Propagation of wiggler focused relativistic sheet electron beams

Abstract

A recent design concept for millimeter-wave free-electron lasers [J. Appl, Phys, 60, 521 (1986) Jwould 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 loo-keV sheet electron beam was transmitted through a S-cm-Iong channel with peak wiggler fields of 800 G. Almost 80% of a 400-keV beam was similarly confined with a 16oo-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.

Design of high-average-power near-millimeter free electron laser oscillators using short period wigglers and sheet electron beams

“…One is therefore led to expect that focusing with planar wigglers would be a natural configuration for stable propagation of sheet beams. This hypothesis has been confirmed by our own research [6].…”

“…To obtain this capability without invoking high current density, we have proposed the use of a sheet or ribbon electron beam [ 5 ] . Such beams are naturally suited to stable and well-focused transport in planar wigglers when an axial magnetic guide field is not used [6]. In addition, a streaming beam without an axial guide field is easier to generate and match to an interaction region than rotating beams with axial fields.…”

Two-plane focusing of high-space-charge sheet electron beams using periodically cusped magnetic fields

“…15 This work investigated the stability of sheet beam transport through a 1 cm, five-period, 800-1600 g planar wiggler array. The ''sheet'' beam actually begins as a planar multiple beamlet array produced by seventeen 1.0 mm holes drilled into an anode plate approximately 3.0 mm apart.…”

W-band sheet beam klystron simulation

“…As with the PPM focussing, astute pole tip shaping can be used effectively to provide force balance in both horizontal and vertical planes. For Wiggler focussing to be stable, the same force balance condition must be met as with the PPM lattice, but owing to the different spatial wavenumber controlling the vertical focussing (it is k w =2π/L w , which scales like the wiggle period length, rather than k y , which scales like the vertical PPM magnet dimension), the condition is (18):…”

“…The electron gun design, although consistent with electron guns that have been or are currently operating (17,18,24,26), must be addressed. The possibility of tailoring the beam impedance to vary commensurately with the gap impedance of the cavities must also be addressed, and the complexities involved weighed against the elaborate output cavity coupling schemes required to maintain a high degree of field flatness.…”