  We present the design of a general-purpose convection chamber that produces a
stable environment for studying the growth of ice crystals from water vapor in
the presence of a background gas. Crystals grow in free fall inside the
chamber, where the temperature and supersaturation are well characterized and
surprisingly uniform. As crystals fall and land on a substrate, their
dimensions are measured using direct imaging and broad-band interferometry. We
also present a parameterized model of the supersaturation inside the chamber
that is based on differential hygrometer measurements. Using this chamber, we
are able to observe the growth and morphology of ice crystals over a broad
range of conditions, as a function of temperature, supersaturation, gas
constituents, gas pressure, growth time, and other parameters.
