Progress Towards Sustainment of Advanced Tokamak Modes in DIII-D.

Download or read book Progress Towards Sustainment of Advanced Tokamak Modes in DIII-D. written by and published by . This book was released on 2001 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Improving confinement and beta limits simultaneously in long-pulse ELMy H-mode discharges is investigated. The product[beta][sub N]H[sub 98y] serves as a useful figure-of-merit for performance, where[beta][sub N][triple-bond][beta]/(I/aB) and H[sub 98y] is the ratio of the thermal confinement time relative to the most recent ELMy H-mode confinement scaling established by the ITER confinement database working group. In discharges with q[sub 0][approximately] 1 (no sawteeth) and discharges with q[sub min]> 1.5 and negative central magnetic shear, [beta][sub N][approximately] 2.9 and H[sub 98y][approximately] 1.4 are sustained for up to 2 s. Although peaked profiles are observed, steep internal transport barriers are not present. Further increases in[beta][sub N] in these discharges is limited by neoclassical tearing modes (NTM) in the positive shear region. In another recently developed regime, [beta][sub N][approximately] 3.8 and H[sub 98y][approximately] 1.8 has been sustained during large infrequent ELMs in non-sawtoothing discharges with 1[sub 0][approximately] 1. This level of performance is similar to that obtained in ELM-free regimes such as VH-mode. The limitation on[beta][sub N] and pulse length in these discharges is also the onset of NTMs.