Speaker
Description
Radio-frequency cavity field mapping is conventionally performed by pulling a perturbing bead through the cavity on a dielectric wire. Although well established, this procedure requires cavity-specific mechanics and can introduce perturbations, vibration, and alignment errors. We demonstrate a compact wire-free alternative in which repeatable liquid drops fall through the cavity under gravity. A photoelectric gate provides a timing reference, a vector network analyzer records the transient phase perturbation, and a calibrated time-to-position relation converts each trace into a field profile. The method completes a longitudinal scan in less than 0.5 s and supports quasi-continuous monitoring at about 2 Hz. Repeated measurements can be combined by singular value decomposition to recover field distributions at low signal-to-noise ratio. Measurements on a 36.136 MHz three-gap buncher reproduce the simulated one- and two dimensional field patterns. Tests on a scaled ten-gap Alvarez type cavity resolve every accelerating gap despite a signal-to-noise ratio close to two. These results establish falling liquid drops as practical perturbators for rapid cavity diagnostics and tuning.
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