Previously, the effect of high electron temperature on plasma polarimetry has been studied theoretically with specific relevance to its use as a tokamak plasma diagnostic. Approximations have been given in both the non-relativistic and weakly relativistic limits but neither has been verified experimentally. This paper compares over 23 000 measurements of induced ellipticity made by the JET polarimeter during 268 selected pulses with predictions based on both temperature corrections and on purely cold plasma wave theory. The cold plasma theory is shown to significantly underestimate while the non-relativistic warm model is shown to significantly over-estimate the induced ellipticity. Good agreement with the relativistic warm model is shown for plasmas in the range 3 keV < Te < 12 keV, which constitutes the first experimental verification of relativistic effects in plasma polarimetry.
Characteristics of ordinary mode in fully relativistic electron plasma