Integrated analysis of high-$\beta_N$ double transport barriers scenario on HL-2A

Abstract

The tokamak is considered the most promising experimental setup for achieving controllable nuclear fusion requirements. The parameter $\beta_N$ is an important parameter for tokamak devices, high $\beta_N$ offer benefits not only to plasma fusion but also to enhancement of fusion reaction efficiency and the facilitation of steady-state operation. The HL-2A tokamak device achieved stable plasma with $\beta_N$ exceeding than 2.5 through NBI heating, and transiently reached $\beta_N$=3.05, with a normalized density ($n_{e,l}/n_{e,G}$) of approximately 0.6, stored energy ($W_E$) of around 46 kJ, and confinement improvement factor ($H_{98}$) of approximately 1.65. This paper uses the integrated simulation platform OMFIT to analyze the plasma at $\beta_N$=2.83 and $\beta_N$=3.05, and the $W_ E$, $n_{e,l}/n_{e,G}$, $H_{98}$, $\beta_N$, and so on are consistent with the experimental parameters. The found of bootstrap current ($f_{BS}$) can reach to $45\%$ and $46\%$. At both of the above moments, there are ion temperature double transport barrier (DTB) generated by the coexistence of internal transport barrier (ITB) and edge transport barrier (ETB), while high $\beta_N$ is usually associated with DTB. In addition, this paper further analyzes the formation of ion temperature ITB in the HL-2A device, attributing it to the dominance of turbulent transport in plasma transport, the suppression of turbulent transport in the core by fast ions and $E\times B$ shear, and the resulting improvement in confinement, ultimately leading to the formation of ion temperature ITB. The ITB of ion temperature and the ETB of H-mode synergistically contribute to the creation of high $\beta_N$ plasma.