Number 114 (Story #1), February 17, 1993 by Phillip F. Schewe and Ben Stein ULTRAHIGH-GRADIENT ACCELERATION OF INJECTED ELECTRONS using laser-driven plasma beat waves has been demonstrated for the first time by scientists at UCLA (C.E. Clayton et al., 4 January 1993 Physical Review Letters; contact Chandrashekhar Joshi, 213-825-7279). Using two laser beams at slightly different wavelengths (10.59 and 10.29 microns), the UCLA researchers create a beat pattern in a hydrogen plasma. This causes electrons in the plasma to be pulled toward and then away from the hydrogen nuclei; the resultant relativistic wave propagates through the plasma, providing, in effect, a surf of high electric fields capable of accelerating particles. A separate beam of 2.1-MeV electrons, injected into the plasma chamber in the direction of the plasma wave, was accelerated across the 10-mm interaction zone up to an energy of at least 9.1 MeV, for an effective gradient of 0.7 GeV/m. Scaled up to a size of hundreds of meters or more, such an acceleration scheme would greatly reduce the size-to-energy ratio of future particle accelerators. No previous plasma-wave experiment had demonstrated acceleration with externally injected electrons. (Science, 5 Feb. 1993.)