INTERPRETATION OF PERTURBED TEMPERATURE-BASED ON X-RAY EMISSIVITY IN FUSION PLASMA-EXPERIMENTS

The relationship between the dynamical response to perturbations of th e soft X ray emissivity (delta E), the electron temperature (delta T-e ), the electron density (delta n(e)) and the impurity concentration (d elta n(i)) for a Maxwellian plasma is analysed in detail. In particula r, the so-called 'impurity function' F(Z(eff)) is also strongly depend ent on T-e via the direct radiative recombination (DRR) contribution t o the X ray emission, which significantly affects the relation between the perturbed quantities as derived from the popular expression E pro portional to F(Z(eff))n(e)(2)T(e)(alpha) even if the impurity content (or Z(eff)) remains constant. In order to overcome this difficulty, a simple analytical approximation is derived for F(Z(eff), T-e) that can be used as a formula to relate the perturbed quantities delta E, delt a T-e, delta n(e) and delta F with ease and accuracy. This simple appr oximation is illustrated by studying saw-toothing discharges on the To kamak de Varennes (TdeV) with T-e, n(e) and E measured by the Thomson scattering, the FIR interferometer and the X ray camera diagnostics, a nd its accuracy is tested against the predictions of a full X ray mode lling code.