Cold cathode vacuum gauge

Positive ions are formed and collected at an electrode and the current is converted to a pressure indication. The discharge is initiated by stray field emission or external events like cosmic rays or radioactive decay. Once started, the gauge's magnetic field constrain the electrons in helical paths, giving them long path lengths and a high probability of ionizing the residual gas. Pictured is Pfeiffer Vacuum IKR 251 with the central molybdenum anode. The measurement range is 10^-2 – 10^-9 mbar.