Tungsten transport and accumulation in JT-60U

Absolute density and radiative power of W ions in the core plasma are determined, from previously published relative data (Nakano et al., 2009 [1]), with an absolutely calibrated VUV spectrometer using atomic data calculated with FAC code. With increasing toroidal rotation velocity in the direction opposed to the plasma current, the W accumulation becomes significant. In the most significant accumulation case, the W density inside a q = 1 layer increases up to ∼0.1% of the electron density and the radiative power increases up to 2 MW, at which time radiative collapse occurs. In contrast, even with W accumulation, at an electron temperature maintained higher than 5 keV, radiative collapse does not occur and the H-mode is preserved. The W sputtering yield of the W-coating decreased from 0.003 to 0.001 of the D flux with decreasing ELM energy loss.