title: Observation of ultrafast nonequilibrium collective dynamics in warm dense hydrogen.
abstract: We investigate ultrafast (fs) electron dynamics in a liquid hydrogen sample, isochorically and volumetrically heated to a moderately coupled plasma state. Thomson scattering measurements using 91.8 eV photons from the free-electron laser in Hamburg (FLASH at DESY) show that the hydrogen plasma has been driven to a nonthermal state with an electron temperature of 13 eV and an ion temperature below 0.1 eV, while the free-electron density is 2.8x10{20} cm{-3}. For dense plasmas, our experimental data strongly support a nonequilibrium kinetics model that uses impact ionization cross sections based on classical free-electron collisions.
authors.affiliation: DESY, Notkestr. 85, 22607 Hamburg, Germany.
authors.forename: R R
authors.initials: RR
authors.lastname: Fäustlin
authors.forename: Th
authors.initials: T
authors.lastname: Bornath
authors.forename: T
authors.initials: T
authors.lastname: Döppner
authors.forename: S
authors.initials: S
authors.lastname: Düsterer
authors.forename: E
authors.initials: E
authors.lastname: Förster
authors.forename: C
authors.initials: C
authors.lastname: Fortmann
authors.forename: S H
authors.initials: SH
authors.lastname: Glenzer
authors.forename: S
authors.initials: S
authors.lastname: Göde
authors.forename: G
authors.initials: G
authors.lastname: Gregori
authors.forename: R
authors.initials: R
authors.lastname: Irsig
authors.forename: T
authors.initials: T
authors.lastname: Laarmann
authors.forename: H J
authors.initials: HJ
authors.lastname: Lee
authors.forename: B
authors.initials: B
authors.lastname: Li
authors.forename: K-H
authors.initials: KH
authors.lastname: Meiwes-Broer
authors.forename: J
authors.initials: J
authors.lastname: Mithen
authors.forename: B
authors.initials: B
authors.lastname: Nagler
authors.forename: A
authors.initials: A
authors.lastname: Przystawik
authors.forename: H
authors.initials: H
authors.lastname: Redlin
authors.forename: R
authors.initials: R
authors.lastname: Redmer
authors.forename: H
authors.initials: H
authors.lastname: Reinholz
authors.forename: G
authors.initials: G
authors.lastname: Röpke
authors.forename: F
authors.initials: F
authors.lastname: Tavella
authors.forename: R
authors.initials: R
authors.lastname: Thiele
authors.forename: J
authors.initials: J
authors.lastname: Tiggesbäumker
authors.forename: S
authors.initials: S
authors.lastname: Toleikis
authors.forename: I
authors.initials: I
authors.lastname: Uschmann
authors.forename: S M
authors.initials: SM
authors.lastname: Vinko
authors.forename: T
authors.initials: T
authors.lastname: Whitcher
authors.forename: U
authors.initials: U
authors.lastname: Zastrau
authors.forename: B
authors.initials: B
authors.lastname: Ziaja
authors.forename: Th
authors.initials: T
authors.lastname: Tschentscher