Progress Toward Sustained High-Performance Advanced Tokamak Discharges in DIII-D.

Download or read book Progress Toward Sustained High-Performance Advanced Tokamak Discharges in DIII-D. written by and published by . This book was released on 2002 with total page 7 pages. Available in PDF, EPUB and Kindle. Book excerpt: Key elements of a sustained advanced tokamak discharge in DIII-D are a large fraction of the total current from bootstrap current (f{sub BS}) and parameters that optimize the capability to use electron cyclotron current drive (ECCD) at [rho] ≈ 0.5 to maintain the desired current profile [1-4]. Increased f{sub BS} results from increasing both the normalized beta ([beta]{sub N}) and the minimum value of the safety factor (q{sub min}). Off-axis ECCD is, for the available gyrotron power, optimized at high [beta]{sub N}, high electron temperature (T{sub e}) and low electron density (n{sub e}). As previously reported [2-4], these required elements have been separately demonstrated: density control at high [beta]{sub N} with n{sub e} ≤ 5 x 1019 m−3 using divertor-region pumping, stability at high [beta], and off-axis ECCD at the theoretically predicted efficiency. This report summarizes recent work on optimizing and integrating these results through evaluation of the dependence of the beta limit on q{sub min} and q95, exploration of discharges with relatively high q{sub min}, testing of feedback control of T{sub e} for control of the q profile evolution, and modification of the current profile time evolution when ECCD is applied.