Superconducting Bulk Magnet Charging for Active Stray Field Shielding
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Solution Overview
Problem
Superconductor bulk magnet systems generate unwanted stray magnetic fields, which can interfere with nearby electrical equipment and pose safety risks, and existing shielding methods using ferromagnetic materials are heavy and space-consuming.
Innovation Solution
A method involving a superconductor magnet system with a main bulk magnet and a shield bulk magnet, where the shield magnet is thermally decoupled and charged with a persistent current of opposite polarity to cancel out the stray field, using a cryostat system with different temperature control for each magnet to achieve active shielding without the need for heavy ferromagnetic materials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If ferromagnetic shielding material is used to reduce stray fields, then stray field reduction is improved, but weight and space consumption increase
Solution Approach 1:
The patent changes the fundamental parameter of shielding material from ferromagnetic to superconducting material. Superconductors exhibit perfect diamagnetism (Meissner effect) below their critical temperature, providing stray field reduction without the weight and space constraints of ferromagnetic materials. The superconducting bulk magnet is cooled below its critical temperature to achieve this shielding effect.
Solution Approach 2:
The patent employs a composite structure combining superconducting material with cryogenic cooling infrastructure. The superconducting bulk magnet serves dual purposes: generating the primary magnetic field and providing stray field shielding through its superconducting properties when cooled below Tcrit. This composite approach eliminates the need for separate ferromagnetic shielding components.
2Object-affected harmful factors
If ferromagnetic shielding material is used to reduce stray fields, then stray field reduction is improved, but space consumption increases
Solution Approach 1:
The patent transitions from ferromagnetic shielding to superconducting shielding, utilizing the Meissner effect in superconductors. This parameter change allows for more efficient space utilization as superconducting materials provide effective stray field reduction with smaller volumes compared to bulky ferromagnetic shielding structures.
Solution Approach 2:
The superconducting bulk magnet performs multiple functions: generating the primary magnetic field for NMR applications and simultaneously providing stray field shielding. This multi-functionality eliminates the need for separate shielding structures, optimizing space utilization in the system design.
3Object-affected harmful factors
If a shield superconductor bulk magnet is added to reduce stray fields, then stray field reduction is improved, but device complexity increases
Solution Approach 1:
The patent merges the shielding function with the primary magnet structure by using a superconducting bulk magnet that serves both purposes. The shield superconductor bulk magnet is integrated into the same cryogenic environment and cooling system as the main magnet, combining multiple functions into a unified system rather than adding separate shielding components.
Solution Approach 2:
The shield superconductor bulk magnet is positioned concentrically around the main superconductor bulk magnet, creating a nested configuration. Both magnets share the same cryostat and cooling infrastructure, with the shield magnet effectively nested within the same thermal and structural envelope, minimizing additional system complexity.
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 method effectively reduces stray fields by using a smaller, lighter shield magnet, providing efficient active shielding while maintaining a stable magnetic field for applications like NMR measurements, without the bulk and weight of traditional ferromagnetic shielding.
Implementation Method 1
superconducting electric currents are induced within the superconductor bulk magnet, opposing the change of magnetic flux, and as a result trapping (or conserving) the magnetic flux
Implementation Method 2
The superconducting state of a superconductor is only assumed below a critical temperature T crit , which is in the cryogenic range
Implementation Method 3
the temperature within the cryostat is lowered below T crit , so that the superconductor bulk magnet becomes superconducting
Implementation Method 4
superconducting electric currents are induced within the superconductor bulk magnet, opposing the change of magnetic flux, and as a result trapping (or conserving) the magnetic flux within a superconductor bore
Implementation Method 5
In order to reduce the stray field, it is known to surround the superconductor bulk magnet with ferromagnetic material
Data Source
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AI summary
The invention relates to a method for charging a superconductor magnet system (3) comprising coaxially a main superconductor bulk magnet (10) and a shield superconductor bulk magnet (11), the method comprising the following steps: step a) arranging the superconductor magnet system (3) at least partially within a charger bore (6) of a charger magnet (2), step b) with Tmain > Tmaincrit and Tshield > Tshieldcrit , applying an electrical current Icharger to the charger magnet (2) and increasing Icharger to a first current I1>0, step c) lowering Tmain to or below an operation temperature Tmainop of the main superconductor bulk magnet (10), with Tmainop< Tmaincrit, while keeping Tshield > Tshieldcrit; step d) lowering Icharger to a second current I2<0, wherein a main persistent current IPmain is induced in the main superconductor bulk magnet (10); step e) lowering Tshield to or below an operation temperature Tshieldop of the shield superconductor bulk magnet (11), with Tshieldop< Tshieldcrit; step f) increasing Icharger to zero, wherein a shield persistent current IPshield is induced in the shield superconductor bulk magnet (11); step g) removing the superconductor magnet system (3) from the charger bore (6) of the charger magnet (2), and keeping Tmain at or below Tmainop with Tmainop<Tmaincrit as well as Tshield at or below Tshieldop with Tshieldop<Tshieldcrit; with Tmain: temperature of the main superconductor bulk magnet (10); Tmaincrit: critical temperature of the main superconductor bulk magnet (10); Tshield: temperature of the shield superconductor bulk magnet (11); and TShieldcrit: critical temperature of the shield superconductor bulk magnet (11). The invention allows to reduce the stray field of the superconductor magnet system, wherein less weight and space is required for shielding purposes.