Tutorial Sessions, Mini-Conferences, Plasma Science Expo Featured at the DPP Meeting
Physicists discussed the latest discoveries in the universe of plasmas when the APS Division of Plasma Physics (DPP) held its annual meeting on November 17-21, 1997 at the Lawrence Convention Center in Pittsburgh, Pennsylvania. More than 1500 papers were presented at the second largest APS meeting of the year, including four review papers, three APS prize recipient addresses, and 84 invited talks. Wednesday evening's banquet featured a keynote address by William Happer of Princeton University, as well as presentation of the 1997 APS Maxwell Prize, Award for Excellence in Plasma Physics, and Award for Outstanding Doctoral Dissertation in Plasma Physics by APS President, Andy Sessler.
A prominent new feature was the organization of five tutorial sessions, aimed at educating non-specialists with a graduate level understanding of important topics in plasma physics. Thirteen tutorial presentations were given, explaining the basic principles, accomplishments, issues and objectives of such topics as laser-induced fluorescence diagnostics in plasmas, magnetic reconnection, laser-driven plasma based accelerators, and controversies in quasilinear theory. The DPP hopes such sessions will be a valuable addition to the annual meeting, and contribute to the continued cross-fertilization of ideas in plasma physics. There were also four "mini-conferences" consisting of contributed presentations throughout the week in the areas of coherent radiation generation, plasma accelerators, nonlinear dynamics, and deep space plasmas.
Latest Fusion News
Magnetic Fusion - Scientists working on the Joint European Torus (JET), the world's largest fusion experiment, presented results of a recent run of experiments on their machine using high-power operation with a 50-50 mixture of deuterium and tritium fuel. The researchers announced a record 14 Megajoules of fusion energy, 16 megawatts of peak fusion power and a record fusion Q (the ratio of fusion power produced to the net input power) of 65%.
On Monday morning, Richard Hawryluk of Princeton Plasma Physics Laboratory gave a twenty-year retrospective on physics experiments of the Tokamak Fusion Test Reactor (TFTR), the experimental nuclear fusion facility in Princeton. Before it ended operations in 1995, TFTR held the previous world record of fusion power yeild and provided deep insights into the nature of fusion plasmas.
ICF - There were many talks on inertial confinement fusion (ICF), especially on topics related to the 192-beam, 2 Megajoule National Ignition Facility (NIF) under construction at LLNL. Not surprisingly, the focus of ICF research revolves around refining the understanding of the underlying physics of interaction of intense light with plasma, capsule implosions, and firming up the designs for ignition. Other ICF highlights presented include talks on the "fast ignition" scheme for ICF, in which an ultra-intense short-laser pulse could supply the ignition spark of a compressed ICF pellet, and impressive increases of x-ray yields from Sandia's Z-pinch.
Medical physics - At a Thursday morning session, Richard London of LLNL described how models developed for laser fision are now being applied to laser medicine. Laser fusion and medicine may be described by similar physics relations which, for example, describe how heat energy from the laser is transported through materials. By simulating the interactions between lasers and human tissue, the model can offer insights into how to optimize laser surgery. It is being applied to animal trials of a laser system for breaking up blood clots in the cerebral vessels which cause strokes.
Accelerator for materials processing - At the same session, Kurt Schoenberg of LANL described the possible application of coaxial plasma accelerators as environmentally sound and economic means for materials processing and advanced manufacturing. Originally developed to provide energetic plasmas for fusion energy experiments, the device uses the Lorentz force to accelerate plasmas to high velocity. Commercial applications are already online.
Plasma Thrusters for Deep Space Transport - Though titles such as "variable specific impulse magnetoplasma rocket" (Jared P. Squire, ASPL/JSC/NASA), "lithium-fed Lorentz force accelerator propulsion" (Nat Fisch, Princeton Univ), or "antiproton-catalyzed microfission/fusion propulsion system" (Gerald A. Smith, Penn State Univ.) sound like the stuff of science fiction, this is indeed not the case. A "mini-conference" held within the DPP annual meeting, drew engineers and researchers from around the world to discuss the latest advances in the theory and designs of plasma-based propulsion systems for deep space travel. A major limiting factor on deep space missions has been the relatively limited exhaust velocities of chemical rockets, which necessitates large initial fuel mass. Plasma thrusters yield high exhaust velocities and energy efficiency.
Plasma applications sessions were interspersed throughout the meeting touching on such varied topics as: klystrons; uses of ion beams; plasma processing of materials, such as for the semiconductor industry; compact accelerators; plasma display panels; environmental cleanup; and plasma 'mirrors' and 'windows.'
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, Nick D'Angelo and their students at the University of Iowa have observed extremely low-frequency waves that propagate through dusty plasmas. According to Merlino, who spoke at a Monday afternoon tutorial, these "dust-acoustic waves" are analogous to sound waves.
Simulating Supernova 1987 A with the NOVA Laser
To better understand Supernova 1987 A (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. Observers of SN1987A soon realized that metal atoms were quickly poking through the hydrogen layer. In experiments at LLNL's NOVA laser, copper plasma (representing the supernova's metal core) is accelerated into a less dense plastic plasma (representing the less dense hydrogen and helium layers). According to Jave Kane of the University of Arizona, this produces features similar to those observed in the supernova.
Laboratory Simulations of Solar Prominences
Solar prominences, huge luminous arches extending outwards from the surface of the sun, 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 in a laboratory experiment which produces controlled, reproducible simulations of erupting prominences, observe twisted, unstable arch-shaped structures very similar to the solar prominences seen by observatories and spacecraft.
In a Monday afternoon session, P.A. Bernhardt of NRL described how he is mapping the plasma density in the earth's upper atmosphere using Computerized Ionospheric Tomography (CIT), a recently developed technique that uses and computer reconstructions to determine both electron and ion densities. New ionospheric imaging instruments are scheduled for launch on numerous spacecraft.
Special thanks to Philip Schewe and Benjamin Stein of AIP's Public Information Division and Bruce Remington, DPP's Public Information Coordinator, for contributing to the coverage of technical sessions in this article.