducing ion-beam noise of vacuum arc ion sources
Authors: Anders André , Hollinger Ralph
Published: July 2002

Vacuum arc ion sources are known for delivering high currents of metal ion beams. By Langmuir probe and Faraday cup measurements it is shown that fluctuations of the ion-beam current are due to the fluctuations of plasma density which in turn are due to the explosive nature of plasma production at cathode spots. Humphries and co-workers and later Oks and co-workers have shown that beam fluctuations can be reduced by inserting biased meshes in the plasma. Here, the idea of ion extraction at kV level with post-acceleration is investigated. The high voltage allows us to use coarse, ridged meshes or grids. The combination of an extractor operating in the overdense plasma regime with post-acceleration lead to very reproducible, practically “noiseless” ion beams, however, at the expense of low ion current density. The noise reduction is due to ion optics effects; more ions supplied by plasma lead to greater ion-beam losses after the first extraction system. Although the current setup is not suitable for a heavy ion fusion injector due to the low beam current and the risk of extractor voltage breakdown, further development of the concept may lead to reproducible beam pulses of sufficiently high current and brightness.
Cylindrical hollow anode ion source
Authors: Miljevic Vujo
Published: July 2002

The hollow anode ion-electron source is based on the hollow anode discharge, a kind of plasma utilizing a cold cathode and a tiny bore or slot in the anode that simultaneously serves as exit aperture of the ion (or electron) source. These sources are particularly suitable, for example, for deposition of films on large flat surfaces. The length of the slot-shaped hollow anode aperture can be sufficient so that, together with sweeping of either source or substrate, large area substrates can be processed, thereby simulating the function of large area plasma sources.
Discharge characteristics and H−-ion production in a bucket ion source
Authors: Kosaka T. , Yamashita H. , Miyamoto S. , Inoue S. , Horiike H.
Published: July 2002

The cusp leak was found to have a profile of multiple peaks, when measured near the filaments. This is attributable to multiple discharge paths of primary electrons. The supercusp magnetic configuration is one of several configurations in which strong magnetic-field lines flow into the backplate from the extraction grid. The negative-ion current was measured with a Faraday cup with a magnetic filter changing current from 0 to 100 A. The plasma characteristics were measured in the driver and the extraction regions.
Performance of the K+ ion diode in the 2 MV injector for heavy ion fusion
Authors: Bieniosek F. M. , Henestroza E. , Kwan J. W.
Published: July 2002

Heavy ion beam inertial fusion driver concepts depend on the availability and performance of high-brightness high-current ion sources. Surface ionization sources have relatively low current density but high brightness because of the low temperature of the emitted ions. We have measured the beam profiles at the exit of the injector diode, and compared the measured profiles with EGUN and WARP-3D predictions. Spherical aberrations are significant in this large aspect ratio diode. We discuss the measured and calculated beam size and beam profiles, the effect of aberrations, quality of vacuum, and secondary electron distributions on the beam profile.
Effects of ion pumping in a pulsed Penning source
Authors: Sato Y. , Miyata T. , Miyoshi T. , Kitagawa A. , Muramatsu M. , Murakami T. , Honma T. , Yamamoto M. , Ogawa H. , Yamada S.
Published: July 2002

We recently reported on the first observation of ion-pumping phenomenon in a low-duty pulsed Penning source at the heavy-ion medical accelerator (HIMAC) in Chiba and its effectiveness to produce multiply charged ions [Y. Sato et al., Nucl. Instrum Methods Phys. Res. A 450, 231 (2000)]. In the Penning-ionized gauge ion source (PIGIS) of the HIMAC, the gas flow is not being pulsed, but there is a transient pressure response in the source when the arc is pulsed that permits the production of high-charge-state ions under a reasonably low gas pressure obtained by ion pumping. The best record for Ar8+ is 700 eμA in a peak under a constant gas flow of 0.2 cc/min, an extraction voltage of 24 kV, and a pulsed arc power of 1 kV and 5 A with a duty factor of 0.5% (25 W on average). This yield is higher than those of cw PIGISs by a factor of 100–1000 having a similar design and power (peak). This article gives a brief review for the mechanism and effects of ion pumping in a pulsed PIGIS.
Radio-frequency ovens for ECR ion sources
Authors: Cavenago M. , Kulevoy T. , Petrenko S.
Published: July 2002

Radio-frequency (rf) ovens have perspective advantages over their Ohmic equivalent in terms of uniformity of heating, separation (extending lifetime and use of reactive sample) and insulation; on the other side, rf losses in the coil must be minimized. Several geometries, crucibles, and coils were tested to optimize efficiency (power in the sample/total power); the final axial geometry with a copper coil is described, discussing the optimization of thermal contacts. A script to simulate the two-dimensional geometry of a rf oven (in particular, the wire separation and shape) was written; optimal working frequencies were found to be about or over 1 MHz, as confirmed by experiments, while the coil should be slightly longer than the sample. A temperature of 1680 K was reached with an iron crucible and 80 W of total rf power; silver and copper evaporations were tested; and carbon crucibles can reach higher temperatures (1750 K in a preliminary version).
Design of an all-permanent-magnet ECR ion source at the Cyclotron and Radioisotope Center
Authors: Yamazaki A. , Fujita M. , Tanaka E. , Shinozuka T. , Yokoi T. , Ozawa T. , Tanaka H.
Published: July 2002

A new electron cyclotron resonance ion source has been designed and equipped with the new cyclotron at the Cyclotron and Radioisotope Center, Tohoku University. The ion source consists of a full permanent-magnet system with a microwave frequency of 14.5 GHz. The source has the following three main features: (1) V-style magnetization, (2) flat-bottomed magnetic-field distribution, and (3) field adjusting system. The measured magnetic-field strength in the plasma chamber is about 8% weaker than the calculated value. The extracted beam current is measured as the preliminary result.
A new ECR ion source for atomic physics research at Institute of Modern Physics
Authors: Zhang Z. M. , Zhao H. W. , Zhang X. Z. , Guo X. H. , Li X. X. , Sun L. T. , Cao Y. , Feng Y. C. , Li J. Y. , Lei H. L. , Wang H. , Gao J. Y. , Ma B. H.
Published: July 2002

A new electron cyclotron resonance (ECR) ion source (LECR3—Lanzhou Electron Cyclotron Resonance Ion Source No. 3) has been constructed this year. The main purpose of this source is to provide highly charged ion beams for atomic physics and surface physics research. The design of this ion source is based on the IMP 14.5 GHz ECR ion source (LECR2—Lanzhou Electron Cyclotron Resonance Ion Source No. 2) with double rf heating by inserting waveguide directly and aluminum chamber. Furthermore, the volume of the plasma chamber is larger than that of LECR2 so as to increase the rf power and improve beam intensity for highly charged ions. But the hexapole field on the chamber wall is kept the same value in order to compare with the performance of LECR2. After only four days conditioning the first test results were obtained. The final result of this ion source is expected to be better than LECR2’s.
A compact 2.45 GHz ECR ion source with permanent magnets for material science
Authors: Tojyo E. , Katayama I. , Jeong S. C. , Oyaizu M. , Ishiyama H. , Kawakami H. , Enomoto K. , Miyatake H.
Published: July 2002

A compact 2.45 GHz electron cyclotron resonance (ECR) ion source has been developed as an etching device for diffusion experiments in the solid-state matter. This source is a little bit different from those of a usual industrial ECR device, i.e., it is to extract high intensity beams from a relatively small single hole with low emittance under the extraction voltage of several kV and high vacuum. Summary of the design, manufacture, and the initial beam extraction tests are described.
ECR ion sources at the Institute of Modern Physics: From classical to fully superconducting device
Authors: Zhao H. W. , Zhang X. Z. , Zhang Z. M. , Guo X. H. , Yuan P. , Cao Y. , Sun, L. T. , Wei B. W. , Wang Y. F. , Zhan W. L. , Xie D. Z.
Published: July 2002

Electron cyclotron resonance (ECR) ion sources are used for cyclotron complex and atomic physics research at the Institute of Modern Physics (IMP). Intense beams of highly charged gaseous and metallic ions could be produced by the IMP 14.5 GHz ECR ion source (LECR2-Lanzhou Electron Cyclotron Resonance Ion Source No. 2). A particular emphasis has been put on the production of metallic ion beams recently. Metallic ion beams of Mg, Ca, Fe, Ni, Cu, Zn, and Pb were tested at the IMP 14.5 GHz ECR ion source (LECR2) to improve beam intensities and long-term stability. A new ECR ion source (Lanzhou Electron Cyclotron Resonance Ion Source No. 3), an upgraded version of the IMP 14.5 GHz ECR (LECR2) but with double-frequency wave heating (10 GHz+14.5 GHz), is under commissioning. The preliminary results of this new source will be presented. To satisfy the requirements of the heavy ion cooling storage ring that is under construction at IMP, a fully superconducting ECR ion source (Lanzhou Electron Cyclotron Resonance Ion Source with Superconducting Coils) with a completely new structure is being developed for the production of intense heavy ion beams of very high charge states, such as Xe30+ and U40+. The superconducting magnet consists of three axial solenoid coils and six saddle-curved sextupole coils with a cold iron structure as field booster and clamp. At full excitation, this magnet assembly will produce maximum peak fields on axis of 4.0 T at the injection, 2.2 T at the extraction region, and a radial sextupole field of 2.0 T at plasma chamber wall. The design features and status of this new superconducting ECR ion source will be presented.
Plasma emission in vacuum arc and rf-discharge plasma sources
Authors: Boonyawan D. , Davydov S. , Yotsombat B. , Chirapatpimol N. , Vilaithong T.
Published: July 2002

Optical emission spectra from plasma produced by a copper vacuum arc with argon and nitrogen have been investigated for the case when the plasma was guided by a straight solenoid. The spectra have been compared with those obtained from inductively coupled rf multicusp discharge in the 10−4–10−2 Torr argon and nitrogen pressure range and at an input power of up to 500 W. It has been found that the spectral line intensity distributions of neutral and ion species for arc and rf discharge were different. Also, the intensity evolutions of the lines have shown a different behavior between the arc current and rf power. Electron excitation temperature (Tex) for rf argon plasma at low pressure has been found to be approximately 2.5 eV which was about ten times higher than for Cu-argon arc discharge. Possible mechanisms of ionization-excitation of guest atoms/molecules in the case of metal vacuum arc discharge are discussed.
Energy distribution of the compact microwave ion source for extremely low voltage ion extraction
Authors: Gotoh Y. , Nakajima K. , Hagiwara T. , Tsuji H. , Ishikawa J.
Published: July 2002

The energy distribution of the ion beam extracted from the compact microwave ion source for extremely low voltage ion extraction was measured with Ar and CO as a discharge gas. The energy distribution was measured by the retarding field method, and changes with respect to the change in gas pressure were observed. The obtained data were arranged by the peak energy and the energy spread. For both gases, the peak energy and the energy spread decreased with an increase in the gas pressure. The energy spread of approximately 5 eV with the peak energy of 15 eV were obtained for Ar gas at the pressure of 10−2 Pa. For CO gas, the peak energy was higher than Ar and approximately 20 eV. The energy spread was 6 eV at the pressure of 10−2 Pa. These values agreed with the peak energy and energy spread that were estimated previously from the mass spectra analysis. Since the ion source was designed to be used in the researches of low energy ion-solid interaction, these characteristics satisfy the requirements for this purpose.
Fabrication of radioactive stents by ion implantation
Authors: Huttel Erhard , Kaltenbaek Johann , Schloesser Klaus , Schweickert Hermann
Published: July 2002

Worldwide about one million patients require treatment of stenosed coronary arteries annually. Often a tubular stainless steel mesh (stent) is implanted to mechanically support the injured vessel. Restenosis, an abundant complication (20%–30%) can be prevented, if the vessel is treated with ionizing radiation. Stents can deliver radiation if they are made radioactive. The radio isotope P32 is well suited when ion implanted. Radioactive ions sources require high efficiency to keep the radioactive inventory small. Reliability, ease of operation, and maintenance are mandatory. A small emittance is important to minimize losses during mass separation and beam transport. A 2.45 GHz ECR source was developed for the implantation of P32. The source consists of two coils for the axial and a permanent hexapole for the radial confinement. The microwaves are fed in radially by a loop connected to a silver plated brass tube surrounding the plasma chamber. The plasma chamber is made from Pyrex. Neutron activated phosphorus, containing 30 ppm P32, is introduced from the rear end on a rod. As support gas D2 is used. By this P+32 can be separated from (31PD)+. The extraction is done in two steps: 60 kV–30 kV–ground. Mass separation is accomplished by a double focusing 90° magnet (radius 500 mm). During four years of operation about 1000 radioactive stents per year have been provided for animal experiments and clinical trials. Only one maintenance to exchange the extraction system due to degradation of high voltage stability was required so far.
Surface plasma source for heavy negative ion production
Authors: Dudnikov Vadim , Dudnikova Galina , Farrell J. Paul
Published: July 2002

Optimization of a surface plasma source for production of heavy negative ions and results of computer simulations used to optimize ion flux formation, negative ion transport, and space charge neutralization are presented.
Spatial uniformity of negative ion production in volume negative ion source
Authors: Morishita T. , Miyamoto K. , Fujiwara Y. , Hanada M. , Kitagawa T. , Kashiwagi M. , Okumura Y. , Watanabe K.
Published: July 2002

A spatial uniformity of negative ion production has been studied experimentally in a tandem-type volume negative ion source, where the plasma is divided into two regions by a magnetic filter, i.e., a driver region and an extraction region near the plasma grid (PG). A plasma density profile and the negative ion beam profile were measured. By the Langmuir probe measurement, a strong nonuniformity of the plasma density was observed near the plasma grid when the plasma grid is biased electrically with respect to the anode. By changing the polarity of the bias voltage, the deviation of the plasma density profile changed to the direction of E×B. In the pure hydrogen operation, the extracted beam profile corresponded to the plasma density profile in the extraction region. In the Cs-seeded operation, on the other hand, the uniformity of the beam current density became uniform despite the nonuniformity of the plasma density profile in the extraction region. The uniformity of the negative ions corresponded to the plasma uniformity in the driver region. These results indicate that the negative ions are not produced by positive ions in the extraction region in the Cs-seeded operation. We conclude that the negative ions are produced mainly by neutral atoms produced in the driver region via the surface production on the PG.
Improvement of a large negative ion source for the Large Helical Device neutral beam injector
Authors: Takeiri Y. , Ikeda K. , Hamabe M. , Osakabe M. , Kaneko O. , Oka Y. , Tsumori K. , Asano E. , Kawamoto T. , Sato M.
Published: July 2002

For compensation of the magnetically deflected beamlets, a new type of grid system has been applied to a large negative ion source of a negative-ion-based neutral beam injector in the Large Helical Device (LHD) fusion experimental machine. Corresponding to deviation of the negative ion beamlet trajectory due to the electron suppression magnetic field at the extraction grid, the exit aperture of the extraction grid is displaced to cancel the beamlet deflection by electrostatic lens effect. As a result, the beamlet deflection was suppressed less than 2 mrad in a wide range of energy of 110–180 keV, and the port-through efficiency of the injected beam was improved to 90%–95% from 70%–75% in the case of the previous compensation by the grounded grid aperture displacement. The injected beam power was increased to 3.5 MW with an energy of 165 keV using one injector. To improve beam uniformity of the large area beam, individual arc currents through filaments are controlled for uniform plasma production, with independent 12 arc power supplies connected to 12 filament power supplies. The initial results show good controllability of the individual arc current distribution at a high arc power. The improvement of the ion source performance would lead to an increase in the injection power in the following LHD experimental campaign.
Power absorption and intense collimated beam production in the pulsed high-power microwave ion source at RIKEN
Authors: Bhattacharjee Sudeep , Nakagawa Takahide , Nomiya Yoshio , Ikegami Yuji , Kase Masayuki , Goto Akira , Yano Yasushige
Published: July 2002

Microwave power absorption and intense collimated beam production is studied in the pulsed high-power microwave ion source at RIKEN by varying the radius of the plasma chamber (circular waveguide) in integer multiples of a quarter wavelength of the wave (nλ/4), where n is an integer (n=2–5) and λ is the vacuum wavelength of microwaves. Optimum wave coupling and power absorption due to a change in the microwave power density and the electric field distribution are investigated from measurements of the total achievable current density and the optical intensity, emitted by the pulsed argon plasma in the visible region at a wavelength of 404.3 nm. Results indicate a nonlinear absorption of microwave power. Depending upon the pressure, a decrease in the chamber radius leads to an enhancement of the electron temperature. Favorable beam conditions, i.e., highest density and temperature are obtained for the chamber with radius ≃λ.
Operation of the Relativistic Heavy Ion Collider Au− ion source
Authors: Steski D. B. , Alessi J. , Benjamin J. , Carlson C. , Manni M. , Thieberger P. , Wiplich M.
Published: July 2002

The Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory is beginning its second year of operation. A cesium sputter ion source injecting into a tandem Van de Graaff provides the gold ions for RHIC. The ion source is operated in the pulsed beam mode and produces a 500-μs-long pulse of Au− with a peak intensity of 290 μA at the entrance of the tandem. After acceleration in the tandem and post-stripping, this results in a beam of Au+32 with an intensity of 80 μA and an energy of 182 MeV. Over the last several years, a series of improvements have been made to increase the intensity of the pulsed beam from the ion source. Details of the source performance and improvements will be presented. In addition, an effort is under way to provide other beam species for RHIC collisions.
Development of a long-life ion source for ion-implantation application
Authors: Miyamoto N. , Miyabayashi K. , Yamashita T. , Fujisawa H.
Published: July 2002

The long-life version of a Bernas ion source is developed. It is called a Bernas-type electron active reflection (BEAR) ion source. The ion source has independently potential controlled reflectors, which are isolated from both an arc chamber and a filament. The potential of the reflectors is over 30 V negative with respect to the cathode potential. Because this potential can reflect enough emission electrons from the filament, the plasma production efficiency can be increased. In this method, we can minimize the arc voltage or a filament current compared with a conventional-type Bernas ion source, resulting in the reduction of a tungsten filament. Overall, the decrease in the filament diameter in the BEAR source was experimentally found to be below 50% of the conventional-type Bernas ion source.
A multiaperture electron filter for volume-type H− ion source
Authors: Hahto S. , Leung K. , Persaud A. , Reijonen J.
Published: July 2002

Negative light ion beams have been used widely in many applications over the past decades. One of the most popular methods of producing H− and D− beams is the so-called volume production, in which a plasma is contained in a multicusp magnetic field. The beam is extracted using an electric field applied in the extraction gap. Accompanying the negative ions is up to 100 times greater number of electrons, which have to be removed from the beam. This is usually done by placing a transverse magnetic field in the extraction region. With this method the electrons can be quite effectively removed from the beam. The problem is that we dump a high intensity, high energy electron beam in the extraction electrode and dissipate a lot of power in the process. The negative ion beam is also deflected in this strong magnetic field which has to be corrected either by tilting the source compared to the extraction or by adding an opposite transverse magnetic field. In the latter method the beam is laterally displaced from the original axis. In the Plasma and Ion Source Technology Group at the Lawrence Berkeley National Laboratory, we are developing a multi-aperture extraction in which the electrons are removed from the beam before they are accelerated to high energy with the use of a honeycomb-structured electron filter and a weak magnetic field. This way the power dissipated by the electrons and the ion beam deflection are minimized. The initial results of these experiments will be described in this presentation.
Direct current surface plasma source with high emission current density
Authors: Dudnikov V. , Schmidt C. W. , Hren R. , Wendt J.
Published: July 2002

A surface plasma source for long-time dc operation with efficient production of negative ions and high emission current density has been designed and tested. Several modifications of the discharge system, beam extraction, cesium supply, and source design have been tested for long-time operation. The emission current density of H− ions has been increased to j=1 A/cm2 in the dc mode of operation with a discharge voltage, Ud=80 V; a discharge current, Id=0.9 A and a discharge power, P=70 W. Corresponding efficiency of the current density production S=j/P=15 A/cm2 kW is much higher than in modern positive ion sources. Source features determining an operational lifetime will be discussed.
Design of nondestructive emittance measurement device for H− beams
Authors: Gabor C. , Jakob A. , Meusel O. , Pozimski J. , Schäfer J. , Ratzinger U.
Published: July 2002

For the diagnostics of high-brightness particle beams as necessary for the European Spallation Source, spallation neutron source IFMIF (D1+), and HIDIF (Bi1+) nondestructive methods have to be developed. Conventional beam diagnostics are established, but are mostly destructive methods and suffer from the power density deposited on surfaces like slits or pinhole plates and beam loss. For negative ions a nondestructive method based on photoneutralization can be used to determine the transverse phase space distribution with high time resolution and a large number of phase space points. The interaction of laser light and H− ions produces a small number of neutral atoms as well as detached electrons. The beam of charged particles is separated magnetically from the neutral beam and the distribution of neutral hydrogen is measured. Under the assumption that the influence of the dipole is small enough, the laser induced emittance measurement can be used, e.g., near the entrance of radio-frequency quadrupole. The basic concept for the laser driven emittance measurement device will be presented together with design considerations and preliminary simulations on ion beam transport.
Analysis of negative ion velocity distribution at the extraction holes in a negative ion source
Authors: Makino K. , Sakurabayashi T. , Hatayama A. , Miyamoto K. , Ogasawara M.
Published: July 2002

Negative H− ion beams produced by a tandem-type H− ion source have good beam optics with a typical beam divergence angle of less than 5 mrad. However, the physical reason has not yet been made clear. To clarify the mechanism, we investigate a velocity distribution of negative ions at the extraction holes by a three-dimensional (3D) Monte Carlo transport code. In this code, surface-produced H− ion trajectories are calculated by numerically solving the 3D equation of motion for H− ions. The energy of the H− ions is relaxed through Coulomb collision with the background plasma (H+ ions), which has a low temperature of ∼1 eV in the tandem-type H− ion source. Therefore, energy relaxation by Coulomb collision plays an important role in good beam optics.
Propulsion technologies for exploration of the solar system and beyond (plenary)
Authors: Johnson Les
Published: July 2002

NASA’s Advanced Space Transportation Program (ASTP) is investing in technologies to achieve a factor of 10 reduction in the cost of Earth orbital transportation and a factor of 2 reduction in propulsion system mass and travel time for planetary missions within the next 15 years. Since more than 70% of projected launches over the next 10 years will require propulsion systems capable of attaining destinations beyond low-Earth orbit, investment in in-space technologies will benefit a large percentage of future missions. The ASTP technology portfolio includes many advanced propulsion systems. From the next-generation ion propulsion system operating in the 5–10 kW range to fission-powered multikilowatt systems, substantial advances in spacecraft propulsion performance are anticipated. Some of the most promising technologies for achieving these goals use the environment of space itself for energy and propulsion and are generically called “propellantless,” because they do not require onboard fuel to achieve thrust. An overview of state-of-the-art space propulsion technologies, such as solar and plasma sails, electrodynamic and momentum transfer tethers, and aeroassist and aerocapture, are described. Results of recent Earth-based technology demonstrations and space tests for many of these new propulsion technologies are discussed.
Two-axis rotatable magnet in ultrahigh vacuum
Authors: Heigl F. , Krupin O. , Kaindl G. , Starke K.
Published: July 2002

We present a rotatable magnet for ultrahigh vacuum (UHV) applications, with a pair of coils for small magnetic fields in the mOe range and an electromagnet for large fields up to 2 kOe. The magnet is based on a mechanism that permits one to exchange electromagnet and coils while keeping the sample in a measurement position. Combined with a rotatable sample, this setup is an excellent tool for in situ studies of magnetism in UHV, in which different techniques are combined.
High intensity challenge for electron cyclotron resonance ion sources (abstract) (plenary)
Authors: Lyneis C.
Published: July 2002

Research in nuclear physics with heavy ions continues to drive the development of electron cyclotron resonance (ECR) ion sources to both higher charge states and greater intensities. Already, the beam intensities from ECR ion sources have reached the 1 emA level for beams such as O6+ and Ar8+. However, the production of mA level beams from heavier, higher charge state beams presents significant challenges. The first challenge is to generate and confine a sufficiently dense plasma with a very low neutral density and high electron temperature to produce the needed ions. Fortunately, the density of the high charge state ECR plasmas scales roughly with the square of the microwave frequency, provided the magnetic field is scaled linearly with frequency and Bconfinement∼2Becr is maintained. At 28 GHz, the optimum confining fields are about 2 T, which can only be produced with superconducting magnets. The second challenge is to produce high intensity beams from solid feeds and this requires specialized ovens located close to the hot electron plasma. The third challenge is to efficiently extract and transport the intense beams without degrading the emittance. Traditionally, ECR sources have operated in the 10–20 kV range but at these voltages the space charge forces cause beam losses when the total extracted currents are many mA. The two main approaches are to operate at higher extraction voltage and to separate the desired charge state from the others extracted as early in the beam transport as possible. In this article we will review the current performance of high-field, high-frequency ECR ion sources such as RIKEN-18 GHz ECR, SERSE, and Phoenix, describe other ion sources now under construction such as the superconducting source VENUS at Berkeley, and discuss progress on the beam transport issues.
Performance of LHD-NBI H− ion source
Authors: Oka Y. , Takeiri Y. , Tsumori K. , Osakabe M. , Kaneko O. , Ikeda K. , Hamabe M. , Asano E. , Kawamoto T. , Grisham L.
Published: July 2002

The Large Helical Device-Neutral Beam Injector (LHD-NBI) system uses 40 A×180 keV (10 s) negative hydrogen ion sources. Three studies of the H− ion source are reported, i.e., conditioned status, co-accelerated electron beam component, and weight loss of tungsten filaments. Total injection numbers through experimental cycles sum up to ∼8000 shots with four ion sources on two beam lines. Injection power reached a maximum of 5.2 MW. The maximum energy achieved was 171 keV. A pulse length up to 80 s was reached with 0.5 MW. Electron fraction in the accelerated H− beam was evaluated by measuring the heat load on the electron beam dump. Total fraction of the power in the electron beam component deposited on the dump was evaluated to be 1.5%–6% with up to ∼1 Pa of H2. Stripped electrons which were produced inside acceleration gap comprised the majority compared to electrons extracted from source plasma. The weight loss of tungsten filament was 0.01–0.103 mgr/shot/filament. The total loss was ∼0.5% after ∼6500 shots. They were evaporated and a bit spotted. Distribution of the loss over the filament location in the plasma source and over the filament length along tungsten wire corresponded to the nonuniformity of the discharge plasma and H− ions.
Development of a Bi+ high current source for heavy ion driven plasma generators
Authors: Galonska M. , Volk K. , Ratzinger U.
Published: July 2002

The development of a high current bismuth ion source is motivated by heavy ion driven fusion (HIF) and is part of the conceptual design of a HIF-relevant Bi+ test injector with four beamlets, which could serve as a HIF driver front end element. Envisaged is the development of a 300 mA Bi+ injector that can deliver four parallel beams from a 500 kV platform with 75 mA per beam. The first prototype source is driven by an arc discharge and provides singly charged Bi ions with a fraction more than 92% of the total extracted current. At its perveance limit this source delivers current of 70 mA, with the corresponding voltage being 27.5 kV. The emittance of a 21 mA/18.2 keV beam was measured and it amounted to 0.27 π mm mrad (80%, normalized, 4 root mean square) provided by a seven hole extraction system. Based on these investigations a new ion source will be designed and tested that will deliver current of 75 mA at ion energies up to 65 keV. In order to fulfill the requirements of HIF the emittance has to be in the vicinity of 0.4 π mm mrad (normalized). In this article we give a brief description of the design of an advanced ion source. Based on experimental experience using the previous prototype source one major modification made is the construction of an external oven. The use of more than one filament to increase the source lifetime is also planned.
Hydrogen defects in Forsterite: A test case for the embedded cluster method
Authors: Braithwaite J. Spencer , Sushko Peter V. , Wright Kate , Catlow C. Richard A.
Published: July 2002

We present a theoretical study of several hydrogen defects in the upper mantle mineral forsterite using a quantum mechanical embedded cluster approach. We make extensive comparisons with results obtained using Mott–Littleton calculations and data from periodic density functional studies by ourselves and other authors. We show that the embedded cluster method gives reliable energies for a range of defect reactions, including cation vacancy formation, binding between defects, and formation of hydrogen defects by reaction with water. We propose that the embedded cluster techniques should be the method of choice when studying point defects in minerals.
A new method of scattering-angle scanning for optical beating light scattering spectroscopy
Authors: Sonehara Tsuyoshi , Tanaka Hajime
Published: July 2002

Heterodyne light scattering spectroscopy is one of the powerful methods used to study the dynamics of density and concentration fluctuations in simple and complex fluids. In conventional optical beating (heterodyne) techniques, however, the beam configuration must be readjusted each time the scattering angle is changed, so as to get the maximum efficiency of the optical mixing of the scattered and the local light. This readjustment process usually takes a long time, and furthermore, leads to the loss of information on the angular dependence of the scattering intensity, which is extremely sensitive to the optical configuration. Here, we report a new method of scattering-angle scanning that is free from the aforementioned problems, which is particularly suitable for optical beating (heterodyne) light scattering spectroscopy. In our method, the maximum optical mixing efficiency between the scattered and the local light can always be maintained amidst change in the scattering angle. Its validity is demonstrated for Rayleigh scattering. Our method also enables us to determine the absolute scattering angle with a very high accuracy, which is particularly important for Brillouin scattering measurements.
Intensity calibration for low energy photoelectrons based on simultaneous photocurrent measurement
Authors: Takeuchi Koichiro , Ushioda Sukekatsu
Published: July 2002

We have devised a method of obtaining an absolute intensity calibration for photoemission measurements. The calibration function a(Ek), where Ek is the measured electron kinetic energy, can be derived solely from the experimental data without any uncertain assumptions. The method is based on the relation between the integrated photoemission intensity and the sample current. This method is especially effective for low energy photoelectrons and is applicable even when the sample is biased with respect to the analyzer.