Analysis of Long-Periodic Permanent Magnet Structures for Electron Beam Focusing

In this paper, a simple approach for the analysis and design of a long-periodic (also called multiperiodic) permanent magnet focusing structure used for focusing an electron beam is presented. A high electron beam transmission in this type of focusing structure can be achieved by careful profiling of the axial magnetic field. The analytical approach presented here is based on the permeance computation of all possible flux paths using magnetic circuit theory. It is very suitable for a quick design optimization of the structure to obtain a desired axial magnetic field profile. The computed axial magnetic field using the present approach is compared with the measured results and the results obtained by simulation using the finite element code ANSYS and show a very good agreement.