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Tzoufras, M.

Paper Title Page
TPAE038 Particle-in-Cell Simulation of LWFA Using 50 fs Pulses in Guided and Unguided Plasmas
 
  • F.S. Tsung, R. Fenseca, C. Joshi, W. Lu, W.B. Mori, L.O. Silva, M. Tzoufras
    UCLA, Los Angeles, California
 
  Funding: Work supported by DOE and NSF.

In 2004, we reported on 3D simulation results that using a modest laser, it was possible to generate a ~250 MeV monoenergetic beam with .5 nC of charge and to generate a few .8GeV electrons (Tsung et al, Phys. Rev. Lett., 93, 185002). We found that the self-injected electrons originated only after the laser distorted from a combination of photon deceleration and longitudinal group velocity dispersion and these electrons originated from the edge of the laser. We also observed that the mono-energetic nature arose due to phase space rotation and beam loading. In the September, 30, 2004 issue of Nature, many experimental groups have reported the observation of mono-energetic beams of electrons in the range of 100 MeV. These experiments have been performed for a range of plasma parameters. We have begun to systematically study (in 2 and 3D) the acceleration mechanisms for plasma conditions under which these experiments operated to verify that what we observed in our simulations is universal. Our 3D simulation of the experiment by Mangles et al produced excellent agreement in electron energy spectrum and we have begun to look at the other two experiments reported in Nature.

 
TPAE040 Nonlinear Theory in the Blowout Regime for Both Particle Beam and Laser Drivers
 
  • W. Lu, R. Fenseca, C. Huang, W.B. Mori, L.O. Silva, F.S. Tsung, M. Tzoufras, M. Zhou
    UCLA, Los Angeles, California
  • T.C. Katsouleas
    USC, Los Angeles, California
 
  Funding: DOE and NSF.

Recent progress in both PWFA and LWFA has confirmed the promising characteristics of the blowout regime. So it is worthwhile to understand the wake excitation process and other relevant issues (e.g. self trapping mechanism, laser self guiding, scaling laws) in this regime. Because the plasma electrons always cross each other in the blowout regime, it is not possible to use a fluid model. Instead, we use a particle picture. Based on the analysis of the innermost particle trajectory, we have developed a self-consistent theory for this regime. For particle beam drivers, we explained why linear theory can be a good approximation in the weakly nonlinear blowout regime and also obtained formulas to predict the wake amplitude. In the strongly nonlinear blowout regime (relativistic or ultra-relativistic), the theory can predict the wake structures and amplitudes in terms of the particle beam or laser pulse intensity. The theory also provides a basis for a beam loading theory in the blowout regime as well a basis for finding optimum driver profile. We will also give some results on the energy gain and total charge scalings based on this theory.

 
TPAE045 Is it Possible To Generate nC, Mono-Energetic Electron Beams at 1GeV and Beyond Using Existing or Near Term Lasers via LWFA?
 
  • M. Tzoufras, S. Fonseca, W. Lu, W.B. Mori, L.O. Silva, F.S. Tsung
    UCLA, Los Angeles, California
 
  Funding: Work supported by DOE and NSF.

Recently, several groups around the world observed mono-energetic beams between 80 MeV and 170 MeV using ~15 TW lasers. We have begun a comprehensive study of the acceleration of electrons by the interaction of ultra-intense short and ultra-short laser pulses with underdense plasma. We concentrate our parameter space to existing and near term laser parameters, i.e., laser parameters between 30 and 100 TW. We use 3D particle in cell simulations using the code OSIRIS. The goal is to show that the generation of mono-energetic beams with energy beyond 1GeV with current and near future laser systems is possible without the need for any external injection. In this ultra-relativistic regime the laser blows out all the electrons forming an almost spherical cavity. Some electrons are self-injected in the blowout region and accelerated by the laser wakefield to ultrahigh energy. In order to maximize the energy gain, the beam charge and quality, we need an improved understanding of the wakefield generation as well as of processes such as self-injection and beam loading. We will provide theoretical estimates and verify their validity with 3D simulations. We will address possible limitations of particle acceleration in this regime.

Tsung et al., Phys. Rev. Lett., 93, 185002. S.P.D. Mangles et al. Nature 431, 535 (2004). C.G.R. Geddes et al. Nature 431, 538 (2004). J. Faure et al. Nature 431, 541 (2004). A. Pukhov and J. Meyer-ter-vehn, Appl.Phys.B, 74, 355 (2002).