Control of fuel recycling and hydrogen content in the Experimental Advanced Superconducting Tokamak (EAST) using various methods is studied for high-power long pulse high confinement mode (H-mode) plasma operation. The results show that long duration first wall baking and discharge cleaning in EAST provides the necessary clean vacuum environment with a high ultimate vacuum of 3.6 × 10−6 Pa and low outgassing rate of ~1.5 × 10−4 Pa m3 s−1 for plasma operation. In-vessel cryopumps are found to provide an efficient method for particle recycling control in the divertor region to decrease global recycling coefficient (Rglobal) from ~1.0 to ~0.8 during ohmic heating plasmas, and it provides a high particle exhausting rate of 1020–1021 D-atoms s−1 in high-power plasma operations. Long duration silicon coating is found to be more powerful than baking and discharge cleaning, which reduces the H/(H + D) ratio gradually to a value as low as 8%, and lithium coating is more effective and more efficient than silicon coating, to further reduce the H/(H + D) ratio to 3%. Real-time lithium powder injection is a novel method for recycling control, which reduces Rglobal from 0.94 to 0.82 under lithium coating wall conditioning. By the combination and optimization of the above methods, H-mode plasmas with low hydrogen content and low fuel recycling have been achieved in EAST and have been extended gradually to 101 s in 2017. Recycling flux has even decreased gradually during 101 s H-mode plasmas due to increased first wall temperature and the resulting increased Li-II emission. These results provide valuable references on hydrogen content and fuel recycling control for long pulse H-mode plasmas of up to 400–1000 s with high-power heating in EAST and future fusion devices.
Investigation of Zeff and impurity behaviour in lithium coating experiments with full metallic first wall in HT-7 tokamak