Study on sawtooth activities of HT-7 tokamak using soft X-ray diagnostic

Several arrays of soft X-ray diagnostic are developed on the HT-7 tokamak and used to study the sawtooth oscillations.The occurrence and characteristics of the sawtooth are related closely with the discharge conditions such as electron density Ne,electron temperature Te,safety factor qα on the plasma edge,as well as the wall condition,etc.In lower hybrid current drive(LHCD) plasmas,an m/n=1/1 mid-mode oscillation can be observed,which appears during sawtooth ramps,rapidly-develops,saturates,damps and disappears before the sawtooth collapse.The sawtooth behaviors in ohmically heated plasma and LHCD plasma are discussed and summarized.