Explore chapters and articles related to this topic
Fundamentals of Vacuum and Plasma Technology
Published in Andrew Sarangan, Nanofabrication, 2016
The operational use of a cryo pump is very similar to that of a turbo pump. The cryo pump has a foreline (exhaust) port that is pumped by a roughing pump, and the inlet has a large diameter. It is connected directly to the chamber to maximize the conductance and probability of gas molecules entering the cryopanels. However, the cryopump cannot be exposed to atmosphere when the chamber is being vented unless the pump is also being regenerated at the same time. An isolation valve has to be installed at the pump’s inlet and closed off during the venting process. A turbo molecular pump, on the other hand, can be exposed to atmosphere as long as its rotation speed has slowed down sufficiently. The turbo pump can also be stopped and started frequently, but a cryopump’s compressor and cold head have to be left running continuously. Furthermore, a turbo pump does not have a gas capacity limit and can be run indefinitely with gas flows without requiring periodic regeneration. As a result, for applications requiring high gas flow rates, such as sputtering and reactive processes, a turbo molecular pump may be more appropriate. However, for a comparable size and inlet diameter, a cryopump has a much higher pumping speed and a lower ultimate pressure, so it can reach lower pressures faster than turbo pumps.
Experimental Investigation of Thermal Properties of Materials Used to Develop Cryopump
Published in Fusion Science and Technology, 2021
R. Gangradey, J. Mishra, S. Mukherjee, P. Nayak, P. Panchal, J. Agarwal, V. Gupta
A commercially built or custom-made cryopump consists of cryopanels cooled to temperatures in the range of 80 to 4 K. The evacuation type of gas species determines the cryogenic temperature level at the cryopanels. In a physiosorption-based cryopump, to pump gases like helium, cryopanels have to be cooled to temperatures ≤5 K; for hydrogen, temperatures must be ≤20 K; for xenon, temperatures are 50 to 60 K (Refs. 1 through 5). The cryopump main parts comprise the vacuum chamber, baffles, radiation shield, and cryopanels. An optimized design of the cryopump aims at a minimum heat load on the cryopanels. The thermal loads are due to conduction, radiation, residual gas conduction, and throughput of gas to be pumped. The quantitative measure of the heat load depends on the thermal properties of the materials. The thermal property, for example, thermal conductivity, of materials shows a marked variation as the temperature approaches cryogenic range.6–8
Thermostructural Analysis of Large Cryopumping Test Facility
Published in Fusion Science and Technology, 2023
Hemang S. Agravat, Samiran S. Mukherjee, Vishal Gupta, Paresh Panchal, Pratik Nayak, Jyoti Shankar Mishra, Ranjana Gangradey
A cryopump is a vacuum pump that captures gases on its cold surfaces when cooled down to temperatures below 120 K. To achieve a UHV by cryopumping, all the gas molecules present in the closed system are pumped by condensation and physisorption. The LN2 temperature on the cold surfaces is sufficient to condense water vapor, carbon dioxide, and major hydrocarbons; a temperature of around 20 K is required to condense nitrogen and oxygen. To pump gases like nitrogen and oxygen at the LN2 temperature, activated charcoal granules are coated on the cold surfaces that pump these gases by physisorption (Refs. 4, 5, and 7). Activated charcoal–coated panels can pump hydrogen and helium gases if operating at a temperature below 20 K (Ref. 8).