Physics of advanced tokamaks
Significant reductions in the size and cost of a fusion power plant core can be realized if simultaneous improvements in the energy replacement time, {tau}{sub E}, and the plasma pressure or beta, {beta}{sub T} = 2 {micro}{sub 0}
/B{sup 2} can be achieved in steady-state conditions with high self-driven, bootstrap current fraction. Significant recent progress has been made in experimentally achieving these high performance regimes and in developing a theoretical understanding of the underlying physics. Three operational scenarios have demonstrated potential for steady state high performance, the radiative improved (RI) mode, the high internal inductance or high {ell}{sub i} scenario, and the negative central magnetic shear, NCS (or reversed shear, RS) scenario. In a large number of tokamaks, reduced ion thermal transport to near neoclassical values, and reduced particle transport have been observed in the region of negative or very low magnetic shear: the transport reduction is consistent with stabilization of microturbulence by sheared E x B flow. There is strong temporal and spatial correlation between the increased sheared E x B flow, the reduction in the measured turbulence, and the reduction in transport. The DIII-D tokamak, the JET tokamak and the JT-60U tokamak have all observed significant increases in plasma performance in the NCS operational regime. Strong plasma shaping and broad pressure profiles, provided by the H-mode edge, allow high beta operation, consistent with theoretical predictions; and normalized beta values up to {beta}{sub T}/(I/aB) {equivalent_to} {beta}{sub N} {approximately} 4.5%-m-T/MA simultaneously with confinement enhancement over L-mode scaling, H = {tau}/{tau}{sub ITER-89P} {approximately} 4, have been achieved in the DIII-D tokamak. In the JT-60U tokamak, deuterium discharges with negative central magnetic shear, NCS, have reached equivalent break-even conditions, Q{sub DT} (equiv) = 1.
- Research Organization:
- General Atomics, San Diego, CA (United States); Los Alamos National Lab., NM (United States); Oak Ridge National Lab., TN (United States); Princeton Univ., Princeton Plasma Physics Lab., NJ (United States); Columbia Univ., NY (United States); Massachusetts Inst. of Tech., Cambridge, MA (United States); Univ. of Texas, Austin, TX (United States)
- Sponsoring Organization:
- USDOE Office of Energy Research, Washington, DC (United States)
- DOE Contract Number:
- AC03-89ER51114; W-7405-ENG-48; AC05-96OR22464; AC02-76CH03073; FG02-89ER53297; FG02-91ER54109; FG05-88ER53266
- OSTI ID:
- 674703
- Report Number(s):
- GA--A22704; CONF-9706131--; ON: DE98003429
- Country of Publication:
- United States
- Language:
- English
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Magnetic shear effects on plasma transport and turbulence at high electron to ion temperature ratio in DIII-D and JT-60U plasmas