Questions from Dan Winter, 4/27/99 (Once the Stubborn Physicists Decide to Use Phi-Ratio'd Sonics to Optimize the Implosion Bubble: Then Fusion Will Sustain & A Principle will be Proven.)

Compare with Implosion Geometry Predicted by Recursion at www.../predictions

& compare with core 7/5 implosion symmetry of Hydrogen, the Human Heart Symmetry, and the "Heart of the Sun" at www.../heartsun

Is this path to Implosion the Golden Based Implosion Symmetry of the GRAIL Itself? www.../grail.html

What Besides Perfect Embedding Geometrically Could Make this Phi-re Self Organizing? & Self Sustaining?

Remember the Sonic Signature Key to the Move "Chain Reaction".. PHYllotaxes is the PERFECT CHAIN!

Informal Literature Review Below Prepared by James Barrett & Thanks to Ray Flowers..

Applied Physics Laboratory

Chairman of Acoustics and Electromagnetics Department , University of Washington, Seattle

ABSTRACT

California Institute of Technology

Pasadena, CA 91125

Enhancement of the sonoluminescence hot spot using control of ultrasound

Principal Investigator: Szeri, Andrew J.*

Location/Administering Unit: University of California at Berkeley/Mechanical

Engineering

Sponsor: University of California Energy Institute (1997-1998)

Year Started: 1997

Energy subject: Energy Supply Technology R&D/Nuclear Fusion: other fusion devices

Index terms: (1) high pressures, in sonoluminescence; (2) high temperatures, in

sonoluminescence; (3) nuclear fusion, induced by sonoluminescence

Disciplines: (1) high-pressure physics; (2) acoustics

Abstract: Sonoluminescence is the production of light within a gas micro-bubble

suspended in liquid water and driven to intense periodic nonlinear volume oscillations by

ultrasound. The mechanism of light production is as-yet poorly understood. Best estimates

put the peak temperatures within the bubble at many times the temperature of the

surface of the sun. Sonoluminescence has been proposed as a possible way to produce

nuclear fusion. However, as yet, researchers have not conclusively detected the

by-products expected in the course of such reactions. This may be because the mechanisms

of diffusion of heat and mass are successful in preventing the buildup of the intense

pressures and temperatures required. In this project, it is proposed that by altering the

character of the ultrasonic forcing of the bubble, it may be possible to better exploit

nonlinear resonances of the bubble and thereby to increase the focusing of energy onto

the center of the bubble. This may make it possible to increase the temperatures and

pressures achieved within the bubble sufficiently to make nuclear reactions possible. This

would lead to an inexpensive laboratory in which to study such reactions, and could

ultimately lead to "table top" fusion energy production.

A new model is presented for the gas dynamics within a bubble at conditions that lead to the phenomenon of sonoluminescence. The spherically symmetric Navier-Stokes equations with variable properties are solved together with momentum and energy equations in the liquid. Calculations are presented for bubbles of argon, helium and xenon in liquid water. The first main result is that in contrast to recent models of air bubbles in water, there are no sharp shocks focusing at the origin of the bubble. An alternative mechanism for energy focusing in noble gas bubbles is proposed that is consistent with a smooth onset of sonoluminescence with increasing acoustic forcing, as observed in experiments. The second main result concerns an observed correlation between sonoluminescence intensity and the thermal conductivity of the gas, which suggests that heat transfer plays a dominant role in the focusing of acoustic energy. It is shown instead that mechanical effects associated with the molecular mass of the gas figure prominently in determining the peak temperatures and pressures in the bubble, when the bubble is forced strongly enough to engender wavy disturbances that focus on the bubble center.

FUTURE OF SONOLUMINESCENCE

The world is searching for the fundamental mechanism in sonoluminescence, but for every question answered, anther five arise. Over the last decade there have been many theories which have given experimenters a broad path to follow in their search. Keith Weninger's doctorate project at UCLA is to determine the radius when light is emitted. His work will help determine the actual bubble radius when light is emitted which will give a better understanding of the temperatures involved. Others are searching for different driving fluids in hopes they will be able to find a liquid for sonoluminescence that will not absorb the spectral peak. This will reduce the uncertainties in the temperature measurements.

If temperatures are in the upper range of those that are predicted there is a high probability for fusion. What ever the case, sonoluminescence is giving scientist a lesson in energy focusing that may be helpful on a larger fusion design.

Sonoluminescence will also be used as a calibration source. Its short pulses and extremely reliable emission competes with, and is in some cases superior to expensive lasers that are used today.

In order to improve, and experiment with sonoluminescence it is necessary to be able to measure the intensity of the light. Figure 13 is the first attempt at this using a photomultiplier detector. The rise and fall time of this system are severally compromised by the high input impedance of the recording oscilloscope. The period is accurately calibrate and the amplitude is a good representation of the intensity, but the pulse shape is distorted. Over the next quarter at California Polytechnic University I will refine and calibrate the PMT system and reproduce some of the fundamental characteristics of sonoluminescence. I expect to measure the intensity of the emission (photons emitted per flash), intensity of the bubble as a function of fluid (e.g., glycerine), fluid temperature, driving pressure, and dissolved gas. Presently I am investigating different methods of spectral analysis to determine the bubble temperature.

I am indebted to Nilson Froula for his advice, financial support, and many valuable discussions that have made my research possible. I am grateful to Dr. Foster for bring this project to the attention of the students at Cal Poly and ultimately me. I appreciate the hours that Don Rodgers spent advising, designing, and building the cavities I have used in this research. The individuals and their companies mentioned in appendix B have been extremely helpful in the donation of both time and technology.

Fundamentals of Sonoluminescence

Single Bubble Sonoluminescence.

By applying ultrasound waves inside this cell, a single bubble (center) continuously expands and collapses to emit flashes of light--mostly in the ultraviolet, but enough in the visible for it to be seen clearly with the naked eye. (Courtesy Lawrence Crum, University of Washington.)

© 1999 American Institute of Physics

One Physics Ellipse, College Park, MD 20740-3843

Email: aipinfo@aip.org Phone: 301-209-3100; Fax: 301-209-0843

Vi Q. Vuong, Marios M. Fyrillas and A. J. Szeri, 1998, The influence of liquid temperature on the sonoluminescence hot spot, Journal of the Acoustical Society of America, to appear.

An explanation is provided for the influence of relatively small changes in liquid temperature on the hot spot within a sonoluminescence bubble. This influence derives from a change in the (stable) equilibrium mass of the bubble due to a variation of the gas solubility in the liquid with temperature. If the acoustic drive amplitude is held constant, a change in the liquid temperature has a large or small effect depending on the variability of the solubility with temperature. For a gas like xenon, which has rapidly decreasing solubility in water with increasing temperature, a decrease in water temperature shifts the stable mass exchange equilibrium to smaller bubble size. This increases the ratio of maximum to minimum bubble radius over an acoustic cycle, resulting in a much higher hot spot temperature. In contrast helium has very little variation of solubility with temperature near room temperature; therefore the hot spot temperature is relatively insensitive to variations in the liquid temperature outside a helium bubble.

Because humankind has learned so much about the physical world in the last two hundred years, the solutions to unanswered questions will, for the most part, require a great deal of effort. In many cases this effort takes the form of large international collaborations working with expensive accelerators.

Every once in a while, however, a puzzle comes along that requires only modest equipment to study. One such puzzle that has been of interest recently is known as sonoluminescence. As the name implies,

sonoluminescence is the creation of light from sound. More precisely, it is a phenomenon where a flash of light is emitted by a bubble of gas suspended in a liquid that is subjected to rapid, large changes in pressure in the form of ultrasonic waves. The ultrasonic waves cause the bubbles to expand and collapse violently; recent work has shown that the collapse takes place a speeds up to four times the speed of sound.

The equipment needed to study this phenomenon could be put together by anyone with reasonable mechanical and electronics skills, and for the less ambitious there are even pre-built kits available. This is not to say it's easy, however; as with any delicate experimental endeavour there are many things that can go wrong.

What really makes sonoluminescence fascinating, however, is that there is no widely accepted explaination for why it occurs. One possibility is that the photons come from zero-point fluctuations in the vacuum surrounding the collapsing bubble.

Even in the absence of an accepted theory, there has been speculation that sonoluminescence might be a way to produce table-top nuclear fusion. This idea played a part in a recent movie.

For now, the study of sonoluminescence continues with ever-refined experimental techniques. And one of these days, the mystery of the flashing bubbles will be solved.

The latest Keanu Reeves action film, released 2 August 1996, features hydrogen as the perfect energy carrier. In the film, entitled Chain Reaction, a team of scientists discover a way to produce cheap, pollution-free energy–hydrogen–through a process called sonoluminescence, but technological espionage intervenes.

For advocates of a clean hydrogen/electric future, an energy strategy that includes a sustainable supply of hydrogen from renewable sources is needed. Sonoluminescence, a little-understood phenomenon, is described as a process in which "intense sound waves in water produce single bubbles of gas containing so much energy that they are bright enough to be seen." While creating a dramatic visual effect for the movie, it is not considered a practical method for producing hydrogen.

Hydrogen is currently produced in several ways. The most common method is through steam reforming natural gas. Another method is electrolysis, where electricity is used to split water (H_O) into its component elements, hydrogen and oxygen. Fuel cells recombine these elements to produce electricity, with heat and water vapor as the only by-products.

Electricity is the most common form of energy manufactured from renewable sources of energy such as solar, wind, and biomass, but it is not storable in large quantities. When "renewable electricity" is used to produce hydrogen, it in effect "stores" renewable energy. Then, when the sun is not shining, the wind is not blowing, and other renewables are not available to produce electricity, hydrogen can be used as a fuel in gas turbines or fuel cells to produce electricity.

The film also depicts dramatic catastropic hydrogen explosions. In reality, hydrogen is a safe energy carrier, as safe as or safer than the more familiar natural gas or gasoline.

While Chain Reaction takes creative license with science, its vision for the opportunity of hydrogen as a nonpolluting, sustainable energy carrier is real.

Chain Reaction also stars Morgan Freeman, Rachel Weisz (above, with Reeves), and Fred Ward; it was directed by Andrew Davis (The Fugitive). For further information on the film,

see http://www.chain-reaction.com/.

For further information on sonoluminescence, see two articles in the February, 1995, issue of Scientific American magazine (volume 272): "Producing Light From a Bubble of Air,"

March 31 – When ultrasound passes through tiny bubbles in a liquid, the bubbles give off even tinier bursts of light. For a decade, scientists have been trying to figure out why – and the quest has fueled way-out theories as well as a Hollywood thriller. Now researchers say they have plumbed the mystery without having to resort to science-fiction physics.

THE PHENOMENON of sonoluminescence was first detected 10 years ago: Experimenters found that ultrasonically driven bubbles of gas within water emitted tiny flashes of light – perhaps 20,000 flashes per second, with each one lasting mere trillionths of a second. Could this be an example of quantum vacuum energy? Minute ice crystals cracking and re-forming? Cold fusion at work? Electron tunneling? Some sort of weird electrical discharge? All these theories were considered, and the 1996 action-thriller "Chain Reaction" even used explosive sonoluminescence as a hook for its scientists-vs.-conspiracy plot. In recent years, the wilder theories about the "star in a jar" have been gradually winnowed out, and research reported in Thursday’s issue of the journal Nature puts the phenomenon purely in the context of conventional hydrodynamics, chemistry and plasma physics. "I think the mystery is resolved," said one of the authors, physicist Detlef Lohse of the University of Twente in the Netherlands. "But clearly there’s more work to do on the subject, to test the theory in different regimes." A SIMPLE PLAN Lohse and his colleagues in the research – Sascha Hilgenfeldt of Harvard University and Siegfried Grossmann of the University of Marburg in Germany – worked out a relatively simple theoretical model that roughly matched the observations. In fact, other researchers in the field worry that it’s too simple. More on that later. Here’s what happens: During the "trough" of a sound wave, the bubble grows from about 5 microns – that’s millionths of a meter – to 70 microns, about the thickness of a human hair. As the sound wave enters a compressive phase, the bubble crashes in on itself, powered by the inertia of the surrounding water. It retains its spherical shape, maximizing the implosive power of the collapse.

Gas caught inside the bubble is rapidly compressed, reaching temperatures of 40,000 or 50,000 degrees Fahrenheit – that’s enough to create a plasma of ions, neutral atoms and electrons. Most of the gas is burned off or dissolves in the surrounding fluid, leaving only noble gases such as argon. As the point of maximum compression passes, the bubble inflates once again. The plasma cools and gives off a flash of photons. Then the gas dissipates, and a new acoustic cycle begins. "When you take these various bits and pieces in the puzzle and you integrate them together you can actually make quantitative predictions and find that they are right on the mark," said Robert Apfel, a Yale engineering professor who wrote a commentary on the research for Nature. NOT SO SIMPLE Apfel, Lohse and other researchers, however, emphasized that it was far too early to close the book on sonoluminesce. One of the pioneers in the field, University of Washington physicist Lawrence Crum, worried that the explanation oversimplified one of the most intriguing, complex natural phenomena to turn up in decades. "I’m a little bit concerned that this will turn off a lot of people in the field," he said. Willy Moss, a researcher at Lawrence Livermore National Laboratory who has long guided experimenters in the field and claims authorship of the phrase "star in a jar," acknowledged that some people would find the new research disappointing. "Even though that was the obvious explanation, there were other people who wanted other explanations," he said. "You want the explanation to be exotic because then you get a Nobel Prize."

Nevertheless, even Lohse contends there are puzzles yet to be addressed. "It’s clearly not new physics, but nonetheless you can create an exotic state, and the direction in the future will be to create more extreme conditions," he said. Crum said researchers had not yet fully investigated whether sonoluminescence occurred in liquids other than water – for example, in liquid metals. Other promising avenues for research could include "goosing" the bubble’s collapse to boost the plasma’s power, scaling up the size of bubbles, even experimenting with heavy water and deuterium gas to see if a hot-fusion reaction would result. "Basically, the conclusion is that table-top thermonuclear fusion may not be impossible. I’m not going to go so far as to say it’s possible, but it’s going to require a detailed study of the system. ... Nature doesn’t want to do it," said Moss, who in this instance was referring to the physical universe rather than the magazine. In any case, the researchers said studying sonoluminescence provides a low-cost way to gain insights that can be used on bigger scales, perhaps leading to future breakthroughs in fusion research. "What this system does is, it gives the average researcher access to densities, temperatures and time scales that previously could be achieved only with $400 million systems," Moss said. "It allows any scientist access to some of these conditions."

About the LLNL sonoluminescence experiment

What is sonoluminescence?

Sonoluminescence is the emission of light by bubbles in a liquid excited by sound. It was first discovered by scientists at the University of Cologne in 1934, but was not considered very interesting at the time.^[1]

In recent years, a number of researchers have sought to understand this phenomenon in more detail. A major breakthrough occurred when Gaitan et al. were able to produce single-bubble sonoluminescence, in which a single bubble, trapped in a standing acoustic wave, emits light with each pulsation.^[2] Before this development, research was hampered by the instability and short lifetime of the phenomenon.

Why is sonoluminescence so interesting?

Sonoluminescence has created a stir in the physics community. The mystery of how a low-energy-density sound wave can concentrate enough energy in a small enough volume to cause the emission of light is still unsolved. It requires a concentration of energy by about a factor of one trillion. To make matters more complicated, the wavelength of the emitted light is very short - the spectrum extends well into the ultraviolet. Shorter wavelength light has higher energy, and the observed spectrum of emitted light seems to indicate a temperature in the bubble of at least 10,000 degrees Celsius, and possibly a temperature in excess of one million degrees Celsius.

Such a high temperature makes the study of sonoluminescence especially interesting for the possibility that it might be a means to achieve thermonuclear fusion.^[3] If the bubble is hot enough, and the pressures in it high enough, fusion reactions like those that occur in the Sun could be produced within these tiny bubbles.

What do we know about sonoluminescence?

The study of sonoluminescence has yielded more puzzles than it has solid clues. Here is a summary of what we know about sonoluminescence:

• The light flashes from the bubbles are extremely short - less than 12 picoseconds (trillionths of a second) long.^[4]
• The bubbles are very small when they emit the light - about 1 micrometer (thousandth of a millimeter) in diameter.
• Single-bubble sonoluminescence pulses can have very stable periods and positions. In fact, the frequency of light flashes can be more stable than the rated frequency stability of the oscillator making the sound waves driving them.
• For unknown reasons, the addition of a small amount of noble gas (such as helium, argon, or xenon) to the gas in the bubble increases the intensity of the emitted light dramatically.^[5]

References:

1. H. Frenzel and H. Schultes, Z. Phys. Chem. B27, 421 (1934)
2. D. F. Gaitan, L. A. Crum, R. A. Roy, and C. C. Church, J. Acoust. Soc. Am. 91, 3166 (1992)
3. B. Barber, C. C. Wu, R. Lofstedt, P. Roberts, and S. Putterman, Phys. Rev. Lett. 72, 1380 (1994)
4. M. J. Moran, R. E. Haigh, M. E. Lowry, D. R. Sweider, G. R. Abel, J. T. Carlson, S. D. Lewia, A. A. Atchley, D. F. Gaitan, and X. K. Maruyama, Nucl. Instr. Meth. B 96, 651 (1995)
5. R. Hiller, K. Weninger, S. J. Putterman, B. P. Barber, Science 266, 248 (1994)

A few more resources for further information

1. "Sonoluminescence," L. A. Crum and R. A. Roy, Science 266, 233 (1994)
2. "Sonoluminescence: Sound into Light," S. J. Putterman, Scientific American, Feb. 1995, p.46
3. "Bubble Shape Oscillations and the Onset of Sonoluminescence," M. P. Brenner, D. Lohse, and T. F. Dupont, Phys. Rev. Lett. 75, 954 (1995)
4. The LLNL Sonoluminescence Experiment

This page was prepared by David Knapp, dk@llnl.gov.

http://www-phys.llnl.gov/N_Div/

http://www-phys.llnl.gov/pst.html

http://www.llnl.gov/

http://www.llnl.gov/disclaimer.html

UCRL-MI-124425

M. J. Moran, R. E. Haigh, M. E. Lowry, and D. R. Sweider
Lawrence Livermore National Laboratory, Livermore, CA 94550

G. R. Abel, J. T. Carlson, S.D. Lewia, A. A. Atchley, D. F. Gaitan, and X. K. Maruyama
Physics Department, Naval Postgraduate School, Monterey, CA 93943

Abstract

The physical processes underlying the phenomenon of sonoluminescence have not been clearly resolved by previous measurements. The possibility that sonoluminescence might involve such extreme conditions that it could produce neutrons makes measurements of parameters such as the source temperature, diameter, and density valuable. We report attempts to measure the diameter and duration of single sonoluminescence flashes. For both parameters, our results were limited by the resolution of the instruments, giving upper limits on source diameters of three microns and upper limits on emission durations of twelve picoseconds.

Introduction

Sonoluminescence (SL) is the emission of flashes of light by imploding air bubbles in liquid. It was first observed as random flashes of light during studies of cavitation. Recently, repetitive emission of SL has been produced under relatively stable, reproducible experimental conditions. The excellent stability of SL from single acoustically levitated bubbles has made possible detailed studies of the emission characteristics.^{2, 3, 4,5} However, since each flash emits only about one million photons, these measurements have generally required averaging the characteristics over a large number of flashes (> 10,000).

We have attempted to measure the images and histories of single SL events. If possible, it is important to know whether these quantities differ substantially from their average values. Clearly, the spatial distribution and temporal history are fundamental to probing the basic nature of SL. Furthermore, given the optical flux from a SL event, the duration and size of the source relate directly to its energy density and thus bear directly on remote possibilities such as inertial confinement fusion.^{4, 5}

At the instant of SL emission, the bubble is so small (diameter about 1 micron), it is collapsing so rapidly³ (wall velocity about mach 1), and the pressure (P >> 1 atm) and effective temperature^2,5,8 (T > 10,000 K) are changing so quickly that standard theories or experimental techniques have not been able to illuminate how these conditions combine to produce very brief SL flashes.

Spectral data have provided some useful insights into the nature of SL. The spectra often show increasing intensity into the UV, sometimes with a broad peak in the near UV. When compared with the Planck distribution of black-body radiation, these spectra indicate source temperatures of 10,000 K to 25,000 K, and higher.^5,8 This simple interpretation may not be entirely valid, but it allows comparison of results from different measurements.

Even modest improvements in data quality can make substantial contributions to our understanding of SL. The total optical emission provides an indication of the product of the area and duration of the light source. For a thermally-emitting SL source, the Stefan-Boltzman law is:

A Dt T4 = 8.46x102 cm2 sec K4 ,

(1)

where T is the effective source temperature in Kelvins. Equation (1) models SL as thermal emission of 10⁶ photons with an average energy of 3 eV radiated in a time Dt from a surface with area A. This model provides a simple relationship between the basic source parameters. Previous experimental results have been consistent with the relationship defined by Eq. (1)^2,7,8: for Dt = 50 picoseconds (ps) and a spherical source of radius 1 micron, Eq. (1) implies a source temperature of 10,000 K (consistent with black-body interpretations of measured spectra). Measurements of smaller emission times or source sizes would imply correspondingly higher source temperatures.

Experiment

With these considerations in mind, we attempted to measure the duration and size of single sonoluminescence sources. A schematic diagram of our system is shown in Fig. 1. The acoustic resonator consisted of a 50-mm diameter quartz flask filled with degassed water and fitted on the outside with four acoustic piezoelectric drivers in a tetrahedral arrangement. Excitation of the assembly at a "breathing mode" resonant frequency of about 26 kHz produced produced stable trains of SL flashes from a single bubble. The SL process was initiated by manual injection of a bubble of air near the center of the flask. The water was a solution of 20% glycerin, by weight, (the glycerin seems to enhance the stability of the SL emission) and 80% distilled water. The temperature of the flask was maintained at a constant temperature of about 10 degrees C by a continuous stream of chilled air.

Figure 1. Schematic layout of streak camera measurement. The SL emission is collected by a 600-micron optical fiber and injected at the input slit of the camera. A combination of optical and electrical signals trigger the streak camera.

A 600-micron diameter optical fiber inserted through the vertical neck of the flask and positioned to within 2 mm of the radiating bubble provided optical coupling between the SL bubble and the streak camera. This fiber collected approximately light from a solid angle of about 0.07 steradians and guided it to the input slit of an EG&G model L-CA-24 intensified streak camera (SC). At the same time, a lens-coupled photomultiplier tube (PM) observing the SL pulses directly through the wall of the flask triggered the control electronics initiating the SC and data recording electronics.

The streak-camera trigger pulses were synchronized to the sinusoidal 26-kHz electrical piezoelectric transducer drive. Inherent delays caused the system to recorded the SL pulse following the receipt of a trigger pulse from the PM. This approach resulted in a jitter of about 100 ps (mostly due to the electronics) in the apparent position of the SL pulse on the streak image. Images on the output phosphor of the SC were recorded by a Photometrics CC200 Camera and stored on a Macintosh fx computer.

Except for some differences in the flask, the system for recording images of single SL flashes, shown in Fig. 2, was similar. The flask was a 250-ml laboratory boiling flask with a circular area ground away from the side and resealed with a flat quartz disk. This flat "window" allowed much improved observation of the radiating bubble, but it degraded the basic symmetry of the SL arrangement. This flask had a "breathing mode" resonant frequency of about 40 kHz. By varying the electrical drive to each transducer, the position of the bubble was adjusted to compensate for asymmetries which otherwise would cause the bubble to be displaced from the center of the flask.

Figure 2. Schematic layout of imaging measurements. Here, a compound optical system images the SL source onto a camera. The camera and MCP gating can be varied to select one or a number of SL flashes for a given image.

A compound telescope consisting of a 44-mm F1.6 lens and microscope objective lenses focused the SL light onto a microchannel plate intensifier (MCP). The microscope lenses allowed quick changes of system magnification from 15X through 120X. A 1:1 lens relayed the image from the MCP to a Photometrics CH250 camera. The imaging system recorded the SL images with a series of increasing magnifications. The magnif

Acoustical Society of America

Star in a Jar: A New Model for Single-Bubble Sonoluminescence

William C. Moss - wmoss@llnl.gov
Douglas B. Clarke
David A. Young
(as told to Michele S. Moss)
Lawrence Livermore National Laboratory
P. O. Box 808
Livermore, CA 94550

Popular version of Science 276, 1398 (1997) and Paper 2aPA10
Presented Tuesday morning, June 17, 1997
133rd ASA Meeting, State College, PA
Embargoed until June 17, 1997

Sonoluminescence (SL) is a mysterious process in which sound waves aimed at a container of water nucleate, grow, and collapse many gas-filled bubbles to create ultrashort light flashes representing a trillionfold focusing of the initial sound energy. SL was discovered in 1933, but the phenomenon could not be studied in detail until 1990, when Felipe Gaitan [1] at the National Center for Physical Acoustics in Mississippi successfully obtained SL from a single air bubble. We have developed a new theoretical model for single bubble sonoluminescence (SBSL) that for the first time is consistent with experimental results and makes predictions about the sensitivity of SBSL to various parameters. For example, this model provides an explanation for the ultrashort light flashes, predicts that the duration and spectrum of the light flashes may be very sensitive to the maximum radius of the bubble, and supports a theoretical prediction by Lohse [2] that the gas inside a sonoluminescing air bubble may be comprised solely of argon.

In single bubble sonoluminescence, sound waves levitate and trap a single micron-sized gas-filled bubble while forcing it to undergo SL repetitively. A bubble of air undergoing SL appears electric blue in color to the naked eye. Using Gaitan's methods, experimental measurements at UCLA [3] showed that single-bubble sonoluminescence from an air bubble produces light flashes that are synchronized with the periodically expanding and compressing sound field. In addition, each flash had a measured duration of less than 50 trillionths of a second, or 50 picoseconds (ps). In addition, the light flashes produce a spectrum of colors consistent with the idea that the sonoluminescing bubble has a temperature of at least 23000 Kelvins.

These results created a scientific stampede in which experimentalists obtained more data and theorists tried to explain the data, especially the mechanisms underlying the ultrashort flashes and high temperatures of the bubble. Scientists proposed exotic mechanisms such as quantum vacuum fluctuations, fractoluminescence, and charged liquid jet collisions. Nevertheless, what remains perhaps the most popular hypothesis for sonoluminescence was first made back in 1960 by Peter Jarman of Imperial College in London. Jarman proposed that the collapsing bubble generates an imploding shock wave that compresses and heats the gas in the bubble.

Although previous theoretical work by us and others suggested that Jarman's explanation may be valid, no theoretical model of SBSL prior to our current work has explained enough of the experimental SBSL data in sufficient detail to establish any model's credibility, nor has any model made predictions that can be tested.

Our model has two basic assumptions. The first assumption is that as the bubble collapses, the gas inside is compressed and heated. This is analogous to the heat that is generated in the housing of a foot pump when it is used to fill a tire. The second assumption is that the hot gas emits light.

We performed fluid dynamics simulations of the growth and collapse of a gas-filled bubble and the liquid surrounding it [4]. We used the computer "code" LASNEX, which contains all of the physics in our model. LASNEX is also the same code used for calculations of a form of thermonuclear fusion known as inertial confinement fusion, in which lasers compress a pellet to such high temperatures and densities that fusion reactions occur between atoms in the pellet.

Our calculations show that during the collapse of the bubble, a shock wave is generated that compresses and heats the contents of the bubble. More heating occurs at the center of the bubble than at its boundary because the shock wave's strength increases as it approaches the bubble's center. In the hotter regions, the atoms and/or molecules which make up the gas trapped inside the bubble begin to break down or "ionize" into negatively charged electrons and positively charged ions. What results is a "plasma," or collection of charged particles that is partially ionized (approximately only 1 free electron per ion). The hot gas emits light by a rapid (on the order of quadrillionths of a second) cascade of energy from the ions in the plasma, to the electrons, to the photons that make up the light pulses.

Figure 1. The final 50 ps of the calculated collapse of an argon bubble. The bubble radius (outermost curve), shock wave location (inner curve), and emitting regions [optically thin (shaded), and optically thick (solid)] are shown. P is the relative emitted power (energy per unit time) of light in the visible part of the spectrum.

The figure shows our calculated results for a collapsing argon bubble. Five snapshots of the final 50 ps of the collapse are shown, during which the radius of the bubble decreases from 0.45 to 0.43 microns. Time is referenced to the instant when the shock wave reaches the center of the bubble.

At -10 ps, the shock wave (solid curve) is near the center of the bubble and light begins to be emitted (lightly shaded region) just behind the shock wave. At 0 ps, the shock reaches the center of the bubble. At this point, the power (energy per unit time) that is emitted in the visible spectrum is one-half its eventual peak value.

The emitting regions of the bubble are very much like those in a miniature star: Visible light from the sun appears yellow, which is indicative of a temperature of approximately 6000K. However, the center of the sun is much hotter, nearly 10⁷ K.

This temperature can't be "seen," because the light that is emitted from the deeper regions is absorbed before it reaches the surface. This deeper absorbing region is described as being "optically thick." The solid black region in the figure shows where the bubble is optically thick. Only the light emission from the "halo" (lightly shaded region) and from the surface of the optically thick region can be seen. At 15 ps, the shock has reflected from the center of the bubble and is moving outward, but the gas outside the shock is still moving towards that bubble's center, compressing, and heating. Consequently, the emitting halo is slightly larger and the emitted visible optical power is at its peak value.

At 25 ps, the light emitting halo is even larger, but the bubble has cooled, so that the emitted visible optical power has decreased to one-half its peak value. At 40 ps, the bubble is too cool to emit light. The bubble temperature decreases for two reasons. First, the gas behind the outgoing shock wave expands and cools. Second, electrons carry away some of the heat that was created during the compression of the bubble. By comparing the times at which one-half peak power occurs, a 25 ps pulse width can be deduced from the figure, which is consistent with the experimentally measured value.

Our model agrees with many experimental results: (i) the durations of the light flashes and the spectra that they produce are very sensitive to the maximum bubble radius; (ii) the spectrum of the emitted light is described by the radiative properties of the hot gas, especially the radiation from decelerating electrons; (iii) the intensity of the emitted light from nitrogen SBSL is approximately 1/25 of that from air SBSL; and (iv) the spectrum of argon SBSL is nearly identical to the measured spectrum of air SBSL, which suggests that a sonoluminescing air bubble is actually an argon bubble undergoing SL [2], and may also explain why SBSL in noble gases (such as argon) is more intense than in diatomic gases (such as the nitrogen or oxygen that exists in our atmosphere). Our model suggests that the mechanisms that are responsible for the ultrashort (picosecond) duration of SBSL are the electrons rapidly carrying away the energy from the bubble and the very strong temperature dependence of the emission properties of the compressed gas. Our model predicts that after the main flash there cannot be an "afterglow" emitted by the expanding hot bubble.

The physics of matter under SL conditions is not yet understood completely. Our results suggest that our basic theoretical and computational strategy is valid, and that semiquantitative predictions are possible. For example, if the collapse of the bubble can be enhanced, thereby raising the bubble temperature even higher, then it may be possible to obtain a small amount of thermonuclear fusion from a micron-sized sonoluminescing bubble filled with heavy isotopes of hydrogen (deuterium or tritium). Although it remains to be confirmed experimentally that shock waves or plasmas are present in a bubble undergoing SL, no other model of which we are aware has been able to explain such a broad array of experimental data.

This work was performed under the auspices of the U. S. Department of Energy by Lawrence Livermore National Laboratory under Contract No. W-7405-Eng-48.

References

[1] D. F. Gaitan et al., J. Acoust. Soc. Am. 91, 3166 (1992).

[2] D. Lohse et al., Phys. Rev. Lett. 78, 1359 (1997).

[3] B. P. Barber and S. J. Putterman, Nature 352, 318 (1991).

[4] W. C. Moss, D. B. Clarke, and D. A. Young, Science 276, 1398 (1997).

Using $1.29 acrylic boxes from a dime store and simple electronics, undergraduate students and their UAH lab instructor are doing cutting edge research into sonoluminesence, a little understood phenomenon sometimes referred to as "a star in a jar."

In a back corner of a teaching lab, the student-built apparatus uses acoustic waves to suspend a microscopic bubble in water. Stretched and compressed by the force of sound waves, the bubble expands to a diameter of only 100 microns, then collapses to one one-millionth of that volume. It does that 30,000 times a second, focusing acoustic energy by a factor of one trillion, generating temperatures hotter than the surface of the Sun and releasing with each cycle a faint flash of light that lasts 30 trillionths of a second.

While scientists at some of the most pretigous laboratories in the U.S. try to explain how sonoluminesence works, UAH physics instructor Fred Seeley and his students may be on the threshold of explaining why the tiny glowing bubble can't be made brighter.

The answer may be in harmonics. When the team looked at harmonics (secondary acoustic waves) in the water-filled vessel without the bubble, it found weak harmonic feedback.

"When you add the bubble, however, you get a rich harmonic structure," Seeley said. "And some harmonic frequencies are almost as powerful as the fundamental wave.

"Our hypothesis is that these harmonics are generated by the shock of the bubble's collapse. The bubble wall collapses at the speed of sound until the water reaches its 'hard core' and can't go anywhere else."

Harmonic waves set up by that periodic shock may destructively interfere with the fundamental drive, limiting the light that is released, Seeley said. The team is trying to control destructive harmonics to see if a brighter bubble.

The National Spherical Torus Experiment fusion reactor at the Princeton University Plasma Physics Laboratory is shaped like a ball festooned with coils. The fusion reaction would be confined within the device's narrow central core.

THE NATIONAL SPHERICAL Torus Experiment, or NSTX, at the Princeton University Plasma Physics Laboratory in Plainsboro already is impressing both officials supporting fusion research funding and the physicists and engineers working on the nationwide collaboration. "The NSTX is an enormous example of the potential" of the technology, Energy Secretary Bill Richardson said recently. "It brings us closer to the reality of fusion energy." Fusion, the process that powers the sun, involves slamming special forms of tiny hydrogen atoms together at very high temperature and pressure in a plasma, a hot mass of electrically charged gas similar to the substance inside a fluorescent light bulb. Proponents say harnessing the power released when the atoms fuse will one day provide a clean energy source far safer than today’s commercial nuclear fission reactors, which split apart large, radioactive atoms. The fuel, hydrogen atoms removed from water, is plentiful. In addition, the fusion process can’t cause a "meltdown" reaction and doesn’t contribute to air pollution, acid rain or the greenhouse effect. Laboratory director Robert J. Goldston said the radioactivity produced by a fusion reactor is 100,000 times less than in an equivalent fission reactor. Fossil fuel supplies are expected to run low in 50 years, and many scientists hope fusion will be a major energy source before then. "In the year 2100, either we’re going to be real toasty and underwater (from flooding induced by global warming), or we’re going to have a completely different energy system," Goldston said. DECADES-LONG QUEST But perfecting the technology to control a self-sustaining "burn" of nuclear fuel will take decades and cost hundreds of millions of dollars. Meanwhile, physicists across the country say progress has been slowed in recent years by the federal government’s inadequate financial commitment: just $27 million annually for the NSTX project and $227 million a year for the country’s entire fusion research program.
"Magnetic fusion research is eminently worthwhile because it solves an energy problem," yet it’s not a high priority for the government, said Patrick Diamond, a University of California-San Diego physics professor whose research focuses on turbulence in reactor plasmas. Limiting that turbulence, which quickly cools down the multimillion-degree plasma and stops the fusion process, is one of the biggest challenges to physicists and a major focus of the NSTX team. Diamond and his Princeton colleagues are particularly worried that, under pressure from Congress, the administration has reduced participation in a planned international collaboration on the next generation of reactor to basically consulting with scientists in Russia, Japan and a European consortium. The only U.S. facility for the project was shut last year, and there is no funding for the collaboration in the proposed budget for fiscal year 2000. The physicists worry this country could end up paying for rights to use the technology, rather than being able to sell it to less-developed nations. SMALLER + CHEAPER = BETTER Given Washington’s push for smaller, cheaper reactors, the compact NSTX is particularly attractive, compared to the gymnasium-sized fusion reactor it replaced here, Goldston said. The Tokamak Fusion Test Reactor was shut down two years ago after 15 years of breakthrough experiments that included producing a record-setting 10.7 million watts of power, about 100 million times the level reactors were able to generate in the 1970s. But the Tokamak reactor would cost nearly 15 times as much to build today as the $24 million NSTX, which uses much of the same peripheral equipment that was part of Tokamak. Construction of NSTX was completed on budget and months ahead of schedule, Richardson noted. Better yet, in two days of preliminary experiments in February, the machine produced nearly six times the current targeted for those first runs. That proved the reactor could create a plasma with its giant magnets and just one of its heating systems, which uses an electrical current, like a toaster or space heater. Technicians now are installing the second, a radio frequency heating system that works like microwaves, and will begin experiments in earnest in July, said Masa Ono, the project director. Come January, experiments will halt while workers connect neutral beam injectors, which shoot super-heated particles into the plasma. Experiments then will run for several years, after which the project team of scientists from the lab and 13 other U.S. research facilities will use what they have learned to adjust the machine for optimal performance. Besides being more economical to build than its predecessor, NSTX has a removable central core containing some of its most complex equipment, so repairs or upgrades to the reactor can be done in days instead of months, limiting downtime, according to Al Vonhalle, the project’s head of technical operations. DIFFERENT DESIGN Another advantage is its slightly different shape. The Tokamak reactor also was a torus, or doughnut shape, while this "spherical torus" is shaped like a ball, with a very narrow central core. Researchers believe that configuration will allow for higher pressures in the plasma, something needed to keep fusion reactions going much longer than the several-second pulses achieved so far. NSTX is one of a handful of this type of reactor with different design variations recently built or under construction in the United States, England, Russia and Japan. The Princeton scientists believe their machine has some significant advantages. "Ours will be the most powerful in the world," Goldston said. "We’ll have the most heating and the longest pulse." http://www.msnbc.com/news/257137.aspProgress in small-scale nuclear fusion http://www.msnbc.com/news/254801.aspScientists dissect sonoluminescence Diamond believes, however, that a reactor in San Diego and one under construction at University of California-Los Angeles are "at least as promising" as NSTX. Comparing findings from the different reactors should allow for more advances in the field. Whether or not fusion reactors can compete with other energy sources in a few decades, Goldston notes the research generates valuable spin-offs. That includes using plasmas to make better computer chips, sterilize medical equipment, make luminous display panels more efficient and provide a lightweight fuel for rocket thrusters in spaceships and on satellite. 1999 Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.
		http://www.pppl.gov/Princeton Plasma Physics Laboratory http://wwwofe.er.doe.gov/U.S. Fusion Energy Sciences Program http://tidweb2.llnl.gov:8001/Queries/llnl-sci-cat/sci-search-topic.qry?function=search&Category=FusionLawrence Livermore National Laboratory: Fusion Research http://www.skypoint.com/members/jlogajanFusion research information news:sci.physicsNewsgroup: sci.physics

R. Fliller, T. Yeo, W. Buell, T. Hemmick, H. Metcalf (SUNY, Stony Brook, 11794-3800)

Sonoluminescence is the conversion of sound into light in a bubble of air in water. The light is produced when the lowest order acoustic wave in a flask causes dramatic collapse to \mum size, but the mechanism of the energy conversion is still not understood. We have begun to measure the light source's size using the Hanbury Brown - Twiss effect(S. Trentalange and S. Pandey, J. Acoust. Soc. Am. 99), 2439 (1996).^,(R. Fliller et al.), BAPS, 41, 1057, WC1 (1996).. The light from the bubble passes through an interference filter (\Delta\lambda=20~nm centered at \lambda=480~nm) into a set of 50~fibers

(\approx1~mm~diam.) having various lengths and arrayed to subtend several angles at the source, and is then recorded by a set of photomultiplier tubes (PMTs). Using the temporal resolution capabilities of our PMTs and CAMAC data acquisition system, we exploit the various fiber lengths to measure correlations at several angles simultaneously, spanning the range from 2~to 75~mrad in just a few sets of measurements by changing the fiber array placement. We have measured the second order correlation function g^(|\vec\deltak|), from which the size of the emitting region can be extracted.

Sonoluminescence

Dustin Froula, Peter Young, Dick Lee, and Andy Hazi

Sonoluminescence is the production of visible light by a gas bubble that is suspended in a fluid (normally water) by an acoustic standing-wave field. Present understanding of the phenomenon suggests that sonoluminescence may result in temperatures of over 105 Kelvin (which approaches the temperature found in the solar corona), pressures of over 107 bar (close to the pressure at the center of the planet Jupiter), light emission of less than 10-9 seconds duration and concentration of mechanical energy of up to 1012. These conditions are created with a small, table-top apparatus that is easy to construct and operate, which makes it particularly attractive as an undergraduate research project. The production of high temperatures on short time and spatial scales is ideal for driving certain chemical reactions where the desired products would dissociate under sustained high temperature. This has led to the development of the field of sonochemistry; the research has applications to the improvement of commercial competitiveness through the development of more efficient chemical production and for the treatment of hazardous waste, for example.

Sonoluminescence

Physics and Space Technology Directorate

Lawrence Livermore National Laboratory

Dustin Froula, Peter Young, Dick Lee, and Andy Hazi

Sonoluminescence is the production of visible light by a gas bubble that is suspended in a fluid (normally water) by an acoustic standing-wave field. Present understanding of the phenomenon suggests that sonoluminescence may result in temperatures of over 105 Kelvin (which approaches the temperature found in the solar corona), pressures of over 107 bar (close to the pressure at the center of the planet Jupiter), light emission of less than 10-9 seconds duration and concentration of mechanical energy of up to 1012. These conditions are created with a small, table-top apparatus that is easy to construct and operate, which makes it particularly attractive as an undergraduate research project. The production of high temperatures on short time and spatial scales is ideal for driving certain chemical reactions where the desired products would dissociate under sustained high temperature. This has led to the development of the field of sonochemistry; the research has applications to the improvement of commercial competitiveness through the development of more efficient chemical production and for the treatment of hazardous waste, for example.

Sonoluminescence at Lawrence Livermore National Laboratory

Sonoluminescence is being studied at Lawrence Livermore National Laboratory as a laboratory test of three dimensional hydrodynamic simulations. It is supported as an activity that will allow undergraduate and graduate students to conduct research at LLNL and gain experience with unique capabilities of the Laboratory: ultrafast diagnostics, ultra short pulse lasers, and state-of-the-art computer simulations.

More Information

Lawrence Livermore Physics and Space Technology Directorate

Bubble Movie

Basics: Historical, basic theoretical, and methodological information on sonoluminescence.

Recent work done at LLNL with regards to the pulse-width, jitter, and bubble radius.

Spring and Summer Interns

Sonoluminescence is an on going project at LLNL and will continue to support the educational outreach program by hiring students to participate in the research. There are positions available for undergraduates interested in experimental physics and engineering related to sonoluminescence. If you are interested please contact Peter Young at peyoung@llnl.gov

For more information about sonoluminescence at LLNL,

Peter Young-- peyoung@llnl.gov

Technical feedback about this page, contact:

Kelly A. Barrett-- kabarrett@llnl.gov

UCRL-MI-130190

Last Modified: 02:50pm PST, January 7, 1998

URL: http://www-phys.llnl.gov/

This site is a wealth, including Discovered! Metallic Hydrogen

This is a shadow graph of a sonoluminesing bubble. Each frame is approximately one microsecond apart, the bubble reaches a maximum of approximately 60 microns. You can see the slow expansion as the bubble stores energy that is then converted into light after a rapid collapse. After it reaches its first minimum, light is emitted and a shock wave perpetrates away from the center. There are small after bounces and the cycle repeats.

For more information about sonoluminescence at LLNL,

Peter Young-- peyoung@llnl.gov

Robert A. Hiller (pages 96-98), and "Sonoluminescence: Sound Into Light," by Seth J.

Putterman (pages 46-51). See also "Sonoluminescence" by Lawrence A. Crum in Physics

Today (Volume 47, September, 1994, pages 22-29). For a more detailed description of the

technology, see the Web page on sonoluminescence at the University of Illinois at

Urbana-Champaign.