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(EXP1/05) Flux Consumption Optimization and the Achievement of 1 MA Discharges on NSTX

J. Menard¹⁾, B. LeBlanc¹⁾, S. A. Sabbagh²⁾, M. Bell¹⁾, R. Bell¹⁾, E. Fredrickson¹⁾, D. Gates¹⁾, S. C. Jardin¹⁾, S. Kaye¹⁾, H. Kugel¹⁾, R. Maingi³⁾, R. Maqueda⁴⁾, D. Mueller¹⁾, S. Paul¹⁾, C. Skinner¹⁾, D. Stutman⁵⁾, and the NSTX Research Team
 
¹⁾ Plasma Physics Laboratory, Princeton University, Princeton, New Jersey, USA
²⁾ Department of Applied Physics and Applied Mathematics, Columbia University, New York, New York, USA
³⁾ Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA
⁴⁾ Los Alamos National Laboratory, Los Alamos, New Mexico, USA
⁵⁾ Johns Hopkins University, Baltimore, Maryland, USA

Abstract.  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 I_P exceeding 1MA have been achieved in NSTX with nominal parameters: aspect ratio A = 1.3 - 1.4, elongation $\kappa$ = 2 - 2.2, triangularity $\delta$ = 0.4, internal inductance l_i = 0.6, and Ejima coefficient C_E = 0.35. Flux consumption efficiency results, performance improvements associated with first boronization, and comparisons to neoclassical resistivity are described.

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