PHASE-DIAGRAMS FOR SONOLUMINESCING BUBBLES

Sound driven gas bubbles ill water can emit light pulses, This phenome non is called sonoluminescence (SL). Two different phases of single bu bble SL have been proposed: diffusively stable and diffusively unstabl e SL. We present phase diagrams in the gas concentration versus forcin g pressure state space and also in the ambient radius versus gas conce ntration and versus forcing pressure state spaces, These phase diagram s ate based on the thresholds for energy focusing in the bubble and tw o kinds of instabilities, namely (i) shape instabilities and (ii) diff usive instabilities, Stable SL only occurs in a tiny parameter window of large forcing pressure amplitude P-a similar to 1.2-1.5 atm and low gas concentration of less than 0.4% of the saturation. The upper conc entration threshold becomes smaller with increased forcing. Our result s quantitatively agree with experimental results of Putterman's UCLA g roup on argon, but not on air. However, air bubbles and other gas mixt ures can also successfully be treated in this approach if in addition (iii) chemical instabilities are considered. All statements are based on the Rayleigh-Piesset ODE approximation of the bubble dynamics, exte nded in an adiabatic approximation to include mass diffusion effects. This approximation is the only way to explore considerable portions of parameter spare, as solving the full PDEs is numerically too expensiv e. Therefore, we checked the adiabatic approximation by comparison wit h the full numerical solution of the advert-ion diffusion PDE and find good agreement. (C) 1996 American Institute of Physics.