Four Principles for Working in High (HV) Vacuum and Ultrahigh (UHV) Vacuum Regimes

High vacuum (HV) and ultra-high vacuum (UHV) systems must be efficient and safe. HV circumstances are between 10-3 and 10-7 torr, whereas UHV conditions are between 10-7 and 10-12 torr. HV is used in space modeling, nuclear physics, analytical equipment, and metallurgical processes. In high-energy physics and MBE, UHVs are employed for surface analysis. 

This article covers the four most important HV/UHV concerns.

  • Cleaning and Working Conditions

Managing outgassing in clean, high- and ultra-high vacuum settings is complicated. Outgassing occurs when dissolved, trapped, adsorbed, or absorbed gas is released.

When non-absorbent materials release enough molecules to disrupt vacuum processes, this occurs. Moisture, sealants, lubricants, and adhesives are the main sources, although flaws or impurities in metals and glasses may release gasses. Bake-out or surface cleaning may remove volatiles. 

A low gas load is needed for high vacuum levels. Thus, under HV/UHV settings, materials should outgas or degas as little as feasible. Effective surface areas must be minimized to decrease outgassing and system pressure.

  • Picking the Right Pump Technology

A fore vacuum pump that charges the main pump is needed to efficiently and successfully produce HV or UHV vacuum levels. While fore pumps lower pressure to a safe level for HV and UHV pumps to take over, matching vacuum pumps for optimal performance is not always easy.  

Each system's needs and use scenario is unique. Selecting the best pump combination requires careful consideration of crucial elements and implications. Noise/vibration, cost (initial and ongoing), tolerance to contaminants, footprint, maintenance schedules, and shock resistance affect pump selection. Even with this knowledge, there is no one option; each pump type has pros and cons.  

Diaphragm pumps, scroll pumps, multi-stage roots pumps, and screw pumps are all dry fine pumps. Diffusion pumps, cryogenic pumps, ion getter pumps (IGP), and turbo pumps are the major secondary pumps that may supply HV and UHV conditions in fast draw-down. 

  • Design of Vacuum Systems, Materials, and Surfaces

The established standards, rules, and protocols that define and govern vacuum factors and matters (such as how to obtain such vacuum levels, the pump set-up, safeguards, measurement methods, and leak detection) must all be thoroughly re-examined and frequently re-engineered, as with all vacuum systems. 

Assessing the vacuum system's design, materials, and condition might increase efficiency by: 

  • Reducing the interior surface area of the chamber
  • Only welding from the inside with materials that have low desorption/outgassing rates
  • Appropriate material pretreatment (e.g. electro-polishing)
  • Ensuring that there are no internal gaps or trapped volumes (for example, tapped blind holes are virtual leaks)
  • Lowering the number of seals, feed-throughs, and so forth
  • Using metallic seals. 
  • Influence of Conductance

Conductance determines how easily gas may (or may not- when operating in the molecular flow mode) flow through a vacuum system or component under HV and UHV conditions.

Conductance is often considered the "inverse" of flow resistance. It is the gas flow between two places divided by the driving pressure drop. It is used to describe pipings and apertures, not vacuum pumps, yet its dimensions are the same as pumping speed (volume per unit time). 

Operating an HV or UHV system requires keeping all these things in mind. It is a necessary process to provide the best possible performance of a vacuum system and reach the targeted HV and UHV levels.  

Keep Your Vacuum Systems Working Seamlessly 

If you notice issues with your vacuum pump, don’t let the problem become a major issue. Contact Vacuum Pump Repair USA as soon as you notice your vacuum pump is acting out of the ordinary.

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