The Electron Cyclotron Resonance (ECR) preionization is important for the reliable start-up of spherical tokamaks.

This study aims to investigate the effects of power deposition, electron density, and electron temperature of ECR pre-ionization process under different power conditions by simulation.

The spherical tokamak device NCST (NanChang Spherical Tokamak) at Nanchang University was selected as research object, and COMSOL Multh-physics, a multi-physics simulation software, was utilized on the basis of the finite element method to simulate the process of ECR pre-ionization forming plasma in the device. Firstly, a three-dimensional model of the NCST device was established by using the parametric modeling method. Then, through the AC/DC, radio frequency (RF) and plasma modules in COMSOL software, and by correctly defining the electromagnetic wave source term, plasma parameters and reasonably setting boundary conditions, the laws of magnetic field, electron density and electron energy changing with time and space were solved through multi-physics field coupling.

The results show that increasing the input power can greatly shorten the ionization time of electrons, and greatly increase the peak electron density and electron temperature of plasma. However, too high input power will also cause too large plasma density generated by ionization, making the incident electromagnetic wave difficult to reach the resonance region, thus reducing the heating efficiency of ECR. Higher power can make the heating effect of ECR better, hence greatly shorten the ionization time of electrons, but the duration of this process will also decrease with the increase of power.