Impact of ion cyclotron range of frequencies wave induced localized fields on electron dynamics in EAST’s scrape-off layer

Abstract In ion cyclotron range of frequencies (ICRFs) heating experiments on tokamaks, the observation of hot spots on the first wall and increased impurities at the plasma boundary in specific parameter regimes has prompted investigations into the underlying mechanisms. While previous studies have highlighted the role of fast ions generated by radio frequency sheaths in contributing to heat flux and impurity production, the influence of electrons has been overlooked. This study addresses this gap by exploring the impact of the localized electric fields induced by ICRF antennas on electron dynamics in the scrape-off layer of the EAST tokamak through test-particle simulations. Simulation results reveal two primary mechanisms through which the ICRF electrostatic wave packet affects electrons. For thermal electrons, low-power ICRF injection leads to a notable decrease of approximately 20% in electron density near the wave packet center due to ponderomotive reflection of low-speed electrons. Consequently, increasing electron temperature can mitigate this effect to some extent. As for fast electrons with velocities in the vicinity of the central phase velocity of the wave packet, significant acceleration occurs upon their quasi-trapping by the wave packet. Specifically, under 2 MW ICRF injection, some initial 1.5 keV fast electrons undergo substantial acceleration, reaching energies of 20 keV, with the average energy flux amplified 7 times. As power levels rise to 8 MW, the trapping velocity range widens, enabling the direct capture and acceleration of even thermal electrons by the ICRF localized field. Furthermore, a higher electron temperature of 80 eV can reduce the power demand to 5 MW. This study will qualitatively assess the impact of localized fields on electron acceleration and parameter dependence across various ICRF power levels, offering insights for controlling ICRF operation parameters in future fusion reactors.