title: Generation of Superponderomotive Electrons in Multipicosecond Interactions of Kilojoule Laser Beams with Solid-Density Plasmas.
abstract: The interaction of a multipicosecond, kilojoule laser pulse with a surface of a solid target has been shown to produce electrons with energies far beyond the free-electron ponderomotive limit m_{e}c^{2}a_{0}^{2}/2. Particle-in-cell simulations indicate that an increase in the pulse duration from 1 to 10 ps leads to the formation of a low-density shelf (about 10% of the critical density). The shelf extends over 100  μm toward the vacuum side, with a nonstationary potential barrier forming in that area. Electrons reflected from the barrier gain superponderomotive energy from the potential. Some electrons experience an even greater energy gain due to ponderomotive acceleration when their "dephasing rate" R=γ-p_{x}/m_{e}c drops well below unity, thus increasing acceleration by a factor of 1/R. Both 1D and 2D simulations indicate that these mechanisms are responsible for the generation of extensive thermal distributions with T_{e}>10  MeV and a high-energy cutoff of hundreds of MeV.
authors.affiliation: Center for Energy Research, University of California, San Diego, California 92093, USA.
authors.forename: A
authors.initials: A
authors.lastname: Sorokovikova
authors.affiliation: Institute for Fusion Studies, The University of Texas, Austin, Texas 78712, USA.
authors.forename: A V
authors.initials: AV
authors.lastname: Arefiev
authors.affiliation: Center for Energy Research, University of California, San Diego, California 92093, USA.
authors.forename: C
authors.initials: C
authors.lastname: McGuffey
authors.affiliation: Center for Energy Research, University of California, San Diego, California 92093, USA.
authors.forename: B
authors.initials: B
authors.lastname: Qiao
authors.affiliation: Central Laser Facility, STFC Rutherford-Appleton Laboratory, Didcot OX11 0QX, United Kingdom.
authors.forename: A P L
authors.initials: AP
authors.lastname: Robinson
authors.affiliation: General Atomics, San Diego, California 92186, USA.
authors.forename: M S
authors.initials: MS
authors.lastname: Wei
authors.affiliation: Lawrence Livermore National Laboratory, Livermore, California 94511, USA.
authors.forename: H S
authors.initials: HS
authors.lastname: McLean
authors.affiliation: Center for Energy Research, University of California, San Diego, California 92093, USA.
authors.forename: F N
authors.initials: FN
authors.lastname: Beg