From achim@slac.stanford.edu Wed Oct 18 16:20:53 2000 -0700 Date: Wed, 18 Oct 2000 14:46:21 -0400 (EDT) From: AIP listserver Subject: update.508 To: physnews-mailing@aip.org Message-id: <200010181846.OAA01355@pinet.aip.org> PHYSICS NEWS UPDATE The American Institute of Physics Bulletin of Physics News Number 508 October 18, 2000 by Phillip F. Schewe and Ben Stein A PLASMA LENS FOR GEV PARTICLE BEAMS. At next week's American Physical Society Division of Plasma Physics/International Congress on Plasma Physics meeting in Quebec City, Hector Baldis of Livermore (925-422-0101, baldis1@llnl.gov) will present experiments showing that plasmas have focused high-density, high-energy electron and positron beams 1000 times better than magnetic quadrupoles used in conventional accelerator technology. In the E150 experiment (http://www.slac.stanford.edu/exp/e150/) carried out at the SLAC Final Focus Test beam, a standard plasma--a gas of ions and electrons--could focus a 30-GeV electron beam to one-third of its original diameter in just 2 centimeters. In addition, the researchers demonstrated plasma focusing of high-energy positron beams for the first time. Technologies have long existed for focusing MeV electron beams, but not for the GeV beams used in state-of-the-art accelerator experiments. How does the plasma focus particle beams so well? To understand this effect, it is important to realize that electrically charged particles in a beam experience two competing forces: a "Coulomb" force which tries to push like charges apart, and magnetic forces which push them together. A high-energy beam redistributes the plasma electrons as it passes through, and this serves to reduce the net Coulomb force while leaving the magnetic force unaffected; this manages to pinch the beam closer together. Conventional plasmas seem to focus the beams very well; no exotic plasmas must be prepared. (Paper BO2.002; more information on meeting at http://www.aps.org/meet/DPP00/press)