Monday, April 15, 2024

Understanding UHV Design.

September 22, 2020 by  
Filed under Health & Wellness, Opinion, Weekly Columns

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( UHV design is not without its challenges, and the importance of sourcing the correct components and using the right pumping procedures cannot be overlooked. But first, let’s explain what ultra-high vacuum, otherwise known as UHV, is; this is a vacuum regime that is characterized by pressures that are less than approximately 10−7 pascal. For this to occur, there is a UHV chamber whereby gas is pumped out of it. 

In this guide, we are going to provide you with some top tips about achieving ultra-high vacuum while also revealing some of the challenges you need to be aware of. 

How To Achieve Effective UHV 

As mentioned in the introduction, special pumping processes and materials are required in order to achieve effective UHV design. The gaskets and seals that are utilized between the components in the high vacuum system design must stop even trace leakage. This is why metal is the preferred choice for nearly all such seals, and on both sides, there are knife-edges that cut into a soft gasket, which is usually made from copper. In regards to the electric chemical transfer pump, one of the following tends to be used – cyropumps, non-evaporative getter, titanium sublimation, ion, or turbomolecular pumps. Ion gauges are used to measure UHV pressures.

We’ve got some tips regarding how to achieve effective UHV designs to help you get started. This includes using low vapour pressure materials, electro polishing all internal metal parts after welding or machining, and avoiding creating pits of trapped gas behind the likes of welding voids and bolts. You should also use high conductance tubing to the pumps, boasting short runs with minimal obstructions and a large diameter, as well as high pumping speeds that use numerous vacuum pumps in a series. A small chamber size is also required in order to lower the surface area. In addition to this, in order to avoid skin oils in fingerprints and all other traces of hydrocarbons, you should use gloves, and finally, chill chamber walls during use to cryogenic temperatures. 

Challenges Regarding Vacuum Design

There are numerous challenges regarding vacuum design that you need to be aware of. The first is deciding what material to manufacture the vacuum chamber out of. In most cases, stainless is used, even in extremely high vacuum designs. However, there are additional construction materials that can also have benefits, for example, copper, titanium, aluminium, and specialised metals. For high thermal conductivity applications and nonmagnetic, radio frequency (RF) applications, copper is ideal. Titanium vacuum chambers provide gettering properties thanks to their low hydrogen permeation rates. 

One of the biggest problems for UHV systems is outgassing, either from the materials of construction or the internal surfaces. You need to choose internal materials carefully, opting for those with low vapour pressures, for instance, ceramics, stainless steel, and glass. Outgassing issues are also created from vessels that are lined with materials, such as palladium, which are highly gas-permeable and have a large capacity for absorbing hydrogen. Another issue, although not as great, is that of outgassing from the surfaces. To make sure you do not experience any of these issues when designing your ultra-high vacuum, you need the assistance of specialists that have the experience to provide you with the UHV instrumentation you require.

Staff Writer; Paula Brown

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