Noise Thermometer Research Articles

A self-contained 3He melting curve thermometer for dissemination of the PLTS-2000 temperature scale

We describe a self-contained 3He melting curve thermometer (MCT), which is compact and easy to operate and makes areliable tool for the direct dissemination of the new provisional low-temperature scale,PLTS-2000. It is based on a cylindrical pressure gauge and uses a tunnel diode oscillatorcircuit for capacitive read-out. The gas-handling system uses a set of relief valves and anelectronic pressure sensor, enabling the thermometer to be fully automated, including thecalibration procedure. The performance of the MCT was evaluated by comparison with acurrent-sensing noise thermometer in the temperature range from 20 to 700 mK.

Noise thermometry in crystal growth facilities for the International Space Station (ISS)

AbstractAlthough noise thermometry is an established technique for absolute temperature measurement, several aspects needed to be clarified before this method can be employed for temperature measurement in a space furnace at 1800°C. First, the electrical insulation resistance for sheathed sensors with different insulation materials were measured. Five test sensors with outer diameters of 3.2 mm or less were fabricated and tested. The measurements clearly show a significant advantage for the pyrolytic boron nitride (pBN) insulation compared to Hafnium oxide. The electrical insulation resistance values at 1800°C for the sensors with HfO2 were below 10 Ω, whereas pBN‐insulated test sensors exhibited values of more than 600 Ω for the same diameter. Furthermore, no difference has been found between the resistance of bent and straight sensors. Based on these results a miniaturised and bent noise thermometer with a diameter of 3.2 mm having a pBN insulation was fabricated. This sensor and additional control thermocouples were subjected to performance tests up to 1800°C in a space‐compatible furnace. All sensor readings exhibited a consistent figure during the tests. The noise thermometer, however, showed always the highest reading indicating that noise thermometry is an appropriate method for accurate measurements of absolute temperatures, even in the harsh environment of a compact multi‐zone space furnace.

Noise thermometer accurate at frigid extremes

Noise thermometer accurate at frigid extremes

An AC Josephson source for Johnson noise thermometry

We have adapted the Josephson arbitrary waveform synthesizer to create a quantized voltage noise source suitable for calibrating the cross-correlation electronics of a Johnson noise thermometer system. The requirements of long term stability and low voltage amplitude allow dramatic simplification of the bias electronics compared to previous bias techniques. We describe the waveform synthesis, the bias technique, and the superconducting integrated circuit used to generate the pseudo-noise waveforms.

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 3 He 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.

Comparison of temperature measurement by noise thermometry and radiation thermometry

Above 962°C the ITS-90 has to be realised by means of a radiation thermometer. In many applications, however, the use of contact thermometers is required for technical reasons. The noise thermometer is the only contact thermometer the temperature signal of which is independent of drift behaviour of the sensor caused by material variation. In order to compare noise and radiation thermometry, a special calibration furnace for temperatures up to 1500°C has been developed featuring both an isothermal black-body cavity to measure the radiation temperature and cavities into which contact thermometers can be inserted. The radiation temperature was measured by means of the high precision radiation thermometer Linearpyrometer LP2. This first direct comparison of the two temperature measurement techniques revealed a difference of 0.32 K at 1300°C and 0.54 K at 1445°C. These values, are in the range of or below the individual uncertainties.

Characterization of YBCO/Au/YBCO resistors for HTS Josephson noise thermometry

It has been proposed that an absolute thermometer based on the linewidth broadening of the Josephson oscillation could be realized in the temperature range 10 K to 50 K with the use of high-temperature-superconducting resistive superconducting quantum interference devices (HTS R-SQUIDs). Although this technique has been successfully demonstrated with LTS devices in the temperature region below 1 K, there are unresolved problems which have so far prevented its translation to higher operating temperatures. A crucial component of a resistive SQUID noise thermometer is the shunt resistor, which is required to have a value <0.1 m/spl Omega/. The often excessive and unpredictable contact resistance between normal metal and HTS superconducting thin films has up to now hindered the successful implementation of an HTS resistive SQUID. YBCO-Au-YBCO shunt resistors with suitable resistance values of /spl sim/20 /spl mu//spl Omega/ have recently been manufactured and their characteristics under cryogenic operating conditions have been measured using the Josephson frequency-voltage relationship.

Quantum Roulette Noise Thermometer: Progress and prospects

A novel form of primary thermometer called the Quantum Roulette Noise Thermometer (QRNT) has been fabricated and is presently undergoing feasibility studies. This device utilises flux quantisation in a high temperature superconducting ring interrupted by two closely spaced, parallel, Josephson junctions. Several devices have been fabricated and different methods investigated for measuring the statistical distribution of trapped flux states. We report the results of these endeavours with emphasis on a method for suppressing I/sub c/ by applying an r.f. field to the junctions.

Temperature dependence of the Josephson linewidth of resistively shunted double junction HTS SQUIDs

Double Josephson junction HTS resistive SQUIDs have been fabricated using an on-chip shunt Au resistor across a gap in an YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// loop, providing a low shunt resistance of R/sub s/ /spl sim/26 /spl mu//spl Omega/ at T/spl les/77 K. The dependence of the heterodyne oscillation linewidth of the R-SQUID on the thermal noise across the shunt resistor is under investigation with a view to the development of an absolute noise thermometer. Signal powers /spl sim/nW have been measured and the device has been shown to be tunable from 5 to 50 MHz. The measured oscillation linewidth (/spl sim/30 kHz at 17 K) is believed to be the narrowest reported for such an HTS device, however non-thermal broadening of the linewidth is also observed, as has been reported for single junctions at GHz frequencies. We describe measurements on such devices over a range of temperatures and bias conditions.

Current sensing noise thermometry for millikelvin temperatures using a DC SQUID preamplifier

We have demonstrated the performance of a current sensing noise thermometer using a low- T c DC SQUID as the front end amplifier. The thermometer is fast, absolute and precise and is usable over a wide temperature range below 4.2 K, in principle down to below 1 mK. We have shown that it is possible to determine absolute temperature with a precision of 1% in a measuring time of 10 sec with a noise temperature of ∼30 μK , and to an accuracy of better than 0.3%. The percentage precision is independent of temperature. A comparison with the 3He melting curve down to 24 mK is reported.

Preamplifier limitations on the accuracy of Johnson noise thermometers

A detailed analysis is presented of noise and input impedance in noise thermometer preamplifiers. The analysis highlights the advantages of cascode amplifiers and the disadvantages of amplifiers employing global feedback. Feedback gives rise to two significant errors, one arising from an increase in the input-noise current, the other from the modification of the amplifier input impedance. With care, the errors arising from thermal-noise sources associated with the preamplifiers can be kept below 1 mK. However the largest error associated with the preamplifiers, typically 10 mK to 30 mK and previously unnoticed, arises from the interaction of the input capacitance and the transmission line inductance. This effect negates the common practice of matching the RC time constants in noise thermometers.

Integrated thin-film dc RSQUIDs for noise thermometry

Integrated thin-film dc RSQUIDs (Resistive Superconducting QUantum Interference Devices) have been developed that significantly simplify noise thermometer operation. We show theoretically that the main equations for noise thermometry deduced for rf RSQUIDs can also be applied to dc RSQUIDs. Our dc RSQUIDs can at least be operated down to 0.04 K. Between 0.14 and 5.9 K the measured noise temperature agrees with the temperature of calibrated reference thermometers. We investigate the errors and uncertainties of a dc RSQUID noise thermometer, in particular errors due to excess noise. A model for excess noise and its impact on the noise temperature is presented and shown to be in agreement with the measurements.

HTS SQUID application as a quantum roulette noise thermometer

We describe a cryogenic primary thermometer called the Quantum Roulette Noise Thermometer (QRNT), which is based on flux quantisation in a HTS superconducting ring. The basis of the QRNT is that the flux state of a double junction SQUID ring (in thermal contact with a heat bath whose temperature is to be measured) is allowed to evolve freely. The flux state is repeatedly interrogated to establish a probability distribution from which the absolute temperature may be derived. The QRNT is in principle dissipationless and has the potential to provide high accuracy with short measuring time. The QRNT prototype device which employs a YBCO thin film on an MgO bi-crystal substrate has been designed and fabricated. The superconducting ring of overall dimensions 6 mm/spl times/8 mm is broken by two grain boundary Josephson junctions of size 5 /spl mu/m/spl times/3 /spl mu/m. The state of the junctions is switched between superconducting and resistive by means of small currents applied to a superconducting strip line located near the junctions. A dc SQUID, which is used to read out the flux state of the QRNT ring, is operated at 77 K while the QRNT device can be set at any desired temperature above 10 K. Ongoing experimental measurements are described with reference to the expected theoretical predictions.

YBCO-noble metal resistors for HTS Josephson Noise Thermometry

Noise thermometry based on HTS Josephson devices has the potential to provide an absolute technique for the realisation of the temperature scale in the range 4 K-50 K. A resistor connected as a shunt across a YBCO grain boundary junction forms an HTS Josephson Noise Thermometer. We present experimental results and mathematical models for the resistivity of a noble metal film which connects two strips of superconducting YBCO. Accurate temperature measurement requires the resistor to be no more than 1/1000th of the intrinsic junction resistance. This sets an upper limit of 1 m /spl Omega/ for the value of the shunt resistor, including any contact resistance which exists between the metal and YBCO films. Essential aims are firstly to determine the lowest achievable contact resistivity, and secondly to demonstrate a very small variation with current of the contact resistance. A one dimensional model of the current transfer from superconducting to normal films has been used to define the necessary overlap length and also to investigate the possible influence of current dependent proximity effects at the interface. The model is compared with experimental behaviour of two designs of shunt resistance, one a simple rectangular patch configuration and the other a meander line.

The quantum roulette noise thermometer

A novel form of primary thermometer called the quantum roulette noise thermometer (QRNT), based on flux quantization in a high temperature superconducting (HTS) ring, interrupted by a Josephson junction, has been proposed. The basis of the QRNT is that the flux state of the ring is allowed to evolve freely, and is repeatedly interrogated to establish a probability distribution from which the temperature of the device is derived. Unlike other superconductivity-based noise thermometers, this device is essentially dissipationless, requires no input or output connections, and may be remotely interrogated. The QRNT has the potential to provide high accuracy with short measuring times. Prototype QRNT devices based on thin HTS films have been fabricated and results of initial experimental measurements are presented. Parameters of the experimental devices are compared with predictions of the theoretical model.

Detection of corruption in Gaussian processes with application to noise thermometry

Statistical tests are given for the detection of corruption in the Gaussian process underlying the measurement of temperature with a Johnson noise thermometer. Principles of hypothesis testing are discussed, with emphasis being placed on the importance of utilizing prior knowledge in the design of a powerful test. Tests are presented for corruption affecting the time signal and frequency spectrum as spikes or as localized deviations. Calculations of the statistical power of the tests are described, and example values given. The statistical power is sufficient for corruption at practical levels of interest to be detected with high probability.

QRNT: a primary thermometer based on an HTS SQUID

We propose a novel form of cryogenic primary thermometer based on flux quantisation in a HTS superconducting ring, interrupted by a Josephson junction which we call the Quantum Roulette Noise Thermometer (QRNT). Unlike other superconductivity-based noise thermometers this device is essentially dissipationless, requires no input or output connections and may be remotely interrogated. The QRNT has the potential to provide high accuracy with short measuring times.

The quantum roulette noise thermometer

Abstract We propose a novel form of cryogenic primary thermometer based on flux quantization in a HTS superconducting ring, interrupted by a Josephson junction which we call the quantum roulette noise thermometer (QRNT). The basis of the QRNT is that the flux state of a double junction SQUID ring (in thermal contact with a heat bath whose temperature is to be measured) is allowed to evolve freely. At regular intervals the (quantized) internal flux state of the ring is interrogated, allowing a probability distribution of flux states to be built up, from which the absolute temperature may be directly derived. Unlike other superconductivity-based noise thermometers this device is essentially dissipationless, requires no input or output connections and may be remotely interrogated. The QRNT has the potential to provide high accuracy with short measuring times. The novel principles behind the device are described and preliminary experimental data will be presented.

Shunted YBCO bi-crystal junctions for noise thermometry

Abstract We present experimental results on YBCO thin film bi-crystal junctions in which additional metallic shunt resistors are added by in-situ evaporation of gold or silver. These junctions are intended for use in the development of an HTS Josephson noise thermometer for primary temperature scale use. The temperature dependence of the critical current and effective shunt resistance are reported and the noise arising from the shunted junctions when biased into the finite voltage regime has been assessed as a function of frequency. This is compared with the predictions of a simple model and the implications for the potential accuracy of the proposed thermometer are considered.

The status of Johnson noise thermometry

Since Johnson's experimental observations of thermal noise in 1927, and Nyquist's explanation of the phenomenon shortly afterwards in 1928, thermal noise has attracted interest as a means of measuring temperature. The independence of the thermal noise from the material nature of the sensor makes it particularly attractive for metrological applications. However, the noise signals are extremely small and some ingenuity is required to make accurate measurements. This paper reviews the foundations of Johnson noise thermometry and the various techniques that have been employed to measure temperature via Johnson noise. Emphasis is placed on key developments in noise thermometers for metrological applications. The review includes the current activities of teams involved in noise thermometry research.