Bench test of interferometer measurement for the Keda Reconnection eXperiment device (KRX)

Motivated by the need of the electron density measurement for the Keda Reconnection eXperiment (KRX) facility which is under development, an interferometer system has been designed and tested in bench. The 320 GHz solid-state microwave source with 1 mm wavelength is used to fulfill the high phase difference measurement in such low temperature plasma device. The results of the bench test show that the phase difference is accurately measured. In contrast to tens of degrees of phase shift expected to be measured on the KRX, the system noise (~1°) is low enough for the KRX diagnostics. In order to optimize the system for better performance, we utilize the Terasense sub-THz imaging system to adjust alignment. The interferometer system has also been calibrated via changing of the optical path length controlled by the piezo inertial motor. Simultaneously, high density polyethylene thin film is introduced successfully to change a tiny phase difference and test the sensitivity of the interferometer system.