Recent advances in high-βN experiments and magnetohydrodynamic instabilities with hybrid scenarios in the HL-2A Tokamak

Over the past several years, high-beta(N) experiments have been carried out on HL-2A. The high-beta(N) is realized using double transport barriers (DTBs) with hybrid scenarios. A stationary high-beta(N) (> 2) scenario was obtained by pure neutral-beam injection (NBI) heating. Transient high performance was also achieved, corresponding to beta(N) >= 3, ne/ne(G) similar to 0.6, H-98 similar to 1.5, f(bs) similar to 30%, q(95) similar to 4.0, and G similar to 0.4. The high-beta(N) scenario was successfully modeled using integrated simulation codes, that is, the one modeling framework for integrated tasks (OMFIT). In high-beta(N) plasmas, magnetohydrodynamic (MHD) instabilities are abundant, including low-frequency global MHD oscillation with n = 1, high-frequency coherent mode (HCM) at the edge, and neoclassical tearing mode (NTM) and Alfvenic modes in the core. In some high-beta(N) discharges, it is observed that the NTMs with mln = 3/2 limit the growth of the plasma energy and decrease beta(N). The low-n global MHD oscillation is consistent with the coupling of destabilized internal (m/n = 1/1) and external (m/n = 3/1 or 4/1) modes, and plays a crucial role in triggering the onset of ELMs. Achieving high-beta(N) on HL-2A suggests that core-edge interplay is key to the plasma confinement enhancement mechanism. Experiments to enhance beta(N) will contribute to future plasma operation, such as international thermonuclear experimental reactor.

Automated summary

High-beta(N) experiments have been conducted on HL-2A in recent years, achieving high-beta(N) through double transport barriers and hybrid scenarios. A stable high-beta(N) scenario was obtained through pure neutral-beam injection heating, while transient high performance included the presence of low-frequency global MHD oscillation, high-frequency coherent mode, neoclassical tearing mode, and Alfvenic modes.