Electric Propulsion. Electric propulsion engines (e.g., ion engines, magnetoplasmadynamic thrusters, and Hall thrusters) can have exhaust velocities that are a factor of ten larger than conventional chemical rockets. These high velocities guarantee a low fuel mass fraction, which is ideal for high-efficiency missions, but also generate low thrust, which necessitates long mission travel times. Recently, Hall thrusters have been under intense scrutiny to improve their performance characteristics so that they can be useful for more than just stationkeeping duties. We are currently developing a 2D fluid model in order to investigate the effect of the magnetic field structure in the acceleration region on the performance characteristics. Two dimensions will include the magnetic field gradients self-consistently and will allow a realistic treatment of the plasma interaction with the walls (i.e., the sheath).
Helicon discharges produce plasmas with a density gradient across the confining magnetic field. Such plasmas can create a radial potential well for nonaxisymmetric whistlers, allowing radially localized helicon (RLH) waves. This work presents new evidence that RLH waves play a significant role in helicon plasma sources. An experimentally measured plasma density profile in an argon helicon discharge is used to calculate the rf field structure. The calculations are performed using a two–dimensional field solver under the assumption that the density profile is axisymmetric. It is found that RLH waves with an azimuthal wave number m = 1 form a standing wave structure in the axial direction and that the frequency of the RLH eigenmode is close to the driving frequency of the rf antenna. The calculated resonant power absorption, associated with the RLH eigenmode, accounts for most of the rf power deposited into the plasma in the experiment.
Assistant Professor of Engineering Physics
Dr. Charles Lee is an Assistant Professor in the Physical Sciences Department at Embry-Riddle Aeronautical University, Daytona Beach College of Arts & Sciences.