W.A. Bosch

A European ultralow temperature scale

Abstract A collaborative research project, supported by the Standards, Measurement and Testing programme of the European Union, has been undertaken to standardise sub-kelvin temperature measurements across European national measurement institutes. Traceability to the resulting European ULT scale has been enhanced by the development of a new prototype superconducting reference device. New glass capacitance thermometers for measurements in high magnetic fields have also been characterised. The main results of the project are presented.

The Specific Heat of ErxY1-xRh1.1Sn3.6 for x=0.4, 0.8 and 1

Specific heat measurements between 50 and 800 mK of the three magnetic superconductors ErxY1-xRh1.1Sn3.6 With x = 0.4, 0.8 and 1, respectively, are presented. For these compounds broad anomalies with maxima at 245, 360 and 435 mK, respectively, were observed. No sharp peaks were detected. This means that magnetic short-range order gives the main if not the full contribution to the specific heat. A low-lying doublet is responsible for the magnetic behaviour below 1 K. The results are compared with some theories.

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

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 3He 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 Comite 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 3He. The SRD employs novel fabrication and detection techniques with up to 10 samples, and is expected to meet the requirement...

First Prototypes of the Superconductive Reference Device SRD1000

In the framework of the European Project “Ultra‐Low Temperature Dissemination (ULT),” a superconductive reference device (SRD1000) and dedicated external measurement electronics were developed to provide direct traceability to the new Provisional Low Temperature Scale (PLTS‐2000). The SRD1000 includes 10 reference points in the temperature range 15 mK to 1 K: W (TC = 15 mK), Be (TC = 23 mK), Ir80Rh20 (TC ≈ 35 mK), Ir92Rh08 (TC ≈ 65 mK), Ir (TC = 100 mK), AuAl2 (TC = 160 mK), AuIn2 (TC = 208 mK), Cd (TC = 520 mK), Zn (TC = 850 mK) and Al (TC = 1180 mK). After extensive research and development in the preparation and in the ultra‐low temperature characterization of superconductive reference materials during the past years, eventually a final selection of the materials to be included in the first SRD1000 prototype sensors was made. In this paper, the superconducting transitions observed for the selected materials and the sample preparations are reported, the SRD1000 sensor and external electronics technology...

EU dissemination of the provisional ultra-low-temperature scale, PLTS-2000

Following the introduction of the provisional low-temperature scale from 0.9 mK to 1K, PLTS-2000, there is a need for primary and secondary thermometers and fixed points, which can disseminate the scale to users. This paper reports on the progress, within the EU collaborative project ‘ULT Dissemination’, in the development and evaluation of several devices with associated instrumentation. Principal among them are a current-sensing noise thermometer, a CMN thermometer adapted for industrial use, a Coulomb blockade thermometer, a second-sound thermometer, a 3He melting pressure thermometer for a direct realisation of the PLTS-2000. A superconductive reference device has also been developed, as a replacement for the NBS SRM-768 which is no longer available.

SRD1000: a superconductive reference device for thermometry below 1 K

A superconductive reference device (SRD1000), providing 10 reference points in the temperature range 10 mK–1 K with dedicated measurement electronics, has been developed and tested to provide direct traceability to the new provisional low temperature scale (PLTS-2000). We report on the repeatability of the transition temperatures of samples of IrxRh100−x alloys (with transition temperatures between 20 and 100 mK) and some single crystals (Cd, Zn, AuIn2,AuAl2 and W).

Traceable low and ultra-low temperatures in The Netherlands

The basis for worldwide uniformity of low and ultra-low temperature measurements is provided by two international temperature scales, the International Temperature Scale of 1990 (ITS-90) for temperatures above 0.65 K and the Provisional Low Temperature Scale of 2000 (PLTS-2000) for temperatures in the range 0.9 mK to 1 K. Over the past 10 years, the thermometry research in the Netherlands provided substantial contributions to the definition, realization and dissemination of these scales. We first give an overview of the Dutch contributions to the ITS-90 realization: a) 3He and 4He vapour pressure thermometer range of the ITS-90, 0.65 K to 4 K (1997), b) 4He interpolating constant volume gas thermometry for the ITS-90 range 3 K to 24.5 K (2007) and c) cryogenic fixed points for the ITS-90 range 13.8 K to 273.16 K (2005). Then we highlight our work on 3He melting pressure thermometry from 10 mK to 1 K (2003) to support the dissemination of the PLTS-2000. Finally we present the current status of the Dutch calibration facilities and dissemination devices providing for traceable low and ultra-low temperatures for use in science and industry: a) the NMi-VSL cryogenic calibration facility for the range 0.65 K to 273.16 K and b) the SRD1000 superconductive reference devices for the range 10 mK to 1 K.

A new superconducting reference device for thermometry below 1000 mK

As part of a European project for the development and realization of a temperature scale below 0.65 K, research has been performed to realize a new superconducting reference device for thermometry below 1000 mK, the SRD1000. This device uses the superconducting transition temperatures of various materials to establish fixed points on the temperature scale. The research consisted of selecting, producing and testing suitable sample materials to be used for the new sensor. As compared to the former SRM 768 device (NBS, U.S.A.), which is not any longer available, the poisonous Be has been omitted and IrRh alloys are introduced to obtain additional fixed points between 15 and 100 mK. At the high temperature end Zn and Al are used to provide an overlap with ITS90. Apart from the research on materials a new detection system for the superconducting transitions was developed and tested, consisting of a planar micro coil system and dedicated electronics. In 1999 we will construct two prototype devices containing the materials W, IrRh alloys, Ir, AuAl2, AuIn2, Cd, Zn and Al. These devices will be tested and calibrated against a 3He melting curve thermometer in the temperature range of 15 mK to 1000 mK. Results of preliminary measurements are presented.