Energy Balance for a Sonoluminescence Bubble Yields a Measure of Ionization Potential Lowering

Abstract

Application of energy conservation between input sound and the microplasma which forms at the moment of sonoluminescence places bounds on the process, whereby the gas is ionized. Detailed pulsed Mie scattering measurements of the radius versus time for a xenon bubble in sulfuric acid provide a complete characterization of the hydrodynamics and minimum radius. For a range of emission intensities, the blackbody spectrum emitted during collapse matches the minimum bubble radius, implying opaque conditions are attained. This requires a degree of ionization >36%. Analysis reveals only 2.1±0.6 eV/atom of energy available during light emission. In order to unbind enough charge, collective processes must therefore reduce the ionization potential by at least 75%. We interpret this as evidence that a phase transition to a highly ionized plasma is occurring during sonoluminescence.

Observation of Shell Structure, Electronic Screening, and Energetic Limiting in Sparks

“…In this dense regime, screening effects and interparticle forces are dominant and can lead to unexpectedly high levels of ionization [1,2,9,19,22]. To determine whether this plasma is strongly ionized, the electron density can be estimated using the requirements for opacity [1,2,23,24]. The absolute spectral intensity I λ at wavelength λ can be calculated using [25],…”

Ultrasonic hammer produces hot spots in solids

“…The energy deposition process is therefore less destructive and also extends over a longer time period. As a delocalized mechanical energy, ultrasound induces acoustic cavitation in liquids and the resulting bubble collapse can generate micronsized hot spots reaching temperatures and pressures of 15,000 K and 1,000 bar with an even hotter plasma core 8,[21][22][23] . Ultrasound is also used for welding, a widely applied industrial technology; substantial frictional heating occurs at defined frictional contact points between two pieces of materials, although the process is highly empirical 24,25 .…”

Nanosecond high-power dense microplasma switch for visible light

“…Blackbody radiation from cavitation can be observed in a wide-ranging parameter space that includes temperatures as low as $1 eV and atomic densities as low as $10 21 cm À3 . [1][2][3][4][5] These parameters can also be achieved in a spark discharge in a high-pressure gas. Furthermore, sparks have an advantage over sonoluminescence in that sparks can be triggered on demand.…”