Plasmas In Pittsburgh

November 13, 1997

College Park, MD--October 24, 1997---Lightning bolts, neon signs, the sun--if you're familiar with these things, then you're familiar with plasmas. Plasmas are gases containing electrically charged particles, such as electrons and protons. Often called the fourth state of matter, plasmas are distinguished from gases of neutral atoms and molecules, such as the nitrogen and oxygen molecules that we breathe in the atmosphere.

PLASMAS IN THE UNIVERSE
We live in a special part of the cosmos--one dominated by solids, liquids, and neutral gases. But plasmas are actually the dominant form of matter in the universe. They make up astrophysical objects such as stars and supernovas. On Earth, they exist naturally as lightning bolts and the bath of charged particles in our upper atmosphere, and come in many different temperatures and compositions. Beams of plasmas engrave the sophisticated patterns in computer chips. And in attempts to provide the world with an abundant source of energy, physicists are striving to make artificial suns--plasmas so hot and so dense that their particles fuse to release energy. This pursuit of nuclear fusion is a major branch of plasma physics research.

THE LATEST DISCOVERIES ABOUT PLASMAS
Physicists will discuss the latest discoveries in the universe of plasmas when the American Physical Society (APS) Division of Plasma Physics holds its annual meeting on November 17-21, 1997 at the Lawrence Convention Center in Pittsburgh, Pennsylvania. More than 1500 papers will be presented. The APS, with over 41,000 members, is the largest professional organization in the world devoted to physics. This is the second largest APS meeting of the year. Only the March APS meeting (to be held in Los Angeles in the coming year) is larger.

PLASMA ON THE WEB
This press release, along with several associated pictures and links, is available at our Physics News Preview web site (www.aip.org/physnews/preview). The complete meeting program can be found on the web at http://www.aps.org/meet/DPP97/index.html

LATEST FUSION NEWS
In September of this year, scientists at the Joint European Torus (JET) in Europe produced 12 megawatts of fusion power, a new world record. Numerous people from JET will present results at the meeting, including JET deputy director Alan Gibson (Friday morning, Nov. 21, Talk sFrAI2.01). Like all fusion experiments to date, the recent JET demonstration did not generate as much power as had been poured into the reactor to start the fusion process. Still, the ratio of output power to input power was a record 50%, about two times greater than the previous record.

Also at the meeting, Richard Hawryluk of Princeton Plasma Physics Laboratory will give a twenty year retrospective on physics experiments at the Tokamak Fusion Test Reactor (TFTR), the experimental nuclear fusion facility in Princeton. (Monday morning, aMoaR.01). Before it ended operations in 1995, TFTR generated the previous world record of 10.7 megawatts of fusion power. During its run, it provided deep insights into the nature of plasmas in fusion devices.

OTHER RESEARCH HIGHLIGHTS AT THE MEETING

---Confining Plasmas Forever. Plasmas can be notoriously difficult to control, whether they exist as the flames of a forest fire or the fuel inside nuclear fusion reactors. Now, a method to confine plasmas indefinitely in the laboratory has been devised by a UC-San Diego group, and subsequently refined by a NIST-Boulder group (contact Pei Huang, NIST, 303-497-3508). These researchers have developed a technique to control a "non-neutral plasma," a plasma made purely of positive particles (such as magnesium ions) or negative particles (such as electrons). These plasmas are often held in Penning traps, devices that use static electric and magnetic fields for confinement. By rotating about the magnetic field, the plasma experiences a Lorentz force (the force acting on charged particles moving in a magnetic field) which holds it together. However, there is a slow loss of angular momentum in these and similar traps, which weakens the Lorentz force, causing the plasma to become less dense and lose particles often in a matter of hours. By introducing additional electric fields that revolve about the magnetic field, the researchers are able to preserve the original plasma for weeks at a time and longer. The additional electrical fields control the plasma's rotation frequency around the magnetic field of the Penning trap. This stabilization technique can be applied to store rare ions (such as antiprotons or bare uranium) for long periods of time. In addition, the rotation control of plasmas is likely to reduce measurement errors in atomic clocks based on ions in Penning traps. This result may also provide clues to the more difficult task of controlling neutral plasmas in magnetic fusion devices. (Tuesday morning, gTuaI2.02)

--Nuclear Fusion Research Benefits Laser Medicine. In the last 25 years, physicists have developed sophisticated computer models to describe the process of laser fusion, in which lasers heat and compress fuel pellets to initiate fusion reactions. At the meeting, Richard London of Lawrence Livermore National Lab (510-423-2021) will describe how these models are now being applied to laser medicine. Although they involve vastly different amounts of energy and temperature scales, laser fusion and medicine can actually be described by the same fundamental mathematical equations. These equations describe, for example, how heat energy from the laser is transported through materials. London and his colleagues have developed a computer model, known as LATIS, which in turn is based on the nuclear fusion computer simulation LASNEX. By simulating the interactions between lasers and human tissue, LATIS can offer insights into how to optimize laser surgery procedures such as removing cataracts and closing wounds. In a specific example, LATIS is being applied to animal trials on a laser system for breaking up blood clots in the cerebral vessels which cause strokes. (Thursday morning, oThaI2.01)

---Dusty Plasmas. Roughly 99% of all matter in the universe exists in the form of a plasma which coexists with dust grains. In this "dusty plasma," the grains exert significant influences on plasma behavior. A one-micron dust grain weighs a trillion times more than a hydrogen ion in the plasma, and can accumulate thousands of electrons with ease. Creating artificial dusty plasmas in their laboratory, Bob Merlino (319-335-1756), Nick D'Angelo and their students at the University of Iowa have observed disturbances that propagate through dusty plasmas in the form of extremely low-frequency waves. Analogous to sound waves, which cause air to compress and expand at regular intervals, these "dust-acoustic waves" compress and expand dust at rates of tens of cycles per second. The presence of charged dust particles can also affect other low-frequency waves in a plasma, and wave disturbances can be produced in situations where, without the dust, the plasmas would otherwise be stable. (Monday afternoon, dMopT.02)

---Simulating Supernova 1987A with the NOVA Laser. To better understand Supernova 1987A (SN1987A), the bright exploding star first observed a decade ago, plasma physicists are creating miniature laboratory versions of the explosion. Right before it explodes, the supernova is believed to be layered like an onion, with a metal core surrounded by helium and hydrogen layers. Before SN1987A, scientists thought the onion simply expanded during the explosion. But observers of SN1987A soon realized that metal atoms were quickly poking through the hydrogen layer. Only if there was some sort of sophisticated mixing going on would this happen. In experiments at Lawrence Livermore National Laboratory, x rays generated by Nova, one of the world's most powerful lasers, strike a model of a supernova--a copper foil (representing the supernova's metal core) against a less dense plastic backing (representing the less dense hydrogen and helium layers). This creates a hot copper plasma that hits the plastic backing, producing features similar to those observed in the supernova. The group is currently working on experiments in which the copper-plastic interface is shaped like an egg crate, designed to create more sophisticated mixing patterns that occur in a real supernova. At the meeting, Jave Kane of the University of Arizona (510-424-5805 is his number at Livermore) will describe this research, possibly including the first results from the latest experiments. (Thursday morning, oThaO2.01)

---Baryons Vary from Cluster to Cluster. X-ray satellites such as ROSAT and ASCA have been training their sights on clusters, large collections of stars or galaxies held together by gravity. Since clusters are so big, they are believed to be representative of the entire universe in the proportions of different types of particles that they contain. As will be reported by Richard Mushotzky of NASA Goddard (301-286-6043), these satellites are finding mounting evidence that clusters vary--by as much as a factor of 3--in what percentage of their total mass is made of baryons, three-quark objects such as protons and neutrons. Since there is no known mechanism which can lead to the difference, researchers speculate that baryons may get removed from clusters, perhaps from exploding stars or merging clusters that expel gas in the process. (Tuesday afternoon, iTpI2.03)

---Laboratory Simulations of Solar Prominences. Solar prominences are huge luminous arches extending outwards from the surface of the sun. These arches are often twisted, forming striking helical patterns. Scientists believe these patterns result from plasmas tracing out the shape of complex twisted magnetic fields emanating from the solar surface. When prominences erupt from the sun's surface, they can indirectly cause magnetic disturbances on Earth, damaging satellites or even causing power outages. Paul Bellan and colleagues at Caltech have recently constructed a laboratory experiment which produces controlled, reproducible simulations of erupting prominences. Inside a vacuum chamber, the researchers put a hydrogen plasma between a horseshoe magnet and introduce electrical currents between the magnet to produce twisted fields. The luminous plasma is photographed by a high-speed camera. The photos show twisted, unstable arch-shaped structures very similar to the solar prominences seen by ground observatories and also by spacecraft such as SOHO and YOHKOH. The Caltech group is now upgrading the experiment to provide more precise control of the electrical and magnetic properties of the simulated prominences. (Monday afternoon, eMopI2.02)
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American Institute of Physics

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