Performance of a Helicon Hall Thruster Operating with Xenon, Argon, and Nitrogen

Abstract

The Helicon Hall Thruster (HHT) is a two-stage thruster that was developed to investigate whether a radiofrequency ionization stage can improve the overall efficiency of a Hall thruster operating at high thrust and low specific impulse. This experiment measured the single-stage and two-stage performance of the HHT for 10-25 mg/s anode mass flow rates of xenon at 100-200 V discharge voltages, and also for 6 mg/s of argon at 300 V, and 2.6 mg/s of nitrogen at 200 V. Argon and nitrogen performance are characterized by low beam divergence efficiency and low propellant utilization efficiency. During two-stage operation, the thrust of the HHT increased slightly with rf power, but the propulsive efficiency and thrust-to-power both decreased with increasing rf power. Probe diagnostics suggest that gains were realized by a slight increase in propellant efficiency, but that the rate of increase was not sufficient to overcome the increase in power. NomenclatureA c,eff = Faraday probe effective collection area [m 2 ] e = elementary charge [C] E 1 = voltage exchange parameter [-] E 2 = mass exchange parameter [-] = Faraday constant [C/mol] I axial = axial component of ion beam current [A] I beam = ion beam current [A] I c = current collected by probe [A] I d = discharge current [A] I sp,a = anode specific impulse [s] I sp,a + = theoretical anode specific impulse of a singly-charged plasma [s] = molar mass [kg/mol] m i = ion mass [kg] = total thruster mass flow rate [kg/s] = anode mass flow rate [kg/s] = cathode mass flow rate [kg/s] P d = discharge power [W] P elec = total electrical power [W] P dc = dc discharge power [W] P mag = magnet power [W] P rf = rf power [W] P thrust = jet power of thruster exhaust [W] 2 r = Faraday probe distance from thruster [m] T = measured thrust [N] T + = theoretical thrust of a thruster with singly-charged plasma [N] = average axial velocity of exhaust particle [m/s] V d = discharge voltage [V] V mp = most probable energy of exhaust ions [V] V p = plasma potential [V] = anode efficiency [-] = anode efficiency of a thruster with singly-charged plasma [-] = cathode efficiency [-] = discharge efficiency [-] = magnet power efficiency [-] = current utilization efficiency [-] = rf power efficiency [-] = total efficiency [-] = voltage utilization efficiency [-] θ = angular position of Faraday probe [radians] λ = effective exhaust divergence angle [degrees] = propellant utilization efficiency [-] = beam divergence efficiency [-]