Study of a low impedance beam position monitor for short bunches

A low coupling impedance beam position monitor based on microwave spectroscopy is proposed. A coaxial cavity is coupled to a circular beam pipe through four small longitudinal slots. Displaced beams excite TE cavity modes that can be detected by two antennas. Applying the modified Bethe's theory, the TE/sub 111/ mode power has been derived as a function of the beam displacement. An aluminium prototype has been constructed with the support of numerical (HFSS) simulations. Bench measurements using a coaxial wire excitation show good agreement with both theoretical and numerical expectations.