Prompt Loss of Energetic Ions during Early Neutral Beam Injection in the National Spherical Torus Experiment Page: 3 of 35
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Prompt Loss of Energetic Ions during Early Neutral Beam Injection
in the National Spherical Torus Experiment
S. S. Medley, D. S. Darrow, D. Liu*, and A. L. Roquemore
Princeton Plasma Physics Laboratory, Princeton, New Jersey, 08543, USA
University of California, Irvine, CA USA
Early neutral beam injection is used in the National Spherical Torus Experiment
(NSTX) to heat the electrons and slow current penetration which keeps q(0) elevated to
avoid deleterious MHD activity and at the same time reduces Ohmic flux consumption, all
of which aids long pulse operation. However, the low plasma current (I - 0.5 MA) and
electron density (ne - 1x1013cm3) attending early injection lead to elevated orbit and shine
through losses. The inherent orbit losses are aggravated by large excursions in the outer
gap width during current ramp up. An investigation of this behavior using various
energetic particle diagnostics on NSTX and TRANSP analysis is presented.
In the National Spherical Torus Experiment (NSTX) [1,2], advanced operational
techniques are employed to induce H-mode during discharge initiation, including early
neutral beam injection near the time of a brief pause or "flat-spot" in the current ramp up
. This scheme aids in the attainment of long pulse discharges by reducing flux
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Medley, S.S.; Darrow, D.S.; Liu, D. & Roquemore, A.L. Prompt Loss of Energetic Ions during Early Neutral Beam Injection in the National Spherical Torus Experiment, report, March 25, 2005; Princeton, New Jersey. (https://digital.library.unt.edu/ark:/67531/metadc786189/m1/3/: accessed April 23, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.