5 things you need to know about working under HV & UHV

August 17, 2020

4 MIN READ

When working with high vacuum (HV) and ultra-high vacuum (UHV) systems, there are specific aspects to consider, to make sure they remain efficient and safe.

What are HV and UHV conditions?

HV pressure ranges are those between 10 x 10-3 and 10 x 10-7 mbar. 

UHV pressure ranges are those between 10 x 10-7 and 10 x 10-12 mbar.

As with all vacuum systems, the established standards, rules, and protocols that govern vacuum factors and matters must be frequently re-examined and re-engineered. 

Users should routinely:

Check vacuum levels
Review the pump setup
Perform safety checks
Evaluate measurement methods

Undergo leak detection processes

Related: Successful leak testing and detection underpins the success of any project relying on HV and UHV systems. Download a copy of our Fundamentals of Leak Detection for an easy-to-read introduction to types of leaks, detection methods and more. 

Download the Free Book

Applications

HV applications include:

Metallurgical processes
Nuclear physics
Space simulations

Analytical instruments

UHV applications include:

Surface analysis
High-energy physics 
Molecular beam epitaxy (MBE)

Related: Find out how aerospace engineers simulate space conditions on Earth in our blog post, How It Works: Vacuum Technology for Space Simulation Chambers. Interested in the HV pumps that make these applications possible? Learn more on our resource page about the Leybold range of High Vacuum Pumps.

Factors to consider when creating HV and UVH conditions

Efficiency considerations

Users should carry out a careful assessment of design, materials, and the condition of the vacuum system to identify problem areas. HV and UHV vacuum system efficiency can be improved by following several best practices:

Minimize the chamber’s internal surface area.
Weld only from the inside.
Use low desorption/outgassing rates.
Pre-treat materials — for example, undergo electro-polishing.
Check for internal gaps or trapped volumes, like tapped blind holes.

Use metallic seals.
Reduce the number of seals and feed-throughs.

Outgassing

Outgassing is the process of releasing gas that was dissolved, trapped or absorbed in some material. To create and maintain clean HV and UHV vacuum environments, users must carefully monitor outgassing.  

Outgassing typically occurs when materials not usually considered absorbent, release enough molecules to interfere with industrial or scientific vacuum processes. Common sources of outgassing include:

Moisture
Sealants
Lubricants

Adhesives
Metal impurities
Glass cracks

Cleaning surfaces, heating individual components, or performing a bake-out can drive off volatiles. 

Gas load

In HV and UHV conditions, outgassing and degassing levels must be kept as low as possible. 

Minimizing effective surfaces reduces the impact of outgassing. The higher the surface area, the greater the outgassing and the higher the system pressure. 

How do I know my operating conditions?

A residual gas analyzer (RGA) is a small quadrupole mass spectrometer, typically designed for environment analysis, process control, and contamination monitoring in vacuum systems. RGA's can monitor the quality of the vacuum by detecting (and measuring) minute traces of impurities in a low-pressure gaseous environment. 

RGA's are usually mounted directly onto, and into, the vacuum chamber. RGAs perform various functions which would be difficult to obtain by other methods, including: the analysis of various gas-phase reactions, monitoring changes that occur in any gas environment, detecting vacuum leaks, and checking mass flow controllers.

Related: Residual Gas Analyzer or Leak Detector — which one is right for the job? Get the answer in our blog post,  When To Use An RGA.

Pump selection considerations

There are many pump types capable of producing HV and UHV vacuum pressure, and most applications require multiple pumps working together. However, pairing different types of vacuum pumps to optimize performance is not always a simple matter. 

Several factors impact the choice of pumps, such as:

Noise and vibrations
Initial and ongoing costs

Contamination tolerance
Footprint
Maintenance requirements
Shock resilience

Related: Did you know that high noise levels can leave your team susceptible to hazards? Check out this blog post for 5 Quick Facts About Noise Pollution in Your Lab, and solutions that keep your team safe

Pump options

Fore Pumps

Fore pump options include:

Secondary Pumps

Main secondary pump options capable of HV and UHV levels include:

Turbomolecular pumps

Diffusion pumps
Cryogenic pumps
Ion getter pumps
Titanium sublimation pumps
Non-evaporable getter pumps

These pumps produce vacuum conditions by rapidly evacuating, capturing, or tying up gas molecules.

Understanding pump types

Each pump type has unique advantages and disadvantages, which adds complexity to the selection process.

For example, turbomolecular pumps advantages include:

Easy,  kinetic operation
Low maintenance
Hydrocarbon-free operation

Disadvantages include:

Vibration-generating moving parts
Reduced pumping speed for light gases
Sensitivity to mechanical shock
Particulate contamination

Buyers should undergo a similar comparison process for each pump type to reach an informed decision. 

Summary

When creating HV and UHV conditions, it is crucial to consider these three factors: efficiency, working condition considerations, and pump selection. If you're finding selection tough, check out our blog post,  How Do I Know Which Vacuum Pump Is Right For Me? With the help of resources like these, an approach that focuses on the key elements of working condition considerations, efficiency and pump selection will keep you on the path to delivering optimum performance and reliable HV and UHV conditions.

And if you've got questions, reach out to the Leybold team! Click the button below and start the conversation. We're always happy to hear from you and can help with all your HV and UHV needs. 

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