Cryocooler Assembly for Intermediate Temperature Heat Extraction
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Solution Overview
Problem
Current MRI scanner systems have high energy consumption and inefficient cooling methods, leading to a significant environmental impact and prolonged cooldown times due to the reliance on cryocoolers operating at low temperatures to maintain superconducting magnets at 4K, while also facing challenges with unshielded gradient coils increasing heat loads on the magnet system.
Innovation Solution
A cryogen-cooled superconducting magnet assembly that focuses on intermediate temperature cooling stages between 80K and 285K, using a cryocooler assembly to efficiently remove heat from the superconducting magnet assembly by extracting thermal energy induced by gradient coils at higher temperatures, reducing power consumption and cooldown times, and incorporating multiple cascaded cold-heads and cryoshields to optimize cooling efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a cryocooler operates at low temperatures (4K) to maintain superconducting magnets, then the superconducting coils can be maintained at required temperatures, but the power consumption is high (about 7 kW) and cooling efficiency is low
Solution Approach 1:
The patent divides the cooling system into multiple independent cold-head units, each responsible for specific temperature zones. Instead of one large cryocooler operating at 4K, multiple smaller cold-heads operate at different temperature levels (including intermediate temperatures like 80K-120K), reducing the total power consumption while maintaining the required 4K temperature for superconducting coils.
Solution Approach 2:
The patent introduces intermediate temperature shields (at 80K-120K) between the room temperature environment and the 4K superconducting coils. These intermediate shields act as thermal barriers that reduce the heat load reaching the coldest zone, allowing the cryocooling system to operate more efficiently with lower power consumption.
2Power
If gradient coils operate at high power and high frequency to generate dynamic magnetic fields, then the MRI imaging function is enabled, but thermal energy is deposited into the superconducting coils through thermal radiation, mechanical vibrations, and electromagnetic induction
Solution Approach 1:
The patent introduces intermediate temperature shields positioned between the gradient coils and the superconducting magnet system. These shields at 80K-120K act as thermal barriers that intercept thermal radiation from the gradient coils before it reaches the 4K superconducting coils, reducing the thermal load and allowing higher gradient coil power operation.
Solution Approach 2:
The patent extracts and isolates the thermal management function by separating the gradient coil system from the superconducting magnet system using intermediate shields. This extraction creates a thermal buffer zone that protects the sensitive superconducting coils from the harmful thermal effects generated by high-power gradient coil operation.
3Temperature
If a thermal shield completely surrounds the superconducting coils at 50K to reduce heat load, then the cooling reserve is limited, but the system requires continuous operation of the cryocooler 24 h a day
Solution Approach 1:
The patent segments the thermal shielding into multiple layers at different temperature levels rather than a single shield at 50K. This multi-layer approach creates better thermal isolation, reducing the heat load on the superconducting coils and allowing the cryocooler to operate more efficiently with reduced continuous operation requirements.
Solution Approach 2:
The patent changes the temperature parameters of the thermal shields from a single 50K level to multiple levels including 80K-120K intermediate shields. This parameter change optimizes the thermal gradient across shielding layers, improving the overall thermal isolation effectiveness and reducing the cooling demand.
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 significantly reduces the power consumption and environmental footprint of MRI scanners, enhances cooling efficiency, and shortens the cooldown time of superconducting magnets by focusing on intermediate temperature cooling, achieving a higher coefficient of performance and minimizing thermal loads on the magnet system.
Implementation Method 1
a cryocooler assembly for removing heat from the superconducting magnet assembly. The cryocooler assembly is configured for extracting heat at intermediate temperatures, namely at temperatures between 80K and 285K
Implementation Method 2
by a thermal path, wherein the gradient coil system is heated up by the high currents. The thermal energy is radiated to the outer vacuum enclosure (OVC) of the superconducting magnet system
Implementation Method 3
The thermal energy is radiated to the outer vacuum enclosure (OVC) of the superconducting magnet system and may penetrate the thermal shield down to the SC coils
Implementation Method 4
the gradient coils strongly vibrate when they are driven by high intensity current pulses due to the Lorentz forces within the strong static magnet field B0
Implementation Method 5
The mechanical vibrations induce eddy currents into the electrically conducting OVC, which in turn induces eddy currents and vibrations into the next conducting layer
Implementation Method 6
the fast-changing stray fields from the gradient coils may penetrate through electrically conductive layers up to the superconducting coils. These fast-changing electromagnetic fields induce eddy currents into any conductive layer with associated ohmic losses
Implementation Method 7
These fast-changing electromagnetic fields induce eddy currents into any conductive layer with associated ohmic losses and thereby increase the thermal load on the superconducting magnet system
Implementation Method 8
The cryocooler cold-head removes boiled-off helium from the liquid helium vessel and condenses the helium gas back to liquid helium
Implementation Method 9
a cryocooler cold-head externally mounted to the outer vacuum enclosure, having its first stage in thermal contact with the thermal shield, and having its second stage in thermal contact with the superconducting main coil
Data Source
Figure 1
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Figure 3~4
AI summary
The invention relates to a cryogen-cooled superconducting magnet assembly (1) for a magnetic resonance imaging scanner, comprising a cryogen container (8) containing a cryogen for providing a cryogenic temperature to a superconducting coil system, at least one cryoshield surrounding the cryogen container (8), an outer vacuum enclosure (6) surrounding the at least one cryoshield, a cryocooler assembly for removing heat from the superconducting magnet assembly (1), characterized in that the cryocooler assembly is configured for extracting heat from a part of the superconducting magnet assembly (1) which is maintained at an intermediate temperature, namely at a temperature between 80K and 285K, preferably between 100K and 273.13K, more preferred between 120K and 200K.