Observation of sawtooth dynamics using tangential EUV/SXR diagnostic system on HBT-EP tokamak

Measurements and analyses of the signals from the extreme ultraviolet (EUV) and soft x-ray (SXR) detectors are used to study the internal characteristics of MHD mode structures, including the time-evolution of local electron temperature and temperature profiles. We present the initial results from the two-color multi-energy EUV/SXR diagnostic system in the HBT-EP tokamak. This system includes a filter wheel with five different groups of dual-filter structures and two AXUV16ELG 16-channel diode arrays. The ratio between the amplitudes of the signals from a 100 nm Aluminum filter and a 200 nm Titanium filter with identical tangential plasma views provides temperature profile information versus time. A two-stage single-channel signal amplifying system is built to improve the frequency response and advance the ability to study fast rotating modes. It has a bandwidth up to 200 kHz and gains varying from 1 MOhm to 60 MOhm corresponding to different channels of the diode arrays to optimize the signal amplitudes. Internal MHD modes are studied using this system. Sawtooth activity accompanying low-amplitude 2/1 tearing mode has been detected and analyzed. Weaker or non-existent sawteeth are correlated with larger and saturated 2/1 mode amplitudes.