Characterization of gyrating electron beams with a pinhole analyzer

Abstract

An instrument for characterizing gyrating electron beams has been built and tested on an annular gyrating beam. Measurements of Larmor radius, axial period, guiding center locations, axial velocity spread, azimuthal velocity spread, and energy spread, all as functions of radial position within a beam, are reported. The instrument consists of a stationary pinhole foil, a rotable slit foil, and a translatable phosphor screen for detecting electrons that pass through the slit and pinhole. The beam used for prototype tests had a current of 0.6 A, an energy of 16.5 kV, a Larmor radius of 3 mm, and an axial period of 35 mm. The beam diameter was nominally 3 cm, and the annular width was 2 mm.<>