Improved high-performance fully non-inductive discharge by optimizing the fast-ion confinement on EAST

The long-pulse high-performance fully non-inductive plasma is one of the major scientific objectives on EAST using the ITER-like tungsten upper divertor.Understanding and optimizing the fast-ion behaviors is the critical issue to extend the performance on EAST.Recently, using both NBI (neutral beam injection) and RF (low hybrid, electron cyclotron and ion cyclotron) heating, fully non-inductive high-β P scenarios with extension of fusion performance at high density and low rotation have been achieved with β P up to 2.5, β N up to 2.0 and H 98y2 >1.1, with the bootstrap current fraction (f BS ) up to 50%.For previous longpulse H-mode plasma at medium density, compared with RF-only discharges, when NBI is added into RF plasma β p is increased from 1.2 to 2.0.In fact, f BS for both discharges are nearly the same ~22%.The analysis shows that the increase in β p is mostly due to fast ions which do not contribute significantly to the neoclassical bootstrap current.Thus, to obtain high performance plasmas with the improved bootstrap current fraction, key parameters (e.g.density, beam energy, etc.) are further optimized.Experimental results show that high density improves bootstrap fraction also by reducing fast-ion slowing down time and loss, as well as the lower beam energy mitigates fast-ion loss which is better for heating and CD performance.The extension of high performance fully non-inductive experiments on EAST at high density and zero/low NBI torque can offer unique contributions towards ITER and CFETR.