European Dissemination of the Ultra-low Temperature Scale, PLTS-2000

Abstract

The first phase of the EU collaborative project on sub-kelvin thermometry, 'ULT Dissemination', is nearing completion, leading to the development of several thermometers and devices, and the instrumentation needed to disseminate the new Provisional Low Temperature Scale, PLTS-2000, to users. Principal among these are a current-sensing noise thermometer (CSNT), a CMN thermometer adapted for industrial use, a Coulomb blockade thermometer, a second-sound acoustic thermometer and a superconductive reference device SRD-1000. Several partners have set up 3 He melting-pressure thermometers to realise the PLTS-2000, and will check it using Pt-NMR, CMN and other thermometers. The scale, which was formally adopted by the Comité International des Poids et Mesures in October 2000, covers the range of temperature from 1 K down to 0.9 mK, and is defined by an equation for the melting pressure of 3 He. The SRD employs novel fabrication and detection techniques with up to 10 samples, and is expected to meet the requirement for fixed points below 1 K, formerly filled by the NIST SRM 767 and 768. Other devices included in the project are ruthenium oxide sensors and a self-contained 3 He melting pressure thermometer. This paper reviews the project progress to date and indicates the potential for research, metrological and industrial application of the devices developed.

The Realization of the Provisional Low Temperature Scale of 2000 at BNM-INM

“…The 3 He used in the MCT was purchased from Chemgas Company. The chemical analysis supplied by Chemgas gives 40 ppm of 4 He in 3 He. As previously tested in Ref.…”

“…This research resulted in a common proposal for an analytical relation, P(T), of polynomial form, and for values given for "in-situ" temperature and pressure fixed points (minimum of the melting curve, superfluid and magnetic transition in solid 3 He). At the same time, as partners of two European projects, the "ULTUltra Low Temperature" [1] and the "ULT dissemination" [3], several European metrological laboratories worked together in order to test the MCT in different environments and to compare the temperatures given by the MCT to that obtained in "local scales." In the context of these European projects, several MCTs were studied and built by PTB.…”

“…For many years, these properties have been investigated for thermometric purposes [2]. In the past few years, extensive efforts were made in national metrological laboratories in order to establish the relation between the 3 He melting pressure P and the temperature T by comparing the melting curve thermometer (MCT) to various primary thermometers [3][4][5][6]. This research resulted in a common proposal for an analytical relation, P(T), of polynomial form, and for values given for "in-situ" temperature and pressure fixed points (minimum of the melting curve, superfluid and magnetic transition in solid 3 He).…”

On-chip Thermometry for Microwave Optomechanics Implemented in a Nuclear Demagnetization Cryostat

“…The use of the word almost here should be understood as follows: we also used resistive thermometers (RuO 2 , carbon Speer-type) calibrated against primary devices, and our primary thermometers (which do follow known temperature dependencies) are calibrated at a single point in temperature for practical reasons. Our laboratory has a long history of working for the construction of the ultra-low temperature scale [59]. In our case, the BF cryostat has been equipped with a Magnicon R MFFT noise thermometer and a CMN paramagnetic salt (Cerium Magnesium Nitrate) thermometer.…”