Characterization of Dust Particles Ranging in Size from 1 nm to 10 µm Collected in the LHD

Abstract

We collected dust particles ranging in size from 1 nm to 10 µm from the Large Helical Device employing two methods: an ex-situ filtered vacuum collection method and an in-situ dust collection method. The size distribution from 1 nm to 10 µm is well expressed by the Junge distribution. Dust particles are classified into three kinds: small spherical dust particles below 1 µm in size, agglomerates consisting of primary particles of 10 nm, and large dust particles above 1 µm in size and irregular in shape; this suggests three formation mechanisms of dust particles: chemical vapor deposition growth, agglomeration, and peeling from walls. In-situ collection shows that agglomeration between dust particles takes place in main discharges. The primary dust particles in agglomerates are around 10 nm in size, suggesting agglomeration between a negatively charged large agglomerate and a positively charged dust particle 10 nm in size. We have also confirmed the important fact that a large number of dust particles move during vacuum vent. Therefore, the in-situ dust collection method is needed to reveal the generation-time and -processes of dust particles and their deposition position during discharges.