Low Temperature Thermometers Research Articles

Processing calibration data of low-temperature thermometer based on clustering algorithm.

The scarcity of cryogenic thermometers often stems from their high cost and lengthy lead times for calibration. Establishing an in-lab temperature calibration system is necessary to quickly make use of uncalibrated sensors or self-made sensors. This paper introduces a straightforward and high-accuracy thermometer calibration system. By employing copper screws as thermal links between the sensor platform and the cryogen-free refrigerator, temperature oscillation on the sensor platform is suppressed to a few millikelvins. In addition, this paper presents a data processing model based on clustering algorithms. These algorithms sort and group data based on distance, which is similar to human visual judgment of data. This paper discusses the parameter optimization process of the clustering algorithm to interpret the automated data process. The cryogenic temperature sensors calibrated by this system exhibited high accuracy, with relative errors of less than 1% compared to standard thermometers. Moreover, automatically processing calibration data from two uncalibrated thermometers takes just over 10min, highlighting the effectiveness of this calibration system.

Low-temperature optical thermometer based on the luminescence of the double perovskite Ba2MgWO6: Nd3+

Low-temperature optical thermometer based on the luminescence of the double perovskite Ba2MgWO6: Nd3+

Ultra-sensitive low-temperature thermometer regulated by the crystal field strength

Developing novel optical thermometry with ultrahigh relative sensitivity and temperature resolution has become a cutting-edge topic. For this purpose, under obeying Boltzmann distribution, a series of Li2Zn0.9992-xAxGe3-yByO8:0.08% Cr3+ (B= Sc3+, In3+, A = Si4+) phosphors were studied, which the luminescence intensity ratio between the transition of 4T2g→4A2g emission and the R line based on thermally coupled energy levels constitutes a temperature sensing work with a relative sensitivity of 9.46% K−1, 9.73% K−1, and 10.38% K−1, respectively. It is worth mentioning that the luminescence intensity of the R line (peak 1) increases significantly with the increase of temperature, while the transition of 4T2g→4A2g (peak 2) with high intensity at low temperature gradually quenching, and this opposite trend is an important advantage for the design of excellent thermometers. Compared the best relative sensitivity of Li2Zn0.9992-xAxGe3-yByO8:0.08%Cr3+ (B= Sc3+, In3+, A = Si4+) with the crystal field Dq/B, it can be concluded that relative sensitivity increasing gradually with decreasing the intensity of crystal field. Finally, by testing the stability of the sample at 50 K, a thermal resolution of 0.082 K, 0.080 K and 0.077 K was obtained, respectively, which is one of the best thermal resolutions so far, while the repeatability of the sample stability at 50 K and 300 K cycles was higher than 99%. Our work is expected to provide guiding insights for optimizing the sensitivity of Cr3+-based luminescence intensity ratio thermometers.

Transparent–Flexible–Moldable Low-Temperature Thermometer Constructed by Harnessing Vibration-Induced Emission of Dihydrophenazine in Polydimethylsiloxane

Transparent–Flexible–Moldable Low-Temperature Thermometer Constructed by Harnessing Vibration-Induced Emission of Dihydrophenazine in Polydimethylsiloxane

Uncertainties in blackbody corrections for low-temperature radiation thermometers

Equations are derived for propagating the uncertainties contributing to the blackbody corrections for the calibration of low-temperature radiation thermometers operating over a spectral range near the 8 µm–14 µm band. These equations include the full Planck treatment of spectral radiance, which is necessary at these long wavelengths, and account for the thermometer bandwidth. The influence quantities include the source emissivity, reference temperature, reflected ambient radiation, detector temperature, and spectral responsivity. Various cases are considered when using either a blackbody cavity or a flat-plate calibrator as the calibration source, and when using a contact thermometer or a radiation thermometer as the reference. Total uncertainties tend to be smallest when a radiation thermometer is used as the reference as, in this case, the influence of the source emissivity is minimised.

Properties of the 100 kHz Quartz Tuning Forks in Strong Magnetic Fields and Very Low Temperatures

We present the properties of the standard, commercial 100 kHz quartz tuning forks at very low temperatures and high magnetic fields up to 8 Tesla. We show that the resonance frequency of the tuning forks depends weakly on the strength of magnetic field. This makes the quartz tuning forks a promising low-temperature thermometer having the B/T ratio up to 1000. We discuss the physical origin of the observed experimental results.

Quartz tuning fork—A potential low temperature thermometer in high magnetic fields

We present the performance of commercial quartz tuning forks (QTFs) operating at resonance frequencies of 32 kHz, 77 kHz, and 100 kHz in the temperature range below 1 K and in high magnetic fields up to 7.5 T. We show that characteristics of the quartz tuning forks, in particular, the normalized QTF resonance frequency, manifest a universal temperature dependence, which is independent of the magnetic field strength. This feature makes the QTFs very promising low temperature thermometers in high magnetic fields in the temperature range below 1 K having the B/T ratio up to 1000. We also discuss the physical origin of the observed dependencies.

Optimising Blackbody Cavity Shape for Spatially Uniform Integrated Emissivity

The emissivity of a blackbody cavity, as seen by a radiation thermometer viewing the cavity, depends on both the field of view of the thermometer and the distribution of local effective emissivity values within the field of view. For cylindro-conical cavities, the local effective emissivity generally attains a maximum value at the apex of the cone and drops along the conical section. Thus, radiation thermometers with different fields of view see different blackbody emissivity values. This impacts, particularly, on the calibration of wide-angle low-temperature radiation thermometers and thermal imaging systems where each pixel responds to a different radiance. The spatial uniformity of the effective emissivity profile depends principally on the cone angle, with a weaker dependence on the length-to-diameter ratio of the cavity, the intrinsic emissivity of the cavity surfaces, and the temperature gradient along the cavity. In this paper, a nonlinear least-squares method is used to determine the optimal cone angle as a function of the cavity parameters. It is concluded that full cone angles close to 160 $${^{\circ }}$$ provide the flattest effective emissivity profile across the conical section of the cavity for typical cavity parameters. A method is also described for calculating the value of integrated emissivity, which includes the umbral and penumbral regions seen by an imaging radiation thermometer.

Realization of PLTS-2000 for Low-Temperature Resistance Thermometer Calibration Services Below 650 mK

In this study, the Provisional Low Temperature Scale of 2000 (PLTS-2000) was realized below 650 mK for the purpose of launching low-temperature resistance thermometer calibration services in Japan. A Straty–Adams-type \(^{3}\)He melting pressure thermometer (MPT) and a dilution refrigerator were used to realize the PLTS-2000. Offsets due to hydrostatic pressure head in a filling capillary line of the MPT were adjusted using the minimum pressure fixed point on the \(^{3}\)He melting curve. A rather large MPT hysteresis between the decreasing and increasing pressures was observed during pressure calibration of the MPT and was the main source of uncertainty. The combined standard uncertainty (\(k = 1\)) between 50 mK and 650 mK was estimated to be in the range of 0.40 mK to 2.62 mK. The MPT and a number of resistance thermometers with negative temperature coefficients were mounted on the experimental platform with a thermal connection to a mixing chamber and compared in a multiple-temperature-point calibration. The temperature range around the melting pressure minimum, 250 mK to 400 mK, was not used for the calibration. The expanded uncertainty (\(k = 2\)) in the calibration based on realization of the PLTS-2000 between 50 mK and 650 mK was estimated to be in the range of 0.86 mK to 5.25 mK.

Avoiding back-action in quantum measurements

Quantum Mechanics The very process of measuring a quantum system has an influence on the system through the process of back-action. Suh et al. used a back-action evasion scheme to monitor the motion of a miniature oscillator without influencing its motion (see the Perspective by Bouwmeester). The scheme should help in the understanding of the fundamental limits associated with measurement and will have practical implications in providing a low-temperature thermometer and a probe of extremely weak forces. Science , this issue p. [1262][1] [1]: /lookup/doi/10.1126/science.1253258

Atomic Layer Deposition of Tunnel Barriers for Superconducting Tunnel Junctions

We demonstrate a technique for creating high quality, large area tunnel junction barriers for normal–insulating–superconducting or superconducting–insulating–superconducting tunnel junctions. We use atomic layer deposition and an aluminum wetting layer to form a nanometer scale insulating barrier on gold films. Electronic transport measurements confirm that single-particle electron tunneling is the dominant transport mechanism, and the measured current–voltage curves demonstrate the viability of using these devices as self-calibrated, low temperature thermometers with a wide range of tunable parameters. This work represents a promising first step for superconducting technologies with deposited tunnel junction barriers. The potential for fabricating high performance junction refrigerators is also highlighted.

Development of an automatic calibration device for high-accuracy low temperature thermometers

Based on the analysis and investigation of calibration systems for high-accuracy low temperature thermometers, a new facility for automatic calibration of high-accuracy low temperature thermometers was developed. Continuous calibration for multiple points can be made automatically with this device. According to the thermophysical characteristics of the constant-temperature block in this device, segmented Fuzzy-PID (proportional-integral-differential) algorithm was applied. The experimental results showed that the temperature fluctuation was smaller than ±0.005 K in 30 min. Therefore, this new device can fully meet the calibration requirement of high-precision low temperature thermometers.

Calibration and use of low-temperature direct-reading radiation thermometers

The calibration and use of low-temperature radiation thermometers with uncooled detectors require special consideration of the many influence variables affecting the readings, including target emissivity, background temperature and instrumental emissivity setting. The readings for instruments with fixed emissivity less than 1 depend on the detector temperature, which is generally not made available to the user. The readings also depend on the spectral responsivity of the thermometer, which is rarely provided in much detail. The effects of all these influence variables are somewhat obscured by the processing algorithm employed by the thermometer to convert the measured signal into a temperature reading. This paper outlines methods for determining expected thermometer readings during calibration against blackbody sources, and for correcting readings during use where large reflection errors are present. These methods are essential for ensuring traceability of measurements made with these instruments, and are easily implemented in spreadsheet applications.

Magnetic properties of erbium in single crystal [formula omitted

In a search of improved materials for magnetic calorimetry and low-temperature thermometers, we have investigated the magnetic properties of erbium diluted in a single crystal of Bi 2 Te 3 . EPR studies carried at 9 and 20 GHz showed no observable resonance signals. The DC magnetization was measured between 2 – 300 K and 0 – 5 T using a SQUID magnetometer. The low-field and low-temperature measurements yielded g ∥ ≈ 13.7 and g ⊥ ≈ 0 . A set of parameters for the spin Hamiltonian were found that were able to fit all of the magnetization measurements assuming the Er 3 + ions are in a site of C 3 v symmetry. The zero field splitting of the two lowest Kramer's doublets is 15 K with all other energy levels lying considerably higher.

Study of Molecular Dynamics and the Solid State Phase Transition Mechanism for Unsymmetrical Thiopyrophosphate Using X-ray Diffraction, DFT Calculations and NMR Spectroscopy

Differential scanning calorimetry (DSC) and low-temperature X-ray diffraction studies showed that 2-thio-(5,5-dimethyl-1,3,2-dioxaphosphorinanyl)2'-oxo-dineopentyl-thiophosphate (compound 1) undergoes reversible phase transition at 203 K related to the change of symmetry of the crystallographic unit. Solid state NMR spectroscopy was used to establish the dynamic processes of aliphatic groups and the phosphorus skeleton. 13C and 31P variable temperature NMR studies as well as T1 and T1rho measurements of relaxation times revealed the different mode of molecular motion for each neopentyl residue directly bonded to phosphorus. It is concluded that molecular dynamics of aliphatic groups causes different van der Waals interactions in the crystal lattice and is the driving force of phase transition for compound 1. Finally, we showed that very sharp phase transition temperature makes compound 1 an excellent candidate as a low-temperature NMR thermometer in the solid phase.

Beneficial effects of annealing on amorphous Nb–Si thin-film thermometers

Amorphous Nb–Si alloys have a temperature-dependent resistivity which can be tuned over many decades by controlling composition and are used for thin-film thermometers. Annealing at temperatures from 100 to 500 °C produces dramatic but easily controlled increases in resistivity, both magnitude and temperature dependence, for insulating and metallic samples with compositions ranging from 8–15 at. %Nb. A transition from metal to insulator is induced by annealing an initially metallic sample. Annealing produces thermal stability against subsequent heat treatment, allowing annealed films to be used as low-temperature thermometers even when they are cycled to temperatures as high as 500 °C. Cross-section transmission electron microscopy and energy-dispersive x-ray analysis show that the initially amorphous films develop Nb-rich clusters within an amorphous Nb-depleted matrix, explaining the observed resistivity increase.

A low-power current regulator for low-temperature thermometers

A battery-supplied current regulator for low-temperature thermometers is described. The regulator operates in the range 1–10 µA and consumes a current of 0.12 mA.

RECENT ADVANCES IN LOW TEMPERATURE THERMOMETRY IN HIGH MAGNETIC FIELDS

The accurate determination of the temperature of an experiment at low temperatures in high magnetic fields is difficult. We present the results of measurements made using a number of new techniques developed over the last few years. In particular we discuss the results of measurements made using a unique capacitor made with Kapton and copper in a cylindrical geometry.1 This capacitance thermometer, dubbed the "Kapacitor", is different from other low temperature thermometers in that the minimum in capacitance vs. temperature can be moved to lower temperatures (to below 20 mK) by changing the construction technique. In addition, we discuss measurements on Coulomb blockade thermometers (CBT's) that offer the possibility of true primary thermomemtry at low temperatures without any magnetic field dependence. Both of these new techniques will be compared to the standard technique of resistance thermometry using RuO chip resistors. The crucial issues of accuracy and precision, usefulness for control, and noise sensitivity will be discussed for each of these technologies. In addition, recent measurements on the magnetic behavior of RuO thermometers at low temperatures and its relationship to anomalous low field peaks in the resistance that develop at temperatures below 50 mK are also presented.

Digital signal processor-based dc superconducting quantum interference device controller

We report on the design and evaluation of a convenient digital signal processor-based (DSP) controller for a dc superconducting quantum interference device (SQUID). Program algorithms for the DSP conveniently replace major functions of an analog flux-locked loop: current bias, modulation signal, demodulation, filtering, integration, feedback, and reset. For the controller described here, the entire system was built using commercially available electronics and sensor units with the addition of a simple operational amplifier circuit for the required gain. The noise level of the nonoptimized dc SQUID controller system at 1 Hz was ∼50μΦ0/Hz. Application of the system was demonstrated as a readout system for a low-temperature magnetic susceptibility thermometer that required flux counting.

Thermal impedance of thick-film resistance thermometers below 0.2 K

Contributions to the thermal impedance of thick-film resistors (TFRs) are discussed. Measurements of the heat flow along the resistance layer, through the substrate and through the glass overcoating, are presented for commercial resistors mounted on a copper plate in the 30–170 mK temperature range. Because of the relatively good thermal conductivity of the film material (three orders of magnitude higher than that of alumina), the contribution to the heat flow of the resistance layer is never negligible in spite of the thinness of the latter. Suggestions are given for the best mounting of the TFRs as low-temperature thermometers. Less conventional uses of TFRs as thermometers in bolometers are also considered.