Commissioning of a 300 GHz Microwave Interferometer on PHASMA

A 300 GHz microwave interferometer system designed to measure the chord averaged electron density in the PHAse Space MApping (PHASMA) device has been installed and tested. A 300 GHz operating frequency was chosen since it is well above the cutoff frequency ~ 60 GHz of PHASMA, corresponding to an electron density ∼5×10¹⁹ m^-3. An additional leg of the system will be installed during a future upgrade for coherent scattering measurements. The interferometer will be used to validate conventional Langmuir probe measurements while avoiding the issues of perturbations, probe tip erosion, and electrical noise pickup issues. The interferometer is configured as a conventional Michelson interferometer with a combination of HDPE lenses, a beam splitter, and metallic mirrors. A chirped-frequency source is used to create a refractive index phase shift. The design details, installation, testing, calibration, and initial measurement will be presented.