Recent advances in high- ${\beta }_N$ 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 ${\beta }_N\ge 3$ , $ne/n{e}_G\sim 0.6$ , $H_{98}\sim 1.5$ , $f_{bs}\sim 30\%$ , $q_{95}\sim 4.0$ , and $G\sim 0.4$ . 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 Alfvénic modes in the core. In some high- ${\beta }_N$ discharges, it is observed that the NTMs with $m/n=3/2$ 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 .