High Perveance Ion Beams Research Articles

Dynamics of ion beam charge neutralization by ferroelectric plasma sources

Ferroelectric Plasma Sources (FEPSs) can generate plasma that provides effective space-charge neutralization of intense high-perveance ion beams, as has been demonstrated on the Neutralized Drift Compression Experiment NDCX-I and NDCX-II. This article presents experimental results on charge neutralization of a high-perveance 38 keV Ar+ beam by a plasma produced in a FEPS discharge. By comparing the measured beam radius with the envelope model for space-charge expansion, it is shown that a charge neutralization fraction of 98% is attainable with sufficiently dense FEPS plasma. The transverse electrostatic potential of the ion beam is reduced from 15 V before neutralization to 0.3 V, implying that the energy of the neutralizing electrons is below 0.3 eV. Measurements of the time-evolution of beam radius show that near-complete charge neutralization is established ∼5 μs after the driving pulse is applied to the FEPS and can last for 35 μs. It is argued that the duration of neutralization is much longer than a reasonable lifetime of the plasma produced in the sub-μs surface discharge. Measurements of current flow in the driving circuit of the FEPS show the existence of electron emission into vacuum, which lasts for tens of μs after the high voltage pulse is applied. It is argued that the beam is neutralized by the plasma produced by this process and not by a surface discharge plasma that is produced at the instant the high-voltage pulse is applied.

Space-charge neutralization of heavy ion beams via electron injection

One key issue in heavy ion beam fusion (HIBF) is how to effectively focus high-current and high-perveance ion beams onto a small target area. Space charge neutralization is needed to prevent defocusing as the ion density compresses during focusing. The present study is concerned with the physics of space-charge neutralization by use of various concepts for injection of electrons into the ion beam in addition to plasma neutralization. To date the most widely studied approaches to neutralization use a preformed plasma or ionize a background gas in the beam line. However, these schemes alone face difficulties due to local non-uniformities in charge neutralization due to beam dynamic/focusing effects. Thus, two supplemental techniques are under study and will be discussed here. One involves axially injection of electrons created in a thin foil in the beam path. The other uses a magnetic field to guide the electrons into the direction of the beam path. Both techniques would be used in combination with conventional background plasma, providing added control of neutralization.

Comparison of experimental data and three-dimensional simulations of ion beam neutralization from the Neutralized Transport Experiment

The Neutralized Transport Experiment at Lawrence Berkeley National Laboratory has been designed to study the final focus and neutralization of high perveance ion beams [E. Henestroza, S. Eylon, P. Roy, S. Yu, A. Anders, F. Bieniosek, W. Greenway, B. Logan, R. MacGill, D. Shuman et al., Phys. Rev. ST-Accel. Beams 7, 083501 (2004)]. Preformed plasmas in the last meter before the target of the scaled experiment provide a source of electrons which neutralize the ion current and prevent the space-charge-induced spreading of the beam spot. Neutralized Transport Experiment physics issues are discussed and experimental data are analyzed and compared with three-dimensional (3D) particle-in-cell simulations. Along with detailed target images, 4D phase-space data at the entrance of the neutralization region have been acquired. These data are used to provide a more accurate beam distribution with which to initialize the simulation. Previous treatments have used various idealized beam distributions which lack the deta...

Investigation of the space-charge compensation process of ion beams using a time-resolving ion energy spectrometer

For low-energy beam transport of pulsed high perveance ion beams under space charge compensated conditions the knowledge of the build up time of compensation is of main interest. An LEBT system consisting of two solenoids has been set up to measure the rise time of compensation. Therefore, the beam potential has been in a residual gas ion energy analyser by time resolved measurements. The measured data has been used together with numerical simulation of different equilibrium states of the beam plasma to investigate the behavior of the compensation electrons as a function of time. The data acquired shows that the theoretical rise time of space-charge compensation is shorter by a factor of two than the build up time determined experimentally. An interpretation of the results is given.

Investigation of space-charge-compensated ion beams with a time-resolving ion energy spectrometer

High perveance ion beams are required for heavy-ion inertial fusion drivers. The current limit of a low energy beam transport line is enhanced by space-charge compensation. It rise time is several hundreds of microseconds under the supposition that electrons are produced by residual gas ionization only. Therefore the rise time depends on the residual gas pressure and ionization cross-section. This is of special interest for pulsed ion beams, with a pulse length close to or below that range. To study this compensation process, we developed a time-resolving residual gas ion energy spectrometer with single-particle detection; the available time resolution is about 2 μs. Experimental results are presented and compared with a theoretical prediction.

Determination of electron temperature in partial space-charge-compensated high-perveance ion beams

For heavy-ion inertial-fusion drivers, high-perveance ion beams are required. Space-charge compensation is enhancing the current limit of low-energy beam transport lines (LEBT). The knowledge of the temperature of the compensating electrons and the charge density of the electrons on axis is needed for the calculation of beam transport under the influence of space-charge compensation. A low-energy beam transport line (typically 9 keV, 3 mA DC, He+) has been set up and the radial density distribution of the beam ions was measured. Using this data in a one-dimensional numerical simulation, a multiplicity of possible states of the compensated beam can be calculated. Comparing the results of the simulation with measured beam potentials, it is possible to determine the electron temperature as well as the electron density on axis. First experimental results are presented together with the fundamental theory.

Low-energy beam transport of intense and partially space-charge-neutralized ion beams

High-perveance ion beams are required for heavy-ion inertial-fusion drivers and cannot be transported without a reduction of space charge forces by space charge neutralization. The rearrangement of beam ions due to the self-field of partly neutralized beams is one source of r.m.s. emittance growth in low-energy sections. Calculations including the influence of compensating electrons have been carried out. A low-energy beam line is being set up to investigate the influence of partial space charge neutralization on the transverse beam emittance of high-perveance beams (typically 9keV, 3.5 mA He+). Theoretical assumptions and results of numerical simulations are presented and compared with first experimental results.

1027. Piezoresistance in n-type silicon inversion layers at low temperatures: G Dorda and I Eisele,Phys Stat Sol (a), 20 (1), 1973, 263–273

One key issue in heavy ion beam fusion (HIBF) is how to effectively focus high-current and high-perveance ion beams onto a small target area. Space charge neutralization is needed to prevent defocusing as the ion density compresses during focusing. The present study is concerned with the physics of space-charge neutralization by use of various concepts for injection of electrons into the ion beam in addition to plasma neutralization. To date the most widely studied approaches to neutralization use a preformed plasma or ionize a background gas in the beam line. However, these schemes alone face difficulties due to local non-uniformities in charge neutralization due to beam dynamic/focusing effects. Thus, two supplemental techniques are under study and will be discussed here. One involves axially injection of electrons created in a thin foil in the beam path. The other uses a magnetic field to guide the electrons into the direction of the beam path. Both techniques would be used in combination with conventional background plasma, providing added control of neutralization.

1030. Ion implantation doping of compound semiconductors: P L Degen,Phys Stat Sol (a), 16, (1), 1973, 9–42

One key issue in heavy ion beam fusion (HIBF) is how to effectively focus high-current and high-perveance ion beams onto a small target area. Space charge neutralization is needed to prevent defocusing as the ion density compresses during focusing. The present study is concerned with the physics of space-charge neutralization by use of various concepts for injection of electrons into the ion beam in addition to plasma neutralization. To date the most widely studied approaches to neutralization use a preformed plasma or ionize a background gas in the beam line. However, these schemes alone face difficulties due to local non-uniformities in charge neutralization due to beam dynamic/focusing effects. Thus, two supplemental techniques are under study and will be discussed here. One involves axially injection of electrons created in a thin foil in the beam path. The other uses a magnetic field to guide the electrons into the direction of the beam path. Both techniques would be used in combination with conventional background plasma, providing added control of neutralization.

1029. Combined hopping and tunnelling mechanism of electro transport and doping effects in chloranil-trimethylamine charge-transfer complex: H Chojnacki et al,Phys Stat Sol (a), 20 (1), 1973, 211–216

One key issue in heavy ion beam fusion (HIBF) is how to effectively focus high-current and high-perveance ion beams onto a small target area. Space charge neutralization is needed to prevent defocusing as the ion density compresses during focusing. The present study is concerned with the physics of space-charge neutralization by use of various concepts for injection of electrons into the ion beam in addition to plasma neutralization. To date the most widely studied approaches to neutralization use a preformed plasma or ionize a background gas in the beam line. However, these schemes alone face difficulties due to local non-uniformities in charge neutralization due to beam dynamic/focusing effects. Thus, two supplemental techniques are under study and will be discussed here. One involves axially injection of electrons created in a thin foil in the beam path. The other uses a magnetic field to guide the electrons into the direction of the beam path. Both techniques would be used in combination with conventional background plasma, providing added control of neutralization.