Measuring Plasma Viscosity with a Fabry-Perot Spectrometer

A Fabry-Perot spectrometer has been developed for measuring ion temperature and inferring the Braginskii viscosity of flowing, unmagnetized plasmas at WiPPL. Ion viscosity is important in coupling the momentum from JxB edge-driven flows throughout the plasma to generate large-scale shear flow. In a Fabry-Perot spectrometer, collimated light is dispersed by an etalon to provide high-throughput, compact, and simple optical design with high resolving-power. The precision needed to measure the fixed etalon plate separation for an absolute wavelength calibration at high order motivates an analysis using multi-modal nested sampling. An experiment has been designed to measure the ion viscosity and the momentum diffusion length of JxB edge-driven flows on the PCX-U using the Fabry-Perot spectrometer and to compare against Mach-probe velocity profiles and Braginskii viscosity.