Effects of thermal instability on density limit disruption in J-TEXT

As an important precursor of density limit disruption, thermal instability under J-TEXT high-density discharges is studied in this paper. An extended MHD code called NIMROD [Sovinec et al.,  J. Comput. Phys. 195, 355 (2004)] is used to explore the intrinsic relationship between density limit disruption and thermal instability. The experimental and simulation results show that radiation from the boundary impurity can cause thermal instability and impurity radiation increases rapidly when the plasma temperature decreases to the nonlinear range of carbon cooling rates, which cools down the plasma and enhances impurity radiation. Further investigations show that the local reduction in thermal instability at the plasma edge shrinks the local current channel and increases the internal current density gradient, which triggers the 2/1 mode and destabilizes the 3/1 and other higher-order modes. Finally, a rapid increase in the MHD instability can cause density limit disruption.