High Flux Neutral Beams
Abstract
The purpose was to study the production of intense negative ion beams in magnetically insulated diodes, and to develop an understanding of this process by measuring the ion beam parameters as a function of diode and cathode plasma conditions in different magnetically insulated diodes. We tried a coaxial diode, a racetrack diode and an annular diode. We used the UCI APEX pulse line that has a nominal output of 1MV, 140kA under matched conditions with a pulse length of 50 nsec. Negative ion intensity and divergence were measured with Faraday-cups and CR-39 track detectors. Cathode plasma was produced by passive dielectric cathodes and later, by an independent plasma gun. This plasma gun was introduced in order to be able to control cathode plasma parameters and production time. Negative ion currents had an intensity of a few A/sq. cm with a divergence ranging between a few tenths milliradians for an active TiH2 plasma gun and 300 milliradians for a passive polyethelene cathode. Negatives ions were usually emitted from a few 'hot spots' on the cathode surface. These 'hot spots' are believed to cause transverse electrical fields in the diode gap responsible for the beam divergence. Mass spectrometry measurements showed that the ion beam consists of mainly H- ions when using a polyethelene or a TiH2 cathodes, and mainly of negative carbon ions when using a carbon cathode. About 10% of the negative ions produced were due to residual gas molecules adsorbed on the cathode surface. This was checked by using a bare aluminum cathode. Negative ion production in the cathode plasma seems to be insensitive to the type of diode used. Beam properties on the other hand, are of course sensitive to diode geometry.
Document Details
- Document Type
- Technical Report
- Publication Date
- Mar 31, 1990
- Accession Number
- ADA236994
Entities
People
- Amnon Fisher
- J. C. Leader
- Norman Rostoker
Organizations
- University of California, Irvine