Experimental and simulation study of argon helicon discharge in the linear plasma device MPS-LD

Abstract

To obtain high-parameter plasma in target region of the linear plasma device MPS-LD and to realize the experimental simulation environment of tokamak divertor plasma, experimental and numerical simulations of argon helicon discharge are carried out. Langmuir probes are used to diagnose the electron density (ne) in source and target regions with different experimental parameters (magnetic field, RF power, puffing flow rate). A three-dimensional discharge model is developed by using drift-diffusion equations of electron density and electron energy with the aid of COMSOL. The helicon discharge with long straight plasma beam and bright blue core is experimentally achieved. The simulation and experiment results are compared, showing the validation of the model. The corresponding spatial ne distribution is obtained, and the dependences of ne on the main experimental parameters are confirmed. The energy conversion relationship between the helicon and plasma is found. Helicon wave prefers to transfer energy to the plasma in source region, where ne is significantly raised. It results in a strong ne gradient, which acts a barrier to prevent the propagation of helicon wave. Therefore, localized standing helicon wave is formed and it limits the increase of plasma density in target region. Increasing magnetic field strength (B < 1500G) and RF power (P < 1500W), ne in source region can be increased, but they have little effect on ne in target region.