Peripheral Cryopump Array Layout for Radiation Shielding and Gas Capture
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Solution Overview
Problem
Conventional cryopumps face a trade-off between high molecular conductance and effective radiation shielding, leading to increased radiation load on the second stage array, which affects the capture probability of gases like hydrogen and the frequency of regeneration cycles.
Innovation Solution
The cryopump design is modified by relocating the second stage array to the outer periphery of the radiation shield, increasing its surface area and using a cylindrical condensing cryopumping array to block direct radiation paths while maintaining high molecular conductance, and incorporating a raised surface to redirect molecules towards the adsorption surfaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the second stage array is positioned centrally within the radiation shield, then radiation shielding is effective, but molecular conductance is reduced and capture probability decreases
Solution Approach 1:
The second stage array is relocated from a central position to the outer periphery of the radiation shield, changing the spatial dimension of the pumping surfaces. This peripheral positioning allows molecules to access the array through the open central volume while the radiation shield continues to protect from radiant heat, simultaneously improving molecular conductance and maintaining radiation shielding effectiveness.
Solution Approach 2:
The cryopumping array is divided into two distinct stages with separate functions: the first stage frontal array handles Type I gases (water vapor) condensation, while the second stage peripheral array handles Type II and Type III gases. This segmentation allows each stage to be optimally positioned for its specific function, with the second stage at the periphery for high molecular conductance.
2Productivity
If the second stage array surface area is increased, then gas capture capacity improves, but radiation exposure increases
Solution Approach 1:
By positioning the second stage array at the outer periphery of the radiation shield rather than centrally, the design exploits the three-dimensional space more effectively. The array can extend along the peripheral surface, increasing its area while the radiation shield walls block direct radiation paths to the enlarged array surface.
3Reliability
If chevrons are used to protect adsorbent material, then regeneration frequency is reduced, but accessibility of non-condensables to adsorbent is decreased
Solution Approach 1:
The adsorbent material is positioned on the peripheral second stage array, creating an open central volume that allows non-condensable gases to access the adsorbent surfaces. This peripheral configuration eliminates the need for chevrons while maintaining adsorbent accessibility, as molecules can reach the adsorbent through the open central path.
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 achieves a hydrogen capture probability of over 20% with a significantly reduced radiation load to the second stage array, less than 5% of the total incident radiation, and minimizes contaminant exposure, enhancing the overall efficiency and longevity of the cryopump.
Implementation Method 1
A radiation shield has sides, a closed end and a frontal opening opposite to the closed end. The radiation shield is thermally coupled to and cooled by the cold stage.
Implementation Method 2
high boiling point gases such as water vapor are condensed on the cold frontal array
Implementation Method 3
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 4
A condensing cryopumping array extends along the primary cryopumping array. The condensing cryopumping array shields the primary cryopumping array from radiation passing through the frontal opening of the radiation shield.
Data Source
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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.