Various melting phenomena of metal plasma facing materials and their influences on plasma operation in EAST*

In future fusion devices, such as the ITER, the W plasma facing materials and components (PFMCs) for divertor will be exposed to both high steady state heat load (10MWm-2) and extreme high pulsed heat flux (up to MJm-2 in a short pulse ~ms), which may induce the melting of metal PFMCs. Thus, understanding melting behaviors and its influence on plasma operation in current tokamak is one of the main concerns. The EAST, as a superconducting tokamak, were installed wide metal PFMs, i.e. W PFMCs for divertor and limiter, and TZM tiles for first wall, which can provide valuable references and experiences to the ITER. During recent plasma campaigns, various melting phenomena, i.e. steady state heat flux induced melting of leading edges on W/Cu monoblocks on upper divertor targets, steady state heat flux induced melting of W plate on W/Cu flat type component on lower divertor, transient heat flux induced melting on TZM first wall, W limiter and divertor dome/ baffle plates during plasma disruption, have been successfully observed/inspected and identified. The melting behaviors, especially melting layer migration and droplets ejection were characterized and compared. The influences of these melting phenomena on plasma discharge and subsequent operations are investigated and discussed. The steady state heat flux induced melting with a lots of droplets ejection into core plasma leads to the sharp increasing of W impurity and core irradiation, significantly influencing the plasma discharge and operation, while the transient heat flux induced melting seems to have negligible influence on plasma operation.