ld 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, wpleemans@lbl.gov, 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
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Contact: James Riordon
riordon@aps.org
301-209-3238
American Physical Society
5-Nov-2004

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