Curvature of Radial Electric Field Aggravates Edge Magnetohydrodynamics Mode in Toroidally Confined Plasmas

Abstract

We show that the radial electric field (E r ) plays a dual role in edge magnetohydrodynamics (MHD) activity. While E r shear (first spatial derivative of E r ) dephases radial velocity and displacement, and so is stabilizing, a new finding here is that E r curvature (second spatial derivative of E r ) tends to synchronize the radial velocity and displacement, and so destabilizes MHD. As a highlighted result, we analytically demonstrate that E r curvature can destabilize an otherwise stable kink mode, and so form a joint vortexkink mode. The synergetic effects of E r shear and E r curvature in edge MHD extend the familiar E × B shearing paradigm. This theory thus explains the experimental findings that a deeper E × B well may aggravate edge MHD, and so trigger the formation of the edge harmonic oscillation. A simple criterion linking E r structure and the edge MHD activity is derived.

Turbulence spreading effects on the ELM size and SOL width

“…Particularly, for the case E r 2.5GREEN, a large crash is observed compared with the other cases. The results of these linear simulations, indicating that the stabilization of high-n modes and destabilization of low-n modes by strong E × B flow shear, are in excellent agreement with previous BOUT++ work conducted in a circular geometry, as referenced by Chen et al (2017) and Zhang et al (2020). These findings contribute to our understanding of the behaviour of dominant modes under varying E r shearing conditions.…”

“…(2017) and Zhang et al. (2020). These findings contribute to our understanding of the behaviour of dominant modes under varying E r shearing conditions.…”

“…The edge E × B shear plays an important role in setting the edge turbulence transport. BOUT++ simulations have revealed that in the ELMy H-mode operation, the E × B shear flow can stabilize the high-n ballooning modes while inducing the Kelvin-Helmholtz instabilities through bootstrap current and rotational shear (Chen et al 2017;Zhang, Guo & Diamond 2020). The stability of the pedestal plasmas and ELM dynamics are the outcome of the competition between these two effects.…”

Physics-informed machine learning techniques for edge plasma turbulence modelling in computational theory and experiment

“…The electric field perpendicular to magnetic field lines is a particularly important quantity as it is a strong drive of cross-field fluxes and thus edge pressure profiles on turbulent scales. These E × B flows are observed to strongly influence edge plasma stability [219,230] and the motion of coherent structures which can account for significant particle losses during standard operation of tokamaks [40,21,111]. Resultant turbulence-induced fluxes impacting walls can cause sputtering, erosion, and impurity injection which can further adversely affect safe operation and confinement of fusion plasmas [40,108,109].…”

Turbulent field fluctuations in gyrokinetic and fluid plasmas

“…A particularly important quantity for testing predic-tive modelling is the turbulence-generated edge electric field since E × B drifts strongly influence edge plasma stability and transport of bloblike structures which can account for over 50% of particle losses during standard operation of tokamaks [24,[26][27][28]. Resultant turbulent fluxes impacting the walls can cause sputtering, erosion, and impurity injection which adversely affect safe operation and confinement of fusion plasmas [24,29,30].…”