Effects of DC substrate bias voltage on dust flux in the Large Helical Device

We measured the dependence of the collected flux of dust particles on the bias potential Δφ with respect to ground in the Large Helical Device at the National Institute of Fusion Science. This is a first step toward developing a novel method for removing dust for fusion reactors based on applying a local bias potential. The collected dust particles were classified into two kinds: spherical carbon particles smaller than 300 nm and stainless-steel flakes smaller than 1 μm. For Δφ = -70 to +70 V, the flux of spherical particles increased exponentially with increasing Δφ. The flux of flakes increased when Δφ was increased from -70 V to +30 V and it decreased at higher Δφ. These results suggest that this method is useful for removing carbon and metal dust particles from the shadow area of fusion devices using appropriate control of the local bias potential.