Observation of Non-Maxwellian Electron Distribution Functions in the Alcator Device by Means of Thomson Scattering and Their Interpretation

In the Alcator device incoherent Thomson scattering always gives Gaussian spectral profiles at low values of the ratio of electron drift velocity to thermal velocity ($\frac{v_D}{v_{\mathrm{th}}}\lesssim 0.1$). However, at higher values of $\frac{v_D}{v_{\mathrm{th}}}$ non-Gaussian profiles are observed and can be interpreted in terms of scattering from electrons with high toroidal velocity (low-energy runaways). This interpretation is supported by soft-x-ray and plasma-resistivity measurements and agrees with a previous theoretical analysis.