Progress of joint ITER/EAST experiments with tungsten plasma-facing materials in support of the ITER new baseline

Recent joint ITER/EAST experiments were performed to address specific ITER questions on the reliability and operability of EAST with tungsten (W) as a plasma-facing material. Plasma start-up and stationary limiter plasmas were achieved on the EAST outboard, fully actively cooled W limiter, when on-axis ECH heating is applied. A constant radiated fraction is found in the stationary phases of limiter plasmas over a significant density range compatible with a self-regulating sputtering mechanism for W which is seen in ITER modeling: higher plasma densities can significantly reduce the influx of medium and high-Z impurities leading to similar radiative fractions as low densities with higher impurity influxes. Boronizations assisted by ICWC and GDC have been compared to investigate the uniformity and quality of the boron coating as well as the retained fuel and its removal. A more uniform plasma was obtained with both toroidal and vertical magnetic field with ICWC leading to more uniform coatings. The neutral particle spectra in ICWC were measured for the first time by the low-energy neutral particle analyzer in ITER relevant conditions, which suggests the importance of uniform gas fueling and minimizing the neutral pressure thereby increasing the mean free path of energetic ions for achieving a uniform particle flux. High confinement H-mode operation has been successfully achieved under both boronized and unboronized wall conditions with type II ELMs at q95 ~ 6 and with ITER-like low input torque/no-torque with total input powers from 3 MW to 5 MW by ECH+NBI/LHW. On the contrary type-I ELMy H-modes in similar conditions show poorer energy confinement associated with high W impurity sources, this is alleviated with ELM suppressed by n = 2 RMPs but without a significant improvement of energy confinement. In addition, long pulse type II H-modes (~ 60 s) with dominant electron heating have been successfully achieved with the W wall without boron coatings.