Research on confinement improvement under optimized injection time of electron cyclotron resonance heating power at EAST

Abstract A primary objective of the experimental advanced super-conducting tokamak (EAST) is to demonstrate steady-state long-pulse high-performance plasma operation for future large-scale devices like ITER and CFETR (Wan et al 2017 Nucl. Fusion 57 102019). The formation of internal transport barriers (ITBs) is one of the key issues to achieve high-performance plasma operation. Optimizing the current density profile is a promising way to improve plasma confinement, which is beneficial to the formation of ITBs. A lot of effort has been dedicated to optimizing the current density profile at EAST over recent years. In this paper, the authors discuss the formation of ITBs leading to a significant improvement of plasma confinement by optimizing the injection time of electron cyclotron resonance heating (ECRH) power at EAST. After ECRH delayed injection, poloidal beta and thermal energy confinement ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:msub> <mml:mi>H</mml:mi> <mml:mrow> <mml:mn>98</mml:mn> <mml:mi>y</mml:mi> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> </mml:mrow> </mml:mrow> </mml:math> ) was observed to increase. The current density distribution and the power deposition distribution were changed. The analysis of the soft x-ray (Xu et al 2020 Phys. Scr. 95 055603) and electron cyclotron emission (Liu et al 2016 Plasma Sci. Technol. 18 1148–54) diagnostics data showed that the structural strength of magnetohydrodynamics was significantly decreased in the core region in this case. The turbulence growth rate calculated by the tokamak global linearized fusion code (Kinsey et al 2008 Phys. Plasmas 15 055908) also shows that trapped electron mode turbulence is stabilized.