An improved high-resolution thermometer (HRT) for use in scientific experiments at temperatures
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 -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.
NPO-20903
This Brief includes a Technical Support Package (TSP).
Small Low-Temperature Thermometer with Nanokelvin Resolution
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Overview
The document presents a technical overview of a newly developed small low-temperature thermometer capable of achieving nanokelvin resolution, designed for use in low-temperature experiments, particularly in space applications. The thermometer, developed by Paul Welander, M. Barmatz, and Inseob Hahn at the Jet Propulsion Laboratory (JPL), utilizes a GdCl3 paramagnetic salt and a Superconducting Quantum Interference Device (SQUID) magnetometer to measure the temperature-dependent magnetization of the salt in a magnetic field.
One of the key innovations of this thermometer is its compact design, which incorporates a pair of small samarium cobalt permanent magnet disks to generate the necessary magnetic field. This design eliminates the need for a heavy, charging solenoid typically used in conventional SQUID-based magnetic thermometer systems, significantly reducing the weight and size of the instrument. The thermometer weighs approximately 7 grams and is a candidate for future experiments on the Space Shuttle and the International Space Station.
The high-resolution thermometer (HRT) operates on the principle of the strong temperature dependence of the magnetization of the paramagnetic salt, allowing it to achieve a temperature resolution better than 10^-9 K. The long-term drift rate of the thermometer is measured to be less than 12 x 10^-13 K/s under optimized conditions, making it suitable for precise measurements in low-temperature physics.
The document also highlights the challenges faced by conventional HRT systems, which are typically large (about 0.3 meters long and weighing around 10 kilograms) and suffer from parasitic heat leaks due to the charging solenoid. The new design addresses these issues by providing a more efficient and compact solution, allowing for a variety of magnetic materials to be used in different applications.
In summary, this document outlines the development and advantages of a novel small low-temperature thermometer with nanokelvin resolution, emphasizing its potential for use in space and other low-temperature experiments. The innovative design and reduced size make it a significant advancement in the field of low-temperature measurement technology.
