Long-Pulse, High-Performance Discharges in the DIII-D Tokamak

Download or read book Long-Pulse, High-Performance Discharges in the DIII-D Tokamak written by and published by . This book was released on 2000 with total page 18 pages. Available in PDF, EPUB and Kindle. Book excerpt: Significant progress in obtaining high performance discharges for many energy confinement times in the DIII-D tokamak has been realized since the previous IAEA meeting. In relation to previous discharges, normalized performance H"0 has been sustained for>5 [tau]{sub E} with q{sub min}>1.5. (The normalized performance is measured by the product [beta]{sub N} H9 indicating the proximity to the conventional [beta] limits and energy confinement quality, respectively.) These H-mode discharges have an ELMing edge and [beta] H" 5%. The limit to increasing [beta] is a resistive wall mode, rather than the tearing modes previously observed. Confinement remains good despite the increase in q. The global parameters were chosen to optimize the potential for fully non-inductive current sustainment at high performance, which is a key program goal for the DIII-D facility in the next two years. Measurement of the current density and loop voltage profiles indicate H"5% of the current in the present discharges is sustained non-inductively. The remaining ohmic current is localized near the half radius. The electron cyclotron heating system is being upgraded to replace this remaining current with ECCD. Density and [beta] control, which are essential for operating advanced tokamak discharges, were demonstrated in ELMing H-mode discharges with [beta]{sub N}H9 H"7 for up to 6.3 s or H"34 [tau]{sub E}. These discharges appear to be in resistive equilibrium with q{sub min} H"1.05, in agreement with the current profile relaxation time of 1.8 s.