Measurement of long-pulse relativistic electron beam perpendicular- to-parallel velocity ratio by Cerenkov emission and radiation darkening on a glass plate

We report measurements of the ratio of the perpendicular velocity to the parallel velocity, a = ul /ull, of a relativistic electron beam gyrating in a magnetic field by the use of ( 1) Cerenkov emission from a glass plate, detected by a gated microchannel plate image intensifier camera, and (2) electron-beam-induced radiation darkening pattern on the same glass plate. The measurements are based on a direct determination of the Larmor radius of an electron beam of known energy. Experiments were performed on a long-pulse electron beam accelerator with e-beam diode parameters: V, = 0.6-0.9 MV, pulse length = 0.5-l pus, IO = l-10 kA. The experimental value of a agrees wit.h simulation results from particle trajectory codes as well as theoretical predictions from Busch’s theorem and adiabatic theory.