Investigation of magnetic field ripple effects on charged particles transport in scrape-off layer of Heliotron J

Abstract The impact of helical magnetic ripples on the transport of plasma and carbon impurities in the scrape-off layer (SOL) of a Heliotron J device was investigated using the EMC3-EIRENE code. Comparisons with a simplified one-dimensional fluid model revealed that the transport behavior varied with the Knudsen number (K), defined as the ratio of the ion-ion collisional mean-free path to the ripple scale length. In the weakly collisional regime (K≫1), the qualitative trends suggested by the fluid model indicate that the magnetic mirror effects become dominant, the conductive heat flux governs the heat transport, and the impurity density follows a Boltzmann distribution. Conversely, in the collisional regime (K≪1), the transport exhibits nozzle-like fluid behavior, convective heat flux governs heat transport, and impurities couple to the bulk plasma. These characteristics underscore the importance of charged-particle transport along magnetic field lines in the SOL of fusion devices, where magnetic ripples fluctuate significantly with changes in the magnetic field configuration.