Description:
There is great potential for improved thermometry and new applications with the development of a scalable primary thermometer that can replace the ITS-90 temperature scale, which consists of fixed point artifact standards. A very promising approach is a purely electronic temperature standard that exploits Johnson noise thermometry (JNT) and a quantum voltage noise source (QVNS) based on pulse-driven Josephson junctions made with high-temperature superconductors (HTS). This novel primary thermometer will enable a new paradigm for disseminating temperature that will be independent of artifact standards for the first time. Any national, military, or corporate metrology laboratory could then possess and operate a single primary thermodynamic temperature standard, including the triple point of water, and be able to calibrate a wide range of secondary thermometers over the range from ~230 K to 1300 K. This would essentially replace ten defined “artifact standard” fixed points based on the phase-change states of ten different materials. Additionally, the perfect scalability of the HTS JNT would eliminate the use of complex mathematical interpolation for measurement of temperatures between these points.
In addition to creating the world’s first quantum-accurate primary thermometry, development of an HTS JNT would also enable improved accuracy in industrial point-of-use applications. These include embedded sensors in extreme environments like nuclear or industrial furnaces, where installed probes can continue to be used in place with only an in-situ resistance measurement, which reduces down time and improves process control (as opposed to artifact probes require periodic replacement). Successful execution of this project will lead to practical application of the first temperature metrology systems incorporating quantum-based voltage synthesizers, elimination of many levels of the temperature calibration chain, and placement with immediate users of the world’s first intrinsically accurate, scalable, primary thermodynamic thermometer.
National Measurement Institutes (NMIs) and corporate metrology labs maintain the international temperature scale (ITS-90) with a series of fixed points and Standard Platinum Resistance Thermometers (SPRTs). Operating all of these artifact standards is complicated, labor intensive, and requires a large amount of both capital equipment and floor space. Calibrating temperatures between the fixed points requires interpolation, which increases uncertainty. A quantum-based electronic primary thermometer is intrinsically linear and programmable. As a single standard it can replace all of these instruments and it can also measure arbitrary temperatures, not just the fixed points, enabling application-specific calibration protocols. NIST currently leads the world in Johnson noise thermometry with a research system designed to measure Boltzmann’s constant using a 4 K quantum voltage noise source (QVNS) chip made of niobium-based junctions and custom-built bias and measurement electronics.
The subtopic goal is to replace the current QVNS chip operating at 4 K in a liquid helium dewar with a HTS QVNS on a compact, closed-cycle cryocooler (smaller than a liter). A successful development under this project could mean direct transition through conversion of the research JNT system into an automated programmable primary standard that can be operated by non-experts.
The goal can be met through the following approach:
1) Develop a compact, closed-cycle system operating at 77 K that requires less than 100 W, preferably using a commercially available cryocooler. This system should be capable of providing DC and RF connections to the chip for proper operation. The electrical connections must be optimized to minimize electrical loss and minimize the thermal impact on the chip. The system will need the development of chip packaging and a cryostat microwave design for 30 GHz pulse-drive bias.
2) Develop a HTS QVNS chip that synthesizes accurate voltage waveforms at a temperature of 77 K. This will require the design, fabrication, and testing of the chip. As few as 4 junctions are required for this device, so several possible junction fabrication methods could be used.
Phase I expected results:
The Phase I goal would be a complete system design for a compact closed-cycle system and the design and fabrication of a HTS QVNS chip.
Phase II expected results:
The Phase II goal would be to build a laboratory demonstration of a complete system with a working HTS QVNS chip.
NIST staff may be available to participate in discussions and provide input on the awardee’s design during the development process through email, teleconference or face-to-face visits. NIST may also be available to do testing, although the awardee will not be able to count this testing towards the testing requirements of Phase II. NIST scientists may be available for demonstration of the device at the awardee’s home site, if desired.
