Temperature control and stabilization in the cryodielectrometer for temperatures 0.5 – 300 K
To meet requirements, which arise while design of equipment for research the dielectric parameters of low-loss materials in the millimeter waveband, the necessity of high-precision temperature stabilization and measurement appear. Despite the fact that a lot of attention [1,2] is devoted to this task already, it reminds still actual, due to a plenty of specific features, which each given measuring complex possess.Thermometers intended to measure low and very low temperatures, as a rule use the temperature dependence of certain physical properties of basis substances. There is known quite large amount of temperature controllers [3-6], which are able to operate in a wide temperature range. However, some of them operate in direct current DC-mode [4], and others, which are used AC-mode, intended for operation in too narrow temperature range ≈ 1 K [3, 6]. Besides, they are able to use only one type of sensor and possess, in our opinion, too complicated feedback scheme for the temperature stabilization [5]. In this paper we consider the scheme of the temperature regulator-stabilizer with two temperature sensors having both positive and negative temperature coefficients of resistance (TCR). It designed for low temperature measurements on the cryodielectrometer “TORNADO” in the temperature range 0.5-300 K. As well results of the low-temperature radiospectroscopy experiment using the device designed are given.
Precise temperature controller for resistance thermometers
We describe here a stable and sensitive temperature controller to be used with resistance thermometers. The temperature resolution provided by this instrument was ΔT≂20 μK at room temperature and ΔT≂1 μK at liquid 4He temperature.
The behavior of the4He viscosity near the superfluid transition
Measurements of the shear viscosity at saturated vapor pressure through the lambda transition indicate a singular behavior of the form |1 − (η/ηλ)|=Aεx, (where ε=|1−(T/Tλ)|, with equal values for the critical exponent on both sides of the transition.