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

Abstract 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 boundary turbulent transport and the high-field-side high-density (HFSHD) front. These phenomena have been extensively investigated using a 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 the boundary quasi-coherent turbulence ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mn>50</mml:mn> <mml:mo>∼</mml:mo> <mml:mn>80</mml:mn> <mml:mstyle scriptlevel="0"/> <mml:mrow> <mml:mtext>kHz</mml:mtext> </mml:mrow> </mml:mrow> </mml:math> ), the increase in 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 ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:msub> <mml:mi>q</mml:mi> <mml:mi>a</mml:mi> </mml:msub> </mml:mrow> <mml:mo stretchy="false">)</mml:mo> </mml:mrow> </mml:math> , it is revealed that the density thresholds for these phenomena are all inversely proportional to <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:msub> <mml:mi>q</mml:mi> <mml:mi>a</mml:mi> </mml:msub> </mml:mrow> </mml:mrow> </mml:math> . The findings offer valuable insights into the mechanisms underlying density limit disruptions in tokamak plasmas, suggesting that the enhancement of edge turbulent transport plays a crucial role 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. In addition, the evolution of the boundary electron temperature across various <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:msub> <mml:mi>q</mml:mi> <mml:mi>a</mml:mi> </mml:msub> </mml:mrow> </mml:mrow> </mml:math> plasmas can further validate the link between the edge turbulent transport and the HFSHD formation.