Current Sensing Noise Thermometer With Superconducting Thermal Breaks
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Solution Overview
Problem
Conventional current sensing noise thermometers suffer from parasitic heat leaks that limit their speed and bandwidth, especially at very low temperatures, leading to long measurement times and reduced accuracy.
Innovation Solution
A current sensing noise thermometer design featuring a sensor resistor thermally coupled to a target, superconducting thermal breaks with low thermal conductance, and a superconducting flux sensor, forming a loop inductively coupled to a flux sensor, with a midpoint connection and noise filter to minimize heat input and maximize bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional current sensing noise thermometer is used, then temperature measurement capability is achieved, but parasitic heat leaks limit bandwidth and increase measurement time
Solution Approach 1:
The patent changes the thermal conductance parameter of the connection between the sensor resistor and the heat sink from conventional values to ultra-low values (below 10^-10 W/K), achieved through superconducting thermal breaks. This parameter change reduces parasitic heat leaks by more than an order of magnitude, enabling faster thermal response and increasing bandwidth to above 1 Hz, thereby reducing measurement time while maintaining temperature measurement capability
Solution Approach 2:
The patent employs composite material structures combining superconducting materials (for electrical conduction with zero resistance) and materials with extremely low thermal conductance (for thermal isolation). This composite approach allows the sensor resistor to be electrically connected to the readout circuit while thermally isolated from heat sources, resolving the contradiction between achieving sufficient signal level and minimizing parasitic heating that limits measurement speed
2Temperature
If low resistance value sensor is used to reduce temperature gradient, then acceptable temperature gradient is achieved, but bandwidth is reduced and measurement time increases
Solution Approach 1:
The patent changes the thermal conductance parameter of the sensor support structure to ultra-low values, allowing the use of higher resistance sensor resistors (in the ohm range) without creating excessive temperature gradients. This parameter change decouples the traditional trade-off between resistance value, temperature gradient, and bandwidth, enabling high bandwidth (>1 Hz) measurements with practical resistance values
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The design achieves ultra-low heat leaks, enabling fast and precise temperature measurements with increased bandwidth, allowing for measurements in high magnetic fields and reducing measurement times to seconds, suitable for quantum technology applications.
Implementation Method 1
superconducting thermal breaks between respective ends of the sensor resistor and respective ends of the superconducting coil
Implementation Method 2
the superconducting thermal breaks SC 0, SC 1 having a thermal conductance less than or equal to 10 nW/K
Implementation Method 3
Temperature measurements are made by measurement of the noise current density
Implementation Method 4
calibrated based on the known temperature at the point where a change in inductance of the coil due to the Meisner effect is observed
Implementation Method 5
the sensor resistor, superconducting coil and superconducting thermal breaks form a loop inductively coupled to the flux sensor
Data Source
Figure 1~3
Figure 4
AI summary
A current sensing noise thermometer comprising: a sensor resistor thermally coupled to a target to be measured; a superconducting coil; superconducting thermal breaks between respective ends of the sensor resistor and respective ends of the superconducting coil; and a superconducting flux sensor; wherein the sensor resistor, superconducting coil and superconducting thermal breaks form a loop inductively coupled to the superconducting flux sensor. There may be a noise filter between the sensor resistor and the superconducting coil.