Observation of sawtooth suppression by flux pumping on HBT-EP

The tangential EUV/SXR diagnostic system has been installed on HBT-EP tokamak for measurements of electron temperature and study of mode dynamics. Analysis of the temperature profile from the system's signals reveals clear sawtooth events. It is observed that sawtooth existence correlates with low-amplitude edge modes, while suppression links to larger and saturated edge mode amplitudes. To further investigate this correlation, the plasma-wall interaction was manipulated by adjusting the positions of conducting walls in HBT-EP, influencing the stabilization of the edge modes. It was found that sawtooth events only occur when the walls and the plasma are in close proximity, facilitating effective edge mode stabilization. Even slight differences in major radius result in divergent shot styles: sawtoothing shots or sawtooth-free shots. Through various mode structure analyses, the coupling between the m/n=3/1 resistive wall mode (RWM) and the m/n=2/1 tearing mode was identified. This coupling induces anomalous current broadening and indicates the occurrence of flux pumping. Based on these findings, we can conclude that sawtooth suppression in the HBT-EP tokamak is achieved through the process of flux pumping. Analysis of internal MHD structures that induce the dynamo effect will be explored using various diagnostic systems on HBT-EP. This research offers valuable insights into the underlying physics of sawtooth dynamics and contributes to the comprehension and control of instabilities in tokamak plasmas.