Design and Results of a Microwave-Driven Gasdynamic Mirror Experiment

Abstract

The gasdynamic mirror is a magnetic confinement device that has been proposed as a concept that could form the basis of a spacecraft propulsion system by accelerating its ionized propellant without the endurance limitations imposed by electrodes. The geometry of the gasdynamic mirror is that of a simple magnetic mirror, with a stronger magnetic field at the ends, called mirrors, than at the center, producing a turning force that helps confine the plasma ions long enough for heating before being ejected through one of the mirrors, which serves as a magnetic nozzle. The main focus of this paper is to describe an experimental gasdynamic mirror device driven by a 2.45 GHz microwave source and present the results from the experiments. Argon was chosen as the propellant, and ionization comes from electron cyclotron resonance heating. Langmuir probe measurements provide two-dimensional maps of the plasma density and temperature inside the device. A maximum ion density exceeding and an electron temperature between 4 and 5 eV were found in the central section of the device. The ion density profile showed a local concentration at the exit mirror due to the magnetic field gradient in that region, and the plasma potential results hinted at the presence of an acceleration zone in the vicinity of the exit mirror.