Some estimates of mirror plasma startup by neutral beam heating of pellet and gas cloud targets Page: 4 of 35
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1. Introduction
In recent years 20-40 kV beams of neutralized hydrogen and deuterium
atoms have been created at equivalent current levels of 20-50 amperes(1).
The twelve neutral beams that are used on the 2XI18 experiment(2) are so
intense that it was found possible to build up a hot plasma by direct
injection of 310 amperes (total equivalent current) into a warm streaming
plasma(3),
These results raise the question whether hot plasma buildup may be
possible by direct neutral beam injection into a neutral gas or pellet
target. Previous unpublished assessments of this possibility were not
hopeful;(4) however, the estimates to be described here are more
encouraging. If these results are confirmed by experiment, then
considerable simplication of mirror plasma experimental hardware is
possible. No laser system would be needed, with its demanding focusing and
alignment requirements.(5) The required number of streaming guns would be
reduced to the smaller number needed for plasma stabilization.(2)
The production of the mirror plasma from a pellet or gas target is
modeled in three successive stages. In the first stage the solid pellet
target is vaporized by the bean to form a gaseous cloud. (Alternatively, a
gas cloud could be directly injected.) Secondly, the gaseous vapor must be
sufficiently well ionized by the neutral beams so that an apprerhible
fraction is trapped in the magnetic mirror field before it escapes to the
walls or the vacuum pumps. Finally, the hot mirror plasma must be built up
by trapping from the ionized target in the same way as the streaming plasma
experiment.(3)
The following pages describe the model and the results in detail. The
estimates are admittedly crude, and could be improved in the future, if
desired.
2. Ablation of Plastic Pellet
Asa "first cut the hydrogen, carbon, and oxygen content of a common
plastic or/amnonia pellet is modeled by assuming that it is equivalent to a
nitrogen sphere of diameter D(cm):
D = (6NA MH/rn )1/3
where Puis the density (gm/cc), MH is the mass of hydrogen, A is the atomic
weight, and N is the total number of atoms in the target. Nitrogen is
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Shearer, James W. & Willmann, Peter A. Some estimates of mirror plasma startup by neutral beam heating of pellet and gas cloud targets, report, July 7, 1978; Livermore, California. (https://digital.library.unt.edu/ark:/67531/metadc1191970/m1/4/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.