Ohmic flux consumption during initial operation of the NSTX spherical torus

Spherical tokamaks, because of their slender central columns, have very limited volt second capability relative to that of standard aspect ratio tokamaks of similar plasma cross-section. Recent experiments on NSTX have begun to quantify and optimize the ohmic current drive efficiency in an MA class ST device. Sustainable ramp rates in excess of 5 MA/s 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 = 1.3-1.4, elongation κ = 2-2.2, triangularity δ = 0.4, internal inductance li = 0.6, Ejima coefficient CE = 0.35. Flux consumption efficiency results, performance improvements associated with first boronization and comparisons with neoclassical resistivityare described.