A Broadband, Crossed-Field Amplifier with 20 db gain and peak power output of several hundred kilowatts will be described. The amplifier uses a choke supported interdigital line for a slow wave circuit and a secondary emitting cold cathode with re-entrant electron stream. The use of programmed interaction space geometry has given results superior to those obtained with symmetrical structures. Programmed interaction space geometry is accomplished by changing the RF properties of the circuit and/or the dc electron optics along the active circuit length. Proper programming of the variation requires maintaining a constant optimum value for Feinstein's "spoke stabilization factor." This factor is essentially the ratio of the RF electric field intensity at the hub surface to the incremental dc electric field intensity above the synchronous field. It attempts to correlate the facts that (1) the RF field intensity limits the amount of space charge that can be phase focussed to the anode in the presence of space charge debunching forces and (2) the dc electric field intensity above the synchronous value determines the amount of space charge entering the base of the electron spoke. Theoretical considerations influencing the proper programming of the interaction space geometry will be discussed and some of the methods which have been employed for realizing the desired variation will be described.
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