title: Investigation of fast-electron-induced Kα x rays in laser-produced blow-off plasma.
abstract: Refluxing of fast electrons generated by high-intensity, short-pulse lasers was investigated by measuring electron-induced Kα x rays from a buried tracer layer. Using planar foils of Au/Cu/CH, the 150-J, 0.7-ps TITAN short-pulse laser was focused on the gold foil to generate fast electrons and the 3-ns, 300-J long pulse beam irradiated on the CH side to create expanding plasma as a conducting medium. By delaying the short-pulse beam timing from the long pulse laser irradiation, the plasma size was varied to change electron refluxing in the target rear. The total yields and two-dimensional images of 8.05-keV Cu-Kα x ray were recorded with an x-ray spectrometer and two monochromatic crystal imagers. The measurements show that the integrated yields decrease by a factor of 10 from refluxing to the nonrefluxing limit. Similar radial profiles of the Kα images in the rear were observed at all delays. Hybrid-particle-in-cell simulations using plasma profiles calculated by a radiation-hydrodynamic code HYDRA agree well with the measured Kα yields. The simulations suggest that conducting plasma with the size of ∼300 μm in the laser direction and ∼600 μm in the lateral direction at the density of 2 × 1020 1/cm3 is sufficiently large to prevent electrons from refluxing in the target. The parameters found in this study can be useful in designing experiments utilizing a Kα x-ray source in refluxing regime or a tracer layer in nonrefluxing regime.
authors.affiliation: Center for Energy Research, University of California San Diego, La Jolla, California 92093, USA.
authors.forename: H
authors.initials: H
authors.lastname: Sawada
authors.affiliation: General Atomics, San Diego, California 92093, USA.
authors.forename: M S
authors.initials: MS
authors.lastname: Wei
authors.affiliation: Center for Energy Research, University of California San Diego, La Jolla, California 92093, USA and Lawrence Livermore National Laboratory, Livermore, California 94550, USA.
authors.forename: S
authors.initials: S
authors.lastname: Chawla
authors.affiliation: Center for Energy Research, University of California San Diego, La Jolla, California 92093, USA.
authors.forename: A
authors.initials: A
authors.lastname: Morace
authors.affiliation: Department of Physics, Ohio State University, Columbus, Ohio 43210, USA.
authors.forename: K
authors.initials: K
authors.lastname: Akli
authors.affiliation: Graduate School of Engineering, Osaka University, 565-0871, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Yabuuchi
authors.affiliation: Photon Pioneers Center, Osaka University, 565-0871, Japan.
authors.forename: N
authors.initials: N
authors.lastname: Nakanii
authors.affiliation: Lawrence Livermore National Laboratory, Livermore, California 94550, USA.
authors.forename: M H
authors.initials: MH
authors.lastname: Key
authors.affiliation: Lawrence Livermore National Laboratory, Livermore, California 94550, USA.
authors.forename: P K
authors.initials: PK
authors.lastname: Patel
authors.affiliation: Lawrence Livermore National Laboratory, Livermore, California 94550, USA.
authors.forename: A J
authors.initials: AJ
authors.lastname: Mackinnon
authors.affiliation: Lawrence Livermore National Laboratory, Livermore, California 94550, USA.
authors.forename: H S
authors.initials: HS
authors.lastname: McLean
authors.affiliation: General Atomics, San Diego, California 92093, USA.
authors.forename: R B
authors.initials: RB
authors.lastname: Stephens
authors.affiliation: Center for Energy Research, University of California San Diego, La Jolla, California 92093, USA.
authors.forename: F N
authors.initials: FN
authors.lastname: Beg