External Dump Resistor Quench Protection for MRI Magnets
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Solution Overview
Problem
Superconducting magnet assemblies in MRI systems face significant challenges during quenching events, leading to undesirable voltage and temperature fluctuations, potential component damage, and substantial cryogen loss, resulting in extensive downtime and increased costs due to the need for re-cooling and re-ramping.
Innovation Solution
A superconducting magnet assembly with an external dump resistor and a quench protection controller that detects quench onset conditions and rapidly disconnects the magnet coil from the power supply, diverting energy to the external dump resistor to mitigate quenching without significant cryogen loss or system downtime.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional quench protection is used without external dump resistor, then the magnet assembly is simpler and cheaper, but quenching causes substantial cryogen loss, component damage, and extensive downtime
Solution Approach 1:
The harmful electromagnetic energy during quench is extracted from the magnet assembly by diverting it to an external dump resistor. This separates the energy dissipation function from the magnet assembly itself, protecting the cryogen and components while allowing the magnet to be trained more aggressively.
Solution Approach 2:
An external dump resistor serves as an intermediary component that safely absorbs the electromagnetic energy during quench events. This mediator prevents direct damage to the magnet assembly and cryogen while enabling more aggressive training protocols.
2Ease of manufacture
If magnet operates closer to critical current for more aggressive design, then cost is reduced and performance is improved, but quenching risk increases causing damage and downtime
Solution Approach 1:
The external dump resistor provides beforehand cushioning by being pre-positioned to absorb quench energy. This protective measure in place allows the magnet to be operated closer to critical current during training, knowing that quench energy will be safely dissipated externally rather than causing damage.
Solution Approach 2:
The harmful quench energy that would normally cause damage is converted into a beneficial protective mechanism by directing it to the external dump resistor. This allows aggressive training near critical current to proceed safely, as the quench events become controlled energy dissipation events rather than damaging failures.
3Loss of substance
If quench protection system is added to prevent cryogen loss, then cryogen retention is improved, but system complexity and cost increase
Solution Approach 1:
The energy dissipation function is extracted from the magnet assembly and placed in an external dump resistor. This prevents the need for complex internal protection systems while effectively preventing cryogen loss by avoiding rapid temperature rises that would cause boil-off.
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 solution effectively protects the magnet assembly from quenching events, reducing cryogen loss and downtime, allowing for more aggressive magnet design closer to critical current operation, thereby lowering costs and improving system reliability.
Implementation Method 1
the electromagnetic energy of the magnet must either be quickly dumped or converted into thermal energy
Implementation Method 2
the resistance of the wires is essentially zero. A power source may be connected to the coils for a period of time to ramp the current up or down through the coils, and the lack of electrical resistance in the coils enables current to continue to flow therethrough after the power source has been disconnected from the coils
Data Source
AI summary
A superconducting magnet assembly comprising a plurality of superconducting magnet coil portions forming a coil series circuit to provide a magnetic field, a power supply to supply power to the plurality of superconducting magnet coil portions during a magnet ramp mode of operation, and a ramp switch coupled to the superconducting magnet coil portions, wherein the ramp switch is configured to be open during a magnet ramp mode and closed during a persistent mode. A dump resistor is disposed externally to the vessel and is connectable by the ramp switch to the superconducting magnet coil portions. Further, a controller is coupled to at least one superconducting magnet coil portion and the ramp switch and is configured to detect a quench onset condition in the at least one superconducting magnet coil portion and to open the ramp switch upon detection of the quench onset condition in order to dump magnet energy.