Cryopump Frontal Array Positioning to Reduce Radiation Loading
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Solution Overview
Problem
Conventional cryopump designs face a trade-off between high gas conductance and low radiation loading on the second stage array, with existing solutions either increasing radiation load or reducing gas capture efficiency.
Innovation Solution
The proposed cryopump configuration features a frontal array thermally coupled to the cold stage, positioned deeper inside the pump and shaped to mimic the second stage array, with a domed design and louvers that focus gas conductance while minimizing radiation loading on the second stage array, allowing for improved thermal conductance and reduced radiation exposure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a conventional frontal array is positioned at the opening of the radiation shield, then gas conductance is improved, but radiation loading on the second stage array increases
Solution Approach 1:
The frontal array is repositioned from the conventional location at the radiation shield opening to a deeper position inside the pump chamber. This spatial repositioning in the third dimension allows the array to be surrounded by the radiation shield on multiple sides, effectively blocking radiation paths while preserving gas conductance pathways to the second stage array.
Solution Approach 2:
The frontal array is nested within the radiation shield structure, positioned deeper inside the pump chamber rather than at the outer opening. This nested configuration allows the radiation shield to envelop the frontal array from multiple directions, providing radiation protection while maintaining access for gas molecules to reach the pumping surfaces.
2Object-affected harmful factors
If the frontal array is positioned deeper inside the pump, then radiation loading is reduced, but gas conductance may be reduced
Solution Approach 1:
The radiation shield provides differential protection: it blocks radiation from reaching the frontal array and second stage array from the opening direction, while allowing gas molecules to conductance to the pumping surfaces. The shield's thermal and structural properties are optimized to differentiate between radiation blocking and gas conductance permitting functions at different locations.
Solution Approach 2:
The pumping chamber is segmented into distinct zones: the frontal array region deeper inside the pump, the radiation shield region providing protection, and the second stage array region. This segmentation allows each component to be optimized for its specific function while maintaining overall system performance for both radiation protection and gas conductance.
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 achieves a hydrogen capture probability of at least 20% with a radiation load of less than 3%, preferably less than 2%, and more preferably below 1%, while maintaining high gas conductance and reducing contamination and radiation exposure on the second stage array.
Implementation Method 1
A radiation shield having sides, a closed end and a frontal opening opposite to the closed end is thermally coupled to and cooled by the cold stage
Implementation Method 2
The primary cryopumping array thermally coupled to and cooled by the colder stage supports adsorbent material
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
high boiling point gases such as water vapor are condensed on the cold frontal array. Lower boiling point gases pass through the frontal array
Data Source
AI summary
A cryopump has a cryogenic refrigerator with cold and colder stages that cool a radiation shield, a primary cryopumping array and a frontal array. The frontal array is coupled to the cold stage and is spaced from and wrapped around the frontally facing envelope of the primary cryopumping array. The frontal array may be recessed from the frontal opening and closer to the primary cryopumping array than to the frontal opening.