Cryopump with peripheral first and second stage arrays
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Solution Overview
Problem
Conventional cryopumps face a trade-off between high molecular conductance and radiation shielding, resulting in either low capture rates of gases like hydrogen or excessive radiation loading on the second stage array, which affects the efficiency and longevity of the cryopump.
Innovation Solution
The cryopump design is modified by relocating the second stage array to the outer periphery of the radiation shield and using a cylindrical condensing cryopumping array with baffles to increase surface area and redirect molecules, while minimizing radiation exposure to the second stage array through a raised surface at the radiation shield's closed end.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a conventional cryopump design with a central second stage array is used, then radiation shielding is provided, but hydrogen capture rate is limited
Solution Approach 1:
The patent transitions from a conventional central second stage array configuration to a peripheral array configuration that extends along the radiation shield sides. This dimensional repositioning increases the surface area available for hydrogen capture while the raised surface at the closed end redirects radiation away from the second stage array, simultaneously improving capture rate and reducing radiation loading.
Solution Approach 2:
The cryopumping array is divided into distinct functional zones: a condensing cryopumping array at the periphery for hydrogen capture and a central volume that is substantially free of cryopumping surfaces for radiation shielding. This segmentation allows each zone to optimize its specific function without interfering with the other.
2Area of stationary object
If the second stage array is positioned centrally within the radiation shield, then radiation shielding is effective, but the surface area for gas capture is reduced
Solution Approach 1:
The second stage array is relocated from the central position to the periphery of the radiation shield, extending along the sides. This positional change in another dimension (from center to perimeter) maximizes the available surface area while the raised surface at the closed end redirects radiation away from this expanded array surface.
Solution Approach 2:
The raised surface at the closed end of the radiation shield acts as an intermediary element that redirects radiation away from the peripheral second stage array. This mediator structure prevents direct radiation exposure to the expanded cryopumping surface area.
3Speed
If a frontal array is used to shield radiation, then radiation protection is provided, but molecular conductance and capture rate are reduced
Solution Approach 1:
The radiation shielding function is moved from a frontal array configuration to a raised surface at the closed end configuration. This dimensional change allows molecules to pass through the central volume with high conductance while the raised surface redirects radiation away from the peripheral second stage array in a different spatial direction.
Solution Approach 2:
The radiation shielding function is extracted from the frontal opening area and relocated to the closed end of the radiation shield. This extraction allows the frontal opening to remain open for maximum molecular conductance while the raised surface at the closed end provides the necessary radiation protection.
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 hydrogen capture rates by up to four times the surface area, achieving a hydrogen pumping speed of over 15,000 liters per second with a radiation load reduced to less than 5% and contaminant exposure minimized to less than 1%, thereby improving overall cryopump efficiency and reducing regeneration frequency.
Implementation Method 1
The radiation shield is thermally coupled to and cooled by the cold stage
Implementation Method 2
inner surfaces of the second stage array may be coated with an adsorbent such as charcoal, zeolite or a molecular sieve. Adsorption is a process whereby gases are physically captured by a material held at cryogenic temperatures
Implementation Method 3
high boiling point gases such as water vapor are condensed on the cold frontal array
Data Source
AI summary
In a cryopump, a primary cryopumping array having adsorbent and cooled by a second refrigerator stage extends along radiation shield sides. That array is shielded by a condensing cryopumping array that extends along the primary cryopumping array. The primary cryopumping array may be a cylinder with adsorbent on an inwardly facing surface, and the condensing cryopumping array may comprise an array of baffles having surfaces facing the frontal opening. A raised surface such as a conical surface at the base of the radiation shield redirects molecules received from the frontal opening toward the primary cryopumping array. The refrigerator cold finger may extend tangentially relative to the radiation shield or connect to the base of the radiation shield.