Numerical Study Of Helicon Plasma Discharge

Helicon Plasma Source-HPS is a kind of high density plasma source,which has special application value in large-scale semiconductor processing,high-power plasma propulsion and fusion material interaction,and gradually becomes the focus of people’s research with its unique advantages.The numerical simulation of helicon plasma is very important to understand the behavior of different physical quantities of ionized gas(such as electrical parameters).In this paper,the coupling of RF antenna with working frequency of 13.56 MHz and cylindrical plasma with cavity radius of 0.075 m is studied.By using HELIC code,the energy deposition,current and electric field radial distribution characteristics of helicon plasma under different electron temperature and gas pressure distribution conditions are studied and calculated,and the influence of temperature and pressure distribution on discharge characteristics is obtained.The results show that the positive radial electron temperature gradient is more conducive to the power absorption at the plasma center,and the type of temperature gradient has little effect on the electric field strength and current density distribution.When the neutral pressure is positive gradient,the induced electric field at the edge of the plasma increases,and the power deposition at the edge is weakened.The depth of wave energy coupling is deepened,which is more conducive to the power coupling absorption at the center.When the radial density of the plasma is parabola distribution,the power deposition at the center and edge of the plasma is larger,especially near the edge,which is significantly higher than the power deposition under the Gaussian density distribution.When the radial density is Gaussian distribution,the electric field intensity at the edge of the plasma is higher,the current density is smaller,and the deposition energy of RF wave at the edge is less and has little change.So the coupling depth of wave energy increases greatly.The results show that the three temperature and pressure distributions have similar effects on the distribution and change trend of electric field intensity and current density in the plasma with two density structures,which proves the stability of M = 1 mode.As one-dimensional HELIC code does not consider the ionization and transport process of plasma,this paper uses COMSOL software to further improve the simulation of helicon wave discharge.According to the structure of HPS,atwo-dimensional axisymmetric model is built,and the corresponding parameters are set up to simulate and calculate the electronic density,electronic temperature,collision loss,power deposition and other important parameters,and the detailed physical mechanism is analyzed.It is concluded that with the gradual increase of RF power,the electronic density,collision power loss(absolute value),power deposition are also increasing,and the change of temperature is not obvious.The higher the pressure of neutral gas is,the higher the density of the number of ionized electrons is,the lower the temperature of electrons is,and the collision power loss(absolute value)and power deposition are on the rise as a whole.Under some static magnetic field strength,the power deposition and electron density are higher,indicating that the magnetic field affects the ionization and energy distribution.In addition,it is concluded that changing the number of loop-antenna in a certain range will also affects the simulation results.This work can provide technical support for the experimental design of the helicon plasma source and the optimal design of devices such as the Helicon Plasma Thruster-HPT.