Construction of scientific base towards reduction of plasma power flow on fusion wall associated by ELM heat pulse

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Experiments have shown power transmission factor (PTF) for nanostructured tungsten (W) is greater than that for normal W over a wide range of sheath voltage. Both a reduction in ion energy reflection coefficient due to fiber-form nanostructure and a cooling effect associated by electron emission from the surface have been considered to explain the difference in PTF, which have been also included in our new PTF theory, and a qualitative agreement between the experiments and the new theory was obtained.Concerning the electron emission from W surface, it is found that Auger effect of incident helium ions contributes to the electron emission in addition to secondary electron emission. Thermoelectron emission due to deuterium plasma heat pulse was found to give a serious influence on a further W temperature increase.Nano-loops were identified to be an initial stage precursor of fiber-form nanostructure growth of W as well as Mo surface due to helium plasma exposure.