Variable Cross-Section Current Leads for Cryostat Heat Management
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Solution Overview
Problem
Superconducting magnet coil systems require high cooling power during charging due to ohmic heat generation in current leads, leading to increased production and maintenance costs, as well as excessive helium consumption, which is not utilized efficiently during normal operation.
Innovation Solution
The current leads have a variable cross-sectional area that decreases from the cold end to the warm end, reducing ohmic resistance and heat introduction, with multiple cold reservoirs thermally coupled along their length to manage heat development and introduction effectively, allowing for reduced cooling power usage during charging and operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the active cooling device is dimensioned sufficiently large to compensate for the thermal load during charging, then the magnet coil system can be charged without excessive temperature increase, but the production costs, maintenance costs, and structural size increase significantly
Solution Approach 1:
The current lead is divided into multiple sections with different cross-sectional areas along its length. The cross-sectional area varies continuously or in steps, creating multiple segments that optimize heat dissipation at different locations. This segmentation allows the cooling system to be much smaller because each segment handles only the local thermal load rather than requiring a single oversized cooling device for the entire system.
Solution Approach 2:
Different sections of the current lead are given different cross-sectional areas tailored to the local thermal conditions. The cross-sectional area is larger where heat generation is higher and smaller where heat generation is lower. This local optimization of the current lead geometry reduces the overall thermal load on the cooling device, enabling a more compact and cost-effective cooling system.
2Reliability
If the active cooling device is dimensioned for peak charging load, then quenching is prevented during charging, but the cooling device is not utilized to capacity during normal operation which lasts weeks or months
Solution Approach 1:
The current lead's cross-sectional area is designed to dynamically adapt to varying operational conditions through its variable geometry. During charging when thermal load is high, the larger cross-sectional areas provide adequate heat dissipation. During normal operation when thermal load is low, the smaller cross-sectional areas suffice. This dynamic geometric design allows a single cooling device to handle both peak and steady-state conditions efficiently, improving utilization without compromising safety.
3Ease of manufacture
If current leads with constant cross-sectional area are used, then the design is simpler, but the ohmic heat generation and thermal load on the cooling device is higher
Solution Approach 1:
The cross-sectional area parameter of the current lead is changed along its length to optimize performance. Rather than maintaining a constant cross-sectional area, the parameter varies continuously or in discrete steps to match the thermal and electrical requirements at different locations. This parameter optimization reduces ohmic losses and thermal load while remaining manufacturable through techniques like extrusion or welding of segmented sections.
4Temperature
If liquid helium is used to cool the current leads during charging by accepting higher coolant consumption, then the thermal load is managed, but high costs are incurred
Solution Approach 1:
The current lead is designed to dissipate heat primarily through conduction to the cryostat walls and the cooling device, rather than relying on high consumption of liquid helium for active cooling. The variable cross-sectional area geometry enables the current lead to self-regulate its thermal profile, with larger areas providing lower thermal resistance where needed. This self-service approach reduces dependence on expensive liquid helium consumption while maintaining effective temperature control.
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 design minimizes cooling power requirements during charging and normal operation, reducing the risk of quenching and lowering operating costs by optimizing heat management in the magnet coil system, enabling the use of cost-effective and compact active cooling devices.
Implementation Method 1
multiple cold reservoirs are thermally coupled to the current leads along the normal-conducting region of the current leads, in order to absorb heat arising in the normal-conducting region during the charging of the magnet coil system
Implementation Method 2
multiple cold reservoirs are thermally coupled to the current leads along the normal-conducting region
Implementation Method 3
The superconducting magnet coil systems can carry large electric currents without loss, using which the strong magnetic fields are generated
Implementation Method 4
During the charging, electric current flows through the current leads, which generates ohmic heat in the normal-conducting region
Implementation Method 5
The current leads have a variable cross-sectional area that decreases from the cold end to the warm end, reducing ohmic resistance and heat introduction
Data Source
AI summary
A magnet assembly (1) with a cryostat (2) has a superconducting magnet coil system (3), an active cooling device (4) for the coil system, and current leads (5a, 5b) for charging the coil system. The current leads have at least one normal-conducting region (15a, 15b), wherein multiple cold reservoirs (20) are thermally coupled to the current leads along the normal-conducting region thereof, in order to absorb heat the normal-conducting region during charging of the magnet coil system. The current leads have a variable cross-sectional area B in the normal-conducting region along the extension direction thereof, wherein at least over a predominant fraction of their overall length in the normal-conducting region, the cross-sectional area B decreases from a cold end (18a, 18b) toward a warm end (19a, 19b). This provides a magnet assembly requiring reduced cooling power during charging, with less heat introduced into the magnet coil system in normal operation.