Time resolved whistler electron cyclotron emission spectra during ECRH on the Michigan Mirror Machine

The authors present the results of time-resolved whistler electron cyclotron emission measurements performed during whistler mode ECRH on the Michigan Mirror Machine (MMM). The spectra illustrate evolution of the plasma from stable, ECRH build-up, to whistler instability and finally to MHD instability. During the build-up phase, the measured spectra are compared to predictions of a computer model developed at the University of Maryland. The data are consistent with a model electron velocity distribution characterized by a ''sloshing-electron'' axial density profile. Velocity space contour plots of the model distribution agree with similar plots resulting from Fokker-Plank numerical simulations of whistler mode ECRH in the MMM. Finally, the sensitivity of measured spectra to radiation reflections in the vacuum vessel is investigated by comparing measurements obtained with and without microwave-absorbent liners. Also, measurements from a dielectric-loaded horn antenna with enhanced forward gain are compared to results from a standard horn