Electron motion and confinement in the orbitip vacuum gauge: I. Theory

Electron motion and confinement inside the “orbitip” ionization vacuum gauge have been studied. The orbitip has two electrodes shaped as coaxial cylinders, and the electrons are injected by a field emission array. Generally, the electrons have helical trajectories with complicated shapes. Electron confinement conditions are studied and several design hints are outlined. It is shown that electron confinement at the device end can be obtained by a small narrowing of the outer electrode. The longest electron trajectories are circular helical ones, with large radius and small helix increment. These optimal trajectories also assure minimal trajectory fluctuations for the electron population.