Existence of Hysteresis Based on Argon Rectification in Single Bubble Sonoluminescence

Abstract

The coupling of the waves launched from a 4.6 GHz lower hybrid (LH) system into PBX-M plasmas has been studied for both L mode and H mode plasmas. The characteristics of the plasma in front of the LH coupler have been measured with a fast Langmuir probe. The reflected power of the coupler has been measured across the transition to the H mode as a function of phase and the distance between the coupler and the separatrix. A transient rise in the LH reflection coefficient was observed near the L-H transition under some conditions. Coupling depends primarily on the electron density in the vicinity of the coupler, and proper positioning of the coupler can compensate for changes in the plasma edge due to H mode transitions. Good coupling can be maintained throughout the H mode.

Bubble dynamics near the onset of single-bubble sonoluminescence

“…The existence of the hysteresis is explained [18] by the different thermodynamic conditions in and chemical makeup of the bubble on either side of the threshold for light emission. The hysteresis was also observed in the light emission of the bubble, which has been reported previously [17]. As in Ref.…”

“…As in Ref. [17] the hysteresis was found to disappear when the DGC increased; however, in the current work, with its disappearance another interesting phenomenon appeared: a time-dependent oscillation of the equilibrium radius at constant acoustic pressure.…”

“…Looking at the plot, perhaps the most interesting feature is that for a small range of acoustic pressures (roughly 1.22 to 1.24 atm) the data for increasing acoustic pressure do not follow the same path as that for decreasing acoustic pressure, i.e., there is a hysteresis in the maximum bubble radius at these pressures. A hysteresis in the light emission has been observed previously by Asai and Watanabe [17] and they attributed it to a hysteresis in the equilibrium bubble size; however, no measurements of the bubble size were made during those experiments. During the present experiments the light emission was measured as well.…”

Plasma Quenching by Air during Single-Bubble Sonoluminescence

“…Under certain conditions, a single bubble acoustically levitated in a liquid can undergo nonlinear oscillations in sync with the applied sound field and emit subnanosecond flashes of light at the point of maximum implosion: single-bubble sonoluminescence, SBSL. , The vast majority of SBSL studies have been conducted in partially degassed water, and some of this previous work has shown how chemistry affects the light emission. , Results suggest that polyatomic molecules that are able to enter the bubble cause a reduction in the overall sonoluminescence (SL) intensity. − This is thought to be due to endothermic processes and the build-up of molecular species inside the bubble. , As one increases the acoustic pressure ( P a ) to some critical threshold ( P c ), the maximum bubble radius initially decreases and then increases with the increasing P a accompanied by the onset of light emission . In addition to this, the SBSL displays hysteretic behavior; SBSL is not quenched until significant reduction below the P a at which light was first observed. , These observations have been attributed to quasiadiabatic heating during the rapid bubble collapse which leads to dissociation of N 2 , O 2 , and H 2 O and formation of soluble and reactive species. For an air bubble in water, this is thought to result in a mostly Ar bubble. , It is evident from these observations that polyatomic species inside the bubble are detrimental to the efficacy of cavitation for generating extreme intracavity temperatures due to the thermodynamics (i.e., lowering of γ, the polytropic ratio) associated with rapid compression of a molecular vapor/gas …”

“…11 In addition to this, the SBSL displays hysteretic behavior; SBSL is not quenched until significant reduction below the P a at which light was first observed. 12,13 These observations have been attributed to quasiadiabatic heating during the rapid bubble collapse which leads to dissociation of N 2 , O 2 , and H 2 O and formation of soluble and reactive species. For an air bubble in water, this is thought to result in a mostly Ar bubble.…”