The l'OASIS Group (Laser Optics and Accelerator Systems Integrated Studies) of Lawrence Berkeley National Lab's Center for Beam Physics performs experimental and theoretical studies of the interaction of high-intensity lasers with particle beams and plasmas. It emphasizes development of such compact, high-gradient, laser-driven particle accelerators (see experimental set-up and set-up near completion of colliding pulse). The experimental program consists of three parts: guiding of high-intensity laser beams (1018 W/cm2) over macroscopic distances (1-10 cm scale length) in a plasma channel; probing of plasma wakefields excited in the channels by the laser pulse using optical techniques; and study of laser-triggered injection of electrons into a plasma structure. The theoretical program develops analytical and computational tools to predict and analyze the physics involved in the interaction of high-intensity laser pulses with beams and plasmas.
A particular highlight of recent work has been the production of high repetition rate (5-10 Hz) relativistic electron beams from plasmas by means of laser wakefield acceleration. By focusing a high-power laser beam onto a high-pressure helium gas jet, electron beams containing multiple nanocoulombs of charge were generated and accelerated to energies up to tens of megaelectron-volts over millimeter-scale distances. Spatially well-collimated beams were measured. The high energy and repetition rate allowed use of the electron beams to produce radioisotopes in Pb and Cu targets. On-line gamma-ray and neutron monitoring was implemented to aid in the tuning of the accelerator.
The energy spread, however, was 100%. To reduce the energy spread, we are currently implementing the colliding-pulse laser injection method, originally proposed by Esarey et al. (Phys. Rev. Lett. 1997). As of this writing, installation of new vacuum chambers and optical hardware for the colliding-pulse laser injection method is underway. This method is expected to produce low emittance (1 pi mm-mrad), low energy spread (1%), and 40 MeV femtosecond electron bunches containing 107 electrons per bunch. By combining this injector with plasma channels on the order of 3 cm, we expect to produce a 1 GeV compact, laser-driven accelerator module using our 10 TW laser system. Future upgrade of the laser system to the 100 TW class is expected to allow us to develop a 10-cm-long, 10 GeV module. We are also exploring the use of this unique tabletop source of femtosecond/attosecond electron bunches. Applications could include a self-amplified stimulated-emission free-electron laser, a high-brightness source for infrared and terrahertz radiation, and perhaps medical isotope production.
For more information, please contact Wim P. Leemans, principal investigator, at
Ernest Orlando Lawrence Berkeley National Laboratory
1 Cyclotron Road, MS 71-259
Berkeley, California 94720
Phone: 510-486-7788
Fax: 510-486-7981
E-mail: wpleemans@lbl.gov
Or visit the Center for Beam Physics web site.
