Self-consistent edge model of NB heated high-β plasmas

The field reversed configuration (FRC) presents a unique approach to fusion exhibiting a high degree of self-organization resulting in a high-beta plasma. The FRC has been extensively studied at TAE Technologies with the C-2W experiment [1]. The plasma in the central section can be separated into three distinct regions: FRC, SOL (Scrape Off Layer) and the halo, which is the topic of this research.

A self-consistent halo model allows identification of heat transfer mechanisms and evaluation of energy fluxes to limiters and vessel walls, which can be compared with experimental measurements. The model describes particle and energy balance in the halo as a radial diffusion of plasma components with parallel losses treated in a τ-approximation. The interaction with the influx of cold neutrals from the wall creates an additional energy loss mechanism that is important for fast ions. Because fast ion orbit size is comparable or larger than characteristic radial gradients in the halo, diffusion of fast ions is formulated through the gyro-center density, To couple to the thermal plasma, a gyro-averaging is performed, leading to a set of integro-differential equations.

We show that a substantial fraction of heating power is deposited to the limiters and walls. The model provides insight into a poorly diagnosed region and sets a basis for finding ways to reduce fast ion losses at the edge.

[1] Gota, H.; Binderbauer, M.W.; Tajima, T.; Smirnov, A.; Putvinski, S.; Tuszewski, M.; Dettrick, S.A.; Gupta, D.K.; Korepanov, S.; Magee, R.M. et al. Overview of C-2W: High Temperature, Steady-State Beam-Driven FRC Plasmas. Nuclear Fusion 2021, 61, 106039.