599 research outputs found
Short Intense Laser Pulse Collapse in Near-Critical Plasma
It is observed that the interaction of an intense ultra-short laser pulse
with an overdense gas jet results in the pulse collapse and the deposition of a
significant part of energy in a small and well localized volume in the rising
part of the gas jet, where the electrons are efficiently accelerated and
heated. A collisionless plasma expansion over 150 microns at a sub-relativistic
velocity (~c/3) has been optically monitored in time and space, and attributed
to the quasistatic field ionization of the gas associated to the hot electron
current. Numerical simulations in good agreement with the observations suggest
the acceleration in the collapse region of relativistic electrons, along with
the excitation of a sizeable magnetic dipole that sustains the electron current
over several picoseconds. Perspectives of ion beam generation at high
repetition rate directly from gas jets are discussed
Scalings for ultra-relativistic laser plasmas and monoenergetic electrons
The similarity theory is derived for ultra-relativistic laser-plasma
interactions. First, it is shown that the most fundamental S-similarity is
valid for both under- and overdense plasmas. Then, the particular case of
tenious plasma is considered in great detail. It is shown that the electron
dynamics in this case has two characteristic scales. The fast scale corresponds
to relaxation to some attractor solution. The slow dynamics describes an
adiabatic evolution of this attractor. This leads to a remarkable wave breaking
exclusion rule in the 3D geometry. A similarity theory for the slow dynamics
allows obtaining simple ``engineering'' scalings for the maximum electron
energies, the number of accelerated electrons, the electron beam density, and
for the acceleration distance. These scalings are aimed at design of a
high-energy laser-plasma accelerator generating electron beams with superior
properties
Towards laser based improved experimental schemes for multiphoton e+ e- pair production from vacuum
Numerical estimates for pair production from vacuum in the presence of strong
electromagnetic fields are derived, for two experimental schemes : the First
concerns a laser based X-FEL and the other imitates the E144 experiment. The
approximation adopted in this work is that of two level multiphoton on
resonance. Utilizing achievable values of laser beam parameters, an
enhancedproduction efficiency of up to 10^11 and 10^15 pairs can be obtained,
for the two schemes respectively.Comment: 6 pages, 4 figure
Excitation of nonlinear two-dimensional wake waves in radially-nonuniform plasma
It is shown that an undesirable curvature of the wave front of
two-dimensional nonlinear wake wave excited in uniform plasma by a relativistic
charged bunch or laser pulse may be compensated by radial change of the
equilibrium plasma density.Comment: 6 pages, 4 figure
Transverse Dynamics and Energy Tuning of Fast Electrons Generated in Sub-Relativistic Intensity Laser Pulse Interaction with Plasmas
The regimes of quasi-mono-energetic electron beam generation were
experimentally studied in the sub-relativistic intensity laser plasma
interaction. The observed electron acceleration regime is unfolded with
two-dimensional-particle-in-cell simulations of laser-wakefield generation in
the self-modulation regime.Comment: 10 pages, 5 figure
Temporary Acceleration of Electrons While Inside an Intense Electromagnetic Pulse
A free electron can temporarily gain a very significant amount of energy if
it is overrun by an intense electromagnetic wave. In principle, this process
would permit large enhancements in the center-of-mass energy of
electron-electron, electron-positron and electron-photon interactions if these
take place in the presence of an intense laser beam. Practical considerations
severely limit the utility of this concept for contemporary lasers incident on
relativistic electrons. A more accessible laboratory phenomenon is
electron-positron production via an intense laser beam incident on a gas.
Intense electromagnetic pulses of astrophysical origin can lead to very
energetic photons via bremsstrahlung of temporarily accelerated electrons
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