The Distribution of Particulate Sizes Observed in \hbox{DIII-D} During Normal Plasma Operation

Large dust particulates of characteristic size greater than $\sim$30~nm have been observed in the scrape-off layer and divertor regions of the \hbox{DIII-D} tokamak during normal plasma operations from Rayleigh scattering of 1.06~$\mu$ light from the existing Nd:YAG laser array and Thomson scattering system [1]. Here we discuss techniques to estimate the particulate size distribution from the measured pulse height distribution of scattered laser light. The data suggest a double-peaked distribution of particulate sizes. One group of particulates is small enough ($\leq \lambda$/10) that the Rayleigh scattering approximation holds. Estimates of the size distribution of the group of larger dust particulates require the Mie scattering formulation.\par \vspace{0.5em} \noindent [1]~B.D.\ Bray, W.P.\ West, and J.~Burkart, ``Dust Measurements with the DIII-D Thomson System," this conference.