A single-probe-beam double-heterodyne polarimeter-interferometer for plasma Faraday rotation measurements

This article describes a novel millimetre-wave polarimeter/interferometer for measuring the Faraday rotation of the plane of polarization of a probing coherent electro-magnetic beam that traverses a magnetized plasma. Independent frequency offset heterodyne carriers for the interferometric and polarimetric angles are generated using a chirped microwave source. The system has the advantage of requiring just a single frequency-modulatable source and a single detector for each spatial probing beam. The paper describes the system operating principles and reports measurements using a benchtop system that demonstrate the measurement principles and expected performance. A system based on this principle is now being constructed for measurements on the HIT-SI tokamak.