Effect of 4.6 GHz LHW on tungsten transport in NBI dominant H-mode plasma in EAST tokamak

Experimental observations in EAST tokamak have revealed a notable suppression of tungsten accumulation during the lower hybrid wave (LHW) injection in the neutral beam injection (NBI)-heated H-mode plasma. The variation in tungsten concentration during the LHW phase is quantified using the intensity of tungsten unresolved transition array (W-UTA), as measured by the extreme ultraviolet spectrometer. After the LHW is turned on, the tungsten concentration, CW = nW/ne, decreased by approximately 45%, from 9.5 × 10−5 to 5.3 × 10−5. Additionally, the peaked tungsten profile is flattened, with the peak position shifted outward, implying a significant alteration in tungsten transport. The observed results suggest that reduced toroidal rotation and increased electron temperature are responsible for the variation in tungsten transport during the LHW heating. Modeling using a simulation code of Transport in Gyrokinetic Plasmas with Rotation and Optimization (TGYRO) indicates that, after the LHW injection, the turbulent diffusion of tungsten ions is enhanced and the neoclassical convection is weakened. Moreover, comparisons of the transport coefficients of tungsten ions under different plasma parameters reveal that the LHW heating enhances the turbulent diffusion of tungsten ions by increasing the electron temperature gradient. It also decreases the plasma toroidal rotation velocity, which in turn reduces the inward neoclassical convection of tungsten ions. These findings provide a feasible solution for the tungsten accumulation induced by the NBI heating, supporting EAST in achieving long-pulse high-performance plasma discharge. This work offers an important reference for the operation of ITER and the design of future fusion reactors.