Spherical tokamak 2.45GHz electron cyclotron resonance Simulation of preionization

[Background]The Electron Cyclotron Resonance (ECR) preionization is important for the reliable start-up of spherical tokamaks. [Purpose]This paper aims to simulate and study the ECR pre-ionization process under different power conditions, and then investigate the effects of power deposition, electron density, and electron temperature. [Method]This paper takes the spherical tokamak device NCST of Nanchang University as the research object and uses COMSOL Multhphysics, a multi-physics simulation software based on 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 is established by using the parametric modeling method. Then, through the AC/DC, 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 are solved through multi-physics field coupling. [Results]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 the plasma density generated by ionization to be too large, and the incident electromagnetic wave is difficult to reach the resonance region, thus reducing the heating efficiency of ECR. [Conclusion]In conclusion, although higher power can make the heating effect of ECR better, can greatly shorten the ionization time of electrons, but the duration of this process will also decrease with the increase of power.