Ionengauges

Ion gauges, also known as ionization gauges, are vacuum measurement devices that determine pressure in low‑pressure environments by ionising residual gas molecules and measuring the resulting ion current. The principle relies on the fact that the number of ions generated in a given volume is proportional to the gas density, and therefore to the pressure. An electron source, typically a heated filament or a cold cathode discharge, emits electrons that collide with gas molecules, producing positive ions. These ions are collected on an electrode, and the measured current is calibrated to correspond to a specific pressure range.

Hot‑cathode (or heated filament) gauges, such as the Bayard‑Alpert gauge, use a thin filament heated to emit a stable electron flow. They are highly sensitive, capable of measuring pressures down to 10⁻¹¹ torr, but the filament can be damaged by sudden pressure spikes. Cold‑cathode gauges, including the Penning and inverted magnetron designs, generate electrons by applying a high voltage across a low‑pressure gas without a heated filament. These gauges are more robust against pressure transients but generally have a higher lower‑limit detection threshold, around 10⁻⁹ torr.

Ion gauges are widely employed in scientific research, semiconductor manufacturing, and space‑flight instrumentation, where precise monitoring of high vacuum conditions is essential. Their advantages include high sensitivity, relatively simple construction, and compatibility with a broad range of gases. Limitations involve sensitivity to magnetic fields, the need for periodic calibration, and the potential for outgassing from the gauge components, which can affect ultra‑high vacuum environments. Modern systems often integrate ion gauges with automated control loops and digital readouts to provide real‑time pressure feedback in sophisticated vacuum apparatuses.