The EAST research program aims to demonstrate steady-state long-pulse advanced high-performance H-mode operations with ITER-like poloidal configuration and RF-dominated heating schemes. Since last IAEA FEC, EAST has been upgraded with all ITER-relevant auxiliary heating and current drive systems, enabling the investigation of plasma profile control by coupling/integration of various combinations. By means of the 4.6 GHz and 2.45 GHz LHCD systems, H-mode can be obtained and maintained at relatively high density, even up to n e ~ 4.5 × 10 19 m-3 , where a current drive effect is still observed. Significant progress has been achieved on EAST, including: i). Demonstration of a steady-state scenario (fully non-inductive with V loop ~ 0.0V at high β P ~ 1.8 and high performance (H 98,y2 > 1.0) in upper single-null (ε ~ 1.6) configuration with the tungsten divertor; ii) Discovery of a stationary ELM-stable H-mode regime with 4.6 GHz LHCD; iii) achievement of ELM suppression in slowly-rotating H-mode plasma with the application of n = 1 and 2 RMPs.
The recent EAST experimental progress since the last IAEA FEC in 2016 is presented. First demonstration of >100 seconds time scale long-pulse steady-state scenario with a good plasma performance (H98(y2) ~ 1.1) and a good control of impurity and heat exhaust with the tungsten divertor has been successfully achieved on EAST using the pure RF power heating and current drive. The extended operation regimes have been obtained (βP~2.5 & βN~1.9 of using RF&NB and βP~1.9 & βN~1.5). High bootstrap current fraction up to 47% was achieved with q95~6.0-7.0. The interaction effect between the ECH and two LHW systems has been investigated for enhanced current drive and improved confinement quality. ELM suppression using the n= 2 RMPs has been achieved at q95 (≈ 3.2-3.7) with standard type-I ELMy H-mode operational window in EAST. Reduction of the peak heat flux on the divertor was demonstrated using the active radiation feedback control. An increase in the total heating power and improvement of the plasma confinement are expected using a 0-D model prediction for higher bootstrap fraction. Towards long pulse, high bootstrap current fraction operation, a new lower ITER-like tungsten divertor with active watercooling will be installed, together with further increase and improvement of heating and current drive capability.
Aimed at high-confinement (H-mode) plasmas in the Experimental Advanced Superconducting Tokamak (EAST), the effect of local gas puffing from electron and ion sides of a lower hybrid wave (LHW) antenna on LHW–plasma coupling and high-density experiments with lower hybrid current drive (LHCD) are investigated in EAST. Experimental results show that gas puffing from the electron side is more favourable to improve coupling compared with gas puffing from the ion side. Investigations indicate that LHW–plasma coupling without gas puffing is affected by the density near the LHW grill (grill density), hence leading to multi-transition of low–high–low (L–H–L) confinement, with a correspondingly periodic characteristic behaviour in the plasma radiation. High-density experiments with LHCD suggest that strong lithiation gives a significant improvement on current drive efficiency in the higher density region than 2 × 1019 m−3. Studies indicate that the sharp decrease in current drive efficiency is mainly correlated with parametric decay instability. Using lithium coating and gas puffing from the electron side of the LHW antenna, an H-mode plasma is obtained by LHCD in a wide range of parameters, whether LHW is deposited inside the half-minor radius or not, implying that a central and large driven current is not a necessary condition for the H-mode plasma. H-mode is investigated with CRONOS.
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