The effect of small transverse magnetic fields on electron beam transmission

The paraxial ray equation for the beam axis of a space charge electron beam in the presence of a small transverse magnetic field is presented and solved for the simple case of a uniform axial focusing and uniform transverse perturbing magnetic field. The solution is used to explain the interception generally observed when the amplitude of the field is changed and the sense of the magnetic field is reversed. Values for permissible transverse fields in electron beam ionization sources (EBIS) devices are discussed.