162 research outputs found
Theory of relativistic radiation reflection from plasmas
We consider the reflection of relativistically strong radiation from plasma
and identify the physical origin of the electrons' tendency to form a thin
sheet, which maintains its localisation throughout its motion. Thereby we
justify the principle of the relativistic electronic spring (RES) proposed in
[A. Gonoskov et al. PRE 84, 046403 (2011)]. Using the RES principle we derive a
closed set of differential equations that describe the reflection of radiation
with arbitrary variation of polarization and intensity from plasma with
arbitrary density profile for arbitrary angle of incidence. PIC simulations
show that the theory captures the essence of the plasma dynamics. In
particular, it can be applied for the studies of plasma heating and surface
high-harmonic generation with intense lasers
Radiation dominated particle and plasma dynamics
We consider the general problem of charged particle motion in a strong
electromagnetic field of arbitrary configuration and find a universal
behaviour: for sufficiently high field strengths, the radiation losses lead to
a general tendency of the charge to move along the direction that locally
yields zero lateral acceleration. The relativistic motion along such a
direction results in no radiation losses, according to both classical and
quantum descriptions of radiation reaction. We show that such a radiation-free
direction (RFD) exists at each point of an arbitrary electromagnetic field,
while the time-scale of approaching this direction decreases with the increase
of field strength. Thus, in the case of a sufficiently strong electromagnetic
field, at each point of space, the charges mainly move and form currents along
local RFD, while the deviation of their motion from RFD can be calculated in
order to account for their incoherent emission. This forms a general
description of particle, and therefore plasma, dynamics in strong
electromagnetic fields, the latter can be generated by state-of-the-art lasers
or in astrophysical environments
Explicit energy-conserving modification of relativistic PIC method
The use of explicit particle-in-cell (PIC) method for relativistic plasma
simulations is restricted by numerical heating and instabilities that may
significantly constrain the choice of time and space steps. To eliminate these
limitations we consider a possibility to enforce exact energy conservation by
altering the standard time step splitting. Instead of particle advancement in a
given field followed by field advancement with current, we split the step so
that each particle is coupled with the field at the nearby nodes and this
coupling is accounted for with enforced energy conservation sequentially for
all particles. Such a coupling method is compatible with various advances,
ranging from accounting for additional physical effects to the use of
numerical-dispersion-free field solvers, high-order weighting shapes and
particle push subcycling. To facilitate further considerations and use, we
provide a basic implementation in a 3D, relativistic, spectral code -PIC,
which we make publicly available. The method and its implementations are
verified using simulations of cold plasma oscillations, Landau damping and
relativistic two-stream instability. The capabilities of the method to deal
with large time and space steps are demonstrated in the problem of plasma
heating by intense incident radiation
Controlling the ellipticity of attosecond pulses produced by laser irradiation of overdense plasmas
The interaction of high-intensity laser pulses and solid targets provides a
promising way to create compact, tunable and bright XUV attosecond sources that
can become a unique tool for a variety of applications. However, it is
important to control the polarization state of this XUV radiation, and to do so
in the most efficient regime of generation. Using the relativistic electronic
spring (RES) model and particle-in-cell (PIC) simulations, we show that the
polarization state of the generated attosecond pulses can be tuned in a wide
range of parameters by adjusting the polarization and angle of incidence of the
laser radiation. In particular, we demonstrate the possibility of producing
circularly polarized attosecond pulses in a wide variety of setups.Comment: 6 pages, 3 figure
Prospects and limitations of wakefield acceleration in solids
Advances in the generation of relativistic intensity pulses with wavelengths
in the X-ray regime, through high harmonic generation from near-critical
plasmas, opens up the possibility of X-ray driven wakefield acceleration. The
similarity scaling laws for laser plasma interaction suggest that X-rays can
drive wakefields in solid materials providing TeV/cm gradients, resulting in
electron and photon beams of extremely short duration. However, the wavelength
reduction enhances the quantum parameter , hence opening the question of
the role of non-scalable physics, e.g., the effects of radiation reaction.
Using three dimensional Particle-In-Cell simulations incorporating QED effects,
we show that for the wavelength nm and relativistic amplitudes
-100, similarity scaling holds to a high degree, combined with
operation already at moderate , leading to photon
emissions with energies comparable to the electron energies. Contrasting to the
generation of photons with high energies, the reduced frequency of photon
emission at X-ray wavelengths (compared to at optical wavelengths) leads to a
reduction of the amount of energy that is removed from the electron population
through radiation reaction. Furthermore, as the emission frequency approaches
the laser frequency, the importance of radiation reaction trapping as a
depletion mechanism is reduced, compared to at optical wavelengths for
leading to similar .Comment: 9 pages, 7 figure
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