PPPL-4060 is available in <a href="PPPL-4060.pdf">pdf</a> format (2.6 MB).

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<b>Prompt Loss of Energetic Ions during Early Neutral Beam Injection in the National Spherical Torus Experiment</b>
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<b>Authors:</b> S.S. Medley, D.S. Darrow, D. Liu, and A.L. Roquemore
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<b>Date of PPPL Report:</b> March 2005
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<b>Submitted to:</b> Plasma Physics and Controlled Fusion</p>


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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<sub>p</sub> ~ 0.5 MA) and electron density (n<sub>e</sub> ~ 1x10<sup>13</sup>cm<sup>-3</sup>) 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 code analysis is presented.



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