Ice Dusty Plasma Experiment Upgrade to use Cryocoolers

Tiny ice grains immersed in plasma occur in noctilucent clouds, Saturn's rings, comet tails, and accretion disks. Experiments at the Max Planck Institut [1] and at Caltech [2,3] showed that ice grains spontaneously form from water vapor in a weakly ionized plasma if the background gas is made extremely cold via contact with refrigerated electrodes. Photos show [2,3] that the ice grains are long and spindly in contrast to the spherical shape commonly assumed in theoretical models; the grain length can exceed half a millimeter and the inter-grain spacing is a fraction of millimeter. The Caltech experiment is being upgraded to have the electrode cooling provided by liquid helium refrigerated cryocoolers; these will replace the liquid nitrogen Dewars now in use. The cryocoolers will provide both a temperature scanning capability and a much lower attainable temperature. These new features open up a new operational dimension and will allow determining the temperature dependence of plasma-instigated ice dust formation, growth, and composition. The design and construction status will be presented. [1] S. Shimizu et al. (2010), JGR 115, D18205. [2] K. B. Chai and~P. M. Bellan~(2015)~ApJ 802, 112. [3] R. S. Marshall, K. B. Chai, and~P. M. Bellan~(2017)~ApJ 837, 56.