Reduced model for direct induction startup scenario development on MAST-U and NSTX-U

摘要: A reduced semi-empirical model using time-dependent axisymmetric vacuum field calculations is used to develop the prefill and feed-forward coil current targets required for reliable direct induction (DI) startup on new MA-class spherical tokamaks, MAST-U NSTX-U. The are constrained by operational limits unique each device, such as geometry of conductive elements active coils, power supply specifications heating stress limits. also models sufficient breakdown, drive, equilibrium stability plasma developed from a shared database. large database DI NSTX NSTX-U leveraged quantify requirements achieving breakdown (I p ~ 20 kA). It observed that without pre-ionization, STs access E/P regime at modest loop voltage (V loop) where electrons in weakly ionized continually accelerating along open lines. This ensures rapid (order millisecond) neutral gas, even pre-ionization or high-quality nulls. timescale initial increase I reproduced provided mechanism impeding applied electric included. Most discharges fail phase due an inconsistency evolution p) loss vertical during burn-through phase. self-consistent fields fully-ionized states derived demonstrated NSTX, MAST. predictive completed illustrate maximum ramp rate (dI p/dt) early limited poloidal coils passive