Simulation on density modification at ICRF antenna proximity and the radial broadening of the direct current plasma potential caused by the ponderomotive force

The nonlinear interaction between radio frequency (RF) wave and plasma could restrict the power coupling of the ion cyclotron resonant frequency (ICRF) antenna. The gradient of the electric field generates a ponderomotive force (PF) that pushes particles from the high field region to the low field region, potentially leading to a decrease of the plasma density. 2D full wave simulation results indicate that the density drops from 8.91×10¹⁷ m⁻³ to 6.79×10¹⁷ m⁻³ (θ = 0°) at the antenna aperture with a ponderomotive potential about 10 V at the antenna aperture, meaning that the converged density has a decrease of density by 24% with respect to the original one. This depletion weakens the power coupling, resulting in a 11% decrease in power coupling when comparing the converged density to the original one (θ = 0°). Besides, the 2D self-consistent sheath and wave for ion cyclotron heating-full wave (SSWICH-FW) simulation shows that such level of PF does not affect significantly the V_DC radial broadening. Moreover, a strong PF may cause the plasma density to drop below the density criterion where the lower hybrid (LH) resonance layer appears, making the LH resonance layer outside the antenna box. However, additional 2D full wave simulations indicate that the LH resonance layer locating outside the antenna box has only a weak effect on power coupling.