Pressures from about 10⁻³ to 10⁻⁷ mbar. The mean free path runs from centimetres to hundreds of metres, longer than the chamber, so gas is in molecular flow and the walls, not the gas volume, supply most of the gas load. Reaching it takes a turbo, cryo or diffusion pump backed or roughed by a mechanical pump, and the pressure is read with ionization gauges. Thin-film coating, electron microscopy and mass spectrometry live here.
Coater only gets to high vacuum after the cryo opens, before that it's all roughing pump.
Also heard as
- HV
- hi-vac
Related terms
Medium vacuum
The band between about 1 and 10⁻³ mbar, where gas flow shifts from fluid-like to molecule-by-molecule.
UHV
Ultra-high vacuum: pressures below about 10⁻⁷ mbar, reached only with baked, metal-sealed systems.
Molecular flow
Flow regime in which molecules bounce between the walls almost without meeting each other.
Turbomolecular pump
High vacuum pump whose rotor blades spin at tens of thousands of rpm and bat molecules toward the exhaust.
Ionization gauge
Gauge that reads high and ultra-high vacuum by ionizing gas molecules and measuring the resulting ion current.