Versatile e-beam prebuncher for FEMs and other high power beam devices

Beam bunching is employed in microwave tubes, FEMs and in other devices. We shall characterize and point out the advantages of using a traveling wave type prebuncher in a table-top compact FEM, which operates successfully at Tel-Aviv University in C-band and for FEMs operating anywhere in the microwave or mm wave range. Our prebuncher utilizes the e-gun and the first 2 “amplifier” sections of a 3-section Traveling Wave Tube (TWT). The 3rd “output” section was severed; an adopting flange was added to permit mounting and alignment of the prebuncher with the FEM resonator. We shall characterize the density modulation of the e-beam exiting from the prebuncher as a function of the RF power input to the prebuncher and as a function of operating frequency. This characterization is made possible by scaling from data of small signal gain, saturation gain, power output vs. power input which was measured on the 3 section TWT for a large frequency range. From this measured data, from the knowledge of the prebuncher operating parameters and from existing information regarding the behavior of TWT bunched beams in the saturation region a good estimate of density modulation vs. Input power and frequency is obtained for our prebuncher