Design And Simulation Of Helicon Plasma Source For Multiple Plasma Simulation Linear Device

It is very important to reduce plasma sputtering and erosion on the wall of the fusion device for high performance and stable operation.Linear Plasma Devices(LPDs)can produce a variety of steady-state plasmas with controllable parameters in the experimental process,easy measurement,short manufacturing cycle and low cost.It will play an irreplaceable role in the study of Plasma-Material Interactions(PMIs).In order to produce high temperature and high density steady-state plasma to simulate the irradiation effect of fusion particles,higher requirements are put forward for plasma sources in LPDs.Based on the research requirements of PMI and boundary Plasma in Tokamak,a Multiple Plasma Simulation Linear Device(MPS-LD)of Dalian University of Technology was proposed.In this paper,the design and simulation of MPS-LD plasma source are carried out.At present,different types of Plasma sources are used for LPDS according to different experimental requirements,including Helicon Plasma Source(HPS)and direct current plasma source of lanthanum hexaboride cathode.HPS produces an axially magnetized plasma in a cylinder with a finite diameter.By adjusting the RF power and magnetic field intensity and other parameters to the spiral wave mode,the electron density n_e can generally reach the magnitude of 10¹⁸-10¹⁹m^-3(argon gas discharge),which has higher efficiency than other RF discharges.In addition,the HPS antenna is located outside the vacuum chamber,which avoids the pollution or sputtering of the electrode and reduces the requirements for wall materials.Therefore,it is selected as the plasma source of MPS-LD.Based on the helicon wave dispersion relationship and the uniform discharge model,the linear relationship between the wavelength and the absorbed power of the HPS antenna is established.Plasma resistance and plasma absorption power were calculated by HELIC Code software,and a Helical antenna with a small radius was selected.The relative power absorption of each spectrum is calculated to determine the wavelength of the antenna.Based on the theoretical relationship,the relationship between antenna wavelength and length was obtained.The length of the antenna was determined by comparing the coupling efficiency of the two antenna lengths,so as to complete the physical design of the HPS antenna.Further simulation of the antenna design shows that the induced magnetic field,electric field and the radial component of current density have a major impact on its distribution,and the Gaussian density distribution of the induced magnetic field,electric field and current density is higher.Combined with the existing experimental and simulation results,the helicon wave discharge theory was summarized,and the HPS designed was simulated by using the simulation software COMSOL Multiphysics.A three-dimensional discharge model was established,and the RF frequency in the experiment was set at 13.56 MHz.The neutral gas argon was entered when the discharge pressure was 30 m Torr to simulate the real discharge state.The helicon wave discharge with electron density of 10¹⁸ m^-3 is simulated,and the electron density jump is generated.It is verified that the capacitive coupling and inductive coupling are converted to helicon wave mode during the discharge process.The power of mode jump is compared with the theoretical design work.