SUMMARY Most of the matter we are familiar with in everyday life comes in three states - solid, liquid, or gas. But much more of the matter in the universe exists in a fourth state known as plasma. Plasmas are gaseous collections of electrically charged particles such as electrons and protons. Stars are primarily composed of hot plasmas. On Earth, plasmas are formed in lightning strikes and produce light in fluorescent bulbs. They are used to inscribe patterns in computer chips and other electronics, and are at the heart of the most promising nuclear fusion devices that may someday lead to an abundance of cheap, clean, and safe power sources.
The APS Division of Plasma Physics Annual Meeting is the world's largest yearly gathering of plasma physicists, with more than 1500 attendees presenting 1425 papers covering the latest advances in plasma-based research and technology.
HIGHLIGHTS: Here is a sampling of some of the topics and events that will be included at the 46th annual Division of Plasma Physics meeting.
1. Compact Particle Beams for Science and Medicine
2. Plasma Window Leads to New Welding Technique
3. Taming Plasma Bursts to Ensure Fusion Chamber Survival
4. Progress in Direct-Drive Inertial Fusion Research
5. X-Ray Vision for the Earth's Most Powerful X-Ray Source
6. New Measurements Link Theory and Experiment in Plasma Heating
7. Plasma Sciences Expo Open to the Public
Compact Particle Beams for Science and Medicine
New techniques for accelerating electrons are producing tightly focused, energetically uniform beams in compact devices that will be ideal for numerous scientific and medical applications. The accelerators, known as laser wakefield devices, are only meters in length and could replace accelerators that are currently miles long. Because of their compact size, laser wakefield accelerators are likely to find applications in laboratories that lack space for conventional accelerators. In laser wakefield machines, electrons in a plasma are accelerated when they ride the wake of an intense laser pulse, much like dolphins riding the wake of a ship on the ocean. Typically, the laser pulses in such machines spread out as they pass through a plasma, leading to diffuse beams with few energetic electrons. Researchers at the Lawrence Berkeley Laboratory have improved the quality of laser wakefield beams by injecting preliminary pulses into a gas to create a plasma channel that guides a subsequent, accelerating laser pulse.. The result is a nearly uniform, 100 million electron volt, bunch of electrons only 10 femtoseconds (10 quadrillionths of a second) long. The devices should fulfill applications in research and medicine that rely on accelerators to produce pulses of x-ray and infrared radiation, including high resolution imaging and treatments for certain types of cancer. (Papers: CO2.004, CO2.006, CP1.126. Contact: W.P. Leemans, email@example.com, 510-486-7788)
Plasma Window Leads to New Welding Technique
Electron Beam Welding (EBW), which relies on beams of electrons to melt and join metal pieces, provides the highest quality welds currently achievable. However, the technique requires parts to be kept under vacuum during welding because the electron guns that produce the beams cannot function in normal atmospheric conditions. EBW, therefore, has not typically been an option for welding of large structures such as cars, airplanes, or ships. Researchers with Brookhaven National Laboratory and Acceleron Inc. have developed a novel plasma window that separates the vacuum of EBW beam sources from ambient pressures while allowing electron beams to pass through. The plasma window is formed of electric and magnetic fields, effectively leading to something resembling 'force fields' trapping a plasma that separates an evacuated electron beam source from atmosphere. The plasma window has allowed researchers to produce welds under normal atmospheric conditions that rival the quality of EBW welds performed in vacuum, which means size may no longer be a factor when it comes to large manufacturing applications that can benefit from electron beam welding. (Paper: JI1B.004. Contact: Ady Hershcovitch, firstname.lastname@example.org, 631-344-4531,)
Taming Plasma Bursts to Ensure Fusion Chamber Survival
Creating a fusion 'sun' on earth, in plasma fusion machines such as tokamaks, will provide a critically needed, environmentally acceptable long-term source of energy. However, the task is complicated by the bursts from the 100-million-degree plasma that reach and threaten the life of the chamber surrounding the manmade sun. International teams of scientists at the PPPL National Spherical Torus Experiment (NSTX) and the GA DIII-D National Fusion Facility carried out a series of investigations of these bursts, their varieties, and their dependence on the plasma conditions. A new type of bursts is identified to be particularly interesting, with much higher frequency and lower energy, and therefore delivers much weaker punches than the more studied varieties. Multiple ultra-fast high-resolution cameras (up to one million frames per second), infrared cameras, spectrometers, edge probes, fast gas puffs, and modern computing and modeling codes were trained to reveal the detailed nature and conditions of these bursts. An advanced diagnostic using atomic lithium beams has been developed to provide information on our understanding of when these bursts arise. Maintaining the proper fusion plasma conditions now holds the potential of taming these 'astrophysical' bursts to ensure the fusion chamber survival. More information on this exciting development and the movies of the bursts at the plasma edge and the surfaces of the chamber are available through the NSTX website at www.pppl.gov/~szweben/NSTX04/NSTX_04.html. (Paper JP1.004. Contact: Martin Peng,MPeng@pppl.gov, 609-243-2305)
Progress in Direct-Drive Inertial Fusion Research
Significant advances on the route to inertial confinement fusion have been achieved by researchers at the University of Rochester's Laboratory for Laser Energetics (LLE). Laser inertial confinement fusion consists of heating and compressing fuel in millimeter-sized capsules irradiated with powerful laser beams. In a series of papers presented at the meeting, LLE researchers will report on tests at the OMEGA, 60-beam laser facility that are helping to set the stage for National Ignition Facility - the nation's premier fusion laser facility scheduled to be completed later in the decade. (Papers: CO1.009, HO1.012. Contact: Robert L. McCrory, email@example.com, 585-275-5286)
X-Ray Vision for the Earth's Most Powerful X-Ray Source
X-ray movies of wire-array z-pinch implosions on Sandia National Laboratories' Z-machine have been made for the first time, revealing a rich array of implosion phenomena. Measuring the mass distribution of dense plasmas is traditionally done using x rays in a fashion similar to dental radiographs; an x-ray source is placed near the plasma and an x-ray photograph of the plasma is recorded. This is nontrivial when the plasma being imaged is a z pinch. Wire-array z-pinches at Sandia National Laboratories' "Z-machine" are the world's most powerful laboratory x-ray sources, producing 1-2 million Joules of x rays in 100-200 TW bursts. Nonetheless, researchers presenting at the APS meeting successfully took x-ray pictures of z-pinch plasmas on the Z facility using a special crystal imaging diagnostic. This diagnostic is only sensitive to x rays of a single photon energy, unlike traditional x-ray imaging diagnostics. This allowed the use of a laser-produced plasma x-ray source only one-millionth as energetic to be used to image z-pinch plasmas. Now, for the first time researchers are able to study the growth and evolution of plasma instabilities during the z-pinch implosion. Z pinches begin as a cylindrical array of wires, each thinner than a human hair, that are vaporized into plasma by 20 million Amperes of current. This plasma is then is "pinched" to the axis of the array where it rapidly heats up and radiates soft x rays. Until now, very little information existed for the earliest stages of the z-pinch implosion. Each stage of this process has now been imaged, providing quantitative information about the mass distribution of the plasma that is being used to constrain existing physical models and simulations of z-pinch implosions. The instabilities formed during the early stages of the implosion are believed to ultimately limit the peak achievable radiation power, so an understanding of these instabilities is important to understanding how radiation is produced by z pinches. (Papers: EI2.002, PO3.007, and HP1.102. Contact: Daniel Sinars, firstname.lastname@example.org, 505-284-4809).
New Measurements Link Theory and Experiment in Plasma Heating
In plasmas that include multiple species of ions, like those expected in potential fusion devices, the long wavelength, penetrating radio waves used to heat the plasma can spontaneously convert into short wavelength waves. It's important to identify where and how these waves convert to understand heating in machines such as tokamaks, which are likely to lead to the first practical fusion energy sources. Researchers at MIT have now succeeded in simultaneously measuring both the short wavelength and long wavelength waves in a tokamak for the first time on the Alcator C-Mod tokamak. The experimental results are consistent with theoretical predictions, bolstering physicists' confidence that they are on the right track in developing models for the complex interactions in plasma fusion machines. Stephen Wukitch (email@example.com, 617-253-8138) will discuss the recent measurements and describe future work along the same lines in presenting paper RI1.002.
Plasma Sciences Expo Open to the Public
Teachers, students, and the general public are invited to explore plasma at the Plasma Sciences Expo, November 18, 6:30 - 8:30 PM at the Savannah International Trade and Convention Center. The program is geared to introduce the local community to the excitement of plasmas and the benefits of plasma research. It is free-of-charge. Scientists from around the country and the world will be there, ready to engage participants in lively hands-on demonstrations and explorations. Those attending will be able to create arcs of lightning, observe their fluctuating body temperature on a special monitor, manipulate a glowing plasma with magnets, watch an electromagnetic wave demonstration, and confine a plasma in a tokamak video game. Students at all levels, teachers, parents and the general public are welcome.