APS News

January 2004 (Volume 13, Number 1)

Quiet Microwave Ovens, Liquid Lithium Walls Among DPP Meeting Highlights

Improvements in fusion plasmas via liquid lithium, quieter microwave ovens, and a "plasmatron" that reduces smog from buses were among the highlights of the 45th Annual Meeting of the APS Division of Plasma Physics (DPP), held from October 27-31, 2003, in Albuquerque, New Mexico. Around 1600 papers were delivered at this meeting

Pool of liquid lithium in the tray that encircles the bottom of the CDX-U device. The tip of the liquid-lithium injector, which is removed before plasma operations, is reflected on the shiny surface of the liquid lithium.
Pool of liquid lithium in the tray that encircles the bottom of the CDX-U device. The tip of the liquid-lithium injector, which is removed before plasma operations, is reflected on the shiny surface of the liquid lithium.

Liquid lithium makes solid improvement in fusion plasmas. Fusion reactors get hot—really hot. Designing a wall that can take the heat requires clever thinking. Scientists at the DOE Princeton Plasma Physics Laboratory (PPPL) have taken important first steps toward a very clever solution to this problem: the idea is to fashion the wall from liquid. Results of the first fusion experiments with liquid components facing the plasma made a splash in fusion research at the DPP meeting. In addition to offering the hope for a better material for reactor walls, the Princeton experiments show that liquid lithium at the plasma boundary absorbs contaminants and excess fuel, and improves the overall efficiency of performance.

A new entry in the science X-games. The emerging field of high-energy-density physics has been described by a recent National Academy of Sciences report as the "X-games" of contemporary science. The term high energy density is used to describe matter with pressures more than 1 million times the pressure on the surface of the earth. While high energy density matter is extreme by terrestrial standards, it can be found throughout the universe in a number of astrophysical settings and can be made for short times and within small volumes in the laboratory. In an invited talk on Monday morning, Mark Herrmann of Lawrence Livermore National Laboratory described recent experiments that provide a new entry for the "X- games": the laser-driven dynamic hohlraum.

The laser-driven dynamic hohlraum consists of a spherical, laser-driven implosion of a plastic shell filled with xenon. As this thin shell implodes it sweeps up the xenon and causes it to radiate x-rays. When enough radiating xenon has been swept up, the xenon begins to trap x-ray radiation on the inside, creating a time-evolving cavity of intense x-rays—a dynamic hohlraum. With this technique, it may be possible to achieve very high energy densities on experiments at the National Ignition Facility, which began initial physics operations this year.

A Little Chaos May Go a Long Way in Future Fusion Energy Reactors. In work that makes practical, large-scale fusion energy production increasingly feasible, plasma physicists working at the DIII-D National Fusion Facility in San Diego are using a little chaos to prevent precious energy from escaping fusion energy devices. In a magnetic fusion device, or tokamak, one of the most crucial regions for reducing the loss of heat and particles is at the plasma region's edge. Particles crossing this edge leave the plasma and carry energy with them, degrading the fusion reactor's walls and making it harder for the desired fusion energy production to occur. This problem will only increase for next-generation fusion energy machines such as the proposed ITER facility.

As the energy content of the fusion fuel increases, plasma in the edges has a tendency to become unstable, exhibiting a kind of turbulence that physicists call "Edge Localized Modes," commonly referred to as ELMs. In experiments presented this week, an international team of researchers applied chaotic magnetic fields, in which the field lines point in unpredictable directions, to a small edge region of the plasma in the DIII-D experiment. With the chaotic magnetic field they applied, the researchers significantly reduced the ELM instabilities in the DIII-D plasma, enabling more heat to stay trapped in the fusion fuel and preserving the favorable conditions that allow fusion energy production to occur. Assuming that this approach can be extended to next-step fusion energy devices, it holds the promise of increasing the lives of materials that make up fusion-energy device walls without degrading the performance of the plasma fuel.

Microwave ovens that won't mess with your cordless phone and wireless computer. A new invention removes noisy microwave signals from microwave ovens and prevents them from interfering with cordless phones and wireless computer networks. The new technology, developed by plasma physicists at the University of Michigan, is also expected to lead to more efficient microwave ovens, with little or no addition to the ovens' cost.

Microwave ovens heat food by emitting microwaves from a device called a magnetron. Those microwaves then heat and cook the food. One problem with magnetrons is that they emit extra "noisy" microwaves at frequencies that can interfere with other devices. Microwave ovens share an unlicensed part of the microwave frequency band with cordless phones and computer communications systems such as Bluetooth and IEEE 802.11b,g (the standards for wireless networks). The new magnetron produces a "clean" signal with essentially zero emissions apart from the 2.45 GHz frequency it is designed to emit. The secret is arranging the magnetic fields in the magnetron in just the right way. Fortunately, this configuration can be implemented very inexpensively in practically all magnetrons of different makes, ages and power outputs, making it feasible for use in consumer microwave ovens.

MIT "plasmatron" drastically reduces smog emissions from a diesel bus. MIT physicists reported a new advance with the plasmatron, a small device that converts part of a fuel into a hydrogen-rich gas that reduces the emission of pollutants from vehicles. Developed by MIT researchers, the plasmatron was tested on a diesel-engine bus in Columbus, Indiana. The bus was tested by a team of engineers from ArvinMeritor, a major automotive and heavy truck components manufacturer which has licensed the plasmatron technology from MIT.

At the meeting, the MIT researchers reported that the plasmatron device, used with a special catalyst that treats the exhaust, reduced nitrous oxides from the vehicle by 90%. Nitrous oxides (NOx) are a major component of smog. In development for a half-dozen years, the plasmatron is showing special promise for early commercialization in diesel engines, which power many buses and trucks. The MIT researchers believe the plasmatron may provide an excellent means for those vehicles to meet stricter EPA standards planned to go into effect by 2007 for buses and heavy trucks. The plasmatron technology can also be used in gasoline engines, and makes them run potentially 30% more efficiently while also being affordable and very clean.


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Editor: Alan Chodos
Associate Editor: Jennifer Ouellette