Physics of advanced tokamaks

Abstract

Significant reductions in the size and cost of a fusion power plant core can be realized if simultaneous improvements in the energy replacement time, τ E , and the plasma pressure or beta, β T = 2 µ 0 P /B 2 can be achieved in steady-state conditions with high selfdriven, 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 steadystate high performance, the radiative improved mode, the high internal inductance or high i scenario, and the negative central magnetic shear, NCS (or reversed shear) 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 × B flow. There is strong temporal and spatial correlation between the increased sheared E × 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 β T /(I /aB) ≡ β N ∼ 4.5% m T MA −1 simultaneously with confinement enhancement over L-mode scaling, H = τ/τ ITER-89P ∼ 4, have been achieved in the DIII-D tokamak. In the JT-60U tokamak, deuterium discharges with negative central magnetic shear have reached equivalent breakeven conditions, Q DT (equiv) = 1.

Off-axis neutral beam current drive for advanced scenario development in DIII-D

“…Advanced tokamak (AT) research [1,2] on DIII-D seeks to provide the scientific basis for steady-state, high-performance operation for ITER and future tokamak reactors. For steady-state operation, all of the plasma current must be driven noninductively (without a transformer).…”

Dynamic optimization of open-loop input signals for ramp-up current profiles in tokamak plasmas

“…Many exciting research topics are surveyed in the book [2] and two special issues of IEEE Control Systems Magazine 4 . Among various challenging research issues, the control of the current profile in tokamak plasmas is known to be critical to plasma confinement, magnetohydrodynamic stability and effective steady-state operation (e.g., [17] and [22]). …”

Radial Electric Field in Tokamak Plasmas as a Physical Consequence of Ehrenfest’s Paradox

“…plays an important role in various modes of improved plasma confinement in a tokamak [24]. Some of those modes will be used in the thermonuclear reactor ITER [25], which is currently under construction.…”