Critical roles of edge turbulent transport in the formation of high-field-side high-density front and density limit disruption in J-TEXT tokamak

This article presents an in-depth study of the sequence of events leading to density limit disruption in J-TEXT tokamak plasmas, with an emphasis on boudary turbulent transport and the high-field-side high-density (HFSHD) front. These phenomena were extensively investigated by using Langmuir probe and Polarimeter-interferometer diagnostics. The research reveals a consistent pattern of events as the plasma density ramps up: the collapse of the sheared radial electric field, the enhancement of a boundary broadband turbulence (50~80kHz), the increase of boundary particle transport induced by this turbulence, edge cooling and the emergence of the HFSHD front. These phenomena occur once the plasma density exceeds a critical value. Importantly, by exploring plasmas with varying edge safety factor (q_a), it’s revealed that the density thresholds for these phenomena are all inversely proportional to q_a. The findings offer valuable insights into the mechanisms underlying density limit disruptions in tokamak plasmas, suggesting that the enhancement of edge turbulent transport plays crucial roles in the edge cooling and triggering the HFSHD front. For the first time, a strong link between the edge turbulent transport and the HFSHD front has been observed.