vacuum

A vacuum is a region of space in which the pressure is much lower than atmospheric pressure, resulting in a sparse gas population. Vacuum quality is described by residual pressure in pascals (Pa) or Torr. Rough vacuum covers roughly 1 to 1000 Torr, medium vacuum from 1 Torr to 10^-3 Torr, high vacuum from 10^-3 to 10^-6 Torr, and ultra-high vacuum below 10^-6 Torr. Outer space represents an extremely low-density environment, but not a perfect vacuum there.

Vacuum is created and maintained by removing gas from a chamber and sealing against leaks. Pumps such as piston or rotary vane pumps are used for rough vacuum, while turbomolecular, diffusion, and ion pumps achieve higher levels. Cryopumps condense gases on cold surfaces, and getter pumps chemically bind residual gases. Systems require bake-out and materials with low outgassing to reduce gas release from surfaces.

Vacuum enables experiments and manufacturing where air would interfere. It underpins surface science, thin-film deposition, electron and ion beam work, semiconductor fabrication, and accelerators. Vacuum tubes and X-ray tubes rely on low-pressure environments, and space missions use the natural vacuum of space for thermal control and instrumentation.

Key challenges include outgassing, leaks, and limited pumping speed dictated by chamber geometry. Achieving ultrahigh vacuum requires multi-stage pumping, chamber bake-out, and careful materials selection. Vacuums are a continuum rather than a single state.