Energy confinement in high-beta plasmas with NB heating

The field reversed configuration (FRC) presents a unique approach to fusion exhibiting a high degree of self-organization resulting in a high 𝛽 plasma. The FRC has been extensively studied at TAE Technologies with the C-2W experiment (1). High 𝛽 plasma consists of three regions - a poorly confined (due to low field) core heated by NB injection surrounded by a mirror-confined SOL and an edge halo where mirror-confinement is low. The purpose of the study is to evaluate the overall confinement time of magnetic configurations having regions with substantially different confinement properties. A theoretical energy transport model is developed describing high 𝛽 plasma core with mirror-confined SOL. It is studied for several dependencies of radial transport on magnetic field and various axial mirror confinement dependencies on mirror ratio. The model recovers scaling 𝜏∼𝜏∥𝑎/Δ as a best possible improvement of axial mirror confinement by employing high 𝛽 configurations as well as sets a limit of its applicability.

To compare theoretical prediction with experiment we included CX losses which constitute substantial fraction of losses in NB-heated plasmas. CX-augmented energy transport model is demonstrated to be consistent with experiment.

(1) Gota, H.; et al, NF 61, 106039 (2021)