Investigation of Beamed-Microwave Plasma Generation in Supersonic Flow

Open Access
Ho, Chien Hsiu
Graduate Program:
Aerospace Engineering
Master of Science
Document Type:
Master Thesis
Date of Defense:
December 01, 2017
Committee Members:
  • Michael Matthew Micci, Thesis Advisor
  • Beamed-Energy propulsion
  • Beamed-Microwave
  • Plasma
Beamed-energy propulsion provides a possible advanced propulsion source for Earth-launch systems with high-specific-impulse electric thrust and high payload mass fraction. The basic concept of beamed-energy propulsion is generating thrust by heating up propellant with outside beamed energy, either by laser or microwaves, instead of with the inner (chemical) energy of propellants in traditional propulsion systems. This method can provide higher theoretical specific impulse than traditional chemical propellants. Furthermore, the separation of the energy source from the vehicle can increase the payload mass fraction. In this research, the proposed method to transform beamed energy of continuous-wave microwaves to thrust is by the focusing of beamed microwaves onto a supersonic nitrogen flow to generate a plasma that can absorb the microwave energy and heat the supersonic flow. The coupling between the plasma and supersonic nitrogen flow is to be experimentally investigated. A converging–diverging (supersonic) nozzle with a parabolic diverging section and a thrust measurement platform, consisting of a non-friction slide stage and load cell, have been designed. To experimentally characterize the coupling of microwave energy to the flow, the supersonic portion of the nozzle is instrumented at six locations with six pressure transducers. The nozzle has an exit diameter of 5 cm to match the microwave beam diameter and is designed to produce an exit Mach number of 5 when expanded to ambient atmospheric pressure. The nozzle and the instruments for pressure and thrust measurements were assembled and tested with a nitrogen flow. To gain understanding about the microwave coupling to the flow, quasi-one-dimensional numerical simulations of the compressible nozzle flow with area change and heat addition were conducted. The simulation allows one to easily vary the location of the heat addition to examine its effect on the expanding flow. In comparison to cold flow, a microwave heated flow results in a 19% increase in thrust, assuming 100% of the 100-kW microwave power is absorbed. The experimentally measured pressures for both heated and cold flow in the nozzle is compared to the numerically predicted values.