Rating Products for Vacuum!
Helium leak-testing at Torr
A big part of working with vacuum technology is showing that our products are hermetically sealed! Being hermetically sealed confirms that products are leak tight, and that nothing can pass through from one side to the other. Leaks in a viewport could allow air or even contaminants such as dust to pass across the barrier.
Vacuum and Hermetic Seals
Not only will leaks raise concerns about contamination, if there is a leak, it can affect the level of the vacuum that can be reached with the product.
Vacuum is a scale ranging from rough vacuum to ultra-high vacuum:
- rough vacuum = below atmosphere to 1 mbar
- medium vacuum =1 mbar to 10-3 mbar
- high vacuum =10-3 mbar to 1×10-9 mbar
- ultra-high vacuum = below 1×10-9 mbar
There is also extreme high vacuum (XHV) which is considered to start below 10-12 mbar
Here at Torr Scientific, the majority of our products are designed for ultra-high vacuum (UHV) applications, with our vacuum viewports rated to 1×10 -11 mbar and we utilise helium leak detection to ensure UHV performance.
Leak detecting can drastically improve the likelihood of reaching ultra-high vacuum; however, leaks are not the only factor which can impact vacuum level.
Another important consideration is that there could be issues with materials in the chamber that might be outgassing!
Helium Leak Testing at Torr
We helium leak test all our vacuum products, including our vacuum viewports and X-ray anodes. The equipment we utilise for leak testing is highly specialised so that we can find leaks as small as 5 x 10-12 mbar L s-1 in our products. This equates to being able to detect leaks even smaller than a nanometre.
For helium leak testing, the specific model we use is called the Leybold PHOENIX Quadro helium leak detector. This leak detector contains a mass spectrometer, which is the most sensitive approach and commonly used in the industry to ensure products can reach ultra-high vacuum.
Mass spectrometers work by ionizing gases, including the helium, through a magnetic field. This means that the helium can be detected, amid these other gases, based on its mass-to-charge ratio (denoted as m/z). This ratio depends on the specific ion of helium; however, it is most often 4 for singly ionized helium.
Why is Helium used for Leak Testing?
Helium is the perfect substance for testing leaks due to its tiny atomic size. It is monatomic, which means it exists as a single atom. This is unlike hydrogen, which is diatomic. This means that, hydrogen will bond with itself to create the molecule H2 – making it a larger molecular gas than helium. This makes hydrogen less useful for leak testing – the smaller the molecule, the smaller leaks it can help discover!
Another advantage for helium is that is inert. It is a noble gas, which means its electron shell is full and it doesn’t try to react with any other atoms. This is an advantage as it will not interfere with the elemental composition of the component being tested or anything else in the vicinity. This contrasts with hydrogen, which is reactive and can cause issues by interacting with the target of the testing.
Finally, helium is non-flammable, whereas hydrogen is highly flammable and could be a fire and explosion risk to use for leak testing!
If you want to learn more about the machines we use in our factory, check out our Facilities page.
