Progress on physics understanding of improved confinement with fishbone instability at low q ₉₅ < 3.5 operation regime in EAST

Abstract

Improved confinement at low q95 &lt; 3.5 operation regime with fishbone instability compared to sawtooth oscillation has been observed and investigated on EAST under dominant electron heating condition with tungsten divertor. The formation of internal transport barrier in ion thermal channel strongly correlates to the excitation of fishbone, accompanying by reduced particle outward transport in the core region identified by central peaked density profile. Current density distribution is found to change from monotonic shape with q0 &lt; 1 during sawtooth oscillation to central flat structure, magnetic shear s ~ 0 at  &lt; 0.4, with fishbone instability at where higher off-axis bootstrap current fraction might play a critical role. Linear gyrokinetic simulation by NLT code has been carried out to investigate the turbulent transport characteristics, which is qualitatively in good agreement with experimental measurement from CO2 laser collective scattering diagnostics. The electron-scale trapped electron mode (TEM) that dominants the turbulent transport during sawtooth is found to be stabilized with fishbone at identical heating power and plasma configuration.

Mechanism of enhanced ion temperature by impurity seeding in EAST H-mode plasma

“…However, for the case with R/L Ti = 7, the corresponding Q i is much larger (almost ten times larger) than the experimental measured one not shown in figure 13 because once R/L Ti is beyond the threshold of ITG, Q i will be very sensitive to R/L Ti (strong stiffness). Pure ITG in the plasma can be achieved by NBI dominating heating [45]. The effect of neon on turbulence in these three situations is investigated as shown from figures 11-13.…”

Electrostatic turbulence in EAST plasmas with internal transport barrier

“…In this work, we present linear and nonlinear simulations of electrostatic turbulence based on EAST tokamak discharge #93890 at 5000 ms [6]. The EAST discharge #93890 is diagnosed with the plasma profiles and magnetic geometry as reported in [6], where both the electron and ion density and the temperature exhibit ITBs in the presence of weakly negative magnetic shear. The detailed parameters are given as follows.…”

“…Thus, it is of great significance to understand the properties of the corresponding microscopic drift wave instability and turbulence. The confinement performance of the tokamak has been significantly improved by forming internal transport barriers (ITBs) in the core region [2][3][4][5][6]. Inside the ITBs, the gradient of the temperature and density is high due to the reduction of anomalous transport caused by turbulence such as the ion temperature gradient (ITG) mode and trapped electron mode (TEM).…”

“…Nonlinear gyrokinetic studies on ITB plasma turbulent transport using realistic experimental parameters, in which the mechanism can be complicated by the Shafranov shift and wave-particle interactions, are desirable. In this work, based on the realistic equilibrium of the Experimental Advanced Superconducting Tokamak (EAST) discharge (#93890) [6], where a core ITB forms in the presence of weakly negative magnetic shear, we carry out linear and nonlinear simulations of electrostatic drift wave instability and turbulence by using the first-principles gyrokinetic toroidal code (GTC) [27].…”

A simple model for internal transport barrier induced by fishbone in tokamak plasmas

“…2021; Zhang et al. 2022). With neutral beam injection (NBI) power increasing step by step, the magnitude of each burst of fishbone becomes larger and the burst frequency becomes higher and, accordingly, the ITB becomes stronger (Zhu et al.…”