Variable Inductance Flux Bank for Superconducting Current Tuning
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Solution Overview
Problem
Current flux pumping techniques for superconducting devices are slow and imprecise due to the need for thermal-based quenching and recovery processes, which limit the speed and accuracy of current adjustments in persistent mode operations.
Innovation Solution
A tunable inductor, or 'flux bank,' is used to store and transfer flux within the superconducting circuit, allowing for rapid and precise adjustments of the magnet coil current without breaking the superconducting loop, using changes in inductance to shift flux between the main coil and the flux bank.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If flux pumping is used to adjust current in persistent mode, then current adjustment is achieved with minimal external power supply, but the adjustment speed is slow due to thermal-based quenching and recovery processes
Solution Approach 1:
The patent extracts the thermal quenching and recovery process from the current adjustment mechanism. By removing the persistent current switch (PCS) that requires thermal cycling, the system eliminates the slow thermal-based process while maintaining the ability to adjust current through alternative means such as flux injection or electronic control, thereby dramatically reducing adjustment time.
Solution Approach 2:
The patent replaces the thermal-based mechanical process (heating and cooling the PCS) with an electrical or magnetic control mechanism. Instead of using thermal energy to break and restore superconductivity, the system uses electrical flux injection or electronic switching that operates on much faster timescales, substituting a slow thermal-mechanical process with a rapid electrical control system.
2Reliability
If thermal-based quenching is used to break superconducting connections, then flux adjustment is achieved, but several watts of heating power are deposited into the cryostat
Solution Approach 1:
The patent removes the heater component and thermal quenching process from the system. By eliminating the PCS that requires heating to break superconductivity, the system avoids depositing several watts of heating power into the cryostat. Current adjustment is achieved through alternative methods that do not require thermal energy input.
Solution Approach 2:
The patent substitutes the thermal-based flux adjustment mechanism with an electrical or magnetic control system. Instead of using Joule heating to quench the superconductor, the system employs electrical flux injection or electronic switching that achieves the same flux adjustment capability without the energy-intensive thermal process, thereby eliminating wasteful heating power deposition.
3Reliability
If persistent current switch recovery process is used, then closed superconducting circuit is restored, but the process provides dynamic resistance that limits current setting accuracy
Solution Approach 1:
The patent extracts the persistent current switch (PCS) and its recovery process from the system. By removing the PCS entirely, the system eliminates the dynamic resistance that arises during the quench and recovery cycle. Current setting accuracy is improved because the alternative control mechanisms (flux injection or electronic control) do not introduce dynamic resistance variations during operation.
Solution Approach 2:
The patent replaces the thermal-based PCS recovery process with an electrical or magnetic control system that maintains stable resistance characteristics. The alternative mechanisms achieve circuit restoration and current adjustment without the dynamic resistance fluctuations that occur during thermal cycling, thereby enabling more precise current setting accuracy.
4Adaptability or versatility
If heater is turned on and off frequently for flux adjustment, then current tuning is achieved, but the thermal process is slow due to competing needs to heat up and re-cool quickly
Solution Approach 1:
The patent removes the heater component and thermal cycling process from the current tuning mechanism. By eliminating the need to repeatedly heat and cool the PCS, the system achieves current tuning through faster electrical or magnetic control methods, thereby resolving the speed limitation imposed by thermal response time.
Solution Approach 2:
The patent substitutes the slow thermal-based heater control system with a rapid electrical or magnetic control mechanism. Instead of relying on thermal diffusion and phase change that are inherently slow, the system uses electrical flux injection or electronic switching that responds on microsecond or nanosecond timescales, achieving the same current tuning capability with dramatically improved speed.
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
This approach enables 'on-the-fly' adjustments of the persistent current with high precision, potentially achieving 10^-9 to 10^-10 relative adjustments, suitable for applications like superconducting electron microscopes, and stabilizes currents against dissipation, offering faster and more accurate control compared to traditional methods.
Implementation Method 1
Flux can be transferred back and forth from this bank to the main coil by simply changing the inductance of the bank
Implementation Method 2
It is well known that closed superconducting circuits conserve flux linkage
Implementation Method 3
The heater is turned on and off to break and then re-close the superconducting loop
Implementation Method 4
the quenched segment is allowed to recover and the closed superconducting circuit is restored
Data Source
AI summary
An alternative approach to flux pumping in superconducting devices is described for fast and extremely precise tuning of the current during persistent mode operation. Rather than bringing in new flux from outside the circuit, the alternative approach stores a small flux in a tunable inductor (also referred to herein as a “flux bank”) at the initial point of powering. Flux can be transferred back and forth from this bank to the main coil by simply changing the inductance of the bank. This allows for fine and fast adjustments of the persistent current without the use of thermal switches found in other approaches (which limit the adjustment speed and accuracy).