Comparative studies on the control algorithm for the high-density ignition regime in FFHR-d1

In the Force Free Helical Reactor FFHR-d1 (R~15.7m, a~2.5m, B_o ~4.5 T, 〈〉 ~5% and the fusion power of 3 GW) [1, 2], it is demonstrated that the thermally unstable operation is better to achieve the higher density and lower temperature plasma (n(0)~ 9 x 10²⁰ m^-3 and T(0)~7 keV) than the impurity injection method. One drawback of the thermally unstable operation is a possibility of the thermal runaway when fueling systems have failures. However, we have found that the inherently safe function exists owing to the plasma outward shift during the thermal runaway. Thus we continue to pursue this high-density operation scenario for FFHR-d1. Preliminary estimation of the alpha energy loss fraction of ~3% is obtained for a broad density profile in the high-density ignition regime.