Helical twystrode experiments

Summary form only given, as follows. Experiments have been performed at NRL to determine the saturation behaviour and maximum conversion efficiency of emission gated electron beams in slow wave circuits. Simulations suggest that single-pass conversion efficiency exceeding 50% to the fundamental harmonic may be achieved with moderately tight bunches in a radically tapered helix having a velocity ratio of 3:1. The NRL Twystrode Experiment is a flexible instrumented amplifier yielding information on a wide parameter space, allowing thorough verification of analytical and simulation models. The electron beam (from a gridded thermionic cathode) can be modulated in any degree from DC up to average-to-peak beam current ratios of less than 0.15. The beam voltage is variable from below to well above synchronism. The Twystrode Experiment operates at UHF (487 MHz), a low frequency for which rugged, longlife gridded thermionic cathodes are available. The experimental results, and especially the experimentally verified simulation models, forecast the X-band performance obtainable with future Field Emission Array cathodes. Such FEA twystrodes are a prime candidate for an improved vacuum power booster in the next-generation Microwave Power Module. The experimental results will be compared to both particle simulations and analytic calculations.