Electron cyclotron emission by non-Maxwellian bulk distribution functions

The problem of the electron temperature measurement in plasmas where the Maxwellian shape of the electron distribution function has been distorted at low energies (in the thermal range) is investigated. For such distributions with a non-Maxwellian bulk, both electron cyclotron emission (ECE) and Thomson scattering (TS) temperature measurements reflect local properties (in momentum space) of the distribution function to which the diagnostics are sensitive, rather than the average energy content of the distribution function. As an example of this type of plasma, the case of strong, on-axis electron cyclotron heating is considered for FTU-like parameters. The simulations are performed with a high-resolution, parallel solver of the kinetic equation, coupled to a set of parallel interpretative codes, computing the ECE and TS spectra from the numerical distribution function. It is shown that discrepancies between ECE and TS temperatures can be used to identify the presence of non-Maxwellian bulk distribution functions; direct measurement of the shape of the distribution function can be performed using oblique ECE, at various angles to the magnetic field.