Effects of electron beam loading on an operating piezoelectric transformer

Piezoelectric transformers (PTs) are currently being used to accelerate charged-particle beams for various applications [1, 2]. Beam interactions at the output of the PT can be treated as a parallel RC electrical load. The impedance of the load can affect the output voltage due to the small, finite amount of charge available in the PT. High output voltages necessary for beam acceleration cannot be achieved if the current output from the PT is too high. A thermionic electron emitter was used to provide a controllable beam current for testing the effects of electrical loading on the PT. The electron beam was operated in vacuum pressures of approximately 10^-5 Torr. Variations in the electron beam current were used to vary the resistive portion of the load while beam distance was used to vary capacitance. The effects of such variations were measured via bremsstrahlung interactions at the output electrode of the PT to determine output voltage and optical techniques for finding internal operating parameters such as electric field. This paper focuses on determining an optimal beam current and PT placement such that high output voltages are still achieved.