H/sup /minus// beam neutralization measurements with a gridded-energy analyzer, a noninterceptive beam diagnostic
Transport of high-perveance H/sup /minus// ion beams frequently depends on space-charge neutralization by a background plasma to reduce or eliminate space-charge defocusing. We have developed a four-grid energy analyzer (FGA) that measures the energy distributions of particles emitted radially from the beam-generated plasma. H/sup /minus// beams of 80- to 90- mA current at 21-keV beam energy (which yields a /minus/400 V potential drop for an unneutralized beam) have been studied in a 55-cm drift region using He and Xe neutralizing gases. At a sufficiently high gas density, ion energy distribution analyses show a several volt positive potential drop across the H/sup /minus// beam, supporting the gas focusing concept of overneutralized H/sup /minus// ion beams. There is a neutralizing gas density threshold below which no radially flowing positive ion current is observed. At low gas density, the GA electron current is noisy (indicating the plasma is unstable) and the measured electron distributions are consistent with an underneutralized beam. With the addition of neutralizing gas, the electron current oscillations and energies decrease. 8 refs., 7 figs., 1 tab.
- Research Organization:
- Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
- DOE Contract Number:
- W-7405-ENG-36
- OSTI ID:
- 6807919
- Report Number(s):
- LA-UR-88-3259; CONF-881049-17; ON: DE89000337
- Resource Relation:
- Conference: Linear accelerator conference, Williamsburg, VA, USA, 3 Oct 1988; Other Information: Paper copy only, copy does not permit microfiche production
- Country of Publication:
- United States
- Language:
- English
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