Measurement And Control Of Ion Energy In Helicon Plasma Of Loop Antenna

The helicon plasma source has broad application prospects due to its high ionization efficiency,high electron density,relatively simple structure,and ability to work at a low pressures,especially in the field of high-power electric propulsion.However,little is known about the helicon plasma until now,and the energy absorption mechanism is not clear.Accurate measurement of plasma parameters is very important to further understand the characteristics of the helical plasma.Even there are some research on the parameters in the helicon plasma,there are relatively few studies on the ion energy parameters.In this paper,the retarding field energy analyzer(RFEA)is used to study the ion energy characteristics in Ar helicon plasma,especially the ion energy excited by the loop and the right-helical antenna.The focus in this thesis is the influence of discharge parameters,such as applied power and working pressure,on ion parameters in the diffusion chamber.The obtained results are:(1)For the loop antenna in the experimental parameter range the ion energy presents an unimodal distribution at the middle and remote end of the diffusion chamber,while it was an unimodal or a bimodal distribution at the near the discharge tube.The ion energy assigned to the IED was single peak or the main peak of the double peaks.The average energies of ions at the three different axial positions all were increased firstly with the increase of the discharge power,and there were decreased after the discharge in helical mode,then stabilizing with the increase of the applied power.As the applied power was increased,the saturation current and the ion flux were gradually increased.The peak energy of the ions was decreased in the direction away from the discharge area.(2)Diagnostic of the discharge characteristics in the helicon plasma with a right-helical antenna was performed by a variety of methods.It was obtained that with the increase of discharge power,the discharge exhibited three modes: capacitive(E)mode,inductive(H)mode and wave(W)mode.In the E and H modes,the ion energy peak was increased along with the discharge power;in the wave mode,the energy peak was significantly dropped,but slightly increasing after the appearance of the blue core(big blue);when the discharge was in blue core mode,the energy peak dropped significantly again,and then remaining unchanged with the increase of the applied power.