A new quadrupole PPM focusing scheme for high density electron beams

The paper discusses a new periodic focusing scheme employing periodic quadrupole magnets. The basic mechanism of focusing is explained as well as the basic dynamics of high density beams subject to a periodic quadrupole field. The main advantage appears to be small demagnetization effects in the quadrupole magnets, so that a larger focusing field is available. Furthermore, since pole pieces are not required, saturation problems are absent. The quadrupole scheme is therefore expected to have merit predominantly for focusing high power beams at extremely high frequencies where dimensions are minute.<>