High performance stationary discharges in the DIII-D tokamak

Recent experiments in the DIII-D tokamak [J. L. Luxon, Nucl. Fusion 42, 614 (2002)] have demonstrated high beta with good confinement quality under stationary conditions. Two classes of stationary discharges are observed-low q(95) discharges with sawteeth and higher q(95) without sawteeth. The discharges are deemed stationary when the plasma conditions are maintained for times greater than the current profile relaxation time. In both cases the normalized fusion performance (beta(N)H(89P)/q(95)(2)) reaches or exceeds the value of this parameter projected for Q(fus)=10 in the International Thermonuclear Experimental Reactor (ITER) design [R. Aymar , Plasma Phys. Controlled Fusion 44, 519 (2002)]. The presence of sawteeth reduces the maximum achievable normalized beta, while confinement quality (confinement time relative to scalings) is largely independent of q(95). Even with the reduced beta limit, the normalized fusion performance maximizes at the lowest q(95). Projections to burning plasma conditions are discussed, including the methodology of the projection and the key physics issues which still require investigation. (C) 2004 American Institute of Physics.