126 research outputs found
Ion acceleration from laser-driven electrostatic shocks
Multi-dimensional particle-in-cell simulations are used to study the
generation of electrostatic shocks in plasma and the reflection of background
ions to produce high-quality and high-energy ion beams. Electrostatic shocks
are driven by the interaction of two plasmas with different density and/or
relative drift velocity. The energy and number of ions reflected by the shock
increase with increasing density ratio and relative drift velocity between the
two interacting plasmas. It is shown that the interaction of intense lasers
with tailored near-critical density plasmas allows for the efficient heating of
the plasma electrons and steepening of the plasma profile at the critical
density interface, leading to the generation of high-velocity shock structures
and high-energy ion beams. Our results indicate that high-quality 200 MeV
shock-accelerated ion beams required for medical applications may be obtained
with current laser systems.Comment: 33 pages, 12 figures, accepted for publication in Physics of Plasma
Laser-driven shock acceleration of monoenergetic ion beams
We show that monoenergetic ion beams can be accelerated by moderate Mach
number collisionless, electrostatic shocks propagating in a long scale-length
exponentially decaying plasma profile. Strong plasma heating and density
steepening produced by an intense laser pulse near the critical density can
launch such shocks that propagate in the extended plasma at high velocities.
The generation of a monoenergetic ion beam is possible due to the small and
constant sheath electric field associated with the slowly decreasing density
profile. The conditions for the acceleration of high-quality, energetic ion
beams are identified through theory and multidimensional particle-in-cell
simulations. The scaling of the ion energy with laser intensity shows that it
is possible to generate MeV proton beams with state-of-the-art 100
TW class laser systems.Comment: 13 pages, 4 figures, accepted for publication in Physical Review
Letter
Improved Filters for Angular Filter Refractometry
Angular filter refractometry is an optical diagnostic that measures absolute
contours of line-integrated density gradient by placing a filter with
alternating opaque and transparent zones in the focal plane of a probe beam,
which produce corresponding alternating light and dark regions in the image
plane. Identifying transitions between these regions with specific zones on the
angular filter (AF) allows the line-integrated density to be determined, but
the sign of the density gradient at each transition is degenerate and must be
broken using other information about the object plasma. Additional features
from diffraction in the filter plane often complicate data analysis. In this
paper, we present an improved AF design that uses a stochastic pixel pattern
with a sinusoidal radial profile to minimize unwanted diffraction effects in
the image caused by the sharp edges of the filter bands. We also present a
technique in which a pair of AFs with different patterns on two branches of the
same probe beam can be used to break the density gradient degeneracy. Both
techniques are demonstrated using a synthetic diagnostic and data collected on
the OMEGA EP laser
Collisionless shock acceleration of narrow energy spread ion beams from mixed species plasmas using 1 m lasers
Collisionless shock acceleration of protons and C ions has been
achieved by the interaction of a 10 W/cm, 1 m laser with a
near-critical density plasma. Ablation of the initially solid density target by
a secondary laser allowed for systematic control of the plasma profile. This
enabled the production of beams with peaked spectra with energies of 10-18
MeV/a.m.u. and energy spreads of 10-20 with up to 3x10 particles within
these narrow spectral features. The narrow energy spread and similar velocity
of ion species with different charge-to-mass ratio are consistent with
acceleration by the moving potential of a shock wave. Particle-in-cell
simulations show shock accelerated beams of protons and C ions with
energy distributions consistent with the experiments. Simulations further
indicate the plasma profile determines the trade-off between the beam charge
and energy and that with additional target optimization narrow energy spread
beams exceeding 100 MeV/a.m.u. can be produced using the same laser conditions.Comment: Accepted for publication in Physical Review Accelerators and Beam
DEVELOPMENT OF PICOSECOND CO 2 LASER DRIVER FOR AN MEV ION SOURCE
Abstract Laser-Driven Ion Acceleration in thin foils has demonstrated high-charge, low-emittance MeV ion beams with a picosecond duration. Such high-brightness beams are very attractive for a compact ion source or an injector for RF accelerators. However in the case of foils, scaling of the pulse repetition rate and improving shot-to-shot reproducibility is a serious challenge. CO 2 laser-plasma interactions provide a possibility for using a debris free gas jet for target normal sheath acceleration of ions. Gas jets have the advantage of precise density control around the critical plasma density for 10 μm pulses (10 19 cm -3 ) and can be run at 1-10 Hz. The master oscillator-power amplifier CO 2 laser system at the UCLA Neptune Laboratory is being upgraded to generate 1 J, 3 ps pulses at 1Hz. For this purpose, a new 8 atm CO 2 module is used to amplify a picosecond pulse to ~10 GW level. Final amplification is realized in a 1-m long TEA CO 2 amplifier, for which the field broadening mechanism provides the bandwidth necessary for short pulses. Modeling of the pulse amplification shows that ~0.3 TW power is achievable that should be sufficient for producing 1-3 MeV H + protons from the gas plasma
Laser-Plasma Interactions Enabled by Emerging Technologies
An overview from the past and an outlook for the future of fundamental
laser-plasma interactions research enabled by emerging laser systems
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