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 2003 with total page 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[approx]10 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] H[sub 89] indicating the proximity to the conventional[beta] limits and energy confinement quality, respectively.) These H-mode discharges have an ELMing edge and[beta][approx][le] 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[approx]75% 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]H[sub 89][approx] 7 for up to 6.3 s or[approx] 34[tau][sub E]. These discharges appear to be in resistive equilibrium with q[sub min][approx] 1.05, in agreement with the current profile relaxation time of 1.8 s.