Illustrating the physics of core tungsten (W) transport in a long-pulse steady-state H-mode discharge on EAST

Abstract

The behavior of core tungsten (W) in a pure radio frequency (RF) heated long-pulse steady-state H-mode discharge on experimental advanced superconducting tokamak (EAST) with ITER-like divertor (ILD) is analyzed with experimental diagnostics data and modeled with a combination of drift-kinetic neoclassical and gyro-fluid turbulent codes. In the stationary state, the experimental core line-averaged W concentration (C_W) is about 〖2×10〗^(-5), which is evaluated by the intensity of the W unresolved transition array (W-UTA) spectral structure in the region of 45-70 Å, composed of W^(27+)-W^(45+) line emissions through the spectroscopic method in extreme ultraviolet (EUV) region. W produces a peak of the radiated power density profile around normalized radius ρ~0.3. Therefore, W does not centrally accumulate in the experiment. A time slice of the stationary state is modeled, accounting for both neoclassical and turbulent transport components of W based on the self-consistent background plasma profiles simulated by TGYRO (J. Candy et al 2009 Phys. Plasmas 16 060704). It is found that turbulent transport dominates over neoclassical transport for W, what is more, turbulent diffusion coefficient is large enough to offset the sum of neoclassical and turbulent pinch (convection) velocity, so that the W density profile for zero particle flux will not be very peaked. Combining TGLF (G.M. Staebler et al 2017 Nucl. Fusion 57 066046) and NEO (E. Belli and J. Candy 2008 Plasma Phys. Control. Fusion 50 095010, 2012 Plasma Phys. Control. Fusion 54 015015) for the W transport coefficient with the impurity transport code STRAHL (R. Dux 2006 STRAHL User Manual), the experimental C_W and radiated information caused by W can be reproduced closely. In addition, the effect of toroidal rotation on the W transport is also clarified.