Measurements of mildly relativistic electron distribution functions during lower hybrid heating and current drive (invited)

Nonthermal electron distribution functions, arising during lower hybrid heating and current drive, have been measured on Alcator C tokamak using vertical electron cyclotron emission and also bremsstrahlung x-ray emission. The methods used for deconvolving the distribution from the radiation measurements are summarized and examples are given of results from different types of plasma, illustrating the present capabilities of the techniques. The cyclotron emission results are consistent with the x-ray analysis but provide additional information, particularly at lower energies (30–100 keV). The x rays are less ambiguous at high energy and give good forward/backward asymmetry diagnosis. The quality of information appears to be already adequate for a quantitative comparison with theory, but further experimental improvements seem possible.