16,747 research outputs found
Comoving acceleration of overdense electron-positron plasma by colliding ultra-intense laser pulses
Particle-in-cell (PIC) simulation results of sustained acceleration of
electron-positron (e+e-) plasmas by comoving electromagnetic (EM) pulses are
presented. When a thin slab of overdense e+e- plasma is irradiated with
linear-polarized ultra-intense short laser pulses from both sides, the pulses
are transmitted when the plasma is compressed to thinner than ~ 2 relativistic
skin depths. A fraction of the plasma is then captured and efficiently
accelerated by self-induced JxB forces. For 1 micron laser and 1021Wcm-2
intensity, the maximum energy exceeds GeV in a picosecond.Comment: 10 pages, 4 figure
On distinguished orbits of reductive representations
Let be a real reductive Lie group and be
a real reductive representation of with (restricted) moment map m_{\ggo}:
V-{0} \longrightarrow \ggo. In this work, we introduce the notion of "nice
space" of a real reductive representation to study the problem of how to
determine if a -orbit is "distinguished" (i.e. it contains a critical point
of the norm squared of m_{\ggo}). We give an elementary proof of the
well-known convexity theorem of Atiyah-Guillemin-Sternberg in our particular
case and we use it to give an easy-to-check sufficient condition for a
-orbit of a element in a nice space to be distinguished. In the case where
is algebraic and is a rational representation, the above condition
is also necessary (making heavy use of recent results of M. Jablonski),
obtaining a generalization of Nikolayevsky's nice basis criterium. We also
provide useful characterizations of nice spaces in terms of the weights of
. Finally, some applications to ternary forms and minimal metrics on
nilmanifolds are presented.Comment: 27 pages (with an appendix), 2 figures, 5 tables. This is a
preliminary version; comments, criticisms and suggestions are welcom
Sustained Acceleration of Over-dense Plasmas by Colliding Laser Pulses
We review recent PIC simulation results which show that double-sided
irradiaton of a thin overdense plasma slab by ultra-intense laser pulses from
both sides can lead to sustained comoving acceleration of surface electrons to
energies much higher than the conventional ponderomotive limit. The
acceleration stops only when the electrons drift transversely out of the laser
beam. We show results of parameter studies based on this concept and discuss
future laser experiments that can be used to test these computer results.Comment: 9 pages 6 figures. AIP Conference Proceedings for 2005 Varenna Conf.
on Superstrong Fields in Plasmas (AIP, NY 2006
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