Numerical study of minority ion heating scenarios in a spherical tokamak plasma

In this study, D(H) minority ion cyclotron resonance heating (ICRH) scenarios in Nan Chang spherical tokamak (NCST) were simulated using the full-wave code TORIC. NCST is a low-aspect-ratio (R/a = 1.67) spherical tokamak, with its core plasma parameters characterized by a magnetic field intensity of 0.36 T and a density of 1018 m−3. Our simulation results demonstrate that the ion cyclotron wave can penetrate the core plasma of the NCST more effectively with a lower toroidal mode number, indicating that resonant ions can absorb the wave energy efficiently. Furthermore, it is found that as the minority ion H concentration is increased, a noticeable decline in the left-handed electric field adjacent to the ion cyclotron resonance layer is observed. Optimal heating efficiency is attained when maintaining a minority ion H concentration within the range 5%–10%. The minority ion velocity distribution was simulated to estimate the tail temperature of minority-ICRH, which is expected to exceed 10 keV. The difference in the power efficiency with different plasma compositions [Ar(H) and D(H)] was also simulated. When the H-ion cyclotron resonance layer is located at the core plasma, the power-absorption fraction of H in Ar(H) plasma surpasses that of D and H combined in D(H) plasma under identical conditions. These simulations provide a crucial foundation and theoretical reference not only for NCST but also for other spherical tokamaks conducting ICRH experiments.