Abstract
During tangential neutral-beam injection into the PBX tokamak, bursts of two types of instabilities are observed. One instability occurs in the frequency range 120-210 kHz and the other oscillates predominantly near the frequency of bulk plasma rotation (20-30 kHz). Both instabilities correlate with drops in neutron emission and bursts in charge-exchange neutral flux, indicating that beam ions are removed from the center of the plasma by the instabilities. The central losses are comparable to the losses induced by the fishbone instability during perpendicular injection.
Highlights
R resulted in instabilities ("fishbones") that degraded the confinement of the beam ions
At normal operating densities ( n e £ 4 x 1 0 1 3 c m - 3 ), two-beam, bean-shaped Princeton Beta Experiment (PBX) plasmas were less susceptible to fishbone instabilities than typical PDX plasmas,[9] making comparison of plasma stability with high-power perpendicular and tangential neutral beam injection difficult
2.7 MW of 44 keV deuterium neutrals were co-injected with a tangency radius of Rtan = 130 cm into a deuterium plasma with Ze/y — 4.5
Summary
R resulted in instabilities ("fishbones") that degraded the confinement of the beam ions. By operating at low densities (ne 5.2.5 x 1 0 1 3 c m - 3 ) with weak plasma shaping, a regime was found where two perpendicular beainr excited strong fishbones.[9] Using this regime to compare perpendicular and parallel injection, we have found that, there are differences between perpendicular and parallel instabilities, the beam-ion losses from the plasma center are comparable in both cases.
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