, Volume 134, Issue 1-2, pp 393-399

Improved Optical Setup to Measure Growth and Megting of Solid 3He Below 1 mK in Magnetic Fields Up to 9 Tesla

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Recent experiments on crystal growth and crystal shape in 3He at zero magnetic field at 0.55 mK by Tsepelin et al. 1, 2 in Helsinki have revealed many new facets and strong anisotropy in the growth rates. Since 3He presents the unique possibility of investigating the influence of a magnetic field on crystal growth properties, we intend to extend our experimental studies of the shape and growth rate of solid 3He to magnetic fields up to 9 T at temperatures as low as possible.For that purpose our optical access cryostat with low temperature CCD has been upgraded and modified. The low temperature LED is replaced by a room temperature source coupled to the cell with an optical fiber to obtain clear images of the growth process. Our Pomeranchuk cell has been fitted with a new optical section with pure quartz windows. It has a larger diameter, a larger distance between the optical windows, and an improved thermal link. Also the heat switches between the nuclear stage and the dilution refrigerator were replaced according to a more sturdy design. Initial resugts show clear crystals with sharp facet edges down to T=0.4 mK.