Anomalous observations using the fast ignition for laser driven fusion energy are interpreted and experimental and theoretical results are reported which are in contrast to the very numerous effects usually observed at petawatt-picosecond laser interaction with plasmas. These anomalous mechanisms result in rather thin blocks (pistons) of these nonlinear (ponderomotive) force driven highly directed plasmas of modest temperatures. The blocks consist in space charge neutral plasmas with ion current densities above 1010A∕cm2. For the needs of applications in laser driven fusion energy, much thicker blocks are required. This may be reached by a spherical configuration where a conical propagation may lead to thick blocks for interaction with targets. First results are reported in view of applications for the proton fast igniter and other laser-fusion energy schemes.
Acceleration of electrons by lasers in a vacuum was
considered impossible based on the fact that plane-wave
and phase symmetric wave packets cannot transfer energy
to electrons apart from Thomson or Compton scattering or
the Kapitza–Dirac effect. The nonlinear nature of
the electrodynamic forces of the fields to the electrons,
expressed as nonlinear forces including ponderomotion or
the Lorentz force, permits an energy transfer if the conditions
of plane waves in favor of the beams and/or the phase symmetry
are broken. The resulting electron acceleration by lasers
in a vacuum is now well understood as “free wave
acceleration”, as “ponderomotive scattering”,
as “violent acceleration”, or as “vacuum
beat wave acceleration”. The basic understanding
of these phenomena relates to an accuracy principle
of nonlinearity for explaining numerous discrepancies
on the way to the mentioned achievement of “vacuum
laser acceleration”, which goes beyond the well-known
experience of necessary accuracy in both modeling and experimental
work experiences among theorists and experimentalists in
the field of nonlinearity. From mathematically designed
beam conditions, an absolute maximum of electron energy
per laser interaction has been established. It is shown
here how numerical results strongly (both essentially and
gradually) depend on the accuracy of the used laser fields
for which examples are presented and finally tested by
the criterion of the absolute maximum.
The nonlinear plasma dielectric function due to relativistic electron motion is
derived. From this, one can obtain the nonlinear refractive index of the plasma
and estimate the importance of relativistic self-focusing in comparison with
ponderomotive non-relativistic self-focusing at very high laser intensities.
When the laser intensity is very high, ponderomotive self-focusing will be
dominant. However, at some point, when the oscillating velocity of the plasma
electrons becomes very large, relativistic effects will also play a role in self-focusing.
This paper presents a numerical and theoretical
study of the generation and propagation of oscillation
in the semiclassical limit τ → 0 of the nonlinear
paraxial equation at laser–plasma interaction. In
a general setting of both dimension and nonlinearity, the
essential differences between the focusing and defocusing
cases is identified due to the nonlinearity, and dispersion
effects involved in the propagation of solitons at laser
plasma interaction. A sequence of codes has been developed
in mathematics to explore the focusing and defocusing of
the soliton formation and propagation.
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