Hysteresis in Sawtooth Crash in ASDEX Upgrade Tokamak

A hysteresis model is used to describe experimental data on sawtooth crash in the ASDEX Upgrade tokamak. The model is based on hysteresis which arises due to the fact that the value of the current density gradient (approximated for the H-mode discharges studied here, by the temperature gradient) at the q = 1surface required to turn on the instability is greater than the gradient required to maintain the instability, once it is turned on. The value of the hysteresis parameter can be chosen such that the model reproduces correctly the two time scales of the sawtooth crash in the ASDEX Upgrade tokamak: the slow rise time (~7 ms) and the rapid crash time (~50 μs).