104 research outputs found
Slowly varying envelope kinetic simulations of pulse amplification by Raman backscattering
A numerical code based on an eikonal formalism has been developed to simulate laser-plasma interactions, specifically Raman backscatter(RBS). In this code, the dominant laser modes are described by their wave envelopes, avoiding the need to resolve the laser frequency; appropriately time-averaged equations describe particle motion. The code is fully kinetic, and thus includes critical physics such as particle trapping and Landau damping which are beyond the scope of the commonly used fluid three-wave equations. The dominant forces on the particles are included: the ponderomotive force resulting from the beat wave of the forward and backscattered laser fields and the self-consistent plasma electric field. The code agrees well, in the appropriate regimes, with the results from three-wave equations and particle-in-cell simulations. The effects of plasma temperature on RBS amplification are studied. It is found that increasing the plasma temperature results in modification to particle trapping and the saturation of RBS, even before the onset of Landau damping of the plasma wave. This results in a reduction in the coupling efficiency compared to predictions based on the three-wave equations.open192
Titania-doped tantala/silica coatings for gravitational-wave detection
Reducing thermal noise from optical coatings is crucial to reaching the required sensitivity in next generation interferometric gravitational-wave detectors. Here we show that adding TiO2 to Ta2O5 in Ta2O5/SiO2 coatings reduces the internal friction and in addition present data confirming it reduces thermal noise. We also show that TiO2-doped Ta2O5/SiO2 coatings are close to satisfying the optical absorption requirements of second generation gravitational-wave detectors
The Wicked Machinery of Government: Malta and the Problems of Continuity under the New Model Administration
This is a study focused on the early years of British rule in Malta (1800-1813). It explores the application to the island of the ânew modelâ of colonial government, one based on direct rule from London mediated by the continuation of existing laws and institutions. Systemic deficiencies are identified. These tended to undermine the effectiveness of direct British rule. This study also reveals, in the context of legal and constitutional continuity, unresolved tensions between modernity and tradition. The political stability of the island was damaged and the possibility of continued British possession was threatened
Thermal noise in interferometric gravitational wave detectors due to dielectric optical coatings
We report on thermal noise from the internal friction of dielectric coatings
made from alternating layers of Ta2O5 and SiO2 deposited on fused silica
substrates. We present calculations of the thermal noise in gravitational wave
interferometers due to optical coatings, when the material properties of the
coating are different from those of the substrate and the mechanical loss angle
in the coating is anisotropic. The loss angle in the coatings for strains
parallel to the substrate surface was determined from ringdown experiments. We
measured the mechanical quality factor of three fused silica samples with
coatings deposited on them. The loss angle of the coating material for strains
parallel to the coated surface was found to be (4.2 +- 0.3)*10^(-4) for
coatings deposited on commercially polished slides and (1.0 +- 0.3)*10^{-4} for
a coating deposited on a superpolished disk. Using these numbers, we estimate
the effect of coatings on thermal noise in the initial LIGO and advanced LIGO
interferometers. We also find that the corresponding prediction for thermal
noise in the 40 m LIGO prototype at Caltech is consistent with the noise data.
These results are complemented by results for a different type of coating,
presented in a companion paper.Comment: Submitted to LSC (internal) review Sept. 20, 2001. To be submitted to
Phys. Lett.
Comparison of advanced gravitational-wave detectors
We compare two advanced designs for gravitational-wave antennas in terms of
their ability to detect two possible gravitational wave sources. Spherical,
resonant mass antennas and interferometers incorporating resonant sideband
extraction (RSE) were modeled using experimentally measurable parameters. The
signal-to-noise ratio of each detector for a binary neutron star system and a
rapidly rotating stellar core were calculated. For a range of plausible
parameters we found that the advanced LIGO interferometer incorporating RSE
gave higher signal-to-noise ratios than a spherical detector resonant at the
same frequency for both sources. Spheres were found to be sensitive to these
sources at distances beyond our galaxy. Interferometers were sensitive to these
sources at far enough distances that several events per year would be expected
Plasma Dynamics
Contains table of contents for Section 2 and reports on four research projects.National Science Foundation Grant ECS-89-02990U.S. Air Force - Office of Scientific Research Grant AFOSR 89-0082-CU.S. Army - Harry Diamond Laboratories Contract DAAL02-89-K-0084U.S. Army - Harry Diamond Laboratories Contract DAAL02-92-K-0037U.S. Department of Energy Contract DE-AC02-90ER-40591U.S. Navy - Office of Naval Research Grant N00014-90-J-4130Lawrence Livermore National Laboratories Subcontract B-160456National Aeronautics and Space Administration Grant NAGW-2048National Science Foundation Grant ECS-88-22475U.S. Department of Energy Grant DE-FG02-91-ER-5410
Plasma Dynamics
Contains table of contents for Section 2 and reports on three research projects.National Science Foundation Grant ECS 89-02990U.S. Air Force - Office of Scientific Research Grant F49620-93-1-0108U.S. Army - Harry Diamond Laboratories Contract DAAL02-92-K-0037U.S. Department of Energy Grant DE-FG02-91-ER-40648U.S. Navy - Office of Naval Research Grant N00014-90-J-4130National Aeronautics and Space Administration Grant NAGW-2048National Science Foundation Grant ECS 88-22475U.S. Department of Energy Grant DE-FG02-91-ER-54109Magnetic Fusion Science Fellowship Progra
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