Experimental Characterization of Plasma Heating with Beating Electrostatic Waves

Abstract

The heating of ions in a magnetized plasma by two electrostatic waves whose frequencies differ by the ion cyclotron frequency is experimentally and analytically characterized. An analytical model is presented for the power absorption by the two waves, and it is shown that the two-wave process will yield superior heating to a single electrostatic wave only in the event that the total wave energy density exceeds a threshold value. An experimental investigation of the increase in ion temperature as a function of the fraction of total energy density in one of the propagating modes subsequently reveals that for a low temperature plasma, heating with a single electrostatic wave is superior to employing two beating electrostatic waves. This result is consistent with the analytical prediction that the available wave energy density in the experiment is below the required threshold for the superiority of the two-wave process.

Numerical Simulations of a Beating Electrostatic Wave Powered Magnetic Null Thruster

“…The conducting walls serve to help confine the plasma in the absence of electrostatic waves, which would typically push the plasma towards the null. While argon is used for testing purposes in the beating electrostatic wave experiment, 8,9 protons are used here to increase our computational speed in these proofof-concept simulations. Because the simulation time-step must resolve the electron cyclotron frequency and the simulation time-length is on the order of multiple ion cyclotron orbits, lighter ions allow us to make fewer total time steps in order to reach steady state.…”

Electrodeless plasma thrusters for spacecraft: a review

“…Ions accelerate stochastically until they reach a velocity that is near to the phase velocity of the wave at which point resonant coupling between the wave and ions increases the acceleration of the ions. BEW heating is more effective than SEW heating only if the total wave energy density exceeds a threshold value [35]. Analysis shows that there are distinct regimes of electrostatic wave energy density in which either BEW or SEW will provide superior heating however, since BEW heating accelerates low energy ions, it is an efficient alternative to SEW heating and coupled to a magnetic nozzle, can form a component of an effective electrodeless plasma thruster.…”

Antenna-Plasma Interactions in the Direct Wave-Drive Thruster

“…Therefore, an attractive option is to couple to the plasma inductively, as done in experiments by Jorns and Choueiri. 11,12 Such an inductive antenna is qualitatively similar to the inductive antennas used in Pulsed Inductive Thrusters (PIT). 13,14 However, instead of discharging a single large pulse, the wave-launching antenna operates continuously.…”