The magnetic field is generated by permanent magnets instead of a solenoid.

An improved high-resolution thermometer (HRT) for use in scientific experiments at temperatures <4 K has been developed. Like other, previously developed low-temperature HRTs, this device is based on the strong temperature dependence of the magnetization of a paramagnetic salt exposed to a magnetic field. However, in comparison with other paramagnetic-salt HRTs, this one is smaller and less massive; hence, it is denoted "sHRT" — short for "small HRT."

This High-Resolution Thermometer is smaller and less massive, relative to prior thermometers based on paramagnetic salts.

The temperature-sensitive part of an HRT of this type is a pill-like piece of the paramagnetic salt GdCl3. The magnetization of the salt pill is measured by use of a superconducting quantum interference device (SQUID). In an older device of this type, the magnetic field needed to magnetize the pill is trapped in a long superconducting tube (flux tube) that must be charged by use of a superconducting solenoid; typically, the overall length and mass of such an HRT are ≈0.3 m and ≈10 kg, respectively. In contrast, the length and mass of the sHRT are ≈3 cm and ≈7 g, respectively.

The reductions in size and mass are made possible by using permanent magnets instead of a charging solenoid and flux tube to impose the magnetic field. In the sHRT (see figure), two small samarium cobalt permanent magnets are placed near opposite ends of a beryllium copper cylinder filled with GdCl3. To enhance the thermal link between the GdCl3 and the immediate surroundings, the ends of the Be-Cu cylinder are capped with oxygen-free high-conductivity (OFHC) copper blocks, into which numerous chimney-shaped fins have been machined. A SQUID pickup coil made of Nb-Ti wire is wound on the Be-Cu cylinder. The sHRT housing is made of Nb, which is a superconductor and thus effective in shielding the pickup coil against any ambient magnetic field.

In tests, the sHRT was found to yield measurements with a temperature resolution of ≈10–9 K at a temperature near the liquid-gas critical point of 3He (≈3.31 K). The drift rate of the sHRT was found to be <2 × 10-13 K/s.

This work was done by Inseob Hahn of Caltech for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.nasatech.com/tsp under the Test and Measurement category.


This Brief includes a Technical Support Package (TSP).

Small Low-Temperature Thermometer with Nanokelvin Resolution (reference NPO-20903) is currently available for download from the TSP library.

Please Login at the top of the page to download.

The U.S. Government does not endorse any commercial product, process, or activity identified on this web site.