Research On Helicon Plasma Source Heating Of Lower Hybrid Waves In Single-ended Magnetic Mirror

As a new thruster device,helicon plasma thruster has high scientific value and wide application prospect.Because of small trust,high specific impulse and long service life,helicon plasma thruster is suitable for deep space exploration and satellite power system.At present,the ion cyclotron heating widely used in the helicon plasma electric propulsion system,which requires a strong background magnetic field that the technology is difficult to achieve.In addition,as one of the main auxiliary heating methods,lower hybrid waves heating(LHWH)has been widely used in the current drive system of Tokamak.If LHWH is used in the helicon plasma electric propulsion device,the magnetic field intensity can be greatly reduced,and the technology is easy to be implemented in engineering.Aiming at the heating process,heating law,heating efficiency and its influencing factors of lower hybrid waves in single-ended magnetic mirror field,the theoretical and simulation studies are carried out in this paper.Firstly,based on magnetohydrodynamics,the resonance condition and the cut-off condition of lower hybrid waves in a single-ended magnetic mirror field are obtained by solving the dispersion equation,and the influence of plasma parameters on the resonance region and the cut-off region is further discussed;then,LHWH process is simulated by the hybrid simulation.The work provides theoretical and technical support for the experimental research and engineering application of LHWH in helicon plasma thruster.The main research results are as follows:Lower hybrid waves can heat the plasma in the mirror magnetic field.However,due to the existence of the cut-off region,lower hybrid waves are damped before reaching to the plasma center region,so plasma cannot be heated in this region.Wave frequency,magnetic field intensity and number density have obvious influence on the resonance region and the cut-off region.The width of the resonance region is easily affected by wave frequency and magnetic field intensity.Number density can impact the heating efficiency by changing the cut-off region,but can’t change the resonance region independently,which need to cooperate with magnetic field intensity and wave frequency together.Compared with single ion model,the double ion model requires lower background magnetic field intensity and higher wave frequency.When the ions are heating by lower hybrid waves in the mirror magnetic field,both the ion velocity component xV and zV are increased.However,the acceleration of the ions along the z axis is different,xV in the strong magnetic field is higher than that in the weak magnetic field,conversely,zV in the strong magnetic field is lower than that in the weak magnetic field.In addition,the ion temperature increment in the horizontal direction is higher than that in the vertical direction.When 3% +H ions are incorporated into the system,ions have a left-handed motion along the z direction by analyzing the change of phase angle.That is the magnetosonic waves propagating in the mirror magnetic field,it not only mode conversion to lower hybrid waves,but also mode conversion to left-handed polarized waves.