SAWTOOTH HEAT PULSE-PROPAGATION IN TOKAMAKS - BALLISTIC RESPONSE AND FOURIER-ANALYSIS

Fourier analysis is proposed as a tool for the recognition of non-diff usive features of heat pulse propagation in fusion plasmas. Applicatio n to a simulated ballistic sawtooth heat pulse shows that Fourier anal ysis can identify the plasma region (often well beyond the mixing radi us) where the heat pulse is diffusive. In this region the initial temp erature perturbation, as recorded by a diagnostic with moderate (appro ximate to 1 kHz) time resolution, is negligible. Fourier analysis of a n example of JET sawtooth heat pulse diagnosed with the new ECE hetero dyne diagnostic is consistent with the results from the simulated ball istic heat pulse. It cannot, however, be used as evidence of a ballist ic effect owing to the limited diagnostic time resolution. When both t he perturbed (chi(e)(p)) and the power balance (chi(e)(PB)) diffusivit y can be determined reliably in recent JET sawtoothing plasmas, their ratio is chi(e)(p)/chi(e)(PB) approximate to 2-4 in agreement with pre vious results.