T.K. Mau1, S.C. Jardin2, J. Menard2, R.L. Miller3, R.D. Stambaugh3 and the ARIES Team
1Fusion Energy Research Program, UC-San Diego, La Jolla, CA 92093-0417
2Princetown Plasma Physics Laboratory, Princeton, NJ 08543-0451
3General Atomics, San Diego, CA 92186-9784
The ARIES group is presently developing a fusion power plant design, ARIES-ST, based on the spherical tokamak concept. This design will have attractive features such as high plasma b, low magnetic field, high self-driven current fraction and power core compactness. This paper reports on the investigation of the physics aspects of plasma performance and machine operations such as profile control and plasma startup.
Detailed physics studies to date appear to indicate that the performance of the spherical tokamak optimizes at high elongations, up to k=3.0, and at aspect ratios in the range of 1.4 < A < 1.6. With a nearby conducting wall to stabilize the low-n kink modes, we find that the maximum stable normalized beta, bn, increases with both triangularity,d, and with k up to a value of 3.0, but that the maximum stable b itself continues to increase with k for values of k > 3.0. Two configurations selected for comparison studies are (1) A=1.4, k=3.4, d=0.55, bn=7.7 and b=55.6%, and (2) A=1.6, k=3.2, d=0.57, bn=7.0 and b=39.8%.
Because of the high pressure-driven current fraction (>95%) and its good alignment to the equilibrium profile, the power requirement for seed current drive will be modest. The central seed current can be maintained by either the low-frequency fast wave or neutral beam injection, while steady-state operation without the need for noninductive drive is a design goal. If required, current profile control at various phases of the plasma operation can be achieved by a combination of high-harmonic fast wave (HHFW) at mid-radius and lower hybrid wave near the edge. In particular, it has been shown that the launched N|| spectrum is an effective knob for controlling the location of HHFW power deposition in the mid-plasma region. Several options for the plasma startup are being explored, including HHFW central heating and current drive, bootstrap overdrive, coaxial helicity injection, and a combination of these techniques. Results for this investigation will be reported.
*Work supported by USDOE grant DE-AC03-95ER-54299.