201 research outputs found
One-to-one full scale simulations of laser wakefield acceleration using QuickPIC
We use the quasi-static particle-in-cell code QuickPIC to perform full-scale,
one-to-one LWFA numerical experiments, with parameters that closely follow
current experimental conditions. The propagation of state-of-the-art laser
pulses in both preformed and uniform plasma channels is examined. We show that
the presence of the channel is important whenever the laser self-modulations do
not dominate the propagation. We examine the acceleration of an externally
injected electron beam in the wake generated by 10 J laser pulses, showing that
by using ten-centimeter-scale plasma channels it is possible to accelerate
electrons to more than 4 GeV. A comparison between QuickPIC and 2D OSIRIS is
provided. Good qualitative agreement between the two codes is found, but the 2D
full PIC simulations fail to predict the correct laser and wakefield
amplitudes.Comment: 5 pages, 5 figures, accepted for publication IEEE TPS, Special Issue
- Laser & Plasma Accelerators - 8/200
Scalar Decay in Chaotic Mixing
I review the local theory of mixing, which focuses on infinitesimal blobs of
scalar being advected and stretched by a random velocity field. An advantage of
this theory is that it provides elegant analytical results. A disadvantage is
that it is highly idealised. Nevertheless, it provides insight into the
mechanism of chaotic mixing and the effect of random fluctuations on the rate
of decay of the concentration field of a passive scalar.Comment: 35 pages, 15 figures. Springer-Verlag conference style svmult.cls
(included). Published in "Transport in Geophysical Flows: Ten Years After,"
Proceedings of the Grand Combin Summer School, 14-24 June 2004, Valle
d'Aosta, Italy. Fixed some typo
Recommended from our members
Microwave generation for magnetic fusion energy applications. Progress report, July 15, 1992--July 14, 1993
This work strives to develop high average power FELs at voltages below I MV allowing for smaller and less costly power supplies. To achieve operation of an FEL with 100 GHZ {approx_lt} f {approx_lt} 150 GHz and with relatively modest voltage, we have been investigating the use of small period ({lambda}{sub {omega}} {approximately} 1 cm) planar wiggler magnets together with sheet electron beams. The sheet beam geometry allows for an FEL interaction region in the form of a narrow slit with high wiggler field at the center plane where the electrons are concentrated. The total current and power may then be increased without making current density excessive by increasing the wide dimension of the sheet beam. Sheet beam FEL design parameters for both a Proof-of-Principle (PoP) FEL experiment, which is current in progress, and an ITER relevant FEL design are shown. A central issue in the sheet beam FEL concept is propagation of the beam through the interaction region without excessive interception by the walls. In section 2 below we describe a successful experimental demonstration of sheet beam propagation through a 56 period uniform wiggler. Cold testing and initial hot test operation of the (PoP) FEL amplifier are also described. Finally, we present a theoretical investigation of the bandwidth of an FEL amplifier with a tapered wiggler operating in saturation is described
Propellant Charring in Pulsed Plasma Thrusters
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76437/1/AIAA-2471-899.pd
Optimization Issues for a Micropulsed Plasma Thruster
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76083/1/AIAA-13954-648.pd
Experimental observation and characterization of the magnetorotational instability
Differential rotation occurs in conducting flows in accretion disks and
planetary cores. In such systems, the magnetorotational instability can arise
from coupling Lorentz and centrifugal forces to cause large radial angular
momentum fluxes. We present the first experimental observation of the
magnetorotational instability. Our system consists of liquid sodium between
differentially rotating spheres, with an imposed coaxial magnetic field. We
characterize the observed patterns, dynamics and torque increases, and
establish that this instability can occur from a hydrodynamic turbulent
background.Comment: 4 pages, 5 figures. Final version, accepted for publication in
Physical Review Letter
Turbulence in a free surface
We report an experimental and numerical study of turbulent fluid motion in a
free surface. The flow is realized experimentally on the surface of a tank
filled with water stirred by a vertically oscillating grid positioned well
below the surface. Particles floating on the surface are used to visualize the
flow. The effect of surface waves appears to be negligible. The flow is
unconventional in that it is confined to two dimensions but does not have
squared vorticity as a conservation law, that it is not divergence free and
that it inherits scaling features of the mean square velocity differences
S_2(R) and the vorticity fluctuations Omega(R) from the bulk 3-d turbulence.Comment: 4 pages, 4 Postscript figure
Deformation Quantization of Bosonic Strings
Deformation quantization of bosonic strings is considered. We show that the
light-cone gauge is the most convenient classical description to perform the
quantization of bosonic strings in the deformation quantization formalism.
Similar to the field theory case, the oscillator variables greatly facilitates
the analysis. The mass spectrum, propagators and the Virasoro algebra are
finally described within this deformation quantization scheme.Comment: 33+1 pages, harvmac file, no figure
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