Non-Maxwellian Thomson scattering spectra at the RTP tokamak as a new diagnostic tool

Non-Maxwellian structures superposed on Maxwellian Thomson spectra are observed with various sizes in wavelength space and in real space. These features are always seen but in some cases they are more pronounced. A new robust fitting method is presented. With this fitting procedure the non-Maxwellian structures can be investigated better than before. In the fitting method presented a transformed relative error is used for calculation of the weight given to the measured data points, instead of the normally used absolute error. The non-Maxwellian structures are investigated in relation to ablating pellets, the temperature profile and the sawtooth cycle. The detected features seem to be related to transport barriers, the q profile, temperature profile and sawtooth cycle. Although a two temperature distribution is a rough approximation it describes some of the characteristics of the observed coherent distortions. A Thomson spectrum for a two temperature Maxwellian velocity distribution is simulated and can partly parameterize the observed features.