Results of electron cyclotron emission (ECE) measurements during low-density non-thermal ASDEX tokamak operation are presented. Particular attention is given to the transition between the thermal plasma state, where the electron velocity distribution is Maxwellian, and the non-thermal state, where the distribution function may be treated as a superposition of low- and high-energy components. The study is aided by the simultaneous use of two complementary ECE diagnostics, a rapid-scan Michelson interferometer for measurement of the entire ECE spectrum and a four-channel polychromator for registration of time-resolved intensities at different wavelengths. Numerical simulations confirm the two-component description of the non-thermal distribution and provide estimates of the population and energy of the high-energy part. By comparing X-mode and O-mode radiation, additional information regarding the optical depth of the low-energy component is obtained.
Bursts of electron cyclotron emission during disruptions of high β discharges in TFTR