Characterization of Magnetoplasmadynamic Thrusters Using Incoherent Thomson Scattering

Magnetoplasmadynamic thrusters (MPDTs) are a compelling option for future space propulsion needs, as they are projected to be more efficient at high-power operation than available electrostatic thrusters, and can also operate with a diverse set of propellants. These thrusters, however, remain underdeveloped and several fundamental questions about their dynamics need to be clarified. To better understand these, an Incoherent Thomson Scattering (ITS) diagnostic system has been developed to probe electron properties.

The ITS setup employs a high-power pulsed laser, precision beam-shaping optics, and a dedicated collection path consisting of a lens assembly, optical fiber bundle, volume Bragg grating notch filters, and an imaging spectrometer coupled to an iCCD camera. The collection optics are aligned with the plasma discharge region to capture scattered photons within a defined solid angle.

The diagnostic enables determination of electron density (via the spectral area, which reflects the number of scattering electrons), electron temperature (or electron energy velocity distribution function, inferred from the Doppler-broadened spectrum of the scattered light), and electron drift velocity (inferred from the degree of the shift of the spectrum away from the probing laser wavelength). From electron property measurements, information on features such as propellant ionization, plasma confinement, current density distribution, and anisotropies, can be inferred. Experimental results on electron properties will be compared with computational models and used to evaluate linear kinetic theory.