No abstract

A thrust model for a Lissajous method has shown that a competitive performance compared with the rockets using, e.g., ion engines or Hall thrusters, can be achieved by electrodeless method which can be a long lived thruster. Previous experiments showed a slight increase of plasma flow velocity by this method, however, experimental conditions were not optimized and the thrust was not measured. In this study, two experiments are reported in order to develop helicon plasma sources and a thrust measurement method by using Ar gas propellant. The first experiment is measurements of thermal thrust in order to characterize thruster performance 26 mm and 50 mm diameter helicon plasma thrusters without Lissajous acceleration. Maximum specific impulse (390 ± 130 s) is observed at a parameter set: the mass flow rate of 0.24 mg/s, the magnetic field: B Z = 0.054 T and RF (radio frequency) input power of 2.0 kW when a 50 mm diameter thruster is used. It is found that the thrust and efficiency is proportional to absorbed power by the plasma. The second experiment is preliminary measurements of Lissajous acceleration by using a laboratory model of 50 mm diameter. Preliminary thrust measurements by using the laboratory model show clear plasma acceleration by applying acceleration power. The observed thrust with acceleration power of 130 W is 3.3±0.3 mN with a specific impulse of 380±40 s and efficiency 2 of 0.40 ±0.08 %. When acceleration power is turned off, the observed thrust is 2.9±0.3 mN with a specific impulse of 330±40 s and efficiency of 0.39 ±0.09 %. The improvement of thruster performance by applying acceleration power is achieved at a non-optimized condition and a small fraction (7 %) of the RF power available for the acceleration. NomenclatureB z = Axial magnetic field c s = Ion sound velocity HDLT = Helicon Double Layer Thruster PM-HDLT= Permanent Magnet HDLT HEAT = Helicon Electrodeless Advanced Thrusters I = r.m.s. RF current I.D. = Inner Diameter LHPD = Large Helicon Plasma Device M = Ion mass P in = RF input power P abs = Absorbed RF power by plasma RF = Radio frequency T e = Electron temperature VASIMR = Variable Specific Impulse Magnetoplasma Rocket Z = Impedance  = Boltzmann constant