Effect of edge magnetic islands on poloidal flow in electron cyclotron heated Heliotron J Plasmas

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Abstract
Magnetic islands are formed at the plasma edge in Heliotron J, a stellarator/heliotron device, by controlling the rotational transform, and the effect of the magnetic islands on the poloidal flow profile was investigated using a Q-band Doppler reflectometer. Comparative measurements were performed for the magnetic configurations with magnetic islands at the plasma edge, referred to as ‘island configuration,’ and those without the magnetic islands, referred to as ‘non-island configuration.’ In all configurations, poloidal flow in the electron diamagnetic direction was observed at the edge in electron cyclotron heated plasmas. In the non-island configuration, the sheared flow maximum was inside the last closed flux surface (LCFS), whereas in the island configuration, the sheared flow was formed around the magnetic island independent of the LCFS position, and increases in electron temperature, T e , and density, n e , were observed at the edge. The fine control of the magnetic island position around the LCFS shows that the poloidal flow structure, particularly the flow shear position, correlates with the position of magnetic islands. An increase in T e and n e is observed at the edge only when the magnetic islands are located outside the LCFS. These results indicate that the edge magnetic islands are a possible means to control the poloidal flow shear position and the edge plasma parameters.
Funding Information
  • JSPS Core-to-Core Program
  • Kyoto University (DAAD-Kyoto University Partnership Program)
  • MEXT (22H00117)
  • JST SPRING (JPMJSP2110)
  • National Institute for Fusion Science (NIFS10KUHL030)

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