X-ray simulation of the sawtooth phenomena on TFTR

The m=1 island size or m=1 deformation of magnetic surfaces during sawtooth crashes is estimated on TFTR by comparing experimental observations of X-rays and ECE electron temperature with a simple simulation which calculates signals of line-integrated X-ray and local electron temperature assuming rigid rotation of the plasma. Sawtooth oscillations with a slow crash (τcrash ∼ several ms) can be simulated by a Kadomtsev-type reconnection model in which an m=1 island grows to the size of the q=1 surface during the sawtooth crash. In the sawtooth which have a fast crash (50 μs∼τcrash∼500 μs), the m=1 island size sometimes (not always) becomes ∼ 1/2 of the sawteeth inversion radius during the crash phase. The final structure, however, is hard to identify, because of the slow plasma rotation frequency. The 'Hot Core' appears to move away from the plasma center in a Kadomtsev-type reconnection without causing very large transport or diffusion. (author)