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Hollow Plasma in a Solenoid

Description: A ring cathode for a pulsed, high-current, multi-spot cathodic arc discharge was placed inside a pulsed magnetic solenoid. Photography is used to evaluate the plasma distribution. The plasma appears hollow for cathode positions close the center of the solenoid, and it is guided closer to the axis when the cathode is away from the center.
Date: November 30, 2010
Creator: Anders, Andre; Kauffeldt, Marina; Oks, Efim M. & Roy, Prabir K.
Partner: UNT Libraries Government Documents Department

On the neutralization of singly and multicharged projectiles during grazing interactions with LiF(100)

Description: Measurements are reported of scattered neutral fractions for Na, K, Cs, and Ne singly and multicharged ions, and of scattered negative ion fractions for incident O, F, and B projectiles grazingly incident on LiF(100) as function of projectile velocity. In the case of the Na and Ne incident ions, significant dependence of the scattered neutral fractions on incident charge state is found, which is most pronounced at the lowest investigated velocities. Possible reasons for the observed initial charge state dependence are considered. In addition, results are reported for the target azimuthal dependence of the final neutral fraction observed for grazingly incident 35 keV Cs{sup +7} ions.
Date: October 1996
Creator: Meyer, F. W.; Yan, Q.; van Emmichoven, P. Z.; Spierings, G. & Hughes, I. G.
Partner: UNT Libraries Government Documents Department

Beam charge and current neutralization of high-charge-state heavy ions

Description: High-charge-state heavy-ions may reduce the accelerator voltage and cost of heavy-ion inertial fusion drivers, if ways can be found to neutralize the space charge of the highly charged beam ions as they are focused to a target in a fusion chamber. Using 2-D Particle-In- Cell simulations, we have evaluated the effectiveness of two different methods of beam neutralization: (1) by redistribution of beam charge in a larger diameter, preformed plasma in the chamber, and (2), by introducing a cold-electron-emitting source within the beam channel at the beam entrance into the chamber. We find the latter method to be much more effective for high-charge-state ions.
Date: October 29, 1997
Creator: Logan, B.G. & Callahan, D.A.
Partner: UNT Libraries Government Documents Department

Calculation of beam neutralization in the IPNS-Upgrade RCS

Description: The author calculated the neutralization of circulating beam in this report. In the calculation it is assumed that all electrons liberated from the background molecules due to the collisional processes are trapped in the potential well of the proton beam. Including the dependence of ionization cross sections on the kinetic energy of the incident particle, the author derived the empirical formula for beam neutralization as a function of time and baseline vacuum pressure, which is applicable to the one acceleration cycle of the IPNS-Upgrade RCS.
Date: January 26, 1995
Creator: Chae, Yong-Chul
Partner: UNT Libraries Government Documents Department

Comments on velocity space relaxation in high charge-state plasma neutralizers

Description: Scaling of velocity space relaxation rates, which affect the final temperature of a natural beam, with ion charge state in plasma neutralizers is examined. Overall, this scaling indicates a substantial enhancement in emittance growth of the neutral beam with increase in the charge state of ions in plasma neutralizers. 9 refs.
Date: January 1, 1989
Creator: Hershcovitch, A.
Partner: UNT Libraries Government Documents Department

Generation of Initial Kinetic Distributions for Simulation of Long-Pulse Charged Particle Beams with High Space-Charge intensity

Description: Self-consistent Vlasov-Poisson simulations of beams with high space-charge intensity often require specification of initial phase-space distributions that reflect properties of a beam that is well adapted to the transport channel--both in terms of low-order rms (envelope) properties as well as the higher-order phase-space structure. Here, we first review broad classes of kinetic distributions commonly in use as initial Vlasov distributions in simulations of unbunched or weakly bunched beams with intense space-charge fields including: the Kapchinskij-Vladimirskij (KV) equilibrium, continuous-focusing equilibria with specific detailed examples, and various non-equilibrium distributions, such as the semi-Gaussian distribution and distributions formed from specified functions of linear-field Courant-Snyder invariants. Important practical details necessary to specify these distributions in terms of usual accelerator inputs are presented in a unified format. Building on this presentation, a new class of approximate initial kinetic distributions are constructed using transformations that preserve linear-focusing single-particle Courant-Snyder invariants to map initial continuous-focusing equilibrium distributions to a form more appropriate for non-continuous focusing channels. Self-consistent particle-in-cell simulations are employed to show that the approximate initial distributions generated in this manner are better adapted to the focusing channels for beams with high space-charge intensity. This improved capability enables simulation applications that more precisely probe intrinsic stability properties and machine performance.
Date: April 3, 2007
Creator: Lund, Steven M.; Kikuchi, Takashi & Davidson, Ronald C.
Partner: UNT Libraries Government Documents Department

Reduction of residual charge in surface-neutralization-based neutral beams

Description: Hyperthermal-neutral beams have been proposed as a charge-free alternative to plasmas in select processing steps. Existing prototype sources include three generic types: gas-dynamic, ion-neutral-charge-exchange and ion-surface-neutralization beam sources. The authors find that in surface-neutralization type sources, which have the highest flux, residual current can still flow to the substrate. However, this charged particle flux is several orders of magnitude smaller than the hyperthermal-neutral flux. Here they discuss the source of this residual current and methods for further reductions. This is important to the semiconductor industry.
Date: April 1, 1997
Creator: Goeckner, M.J.; Bennett, T.K.; Park, J.; Wang, Z. & Cohen, S.A.
Partner: UNT Libraries Government Documents Department

Simulations of the LEDA LEBT H{sup +} beam

Description: The computer codes TRACE and SCHAR model the Low-Energy Demonstration Accelerator (LEDA) Low-Energy Beam Transport (LEBT) for 75-keV, 110-mA, dc H{sup +} beams. Solenoid-lens location studies verify that the proposed LEBT design gives a near-optimum match to the LEDA RFQ. The desired RFQ transmission ({ge} 90%) and output emittance ({le} 0.22 {pi} mm mrad, transverse) are obtained when PARMTEQM transports the file for the SCHAR-generated optimum beam through the RFQ.
Date: August 1, 1997
Creator: Smith, H.V. Jr.; Sherman, J.D.; Stevens, R.R. Jr. & Young, L.M.
Partner: UNT Libraries Government Documents Department

Dynamics of neutralized electrons and the focusability of intenseion beams in HIF accelerating structures

Description: In most of the proposals for HIF reactors, beams propagate ballistically through the containment chamber. To get the required final radius ({approx} 3 mm), the charge of the beam must be neutralized to some extent. Several neutralization schemes are possible, as co-injection of negative-ions beams, inclusion of external sources of electrons, or it can be provided by electrons coming from ionization of the background gas. In this work, we study the role of the electron dynamic on the neutralization and final radius of the beam. This is done by performing fully-electromagnetic PIC simulations of the beam ballistic transport using the BPIC code[1]. In agreement with previous works we found that the evolution of an isolated beam is well described as a bidimensional adiabatic compression, and the beam neutralization degree and final radius can be estimated from the initial electron transversal temperature. When a background gas is present the evolution differs significantly from an adiabatic compression. Even for low gas densities, the continuous electrons flow coming from gas ionization limits efficiently the compressional heating, thus reducing the final radius. Aspects of beam neutralization by background gas ionization are discussed.
Date: January 18, 2005
Creator: Lifschitz, A. F.; Maynard, G. & Vay, J.-V.
Partner: UNT Libraries Government Documents Department

An orthotropic source of thermal atoms

Description: A highly efficient source that produces a narrow beam of neutral atoms at thermal velocity with small angular divergence is described. It uses a high work function interior surface to evaporate alkali atoms as ions and a low work function neutralizer, biased to collect the ions and evaporated them as neutral atoms. The neutralizer is located opposite an exit aperture so that the beam characteristics are determined by the geometry of the neutralizer and aperture. The orthotropic source is especially well suited for atomic clocks and for efficient loading of short lived radioactive alkali atoms into an optical trap.
Date: June 1, 1995
Creator: Dinneen, T.; Ghiorso, A. & Gould, H.
Partner: UNT Libraries Government Documents Department

Modeling Chamber Transport for Heavy-Ion Fusion

Description: In a typical thick-liquid-wall scenario for heavy-ion fusion (HIF), between seventy and two hundred high-current beams enter the target chamber through ports and propagate about three meters to the target. Since molten-salt jets are planned to protect the chamber wall, the beams move through vapor from the jets, and collisions between beam ions and this background gas both strip the ions and ionize the gas molecules. Radiation from the preheated target causes further beam stripping and gas ionization. Due to this stripping, beams for heavy-ion fusion are expected to require substantial neutralization in a target chamber. Much recent research has, therefore, focused on beam neutralization by electron sources that were neglected in earlier simulations, including emission from walls and the target, photoionization by the target radiation, and pre-neutralization by a plasma generated along the beam path. When these effects are included in simulations with practicable beam and chamber parameters, the resulting focal spot is approximately the size required by a distributed radiator target.
Date: October 1, 2002
Creator: Sharp, W. M.; Callahan, D. A.; Tabak, M.; Yu, S. S.; Peterson, P. F.; Welch, D. R. et al.
Partner: UNT Libraries Government Documents Department

Simulation of chamber transport for heavy-ion fusion

Description: Beams for heavy-ion fusion (HIF) are expected to require substantial neutralization in a target chamber. Present targets call for higher beam currents and smaller focal spots than most earlier designs, leading to high space-charge fields. Collisional stripping by the background gas expected in the chamber further increases the beam charge. Simulations with no electron sources other than beam stripping and background-gas ionization show an acceptable focal spot only for high ion energies or for currents far below the values assumed in recent HIF power-plant scenarios. Much recent research has, therefore, focused on beam neutralization by electron sources that were neglected in earlier simulations, including emission from walls and the target, photoionization by radiation from the target, and pre-neutralization by a plasma generated along the beam path. The simulations summarized here indicate that these effects can significantly reduce the beam focal-spot size.
Date: October 4, 2002
Creator: Sharp, W.M.; Callahan, D.A.; Tabak, M.A.; Yu, S.S.; Peterson, P.F.; Rose, D.V. et al.
Partner: UNT Libraries Government Documents Department

Electron beam spot size stabilization for radiographic application

Description: The authors have demonstrated through computer simulations that self-biasing the target can effectively control the ion column which causes radial pinching of the electron beam, resulting in the growth of spot size on target. This method has the unique features in simplicity and non-intrusiveness in its implementation into radiographic systems. The concept is being actively explored experimentally at the Integrated Test Stand (ITS).
Date: December 31, 1998
Creator: Kwan, T.J.T. & Snell, C.M.
Partner: UNT Libraries Government Documents Department

A feasibility study of space-charge neutralized ion induction linacs: Final report

Description: Applications for high current (> 1 kA) ion beams are increasing. They include hardening of material surfaces, transmutation of radioactive waste, cancer treatment, and possibly driving fusion reactions to create energy. The space-charge of ions limits the current that can be accelerated in a conventional ion linear accelerator (linac). Furthermore, the accelerating electric field must be kept low enough to avoid the generation and acceleration of counter-streaming electrons. These limitations have resulted in ion accelerator designs that employ long beam lines and would be expensive to build. Space-charge neutralization and magnetic insulation of the acceleration gaps could substantially reduce these two limitations, but at the expense of increasing the complexity of the beam physics. We present theory and experiments to determine the degree of charge-neutralization that can be achieved in various environments found in ion accelerators. Our results suggest that, for high current applications, space-charge neutralization could be used to improve on the conventional ion accelerator technology. There are two basic magnetic field geometries that can be used to insulate the accelerating gaps, a radial field or a cusp field. We will present studies related to both of these geometries. We shall also present numerical simulations of {open_quotes}multicusp{close_quotes} accelerator that would deliver potassium ions at 400 MeV with a total beam power of approximately 40 TW. Such an accelerator could be used to drive fusion.
Date: March 1, 1997
Creator: Slutz, S.A.; Primm, P.; Renk, T. & Johnson, D.J.
Partner: UNT Libraries Government Documents Department

Stabilization of electron beam spot size by self bias potential

Description: In high resolution flash x-ray imaging technology the electric field developed between the electron beam and the converter target is large enough to draw ions from the target surface. The ions provide fractional neutralization and cause the electron beam to focus radially inward, and the focal point subsequently moves upstream due to the expansion of the ion column. A self-bias target concept is proposed and verified via computer simulation that the electron charge deposited on the target can generate an electric potential, which can effectively limit the ion motion and thereby stabilize the growth of the spot size. A target chamber using the self bias target concept was designed and tested in the Integrated Test Stand (ITS). The authors have obtained good agreement between computer simulation and experiment.
Date: December 31, 1998
Creator: Kwan, T.J.T.; Moir, D.C.; Snell, C.M. & Kang, M.
Partner: UNT Libraries Government Documents Department

Effects on axial momentum spread on the electron-ion two-stream instability in high-intensity ion beams

Description: Use is made of the Vlasov-Maxwell equations to describe the electron-ion two-stream instability driven by the directed axial motion of a high-intensity ion beam propagating through a stationary population of (unwanted) background electrons. The ion beam is treated as continuous in the z-direction, and the electrons are electrostatically confined in the transverse direction by the space-charge potential produced by the excession charge. The analysis is carried out for arbitrary beam intensity, consistent with transverse confinement of the beam particles, and arbitrary fractional charge neutralization by the background electrons. For the case of overlapping step-function ion and electron density profiles, corresponding to monoenergetic electrons and ions in the transverse direction, detailed stability properties are calculated, including the important effects of an axial momentum spread, over a wide range of system parameters for dipole perturbations with azimuthal mode number l=1. The two-stream instability growth rate is found to increase with increasing beam intensity, increasing fractional charge neutralization, and decreasing proximity of the conducting wall. It is shown that Landau damping associated with a modest axial momentum spread of the beam ions and background electrons has a strong stabilizing influence on the instability.
Date: June 15, 2000
Creator: Davidso, R. & Qin, H.
Partner: UNT Libraries Government Documents Department

Schemes and Optimization of Gas Flowing into the Ion Source and the Neutralizer of the DIII-D Neutral Beam Systems

Description: Performance comparisons of a DIII-D neutral beam ion source operated with two different schemes of supplying neutral gas to the arc chamber were performed. Superior performance was achieved when gas was puffed into both the arc chamber and the neutralizer with the gas flows optimized as compared to supplying gas through the neutralizer alone. To form a neutral beam, ions extracted from the arc chamber and accelerated are passed through a neutralizing cell of gas. Neutral gas is commonly puffed into the neutralizing cell to supplement the residual neutral gas from the arc chamber to obtain maximum neutralization efficiency. However, maximizing neutralization efficiency does not necessarily provide the maximum available neutral beam power, since high levels of neutral gas can increase beam loss through collisions and cause larger beam divergence. Excessive gas diffused from the neutralizer into the accelerator region also increases the number of energetic particles (ions and secondary electrons from the accelerator grid surfaces) deposited on the accelerator grids, increasing the possibility of overheating. We have operated an ion source with a constant optimal gas flow directly into the arc chamber while gas flow into the neutralizer was varied. Neutral beam power available for injecting into plasmas was obtained based on the measured data of beam energy, beam current, beam transmission, beam divergence, and neutralization efficiency for various neutralizer gas flow rates. We will present the results of performance comparison with the two gas puffing schemes, and show steps of obtaining the maximum available beam power and determining the optimum neutralizer gas flow rate.
Date: November 1, 1999
Creator: Hong, R.M. & Chiu, H.K.
Partner: UNT Libraries Government Documents Department

Focusing and neutralization of intense beams

Description: In heavy ion inertial confinement fusion systems, intense beams of ions must be transported from the exit of the final focus magnet system through the target chamber to hit millimeter spot sizes on the target. Effective plasma neutralization of intense ion beams through the target chamber is essential for the viability of an economically competitive heavy ion fusion power plant. The physics of neutralized drift has been studied extensively with PIC simulations. To provide quantitative comparisons of theoretical predictions with experiment, the Heavy Ion Fusion Virtual National Laboratory has completed the construction and has begun experimentation with the NTX (Neutralized Transport Experiment) as shown in Figure 1. The experiment consists of 3 phases, each with physics issues of its own. Phase 1 is designed to generate a very high brightness potassium beam with variable perveance, using a beam aperturing technique. Phase 2 consists of magnetic transport through four pulsed quadrupoles. Here, beam tuning as well as the effects of phase space dilution through higher order nonlinear fields must be understood. In Phase 3, a converging ion beam at the exit of the magnetic section is transported through a drift section with plasma sources for beam neutralization, and the final spot size is measured under various conditions of neutralization. In this paper, we present first results from all 3 phases of the experiment.
Date: May 1, 2003
Creator: Yu, Simon S.; Anders, Andre; Bieniosek, F.M.; Eylon, Shmuel; Henestroza, Enrique; Roy, Prabir et al.
Partner: UNT Libraries Government Documents Department

High-current beam dynamics and transport, theory and experiment

Description: Recent progress in the understanding of beam physics and technology factors determining the current and brightness of ion and electron beams in linear accelerators will be reviewed. Topics to be discussed including phase-space density constraints of particle sources, low-energy beam transport include charge neutralization, emittance growth due to mismatch, energy exchange, instabilities, nonlinear effects, and longitudinal bunching.
Date: January 1, 1986
Creator: Reiser, M.
Partner: UNT Libraries Government Documents Department

Laser neutralization

Description: Laser photodetachment of the excess electron to neutralize relativistic ions offers many advantages over the more conventional collisional methods using gases or thin foils as the neutralization agents. Probably the two most important advantages of laser photodetachment are the generation of a compact and low divergence beam, and the production of intense neutral beams at very high efficiency (approximately 90%). The high intensities or high current densities of the neutral beam result from the fixed maximum divergence that can be added to the beam by photodetachment of the charge using laser intensity of fixed wavelength and incident angle. The high neutralization efficiency is possible because there is no theoretical maximum to the neutralization efficiency, although higher efficiencies require higher laser powers and, therefore, costs. Additional advantages include focusability of the laser light onto the ion beam to maximize its efficacy. There certainly is no residual gas left in the particle beam path as is typical with gas neutralizers. The photodetachment process leaves the neutral atoms in the ground state so there is no excited state fluorescence to interfere with the subsequent beam sensing. Finally, since the beams to be neutralized are very high powered, for a large range of neutralization efficiencies the neutral beam can be increased more by increasing the power to the laser neutralizer than by adding an equal amount of power to the primary accelerator. 26 figs.
Date: June 17, 1986
Creator: Peterson, O.G.
Partner: UNT Libraries Government Documents Department

Influence of a biased beam dump on H/sup /minus// beam neutralization measurements with a four-grid energy analyzer

Description: A four-grid energy analyzer (FGA) diagnostic has been developed for the study of H/sup /minus// beam space-charge compensation, and first measurements have been reported previously. Biased beam-dump measurements were undertaken to clarify the origin of electron currents measured in the FGA because they far exceeded predictions based on H/sup /minus// beam ionization and stripping processes. This experiment partially explains the anomalously large radial electron current. The FGA observations for beam-dump bias <0 suggest electron ionization of the background gas is an additional mechanism for producing positive ions, where the electron kinetic energy is derived form the beam-dump voltage. 6 refs., 4 figs.
Date: January 1, 1989
Creator: Sherman, J.; Pitcher, E. & Allison, P.
Partner: UNT Libraries Government Documents Department

High-powered pulsed-ion-beam acceleration and transport

Description: The state of research on intense ion beam acceleration and transport is reviewed. The limitations imposed on ion beam transport by space charge effects and methods available for neutralization are summarized. The general problem of ion beam neutralization in regions free of applied electric fields is treated. The physics of acceleration gaps is described. Finally, experiments on multi-stage ion acceleration are summarized.
Date: November 1, 1981
Creator: Humphries, S. Jr. & Lockner, T.R.
Partner: UNT Libraries Government Documents Department

Method of generating intense nuclear polarized beams by selective photodetachment of negative ions

Description: A novel method for production of nuclear polarized negative hydrogen ions by selective neutralization with a laser of negative hydrogen ions in a magnetic field is described. This selectivity is possible since a final state of the neutralized atom, and hence the neutralization energy, depends on its nuclear polarization. The main advantages of this scheme are the availability of multi-ampere negative ion sources and the possibility of neutralizing negative ions with very high efficiency. An assessment of the required laser power indicates that this method is in principle feasible with today's technology.
Date: January 1, 1986
Creator: Hershcovitch, A.
Partner: UNT Libraries Government Documents Department

Plasma production and flow in negative ion beams

Description: Plasma generated in low-density vapor by a negative ion beam has been studied experimentally and computationally. We show that space charge neutralization of the beam occurs at very low vapor density, and that correspondingly the electron density may be much less than the beam and plasma ion densities. When there is a large local gas density, as in a charge changing cell, the resulting high electron density is also localized to the same region. Therefore, very few electrons will reach a negative ion accelerator even if it is placed one or two beam diameters from such a cell.
Date: September 21, 1977
Creator: Anderson, O.A. & Hooper, E.B. Jr.
Partner: UNT Libraries Government Documents Department