Pressure wave induced sound measurement for diagnosing the operation status of the J-PARC pulsed spallation neutron source

Abstract

A liquid mercury target for the pulsed spallation neutron source is installed at the J-PARC. The liquid mercury is enclosed within a multi-walled stainless-steel vessel. When the highly intense proton beams hit the target at 25 Hz, pressure waves are generated by the rapid thermal expansion of the mercury. The pressure waves causes severe erosion damage on the interior, mercury-facing surface, owing to the cavitation, as well as imposing cyclic impact on the vessel walls. A target diagnostic system, consisting of a laser Doppler vibrometer (LDV) and a microphone, has been installed to remotely investigate the structural integrity of the target vessel in a high-radiation environment. In this study, to investigate the applicability of the sound measurement for the alternative method of the LDV diagnostic system of the target vessel, the correlation between the proton-beam-induced sound and the operational conditions (the proton beam power, the beam profile, and the gas flow rate for injecting microbubbles) was evaluated. The results showed that the sound propagation through the piping and the gap in the radiation shield was well correlated with the operational conditions as well as the LDV results.