A NOVEL TECHNIQUE FOR TEMPERATURE STABILIZATION VERY NEAR A PHASE-TRANSITION - RESULTS FOR HE-II

A novel method for achieving high temperature stability at very small reduced temperatures near a phase transition is described. In this tec hnique, fluctuations in a temperature dependent property of the system were used to regulate the system's temperature. This technique has be en implemented in liquid helium just below the superfluid phase transi tion. In this case, the technique is based on second sound phase locki ng and uses the fact that the second sound velocity is strongly temper ature dependent near the lambda transition. Phase fluctuations of a co ntinuous second sound signal are detected and used to regulate the tem perature of the system. The long term temperature stability as inferre d from the stability of the second sound velocity is better than 3 X 1 0(-7) K, at a reduced temperature of less than 10(-5), making the tech nique particularly useful near the superfluid phase transition. (C) 19 96 American Institute of Physics.