Simulating ICH on ions in a VASIMR

Ion Cyclotron Heating (ICH) is used to heat a plasma and create thrust in a Variable Specific Impulse Magnetoplasma Rocket (VASIMR) engine. An ICH Radio Frequency (RF) antenna is placed near the throat of a magnetic nozzle. It produces a localized circularly polarized electric field near the ion cyclotron frequency. An ion is accelerated by pumping its magnetic moment, μ, which is the ratio of perpendicular kinetic energy to the magnitude of the B-field. Outside the antenna region, μ is conserved and the additional kinetic energy is converted into thrust as ions traverse the nozzle into the region of expanding and weakening B-field . This study looks at the efficiency of the pumping process by simulating individual ions generated from an initially cool Maxwellian distribution and looking at the average increase in total energy of ions as they pass through the engine. The resulting heated distribution of ions may be used to estimate the specific impulse and efficiency of the VASIMR engine. Since the model does not yet incorporate any collisional losses, it represents an upper limit on heating efficiencies for a given ICH input. Computational checks on the instantaneous and average value of μ serve to verify the energy and power inputs to the plasma.