Boiling bubbles monitoring for the protection of the LIPAc beam-dump

Abstract Local boiling in the cooling water of the LIPAc beam dump is an indication of abnormal conditions and will be used to trigger a fast beam shutdown through the Machine Protection System before any mechanical damage occurs. A prompt detection of boiling can be done thanks to the use of hydrophones recording the boiling sound. The sensors must have a broad and flat frequency range as well as a high sensitivity. In order to study the characteristics of the sound produced by localized boiling in different situations, an experiment has been carried out on a 1:1 prototype of the beam dump. A hydrophone was placed inside the cooling loop and the sounds produced by the bubbles were recorded. The heating was provided by means of an isolated “hot finger” giving up to 300 W/cm 2 of controlled localized power density. The experimental setup allows the characterization of the time-spectral content for different cooling flows, which is required for the design of the final protection subsystem.