The mechanism research of double strike points of the divertor particle flux in hl-2a ecrh plasmas

Double strike points (DSP) of the particle flux have been observed on the outer divertor target during the HL-2A electron cyclotron resonance heating (ECRH) plasma discharge in the normal magnetic field direction using the Langmuir probe arrays. The analysis shows that the poloidal drift velocity, which is estimated to be the same order as the ionacoustic velocity, plays an important role in the forming of the dip of the particle flux. The peak of the electron temperature is far away from the peak of the particle flux in the SOL due to the large radiation of the long leg of the divertor, resulting in an outer shift of the plasma potential peak compared with the particle flux peak, and a positive radial electric field is generated, which is large enough to cause a reversed poloidal drift flow in the normal magnetic field scenario. What is more, the statistical results show that the DSP phenomenon occurs in the high ECRH power and the low density region, which supports the generation mechanism of the poloidal drift. The paper highlights the important role of the poloidal drift and the long leg divertor in the control of the particle flux, which provides some reference for the heat flux mitigation in the future fusion devices.