Application of Ultrasound for Bubble Measurement in Water and Mercury

Spallation Neutron Source at Oak Ridge National Laboratory is a neutron source operating with a liquid mercury target. Pulsed energy deposition in the target from the proton beam causes pressure waves that limit operation due to cavitation damage on the target container. Damage mitigation is proposed through the introduction of a 0.5 per cent gas volume fraction of small diameter bubbles to create compressibility in mercury. Desired bubble diameter is 30 microns, and two ultrasonic methods are studied for detection and characterization of such bubbles. These methods are tested first in water, and then in mercury. Ultrasound Doppler velocity profiler directly measures bubble rise velocity, which is then used to determine bubble diameter. Ultrasonic imaging allows direct observation of the bubbles both in water and in mercury. However, challenges were encountered in medical ultrasound image optimization and interpretation for this engineering application. This research explores techniques for implementing ultrasound in opaque fluids for bubble rise velocity and diameter characterization