Compact Steady State Tokamaks

The small aspect ratio tokamak combines the attractive features of the tokamak, reverse field pinch and spheromak to produce a compact, stable, high-β configuration with low external fields. Experiments on the Small Tight Aspect Ratio Tokamak (START) at Culham have demonstrated the production of stable, high temperature (T_e ≤ 1keV), naturally elongated plasmas with good confinement, at aspect ratios down to 1.25. These plasmas are, so far, free from current-terminating disruptions and exhibit a natural divertor action. Theoretical studies have demonstrated robust stability at high β (> 30%) and self-consistent steady-state equilibria using pressure and beam driven currents. Such steady-state solutions exist for devices at the Mega Amp level, compact component test facilities and fusion power plants of modest size (R_o~2–3m).