Propagation of wiggler focused relativistic sheet electron beams

A recent design concept for millimeter-wave free-electron lasers [J. Appl. Phys. 60, 521 (1986)] would require the stable propagation of a sheet electron beam through a narrow waveguide channel. Experimental results reported in this article support the feasibility of such a configuration by demonstrating the stable propagation of relativistic sheet electron beams through a narrow waveguide gap (3.2 mm) using focusing by a short-period electromagnet wiggler. 90% of the electron current in a 100-keV sheet electron beam was transmitted through a 5-cm-long channel with peak wiggler fields of 800 G. Almost 80% of a 400-keV beam was similarly confined with a 1600-G wiggler field. The data were consistent with single electron trajectory models, indicating that space-charge effects were minimal. No evidence of beam breakup or filamentation instabilities was observed.