Control of dust flux in LHD and in a divertor simulator

We have analyzed dust particles collected in the LHD and a divertor simulator by using the DC-bias substrates. The collection in the LHD was conducted in the 15th campaign on 11th and 12th August, 2011. In this campaign, spherical particles and flakes have been collected. The dependence of total flux of dust particles on the substrate bias voltage Vbias showed that appropriate bias control can control the dust flux generated by applying a local bias and is useful for removing carbon and metal dust particles from the shadow area of fusion devices. While, for the flakes, the mass deposition rate and hydrogen atom accumulation rate deduced from the size distribution of the dust fluxes changed in the same manner as the total flux, those of mass deposition rate and H accumulation rate for spherical particles were different from that of the total flux. The reasons of the difference should be studied using laboratory plasmas. To confirm availability of study on the dust flux control using the divertor simulator, we have compared the total flux of dust collected in the divertor simulator with that in the LHD. The collected dust particles in the divertor simulator can be classified into three kinds: spherical particles, agglomerates, and flakes. The spherical dust flux increases exponentially with increasing the Vbias , while the fluxes of agglomerates and flakes are irrelevant to the bias voltages. The results suggest that the divertor simulator can be simulated the flux control of spherical particles in the LHD using DC-biased substrates. (author)