Cold cathode ionization vacuum gauges

Cold cathode ionization gauges are discharge tubes, however a little bit different, due to the additional magnetic field generated by an external permanent magnet. In standard discharge tubes residuary gas pressure is proportional to ionization current in the pressure range 1-0,01 mbar. However, with the reduction of gas density, the value of the current decreases and comes to zero at about 10(-3) mbar. When adding a magnetic field to such tubes, due to the increased length of the trajectories of electrons, avalanche ionization of the gas molecules is maintained even at a much lower gas pressure. Measuring low ionisation currents, pressures in the range between 10(-3) - 10(-6) mbar can be assessed. There are various configurations of cold cathode vacuum gauges, and some optimised designs reach a usefull pressure range of 10(-8) mbar and lower. In the article the basic operating principles and modem types of such vacuum gauges are described, and the prototype of IEVT design is presented.