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Plasma Turbulence, ELM Insights Highlight 2005 DPP Meeting

Demonstrations of plasma, its mystery, beauty, and power, were available at the DPP-sponsored Plasma Sciences Expo.
Demonstrations of plasma, its mystery, beauty, and power, were available at the DPP-sponsored Plasma Sciences Expo.

Using the solar wind to study the flow patterns of plasma, new insights into plasma instabilities, and the development of novel approaches to designing effective containment walls for fusion reactors were among the technical highlights of the 47th Annual Meeting of the APS Division of Plasma Physics (DPP), held October 24-28, 2005, in Denver, Colorado. More than 1500 attendees presented 1600 papers covering the latest advances in plasma-based research and technology.

In addition to the regular technical program, the meeting featured four mini-conferences throughout the week, on astrophysical explosions; reconnection and turbulence in fluids and plasmas; status and progress of the fast ignition concept for compressed fuel; and the dynamics of magnetic flux tubes in space and laboratory plasmas. Two special poster sessions focused on physics research at the high school and undergraduate levels, featuring presentations from summer and thesis research by participating students.

The DPP also scheduled a series of educational events to encourage teachers, students and the general public to explore plasma. At the Plasma Expo, offered without charge to teachers and their students, scientists from around the world were on hand to engage participants in lively hands-on demonstrations and explorations. Those attending were able to create arcs of lightning, observe their fluctuating body temperature on a special monitor, manipulate a glowing plasma with magnets, and learn how to confine a plasma by playing a tokamak video game.

Turbulence of the Solar Wind. Researchers at Los Alamos National Laboratory are using the solar wind and Earth's magnetosphere as a planet-sized "wind tunnel" to study the flow properties of plasma, much as engineers use wind tunnels to study airflow when designing aircraft. A recent study has shown that turbulence in the solar wind affects the way the wind interacts with Earth's magnetosphere, just as turbulence in the air affects airflow around an aircraft. This research is important if astronomers are to understand the large-scale flows of plasma throughout the universe.

Where Do Magnetic Fields Come From? Research on the Madison Dynamo Experiment at the University of Wisconsin at Madison has provided new insights into the behavior of the magnetic fields generated by Earth and other rotating objects, including planets, stars, and galaxies. The experiment uses a spherical vessel –a dynamo–that holds a cubic meter of molten sodium. Under experimental conditions, propellers drive flows of the sodium and create conditions necessary to generate a magnetic field in a similar manner to the the processes that generate fields surrounding Earth and the Sun. The device's operating parameters can be manipulated to yield experimental data on a range of magnetic-field-generating systems–including entire galaxies, stars, and Earth and other planets–that previously could only be observed and modeled.

Ripples at the Edge of Hot Plasma. Physicists have opened a new window into the complex behavior that occurs at the edge of a 100 million-degree fusion plasma, of the type that will be produced in Tokamak fusion reactors, revealing the mechanisms behind fusion plasma instabilities. Using advanced high-speed cameras, physicists obtained very detailed, three-dimensional images of plasma instabilities known as Edge Localized Modes (ELMs). Additional images also provided researchers with their first glimpse of how particles and energy are transported during an ELM instability, which can hamper a Tokamak's operation. The images captured by researchers on the DIII-D Tokamak at General Atomics in La Jolla, California, have led to a much better understanding of ELM instabilities, with several theoretical predictions verified by these measurements.

Keeping the Fusion Fires Burning. In research with important implications for the development of the International Thermonuclear Experimental Reactor (ITER), recent experiments on the DIII-D fusion facility at General Atomics in La Jolla, California, and on the National Spherical Torus Experiment (NSTX) at the Princeton Plasma Physics Laboratory in Princeton, New Jersey, have simulated the behavior of alpha particles and Alfvén waves expected in the plasma of a fusion reactor. NSTX and DIII-D researchers can now address whether super Alfvénic ions interacting with short-scale Alfvén waves can lead to loss of energetic particles in ITER and how these Alfvén waves might affect thermal plasma particles.

Accelerating Electrons with Bright Sparks. A train of ultra-intense radiation spikes can be created for use as an advanced electron accelerator with potential medical and physics applications. Scientists at the University of Texas have discovered a new method to amplify and compress laser power, which uses a plasma of ions and electrons. The researchers directed two laser beams, with slightly different frequencies but traveling in the same direction, into a series of plasmas, eventually creating sparks that produce plasma wave "buckets." The buckets grab and accelerate low-energy electrons up to hundreds of millions of electron volts. If this method is proven in experiments, the technique could lead to tabletop electron accelerators for portable X-ray sources in medical applications or for gamma-ray radiography of tiny objects.

Up Against the Wall. Experiments at the Massachusetts Institute of Technology and Princeton University have demonstrated novel approaches to designing effective containment walls for fusion reactors. The new methods, coating wall materials with an ultra-thin layer of boron and using liquid metal lithium as a wall material, have important implications for the design of fusion reactors.

Infrared image of liquid lithium in the tray that encircles the bottom of the LTX device. The swirling pattern that indicates the circulation of the liquid lithium is clearly evident. The electron beam hits the lithium immediately to the left of the picture.
Infrared image of liquid lithium in the tray that encircles the bottom of the LTX device. The swirling pattern that indicates the circulation of the liquid lithium is clearly evident. The electron beam hits the lithium immediately to the left of the picture.

When subjected to heat loads greater than those expected in a fusion reactor, the lithium liquefied and began to swirl rapidly, distributing the heat in much in the same way stirring makes all of the soup in a pot reach the same temperature. The "self-stirring" of the lithium observed in the Lithium Tokamak Experiment (LTX) at the U.S. Department of Energy's Princeton Plasma Physics Laboratory suggests a simple and efficient technique for heat dissipation without the use of expensive pumps and complex plumbing. It is a new concept that has potential to solve the heat load challenge in fusion reactors and other high heat load environments, such as "dumps" for high intensity beams.



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