Recent directions in plasma physics and its impact on tokamak magnetic fusion design

Abstract

Steady progress has been made in recent years towards achieving fusion breakeven and reactor-relevant plasma conditions in the largest tokamak experiments. In particular, the experimental observation of a large self-sustaining bootstrap current in the plasma permits development of steady-state reactor concepts with modest current drive power and relatively high plasma energy gain ( Q). The SSTR (Japan) and ARIES-I (USA) designs reported in this paper are first-stability, steady-state tokamak reactors based on “modest” extrapolations from the present tokamak physics database. The plasma is characterized by a high edge safety factor ( q a) and a high poloidal beta ( β p) in order to increase bootstrap current fraction (∼70%). This mode of operation is achieved by selecting high values of both aspect ratio ( A = R/ a = 4−4.5) and toroidal magnetic field on axis (9–11 T) in these reactors. Both reactor studies suggest that the tokamak system can be a steady-state power reactor with net electricity of ∼1 GW and with plant efficiency 30–40%. The SSTR is characterized by its technical feasibility in the near future. On the other hand, the ARIES-I focuses on better safety and environmental aspects and a longer time frame. The SSTR and ARIES-I studies show that, with proper R&D programs, tokamak fusion reactors can be developed that will have acceptable cost of electricity.