This work was motivated by questions raised from multifrequency microwave interferometer measurements taken in a cylindrical plasma on the Variable Specific Impulse Magnetoplasma Rocket (VASIMR) project. Standard data analysis based on a thin beam model neglecting refraction yields inconsistent electron densities and density profiles for different frequencies. This work focuses on the development of a model for the wave propagation through cylindrical plasmas when the plasma radius is on the order of the beam waist. For the calculations presented a Gaussian beam profile and plasma spatial profile were assumed. Both refraction by density gradients and finite beam sizes are found to play important roles and explain polychromatic differences in the electron densities and profiles. Calculations for the new model are compared to a thin beam model not accounting for refraction and experimental data from VASIMR.

The numerical simulation and modeling of plasma detachment from a magnetic nozzle is presented. The detachment problem is of key importance to the plasma-based propulsion concepts that employ a guiding magnetic field to control plasma flow and motivated by the needs of the VASIMR (Variable Specific Impulse Magnetoplasma Rocket) project. The detachment of the plasma exhaust is required to produce directed thrust. In the present scenario plasma can stretch the magnetic field lines to infinity, similar to the solar wind. In order to extend the magnetic nozzle model beyond the limitations of analytic theory, a numerical code is developed to simulate steady-state kinetic plasma flows and to evaluate nozzle efficiency. The direct solution of a steady-state problem, as opposed to an initial value problem, eliminates the need to deal with transient phenomena that are of secondary importance for continuously operated plasma thrusters. The new simulation code is verified against the analytic results and then used to model the plasma behaviour for the conditions of the Detachment Demonstration Experiment (DDEX) at the NASA Marshall Propulsion Research Center, Huntsville, Alabama. / text

This work is motivated by the Variable Specific Impulse Magnetoplasma Rocket (VASIMR) experiment. This device uses a helicon antenna to generate a plasma inside a dielectric tube, which is radially confined and directed towards the rocket nozzle by an axial magnetic field. An ion cyclotron heating antenna further heats the ions, and a magnetic nozzle accelerates the plasma along the confining magnetic field as it leaves the rocket, ultimately allowing it to detach from the magnetic field and produce thrust. The experimental research presented here provides insight into the physical mechanisms of power flow in a helicon system by providing an overall system power balance in the form of heat flux measurements, and exploring changes in the heat fluxes in different parts of the system in response to varying operational parameters. An infrared (IR) camera measures the total heat flux into the dielectric tube surface, and axially scanned bolometer and UV photodiode probes measure the radial power loss from particles and radiation. Results from IR camera measurements on three different helicon systems are presented: the VASIMR VX-50 experiment, the VASIMR VX-CR experiment, and the University of Texas at Austin (UT) helicon experiment. These results demonstrate the development of the IR camera diagnostic for use on helicon systems of varying scale and geometry, and show reasonable agreement as to the fraction of input power lost to the dielectric tube walls. On the UT experiment, the results presented account for essentially all of the input power, providing a full system power balance. The data from all three experiments indicate that radial transport of ions to the interior wall is the dominant mechanism of power loss, with UV radiation contributing a small percentage. Additional experiments on the UT helicon explore energy and particle transport to the wall due to capacitive coupling of ions near the antenna. These experiments show clear damage to the dielectric tube surface directly under the antenna, due to physical plasma etching of the surface by bombarding ions that are accelerated into the wall by local electric fields from the antenna. / text

This thesis explores the potential of utilizing metal-based plasma sources as a sustainable solution for high-powered electric propulsion and its implications for future interplanetary travel. Focusing on the Vacuum Arc Thruster and the Variable Specific Impulse Magnetoplasma Rocket engine, the study encompasses numerical simulations, analytical comparisons, and performance analyses to assess the feasibility of metal plasma fuels in space missions.The numerical analysis employs COMSOL Multiphysics to delve into the magnetohydrodynamics behavior within the VAT. Such simulation setup could provide valuable insights. Although the numerical results are disappointing for this paper, there exist possibilities within future work. The main hurdle is the simulation of vacuum. There are workarounds in COMSOL's Vacuum System Modeling tool which was not available for this thesis. Also, the used material properties were not suited for this high temperature plasma environment. The lack of material properties is a consequence of the insufficient research in the metal plasma field.Performance analysis is conducted on both the VAT and VASIMR engine, exploring efficiency, thrust capabilities, and feasibility for interplanetary missions. The results demonstrate the potential of metal-based plasma sources to reduce dependence on Earth for refueling and decrease mission costs. It is found that aluminum and magnesium have similar performance as the argon gas used in the VASIMR.Although challenges exist, such as integration problems and availability of material properties for metals in plasma states, the study underscores the promise of metal plasma fuels for sustainable space exploration. By advancing high-powered electric propulsion technologies, we move closer to realizing humanity's ambitious journey to distant celestial bodies. This research paves the way for future innovations, enabling a more self-sustaining space economy and unlocking new horizons of interplanetary travel.