Multi-Refrigerator Cryopump Design for High Thermal Load Management
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Solution Overview
Problem
Conventional cryopumps face limitations in size due to thermal load constraints, leading to reduced pumping speed and increased weight and cost, as they rely on single refrigerators that struggle to manage high thermal loads efficiently across large surfaces.
Innovation Solution
The implementation of a dual-refrigerator system, where a single-stage and a two-stage refrigerator are thermally coupled via a base plate with a thermal choke, allowing for controlled heat flux and uniform temperature distribution across the frontal array, thereby optimizing refrigeration capacity and reducing weight.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a single refrigerator is used to cool the radiation shield and primary pumping surface, then the device complexity is reduced, but the refrigeration capability is insufficient to handle high thermal loads on large surfaces
Solution Approach 1:
The radiation shield is divided into multiple zones (first region and second region) with different thermal requirements. The first region is thermally coupled to the first stage heat sink, while the second region is thermally coupled to the second stage heat sink. This segmentation allows each refrigerator stage to handle specific thermal loads independently, increasing overall refrigeration capability without requiring a single oversized refrigerator system.
2Temperature
If high conductivity materials such as copper are used in the radiation shields to reduce temperature differential, then the temperature uniformity is improved, but the weight and cost increase
Solution Approach 1:
Different regions of the radiation shield are assigned different thermal conductance characteristics. The first region has higher thermal conductance to the first stage heat sink, while the second region has lower thermal conductance to the second stage heat sink. This local differentiation allows temperature uniformity to be maintained through strategic thermal coupling rather than using high-conductivity materials throughout the entire structure, thereby reducing weight.
3Temperature
If the cross sectional area of the radiation shielding is increased to increase thermal conductance, then the temperature differential is reduced, but the cool down time and regeneration time increase
Solution Approach 1:
The radiation shield is segmented into multiple thermally coupled regions that connect to different refrigerator stages. This segmentation creates multiple parallel thermal pathways, increasing overall thermal conductance without requiring a single large cross-sectional area. The distributed thermal coupling reduces the effective thermal resistance while maintaining a compact structure that cools down quickly.
4Power
If the temperature differential across the thermal path is reduced to allow higher operating temperature of the first stage heat sink, then the cryocooler can accept higher heat load, but the thermal path length must be reduced
Solution Approach 1:
Instead of reducing the length of a single thermal path, the system adds a dimensional aspect by introducing multiple thermal paths at different stages. The first region connects to the first stage heat sink while the second region connects to the second stage heat sink, creating a multi-dimensional thermal management architecture. This allows the system to handle higher heat loads by distributing thermal pathways across multiple spatial and thermal dimensions.
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 configuration enhances refrigeration capability, maintains uniform frost growth, and increases mechanical rigidity, allowing for larger cryopumps with improved pumping speed and reduced weight, while optimizing the use of available refrigeration resources.
Implementation Method 1
a thermal coupling between the first stage heat sink and the second stage heat sink
Implementation Method 2
a cryogenically cooled radiation shield surrounds the primary pumping surface and provides radiation shielding
Implementation Method 3
The utility of the cryopumps is to create a contaminant-free vacuum by freezing or adsorbing gases from a work environment
Implementation Method 4
an adsorbent, such as activated carbon, is placed on portions of these primary pumping surfaces to adsorb gases
Data Source
AI summary
A refrigerator system or cryopump includes a first refrigerator having at least first and second stages, and a second refrigerator. A thermal coupling between the first stage of the first refrigerator and a cold end of the second refrigerator is restricted to maintain a temperature difference between the cold end of the second refrigerator and the first stage of the first refrigerator. The refrigerator system or cryopump also includes a radiation shield in thermal contact with the cold end of the second refrigerator, and a condensing surface, spaced from and surrounded by the radiation shield, and in thermal contact with a second stage, e.g., coldest stage, of the first refrigerator. The restricted thermal coupling can be configured to balance the cooling load on the two refrigerators.