Evaluation of Current Drive Requirements and Operating Characteristics of a High Bootstrap Fraction Advanced Tokamak Reactor

The reactor potential of some advanced physics operating modes proposed for the TPX physics program [1] are examined. A moderate aspect ratio (A = 4.5 as in TPX), 2 GW reactor (see Table I for parameters) is analyzed because of its potential for steady-state, non-inductive operation with high bootstrap current fraction. Particle, energy and toroidal current equations are evolved to steady-state conditions using the 1-1/2-D time-dependent WHIST transport code [2]. The solutions are therefore consistent with particle, energy and current sources and assumed transport models. Fast wave current drive (FWCD) provides the axial seed current. The bootstrap current typically provides 80–90% of the current, while feedback on the lower hybrid current drive (LHCD) power maintains the total current. The sensitivity of the plasma power amplification factor, Q ≡ P_fus/P_aux, to variations in the plasma properties is examined. The auxiliary current drive power, P_aux = P_LH + P_FW; bootstrap current fraction; current drive efficiency; and other parameters are evaluated. The plasma is thermodynamically stable for the energy confinement model assumed (a multiple of ITER89P). The FWCD and LHCD sources provide attractive control possibilities, not only for the current profile, but also for the total fusion power since the gain on the incremental auxiliary power is typically 10–30 in these calculations when overall Q ≈ 30.