PPPL-3490 is available in <a href="PPPL-3490.pdf">pdf</a> or 
<a href="PPPL-3490.ps">postscript</a> formats.

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<b>Ohmic Flux Consumption during Initial Operation of the NSTX Spherical Torus</b>
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<b>Authors:</b> J.E. Menard, B.P. LeBlanc, S.A. Sabbagh, M.G. Bell, R.E. Bell, E.D. Fredrickson, D.A. Gates, S.C. Jardin, D.W. Johnson, S.M. Kaye, H.W. Kugel, R. Maingi, R.J. Maqueda, D. Mueller, M. Ono, F. Paoletti, S.F. Paul, C.H. Skinner, D. Stutman, and the NSTX Research Team.

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<b>Date of PPPL Report:</b> October 2000
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<b>Submitted to:</b> Nuclear Fusion <b> 41 </b>(September 2001) 1197-1206.
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The spherical tokamak (ST), because of its slender central column, has very limited volt-second capability relative to a standard aspect ratio tokamak of similar plasma cross section. Recent experiments on the National Spherical Torus Experiment (NSTX) have begun to quantify and optimize the ohmic current drive efficiency in a MA-class ST device. Sustainable ramp-rates in excess of 5MA/sec during the current rise phase have been achieved on NSTX, while faster ramps generate significant MHD activity. Discharges with <font face = "times">I<sub>P</sub></font face ="times"> exceeding 1 MA have been achieved in NSTX with nominal parameters: aspect ratio A = 1.3 to 1.4, elongation <font face = "symbol">k</font face ="symbol"> = 2 to 2.2, triangularity <font face = "symbol">d</font face ="symbol"> = 0.4, internal inductance l<font face = "times"><sub>i</sub></font face ="times">= 0.6, and Ejima coefficient <font face = "times">C</font face = "times"><font face = "symbol"><sub>E</sub></font face ="symbol"> = 0.35. Flux consumption efficiency results, performance improvements associated with first boronization, and comparisons to neoclassical resistivity are described.

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