It is well known that cavitation collapse can generate intense concentrations of mechanical energy, sufficient to erode even the hardest metals and to generate light emissions visible to the naked eye [sonoluminescence (SL)]. Considerable attention has been devoted to the phenomenon of "single bubble sonoluminescence" (SBSL) in which a single stable cavitation bubble radiates light flashes each and every acoustic cycle. Most of these studies involve acoustic resonators in which the ambient pressure is near 0.1 MPa (1 bar), and with acoustic driving pressures on the order of 0.1 MPa. This study describes a high-quality factor, spherical resonator capable of achieving acoustic cavitation at ambient pressures in excess of 30 MPa (300 bars). This system generates bursts of violent inertial cavitation events lasting only a few milliseconds (hundreds of acoustic cycles), in contrast with the repetitive cavitation events (lasting several minutes) observed in SBSL; accordingly, these events are described as "inertial transient cavitation." Cavitation observed in this high pressure resonator is characterized by flashes of light with intensities up to 1000 times brighter than SBSL flashes, as well as spherical shock waves with amplitudes exceeding 30 MPa at the resonator wall. Both SL and shock amplitudes increase with static pressure.
Cavitation collapse can generate intense concentrations of mechanical energy, sufficient to erode even the hardest metals and to generate light emissions visible to the naked eye, e.g., single bubble sonoluminescence. We describe a high-quality factor, spherical resonator capable of achieving acoustic cavitation at ambient pressures in excess of 30 MPa. In this presentation, the dynamics of the resonator and the cavitation in general will be discussed, e.g., driver configuration, quality factor, resonance modes, power and pressure amplitude threshold for cavitation, etc., as a function of static pressure, as well as other parameters. [Funded and directed by Impulse Devices, Inc., ACPT Contract W9113M-07-C-0178.]
Details of the observed evolution of a high pressure transient cavitation event are described. The combination of photomultiplier tubes, hydrophones, fiber optic hydrophone, laser to photo diode light blocking methods are used to explore the evolution of a transient bubble cloud event from ns to ms time scales. [Work supported by SMDC Contract No. W9113M-07-C-0178.]
The behavior of shocks emitted from transient cavitation in acoustic cavitation systems with static pressures up to 300 bar is explored using photomultiplier tubes, hydrophones, Schlieren, and Shadowgraphic methods. Shocks emitted from strong implosions travel initially at supersonic velocities, leading to a shortening of the time of flight (TOF) from implosion site to detector as compared to sound speed motions. A larger difference between expected sonic and actual supersonic translation times is indicative of higher stagnation pressures. Experimental results are indicative of possible stagnation pressures in the Mbar range and place constraints on computer models. [Work supported by SMDC Contract no. W9113M-07-C-0178.]
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