  We describe a dual diffusion chamber for observing ice crystal growth from
water vapor in air as a function of temperature and supersaturation. In the
first diffusion chamber, thin c-axis ice needles with tip radii ~100 nm are
grown to lengths of ~2 mm. The needle crystals are then transported to a second
diffusion chamber where the temperature and supersaturation can be
independently controlled. By creating a linear temperature gradient in the
second chamber, convection currents are suppressed and the supersaturation can
be modeled with high accuracy. The c-axis needle crystals provide a unique
starting geometry compared with other experiments, and the dual diffusion
chamber allows rapid quantitative observations of ice growth behavior over a
wide range of environmental conditions.
