Cooling Superfluid 3He to the Zero-Temperature Limit
S.N. Fisher, G.R. Pickett
Department of Physics, Lancaster University, Lancaster, LA1 4YB, United Kingdom
The behaviour of superfluid 3He in the near-zero temperature regime of negligible normal fluid density is very interesting and very simple. With the normal fluid reduced to a tenuous gas of quasiparticles, the behaviour is dominated by the properties of the condensate, and several properties, otherwise masked by the normal fluid, become observable. For example, we can track coherent spin precession of the condensate as it persist for thousands of seconds after the initial excitation. The rapid thermal response of the dilute quasiparticles gas also allows us to probe many fundamental aspects of the various condensate phases and phase boundaries. Here we discuss the special Lancaster multiple-cell techniques which can cool the superfluid to T < 0.1 Tc. We also present some of our experiments to measure fundamental properties of the superfluid which actually rely on the low temperature behaviour for their accomplishment.
Operation of a Dilution Refrigerator in a Micromode
V.S. Edelman
P.L. Kapitza Institute for Physical Problems RAS, ul. Kosygina 2, Moscow 117334, Russia
Two types of a 3He-4He dilution refrigerator with the 3He pumping out due to its condensation on a cold wall are described: a classical refrigerator with a heat exchanger and a refrigerator with a collector that allows the operation in a quasi-single cycle refrigeration. The refrigerator operated stably in both cases, when a power of 30 mW was fed to the still, i.e., at a circulation rate of 3He of a few micromoles per second. In this case, the mixing chamber was cooled down to a temperature below 0.05 K.
Superfluidity and Quantized Vortex Studies under Rotation up to 3 (1) revolution(s) per second at down to milli (sub-milli) Kelvin Temperatures
Minoru KUBOTA
Institute for Solid State Physics, Univ. Tokyo, Kashiwanoha 5-1-5, Kashiwa, Chiba, 277-8581 JAPAN.
Two new high-speed rotaing cryostats at the ISSP, University of Tokyo, capable of operating at mK temperatures, are currently employed for studies of superfluidity and quantized vortex states in 4He and 3He. A stable high-Q torsional oscillator is used for the study of superfluidity in low-density 4He films adsorbed on 3-D connected porous substrates. At Tc, the critical phenomena of 3-D Bose superfluids is seen. Under rotation a new type of vortex state is observed. High-resolution NMR studies of superfluid 3He, contained in capillary arrays of two different diameters, are made as a function of rotational speed. In these experiments, single vortex intrusion events as well as texural modification under rotation are clearly resolved.