MHD instability dynamics and turbulence enhancement towards the plasma disruption at the HL-2A tokamak

Abstract

The evolutions of MHD instability behaviors and enhancement of both electrostatic and electromagnetic turbulence towards the plasma disruption have been clearly observed in the HL-2A plasmas. Two types of plasma disruptive discharges have been investigated for similar equilibrium parameters: one with a distinct stage of a small central temperature collapse ($$\sim$$ ∼ 5–10%) around 1 millisecond before the thermal quench (TQ), while the other without. For both types, the TQ phase is preceded by a rotating 2/1 tearing mode, and it is the development of the cold bubble from the inner region of the 2/1 island O-point along with its inward convection that causes the massive energy loss. In addition, the micro-scale turbulence, including magnetic fluctuations and density fluctuations, increases before the small collapse, and more significantly towards the TQ. Also, temperature fluctuations measured by electron cyclotron emission imaging enhances dramatically at the reconnection site and expand into the island when approaching the small collapse and TQ, and the expansion is more significant close to the TQ. The observed turbulence enhancement near the X-point cannot be fully interpreted by the linear stability analysis by GENE. Evidences suggest that nonlinear effects, such as the reduction of local $$E_r\times B$$ E r × B shear and turbulence spreading, may play an important role in governing turbulence enhancement and expansion. These results imply that the turbulence and its interaction with the island facilitate the stochasticity of the magnetic flux and formation of the cold bubble, and hence, the plasma disruption.

Investigation of electromagnetic fluctuations in a magnetically screened high beta plasma

“…Solar winds describe the presence of magneto hydrodynamic (MHD) turbulence [2]. In laboratory environments, plasma turbulence manifests 3 Ex post-doctoral fellow at Institute of Plasma Research. * Author to whom any correspondence should be addressed.…”

“…In laboratoryscale fusion devices, i.e. tokamaks, turbulence in the scrapeoff layer (SOL) region can cause disruptions in the core plasma [3]. Intense plasma turbulence triggers significant cross-field transport through anomalous diffusion, resulting in increased plasma loss at the edge of the plasma in fusion devices [3,4].…”

“…tokamaks, turbulence in the scrapeoff layer (SOL) region can cause disruptions in the core plasma [3]. Intense plasma turbulence triggers significant cross-field transport through anomalous diffusion, resulting in increased plasma loss at the edge of the plasma in fusion devices [3,4]. Hence, it is crucial to explore the complexities of plasma turbulence within an environment characterized by intricate magnetic field lines and the dependency of the turbulence on parametric gradients.…”

On how structures convey non-diffusive turbulence spreading

“…It is important in the core-boundary coupling, and thus affects the H-mode pedestal structure as well as the divertor heat load width [11][12][13][14][15]. Increased turbulence spreading is also associated with the edge cooling approaching density limit and the thermal quench [16][17][18]. Numerous theoretical [19][20][21][22][23][24][25][26][27][28][29] and simulation [30][31][32][33][34][35][36] works have explored the spreading models.…”