A static diffusion chamber for measuring ice particle growth at low and high ice supersaturations

A static, thermal gradient diffusion chamber has been designed for the growth of small ice crystals over ranges of temperature and supersaturation characteristic of the troposphere. The device consists of parallel copper plates cooled by a circulating coolant in Plexiglas housings that cover the top and bottom plates. Temperature within the chamber is measured by thermocouples embedded in each plate. Supersaturation is controlled by filter paper that is soaked and applied to the top and bottom plates. The chamber design is relatively unique in that particles are levitated inside the chamber. Charged droplets (about 10 microns in size) are launched into the chamber through a launcher placed into the upper housing. The drops are levitated inside the chamber by applying a voltage to the bottom copper plate, which therefore supplies the repulsive force counteracting gravity. Lateral stability of the particles are controlled by small quadrupole ends that extend a small distance from the upper plate. The quadrupole ends are sufficiently removed from the growth region of the particle such that the diffusion field in the vicinity of the particle is not affected. Characterization tests with the new instrument are underway, and ice crystal growth measurements with the new device will be presented at the meeting.