Wave penetration and power deposition of helicon current drive for magnetic fusion plasma with sharp edge gradient

Abstract To enhance power absorption efficiency in ion cyclotron resonance heating and lower hybrid current drive systems for advanced tokamaks, this study investigates helicon wave utilization through electromagnetic simulations of wave penetration and power deposition in plasmas with sharp density and temperature gradients. Employing an axisymmetric Maxwell-equation solver electromagnetic solver incorporating cold plasma dielectric tensor, we model tokamak conditions through radial profiles combining uniform core parameters and exponentially decaying edge distributions. The analysis systematically examines wave frequency, profile gradients, and antenna lengths effects on electromagnetic field patterns and power deposition characteristics, incorporating an equivalent collision frequency model to capture Landau damping and related dissipation mechanisms. Simulation results demonstrate that maximum power absorption occurs near the last closed flux surface, primarily governed by Landau damping spatial distribution. A frequency-dependent enhancement of absorbed power emerges, accompanied by undamped zones at larger radii whose spatial extent scales with both wave frequency and plasma gradient magnitude, leading to axial standing wave formation. Extended antenna lengths promote bidirectional wave propagation. Although excluding ionization dynamics and transport processes beyond the immediate scope, these findings establish fundamental insights into helicon wave penetration and power deposition within scrape-Off Layer plasmas. This work provides critical foundations for experimental optimization of radiofrequency heating schemes in high-density tokamak regimes.