The influence of electrode biasing on the up–down asymmetry of HFS-MSN divertor configuration in J-TEXT

Abstract The <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:mrow> <mml:mi mathvariant="bold">E</mml:mi> </mml:mrow> </mml:mrow> <mml:mo>×</mml:mo> <mml:mrow> <mml:mrow> <mml:mi mathvariant="bold">B</mml:mi> </mml:mrow> </mml:mrow> </mml:mrow> </mml:math> drift is considered a key factor affecting particle and heat fluxes in the divertor. Recently, active modulation of the up–down asymmetry in high-field-side mid-plane single null (HFS-MSN) divertor configuration on J-TEXT was successfully achieved by utilizing an electrode biasing (EB) to alter the edge radial electric field and drive the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:msub> <mml:mrow> <mml:mrow> <mml:mi mathvariant="bold">E</mml:mi> </mml:mrow> </mml:mrow> <mml:mrow> <mml:mrow> <mml:mi mathvariant="bold">r</mml:mi> </mml:mrow> </mml:mrow> </mml:msub> </mml:mrow> <mml:mo>×</mml:mo> <mml:mrow> <mml:mrow> <mml:mi mathvariant="bold">B</mml:mi> </mml:mrow> </mml:mrow> </mml:mrow> </mml:math> poloidal flow. The density and heat flux in the divertor region aligned with the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:msub> <mml:mrow> <mml:mrow> <mml:mi mathvariant="bold">E</mml:mi> </mml:mrow> </mml:mrow> <mml:mrow> <mml:mrow> <mml:mi mathvariant="bold">r</mml:mi> </mml:mrow> </mml:mrow> </mml:msub> </mml:mrow> <mml:mo>×</mml:mo> <mml:mrow> <mml:mrow> <mml:mi mathvariant="bold">B</mml:mi> </mml:mrow> </mml:mrow> </mml:mrow> </mml:math> drift direction both increased. The EB model was first established using the SOLPS-ITER, incorporating the influence of the EB on the boundary potential. Both experimental and simulation results indicate that the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:msub> <mml:mrow> <mml:mrow> <mml:mi mathvariant="bold">E</mml:mi> </mml:mrow> </mml:mrow> <mml:mrow> <mml:mrow> <mml:mi mathvariant="bold">r</mml:mi> </mml:mrow> </mml:mrow> </mml:msub> </mml:mrow> <mml:mo>×</mml:mo> <mml:mrow> <mml:mrow> <mml:mi mathvariant="bold">B</mml:mi> </mml:mrow> </mml:mrow> </mml:mrow> </mml:math> poloidal flow driven by the EB and its induced parallel return flow jointly determine the poloidal transport of plasma, altering the density distribution asymmetry between the upper and down divertors. The biasing primarily modulates the asymmetry and decay length of the divertor target heat flux by affecting the ion thermal convection term. Finally, the influence of the EB on impurity radiation distribution is preliminarily discussed. This study employs a combined experimental and simulation approach to investigate the physical mechanisms of EB modulation on divertor asymmetry. The results provide data support for a deeper understanding of the contribution of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:msub> <mml:mrow> <mml:mrow> <mml:mi mathvariant="bold">E</mml:mi> </mml:mrow> </mml:mrow> <mml:mrow> <mml:mrow> <mml:mi mathvariant="bold">r</mml:mi> </mml:mrow> </mml:mrow> </mml:msub> </mml:mrow> <mml:mo>×</mml:mo> <mml:mrow> <mml:mrow> <mml:mi mathvariant="bold">B</mml:mi> </mml:mrow> </mml:mrow> </mml:mrow> </mml:math> drift to boundary particle and heat flux distributions.