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Experimental data are presented showing maximum carbon C6+ ion energies obtained from nm-scaled targets in the relativistic transparent regime for laser intensities between 9 × 1019 and 2 × 1021 W/cm2. When combined with two-dimensional particle-in-cell simulations, these results show a steep linear scaling for carbon ions with the normalized laser amplitude a0 (
$a_0 \propto \sqrt ( I)$
). The results are in good agreement with a semi-analytic model that allows one to calculate the optimum thickness and the maximum ion energies as functions of a0 and the laser pulse duration τλ for ion acceleration in the relativistic-induced transparency regime. Following our results, ion energies exceeding 100 MeV/amu may be accessible with currently available laser systems.
Fast ignition of inertial fusion targets driven by quasi-monoenergetic ion beams is investigated by means of numerical simulations. Light and intermediate ions such as lithium, carbon, aluminum and vanadium have been considered. Simulations show that the minimum ignition energies of an ideal configuration of compressed Deuterium-Tritium are almost independent on the ion atomic number. However, they are obtained for increasing ion energies, which scale, approximately, as Z2, where Z is the ion atomic number. Assuming that the ion beam can be focused into 10 µm spots, a new irradiation scheme is proposed to reduce the ignition energies. The combination of intermediate Z ions, such as 5.5 GeV vanadium, and the new irradiation scheme allows a reduction of the number of ions required for ignition by, roughly, three orders of magnitude when compared with the standard proton fast ignition scheme.
Self-supporting, thin single crystal membranes can be fabricated from silicon wafers using ion implantation, anodic etching and subsequent annealing. Typically, membranes approximately 1200Å thick and about 250μm in diameter are formed in wafers 4 mil thick. Discs surrounding the membranes can be cut out to provide suitable TEM samples. In this paper, the steps for preparing such samples are presented with as much attention paid to experimental details as possible.
Los Alamos National Laboratory short pulse experiments have shown
using various target cleaning techniques such that heavy ion beams of
different charge states can be produced. Furthermore, by controlling the
thickness of light ions on the rear of the target, monoenergetic ion
pulses can be generated. The spectral shape of the accelerated particles
can be controlled to yield a range of distributions, from Maxwellian to
ones possessing a monoenergetic peak at high energy. The key lies in
understanding and utilizing target surface chemistry. Careful monitoring
and control of the surface properties and induction of reactions at
different temperatures allows well defined source layers to be formed,
which in turn lead to the desired energy spectra in the acceleration
process. Theoretical considerations provide understanding of the process
of monoenergetic ion production. In addition, numerical modeling has
identified a new acceleration mechanism, the laser break-out afterburner
that could potentially boost particle energies by up to two orders of
magnitude for the same laser parameters. This mechanism may enable
application of laser-accelerated ion beams to venues such as compact
accelerators, tumor therapy, and ion fast ignition.
The TRIDENT laser system at the Los Alamos National
Laboratory is being used for fundamental experiments which
study the interaction of self-focusing, stimulated Raman
scattering (SRS) and stimulated Brillouin scattering (SBS)
in a near-diffraction-limited (single) laser hot spot in
order to better understand the coupling between these plasma
instabilities. The diffraction limited beam mimics a single
hot spot found in speckle distributions that are typical
of random or kinoform phase plates (RPP or KPP) used for
spatial smoothing of laser beams. A long scale length,
hot plasma (∼1 mm, ∼0.6 keV) is created by a separate
heater beam, and the single hot spot beam is used to drive
parametric instabilities. The focal plane distribution
and wave-front of the interaction beam are characterized,
and its intensity can be varied between 1014–1016
W/cm2. The plasma density, temperature, and
flow profiles are measured using a gated imaging spectroscopy
of collective Thomson scattering from the heater beam.
Results of the laser and plasma characterization, and initial
results of backscattered SRS, SBS, and beam steering in
a flowing plasma are presented.
A Fréchet lattice E is an AL-space if its topology can be defined by a family of lattice seminorms that are additive in the positive cone of E. Grothendieck proved that AL-Banach spaces have the Dunford-Pettis property. This result was recently extended by Fernández and Naranjo to AL-Fréchet spaces with a continuous norm and weak order unit. In this note we show how to remove both hypotheses.
A case is reported of a transfusion syndrome in a triplet pregnancy with intrauterine death of two of the fetuses. This is an exceptional occurrence in a triplet pregnancy and raises the problem of the management of multiple pregnancies associated with the death of one or more of the fetuses. The problem of the method of delivery and the complications arising in triplet dizygotic pregnancies is discussed.
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