197 research outputs found
Linear theory of nonlocal transport in a magnetized plasma
A system of nonlocal electron-transport equations for small perturbations in
a magnetized plasma is derived using the systematic closure procedure of V. Yu.
Bychenkov et al., Phys. Rev. Lett. 75, 4405 (1995). Solution to the linearized
kinetic equation with a Landau collision operator is obtained in the diffusive
approximation. The Fourier components of the longitudinal, oblique, and
transversal electron fluxes are found in an explicit form for quasistatic
conditions in terms of the generalized forces: the gradients of density and
temperature, and the electric field. The full set of nonlocal transport
coefficients is given and discussed. Nonlocality of transport enhances electron
fluxes across magnetic field above the values given by strongly collisional
local theory. Dispersion and damping of magnetohydrodynamic waves in weakly
collisional plasmas is discussed. Nonlocal transport theory is applied to the
problem of temperature relaxation across the magnetic field in a laser hot
spot.Comment: 27 pages, 13 figure
Powerful laser-produced quasi-half-cycle THz pulses
The Maxwell equations based 3D analytical solution for the terahertz
half-cycle electromagnetic wave transition radiation pulse has been found. This
solution describes generation and propagation of transition radiation into free
space from laser-produced relativistic electron bunch crossing a target-vacuum
interface as a result of ultrashort laser pulse interaction with a thin
high-conductivity target. The analytical solution found complements the theory
of laser initiated transition radiation by describing the generated THz wave
shape at the arbitrary distance from the generating target surface domain
including near-field zone rather than the standard far-field characterization.
The analytical research has also been supplemented with the 3D simulations
using the finite-diference time-domain (FDTD) method, which makes it possible
for description of much wider spatial domain as compared to that from the
particle-in-cell (PIC) approach. The results reported fundamentally shed light
on the interfere of an electron bunch field and THz field of broadband
transition radiation from laser-plasma interaction studied for a long time in
the experiments with solid density plasma and may in future inspire them to
targeted measurements and investigations of unique super intense half-cycle THz
radiation waves near the laser target
High‐Intensity Laser Triggered Proton Acceleration from Ultrathin Foils
The recently developed PIC code MANDOR features arbitrary target design including 3D preplasma and the 6‐component laser fields of a tightly focused laser beam. The 3D simulations have been performed to model recent HERCULES experiments on proton acceleration, where protons with energy greater than 20 MeV were produced using just 1.5 J laser pulses focused to intensity of 2 × 10 21 W/cm 2 . By adapting the 3D target geometry relating to ps‐prepulse effect, reasonable agreement with experimental data for the proton energy spectrum has been achieved. The effect of the 3D preplasma shape on efficiency of proton acceleration is discussed. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/96347/1/161_ftp.pd
Enhanced inverse bremsstrahlung heating rates in a strong laser field
Test particle studies of electron scattering on ions, in an oscillatory
electromagnetic field have shown that standard theoretical assumptions of small
angle collisions and phase independent orbits are incorrect for electron
trajectories with drift velocities smaller than quiver velocity amplitude. This
leads to significant enhancement of the electron energy gain and the inverse
bremsstrahlung heating rate in strong laser fields. Nonlinear processes such as
Coulomb focusing and correlated collisions of electrons being brought back to
the same ion by the oscillatory field are responsible for large angle, head-on
scattering processes. The statistical importance of these trajectories has been
examined for mono-energetic beam-like, Maxwellian and highly anisotropic
electron distribution functions. A new scaling of the inverse bremsstrahlung
heating rate with drift velocity and laser intensity is discussed.Comment: 12 pages, 12 figure
Ultrashort PW laser pulse interaction with target and ion acceleration
We present the experimental results on ion acceleration by petawatt
femtosecond laser solid interaction and explore strategies to enhance ion
energy. The irradiation of micrometer thick (0.2 - 6.0 micron) Al foils with a
virtually unexplored intensity regime (8x10^19 W/cm^2 - 1x10^21 W/cm^2)
resulting in ion acceleration along the rear and the front surface target
normal direction is investigated. The maximum energy of protons and carbon
ions, obtained at optimised laser intensity condition (by varying laser energy
or focal spot size), exhibit a rapid intensity scaling as I^0.8 along the rear
surface target normal direction and I^0.6 along the front surface target normal
direction. It was found that proton energy scales much faster with laser energy
rather than the laser focal spot size. Additionally, the ratio of maximum ion
energy along the both directions is found to be constant for the broad range of
target thickness and laser intensities. A proton flux is strongly dominated in
the forward direction at relatively low laser intensities. Increasing the laser
intensity results in the gradual increase in the backward proton flux and leads
to almost equalisation of ion flux in both directions in the entire energy
range. These experimental findings may open new perspectives for applications.Comment: 6 pages, 5 figures, 3rd EAAC worksho
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