Two-dimensional Fluid Simulation Of Dual-Chamber Radio-Frequency Inductively Coupled Argon Plasma Source Based On COMSOL Software

It is the aim of International Thermonuclear Experimental Reactor Project(ITER Project)to generate energetic plasmas and realize controllable nuclear fusion in Tokamak.However,it is well known that the conventional internal Ohmic heating scheme is not so strong enough as to maintain such energetic plasmas.Hence,many types of auxiliary heating methods are advised and applied.One of these important advices is Neutral Beam Injection(NBI)heating setup.NBI means the injection of energetic neutral beam into Tokamak to achieve intense extra heating power.The core of a NBI system is the ion source.And the radio-frequency negative hydrogen ion source is used in ITER Project by comprehensive consideration.To avoid substantial energy loss of ions as they are accelerated by grids of high electric field through frequent collision with background gas molecules,usually very low pressures discharge condition is needed for ion source.This work builds up a hybrid model that couples Boltzmann equation solver to the fluid model,aiming at a double chamber inductively coupled plasma source(with driver and expansion regions)that is established in our lab.For low pressure radio-frequency(RF)inductively coupled plasmas,the discharge is supported by Ohmic heating(collisional heating)and wave heating(collisionless heating)mechanisms.But the heating mechanism in Plasma Module of COMSOL only includes the Ohmic heating that is only accurate in high pressure discharge simulations.This paper advances two modules of this software,i.e.,Plasma Module and Electromagnetic Module,by including both the two heating mechanisms.Hence,it can simulate the low pressure discharge case suitable for ion source device.In this paper,we first deduce the analytical form of induced electric field and RF deposited power density,based on the Maxwell's equations and the Vlasov's equation.Then the analytical power profile are coupled to plasma fluid model of the software.This paper gets the following conclusions with this amended fluid model:(1)In case of other discharge conditions unchanged,plasma density is higher and electron temperature is lower at higher pressures;the bulk electron density increases with increasing power,while the electron temperature decreases conversely;coil frequency has a little influence on plasma density.(2)Electron temperature near quartz window increases with increasing power,because the electromagnetic energy is transferred to plasma mainly by skin layer there.Increasing coil frequency elevates electron temperature near quartz window.(3)At low pressures(<5Pa),the traditional fluid model based on Ohmic heating becomes inaccurate,and the collisionless heating(stochastic heating)mechanism gradually dominates with decreasing pressures.(4)At specific discharge parameters,abnormal spatial profile of induced electric field and the anomalous skin effect appears,and negative power absorption is also observed.In addition,part of the simulation results are compared with experiment data,for verifying the accuracy of the model.At high pressures,they match with each other well.