Enhanced transport at high plasma pressure and sub-threshold kinetic ballooning modes in Wendelstein 7-X

P. Mulholland; K. Aleynikova; B. J. Faber; M. J. Pueschel; J. H. E. Proll; C. C. Hegna; P. W. Terry; C. Nührenberg

paper

Enhanced transport at high plasma pressure and sub-threshold kinetic ballooning modes in Wendelstein 7-X

arXiv:2306.03694

Abstract

High-performance fusion plasmas, requiring high pressure $β$ , are not well-understood in stellarator-type experiments. Here, the effect of $β$ on ion-temperature-gradient-driven (ITG) turbulence is studied in Wendelstein 7-X (W7-X), showing that subdominant kinetic ballooning modes (KBMs) are unstable well below the ideal MHD threshold and get strongly excited in the turbulence. By zonal-flow erosion, these sub-threshold KBMs (stKBMs) affect ITG saturation and enable higher heat fluxes. Controlling stKBMs will be essential to allow W7-X and future stellarators to achieve maximum performance.

16 pages, 5 figures