Time-dependent modeling of the X-I ECH and ECCD for solenoid-free start-up of a compact pilot plant

The elimination of OH solenoid maybe the most impactful design driver for an economical compact fusion tokamak reactor system. To address this challenge, an efficient solenoid-free start-up and ramp-up scenario utilizing the X-mode at w = Ω_e (X-I) was investigated to drive ~ 10 MA of plasma current for a compact Sustained High Power Density tokamak facility with a modest ECH power of ~ 10 MW utilizing the 170 GHz gyrotrons. The high ECCD efficiency is due to the strong wave-particle interactions at the Doppler broadened w = Ω_e resonance, together with the accessibility constrained absorption on uni-directional passing electrons. The efficiency of the well localized current drive remains high for a broad range of launched parallel index of refraction suggesting that a relatively simple waveguide launcher placed outboard could be used. As a next step, a time dependent model of the X-I solenoid-free start-up and ramp-up is been developed. Interestingly, the X-I current ramp-up process appears to possess a positive feed-back of key parameters, ECCD, Ip, L-mode confinement time, and T_e, where increase in any one of the parameters results in corresponding increases in other parameters resulting in a virtuous cycle of continuous current ramp-up even with a constant applied power.