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  • 2000-2004  (1)
  • 1995-1999  (8)
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  • 1
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 2847-2854 
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Energy spectra of ions and fast electrons accelerated by a channeling laser pulse in near-critical plasma are studied using three-dimensional (3D) Particle-In-Cell simulations. The realistic 3D geometry of the simulations allows us to obtain not only the shape of the spectra, but also the absolute numbers of accelerated particles. It is shown that ions are accelerated by a collisionless radial expansion of the channel and have nonthermal energy spectra. The electron energy spectra instead are Boltzmann-like. The effective temperature Teff scales as I1/2. The form of electron spectra and Teff depends also on the length of the plasma channel. The major mechanism of electron acceleration in relativistic channels is identified. Electrons make transverse betatron oscillations in the self-generated static electric and magnetic fields. When the betatron frequency coincides with the laser frequency as witnessed by the relativistic electron, a resonance occurs, leading to an effective energy exchange between the laser and electron. This is the inverse free-electron laser mechanism. Electrons are accelerated at the betatron resonance when the laser power overcomes significantly the critical power for self-focusing. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
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  • 2
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 1880-1886 
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Interaction of relativistically strong laser pulses with plasmas is investigated by a multi-dimensional particle-in-cell (PIC) code VLPL (Virtual Laser Plasma Laboratory) [Bull. Am. Phys. Soc. 41, 1502 (1996)]. Acceleration of background electrons to multi-MeV energies, generation of 100 MG magnetic fields, and dynamics of ion channel boring are studied. It is shown that direct v×B push by the laser pulse in the presence of an azimuthal dc magnetic field effectively accelerates background plasma electrons to energies significantly higher than the ponderomotive potential. The authors call this novel effect "B-loop" acceleration mechanism. It is dominant in near-critical plasma, or when plasma waves disappear due to wavebreaking. Laser channeling in under- and overdense plasmas is also studied. Energy spectra of the accelerated electrons and ions and the laser energy conversion efficiency at the critical surface are presented. It is shown that the accelerated electrons propagate in the form of magnetized jets. This physics is crucial for the fast ignitor concept in inertial confinement fusion. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 3425-3437 
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The generation of harmonics by interaction of an ultrashort laser pulse with a step boundary of a plane overdense plasma layer is studied at intensities Iλ2=1017–1019 W cm−2 μm2 for normal and oblique incidence and different polarizations. Fully relativistic one-dimensional particle-in-cell (PIC) simulations are performed with high spectral resolution. Harmonic emission increases with intensity and also when lowering the plasma density. The simulations reveal strong oscillations of the critical surface driven by the normal component of the laser field and by the ponderomotive force. It is shown that the generation of harmonics can be understood as reflection from the oscillating surface, taking full account of retardation. Describing the oscillations by one or more Fourier components with adjustable amplitudes, model spectra are obtained that well reproduce the PIC spectra. The model is based on relativistic cold plasma equations for oblique incidence. General selection rules concerning polarization of odd and even harmonics depending on incident polarization are derived. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
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  • 4
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 1302-1308 
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Nonlinear channel dynamics and magnetized transport of relativistic electron currents in plasma have been investigated, using transverse two-dimensional particle-in-cell simulations allowing for movable ions and fully relativistic binary collisions. Current filaments self-organize in coaxial structures where the relativistic beam in the center is surrounded by magnetized vacuum and a thin return current sheath outside. The current sheath explodes radially. The filament as a whole is current-neutral with almost vanishing magnetic field at the outside. Ion dynamics play an important role, leading to enhanced self-pinching of the filament cores. Collisional effects become significant in the slowly moving return currents. It is shown that electron currents of 100–1000 MA can be transported through dense plasma, but only through a large number of current filaments, each carrying about one Alfvén current. This aspect is essential for relativistic electron transport in fast ignition of targets for inertial confinement fusion (ICF). © 2000 American Institute of Physics.
    Materialart: Digitale Medien
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  • 5
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 493-495 
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A unified description of wave breaking for relativistic plasma waves having arbitrary phase velocity is obtained on the basis of warm relativistic electron fluid theory [Phys. Fluids 25, 846 (1982)]. Limiting cases found in the literature are reproduced. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
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  • 6
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 641-644 
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Electron acceleration by intense laser pulses is studied in the presence of a stochastic field representing a background plasma. Electron distributions are generated peaked in the direction of laser propagation and having a quasi-thermal energy spectrum. Effective temperatures are obtained above the ponderomotive energy. They scale with laser intensity I0 and interaction time t0 proportional to I01/2t0α with α(approximate)0.5−1.0. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
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  • 7
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 3764-3773 
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Magnetic field generation by a laser-induced wakefield is studied in two-dimensional (2D) planar geometry, both analytically and numerically via particle-in-cell (PIC) code simulations. Generally, the magnetic field in the wake is perpendicular to the 2D plane and can be separated into two components: one is independent of time and uniform in the longitudinal (laser propagation) direction; the other depends on time and varies longitudinally. The scaling of magnetic field strength changes from dIL2/dr⊥ at low light intensities to dIL/dr⊥ at high intensities, where IL is the laser intensity and r⊥ the transverse coordinate. Furthermore, the varying component changes from a periodic to a rather complicated structure and tends to increase with the distance from the pulse front. In addition to the quasistatic component, the magnetic field contains a transient component radiating at nearly twice the plasma frequency during the early stage of wakefield buildup. Phase velocities of the wakefield equal to and less than the vacuum speed of light are considered. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
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  • 8
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 9 (1997), S. 1462-1469 
    ISSN: 1089-7666
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Self-similar gas flow with similarity coordinate ξ=re(minus-plus)t, exponential in time, is investigated for plane, cylindrical and spherical geometry. The underlying Lie group symmetry is pointed out and also how it is obtained from flow with power-law self-similarity (ξ=r/|t|α) in the limit α→∞. Six distinct types of solutions are derived and plotted in r−t coordinates. They are characterized by steep density gradients. Also, solutions with strong shock boundaries are discussed. A completely analytical solution is presented, related to Sedov's solution of a strong point explosion. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
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  • 9
    ISSN: 1090-6487
    Schlagwort(e): 52.50.Jm ; 65.70.+y
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract Recent experiments have utilizied high-power subpicosecond laser pulses to effect the ultrafast heating of a condensed material to temperatures far above the critical temperature. Using optical diagnostics it was established that a complicated density profile with sharp gradients, differing substantially from an ordinary rarefaction wave, forms in the expanding heated matter. The present letter is devoted to the analysis of the expansion of matter under the conditions of the experiments reported by D. von der Linde, K. Sokolowski-Tinten, and J. Bialkowski, Appl. Surf. Science 109/110, 1 (1996); K. Sokolowski-Tinten, J. Bialkowski, A. Cavalleri et al., Proc. Soc. Photo-Opt. Instum. Eng. 3343, 46 (1998); and, K. Sokolowski-Tinten, J. Bialkowski, A. Cavalleri et al., Phys. Rev. Lett. 81, 224 (1998). It is shown that if the unloading adiabat passes through the two-phase region, a thin liquid shell filled with low-density two-phase matter forms in the expanding material. The shell moves with a constant velocity. The velocity in the two-phase material is a linear function of the coordinate (flow with uniform deformation), and the density is independent of the coordinate and decreases with time as t −1.
    Materialart: Digitale Medien
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