VIBRATING - WIRE MEASUREMENTS IN VACUUM, LIQUID-HE-3 AND LIQUID HE-3-HE-4 MIXTURES

Abstract

In order to overcome the "200 muK - barrier" in the refrigeration of liquid He-3-He-4 mixtures we have constructed an experimental cell using only pure materials to minimize possible origins for heat leaks into the liquid. With this arrangement we were able to cool a saturated 6.8%- mixture to a temperature of less-than-or-equal-to 150 muK. A vibrating wire which was immersed in pure He-3 floating on top of the phase-separated mixture was used as a thermometer. This wire was calibrated in a second experiment with pure He-3 only in the cell. In superfluid He-3-B at T less-than-or-equal-to mK the damping of the wire due to the quasiparticles becomes very small, and we observe typical characteristics of the vacuum damping of the wire which was extensively examined before filling any liquid into the cell.