Experimental research of the threshold conditions of runaway electron in tokamk

The experimental study of onset threshold conditions of runaway electrons was analyzed in ohmic discharge. The plasma loop voltage and line-average electron density of the moment when Hard X-ray appeared were obtained as the runaways threshold. The comparison of the experimental threshold and the theoretical threshold under the primary generation process showed that the threshold electric field is much higher than that predicted by relativistic collisional theory, and the critical electron density of suppressing runaways is significantly lower than the theoretical calculations, which are consistent with the experimental results gotten by ITPA (International Tokamak Physics Activity) on D3D, TEXTOR, FTU, KSTAR and so on. It was found that the growth rate of runaways under the Dreicer mechanism grows with the increasing electric field intensity, and decays with the decreasing electron density through the analysis of HXR growth rate in the moment when REs appeared, which demonstrated that the decrease of loop voltage and the increase of electron density could suppress the generation of runaways. (authors)