PPPL-3490 is available in pdf or postscript formats.

Ohmic Flux Consumption during Initial Operation of the NSTX Spherical Torus

Authors: 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.

Date of PPPL Report: October 2000

Submitted to: Nuclear Fusion 41 (September 2001) 1197-1206.

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 IP exceeding 1 MA have been achieved in NSTX with nominal parameters: aspect ratio A = 1.3 to 1.4, elongation k = 2 to 2.2, triangularity d = 0.4, internal inductance li= 0.6, and Ejima coefficient CE = 0.35. Flux consumption efficiency results, performance improvements associated with first boronization, and comparisons to neoclassical resistivity are described.