Low Profile Cryopump Thermal Bus and Shield Design
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Solution Overview
Problem
Low-profile cryopumps face challenges in efficiently cooling and managing gas freeze-out in limited space applications, particularly with Group II gases like Ar, which can lead to 'Ar hang up' and inefficient heat management.
Innovation Solution
The design features straight inlet louvers oriented transverse to the expander cylinder axis, attached to tapered thermal busses directly connected to the first stage heat station, and second stage cryopanels with flat surfaces forming a nested structure to shield the expander cylinder, reducing material weight and enhancing cooling efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional in line cryopump design is used, then gas freeze-out efficiency is improved, but space consumption increases and profile height increases
Solution Approach 1:
The patent transitions from the conventional in-line configuration where the inlet is perpendicular to the expander axis to a low-profile configuration where the inlet is parallel to the axis. This dimensional change allows the cryopump to achieve similar gas freeze-out efficiency while reducing the profile height and space consumption, making it suitable for limited space applications.
2Productivity
If Group II gases like Ar are present, then pumping capability is improved, but gas hang-up occurs on the second stage cylinder
Solution Approach 1:
The patent introduces a shield structure positioned between the second stage cylinder and the incoming gas flow. This shield acts as an intermediary that prevents Group II gases like Ar from directly contacting and freezing on the second stage cylinder surface, thereby eliminating gas hang-up while maintaining the pumping capability for these gases.
Solution Approach 2:
The patent converts the harmful effect of Ar freezing on the cylinder into a beneficial design feature by positioning the shield to intercept Ar flow before it reaches the cylinder. The shield structure, which might otherwise be seen as an obstruction, is instead designed to guide Ar flow around the cylinder, transforming the potential harm into a controlled gas distribution pattern.
3Temperature
If complex heat management structures are added, then cooling efficiency is improved, but device complexity increases
Solution Approach 1:
The patent segments the heat management function into distinct components: the shield structure, the second stage cryopanel, and the thermal bus. This segmentation allows each component to perform its specific thermal function independently, improving overall cooling efficiency while keeping the design modular and manageable rather than requiring a single complex integrated structure.
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 results in faster cooldown times, simplified construction, and uniform gas distribution for efficient freeze-out, reducing material weight by over 20% and preventing gas hang-up on the second stage cylinder.
Implementation Method 1
The thermal busses are tapered so the temperature gradient is fairly uniform
Implementation Method 2
the second stage cryopanels, which consist of folded flat sheets of copper, can be attached any place along their length
Implementation Method 3
Two stage G-M ('Gifford-Mchon') refrigerators are used to cool cryopumps. These cool a first stage cryopanel at 50 to 100 K and a second stage cryopanel at about 15 K
Implementation Method 4
Group III gases are adsorbed in an adsorbent on the backside of the cold panel
Data Source
AI summary
Faster cool down time is achieved in a low profile cryopump by having heat transferred directly from the inlet louver to the first stage heat station through one or more tapered thermal busses, and by obviating the need of a thermal shield over the second stage cylinder of the expander by having second stage cryopanels that form a nested tent like structure, at least one of which, extends over the cylinder.