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 twodimensional field patterns. Tests on a scaled ten-gap Alvareztype cavity resolve every accelerating gap despite a signal-tonoise ratio close to two. These results establish falling liquid
drops as practical perturbators for rapid cavity diagnostics
and tuning.
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