Optimization of ECR assisted pre-ionization in GLAST-III via Multiphysics simulation

Abstract Electron cyclotron resonance (ECR) is a common pre-ionization technique to assist ohmic startup in tokamaks. In this research, ECR assisted pre-ionization in GLAST-III tokamak is comprehensively investigated via Multiphysics 3D COMSOL simulations. Optimal conditions for ECR microwave absorption at fundamental mode are determined to achieve reliable plasma startup. The effect of filled gas pressure on the ECR plasma parameters such as plasma density and plasma temperature is thoroughly investigated in the range of 0.08–1 Pa. The results reveal that the ECR absorption of the incident microwaves is significantly enhanced at low enough filled argon pressure. The behavior of absorbed microwave power is significantly changed for different filled gas pressures. In case of high gas pressure, the microwave power is deposited locally in front of the waveguide, whereas in case of low pressure (0.08 Pa), the microwave power is uniformly deposited along the resonance layer. Moreover, the experimental investigation extends to nearly identical operating conditions, confirming the ECR absorption. The experimental data aligns with the simulation results, collectively affirming the efficacy of optimized pre-ionization in the low gas pressure scenario (0.08 Pa) within the GLAST-III tokamak.