Cryopump First-Stage Array Layout for Gas Shielding and Conductance
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Solution Overview
Problem
Cryopumps face challenges in maintaining high conductance for type II and type III gases while effectively shielding the second stage surfaces from type I gases and thermal radiation, leading to reduced pumping performance due to saturation and contamination.
Innovation Solution
A cryopump design with a first stage array comprising elements at varying distances from the inlet, providing targeted shielding and gas flow paths, combined with a refrigerator positioned remotely from the inlet to minimize interference and enhance gas capture.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the radiation shield provides extensive shielding of the second stage cryopanels from type I gases, then the shielding effectiveness is improved, but the conductance of type II and type III gases into the pump is reduced
Solution Approach 1:
The first stage array is segmented into multiple elements arranged at different distances from the inlet, creating a multi-layered shielding structure that selectively blocks type I gases while allowing type II and type III gases to pass through to the second stage cryopanels
Solution Approach 2:
Different regions of the first stage array have different properties - elements closer to the inlet provide more shielding, while elements further away allow greater gas flow, creating a gradient that optimizes both shielding effectiveness and conductance for different gas types
2Device complexity
If the refrigerator is positioned close to the inlet for compact design, then the device complexity is reduced, but the thermal load on the second stage cryopanels increases
Solution Approach 1:
The first stage array acts as an intermediary between the inlet and the second stage cryopanels, absorbing thermal radiation from the inlet region and protecting the second stage from excessive thermal load, while the refrigerator can be positioned more compactly
3Manufacturing precision
If the first stage array elements are arranged at uniform distances from the inlet, then the manufacturing precision is improved, but the gas flow regulation and shielding effectiveness are reduced
Solution Approach 1:
The first stage array elements are deliberately arranged asymmetrically at varying distances from the inlet rather than at uniform intervals, creating a non-uniform shielding pattern that optimizes gas flow regulation and selective blocking of type I gases while remaining manufacturable
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
The design achieves increased pumping speeds for type III gases, improved shielding from type I gases, and reduced thermal load on the second stage, resulting in enhanced vacuum performance and longer pump lifetime.
Implementation Method 1
when gases pass through the inlet into the pump vessel, at least some of the type I gases such as water vapour are condensed on the frontal array
Implementation Method 2
Type II gases, such as nitrogen, condense on the second stage array
Implementation Method 3
type III gases, such as hydrogen, helium and neon which have appreciable vapour pressures at 4K are adsorbed by an adsorbent such as activated carbon, zeolite or a molecular sieve that coats the second stage cryopanels
Implementation Method 4
a first stage radiation shield that operates in the temperature range of 40-130 K, and provides radiation shielding to the lower temperature array
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
A cryopump comprising: a vessel comprising a frontal open area, the frontal open area comprising an inlet to the vessel; a radiation shield; a two stage refrigerator extending into the vessel, a first stage of the refrigerator being thermally coupled to the radiation shield. A first stage array is arranged within the vessel and is also thermally coupled to the first stage of the refrigerator. A cryopanel structure is coupled to a second stage of the refrigerator. The first stage array comprises a plurality of elements arranged at increasing distances from the inlet, the element closest to the inlet being between the cryopanel structure and the inlet and elements further from the inlet having a passage through a central portion. The element closest to the inlet has a smaller outer perimeter than the elements further from the inlet.