185,544 research outputs found
Laser production and heating of plasma for MHD application
Experiments have been made on the production and heating of plasmas by the absorption of laser radiation. These experiments were performed to ascertain the feasibility of using laser-produced or laser-heated plasmas as the input for a magnetohydrodynamic (MHD) generator. Such a system would have a broad application as a laser-to-electricity energy converter for space power transmission. Experiments with a 100-J-pulsed CO2 laser were conducted to investigate the breakdown of argon gas by a high-intensity laser beam, the parameters (electron density and temperature) of the plasma produced, and the formation and propagation of laser-supported detonation (LSD) waves. Experiments were also carried out using a 1-J-pulsed CO2 laser to heat the plasma produced in a shock tube. The shock-tube hydrogen plasma reached electron densities of approximately 10 to the 17th/cu cm and electron temperatures of approximately 1 eV. Absorption of the CO2 laser beam by the plasma was measured, and up to approximately 100 percent absorption was observed. Measurements with a small MHD generator showed that the energy extraction efficiency could be very large with values up to 56 percent being measured
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Early time dynamics of laser-ablated silicon using ultrafast grazing incidence X-ray scattering
Controlling the morphology of laser-derived nanomaterials is dependent on developing a better understanding of the particle nucleation dynamics in the ablation plume. Here, we utilize the femtosecond-length pulses from an x-ray free electron laser to perform time-resolved grazing incidence x-ray scattering measurements on a laser-produced silicon plasma plume. At 20 ps we observe a dramatic increase in the scattering amplitude at small scattering vectors, which we attribute to incipient formation of liquid silicon droplets. These results demonstrate the utility of XFELs as a tool for characterizing the formation dynamics of nanomaterials in laser-produced plasma plumes on ultrafast timescales
Laser-heater assisted plasma channel formation in capillary discharge waveguides
A method of creating plasma channels with controllable depth and transverse
profile for the guiding of short, high power laser pulses for efficient
electron acceleration is proposed. The plasma channel produced by the
hydrogen-filled capillary discharge waveguide is modified by a ns-scale laser
pulse, which heats the electrons near the capillary axis. This interaction
creates a deeper plasma channel within the capillary discharge that evolves on
a ns-time scale, allowing laser beams with smaller spot sizes than would
otherwise be possible in the unmodified capillary discharge.Comment: 5 pages, 3 figure
Laser Shaping and Optimization of the Laser-Plasma Interaction
The physics of energy transfer between the laser and the plasma in laser
wakefield accelerators is studied. We find that wake excitation by arbitrary
laser shapes can be parameterized using the total pulse energy and pulse
depletion length. A technique for determining laser profiles that produce the
required plasma excitation is developed. We show that by properly shaping the
longitudinal profile of the driving laser pulse, it is possible to maximize
both the transformer ratio and the wake amplitude, achieving optimal
laser-plasma coupling. The corresponding family of laser pulse shapes is
derived in the nonlinear regime of laser-plasma interaction. Such shapes
provide theoretical upper limit on the magnitude of the wakefield and
efficiency of the accelerating stage by allowing for uniform photon
deceleration inside the laser pulse. We also construct realistic optimal pulse
shapes that can be produced in finite-bandwidth laser systems and propose a
two-pulse wake amplification scheme using the optimal solution.Comment: 12 pages, 5 figures, contributed to the Advanced Accelerator Concepts
2000 worksho
Laser irradiated foam targets: absorption and radiative properties
An experimental campaign to characterize the laser radiation absorption of foam targets and the subsequent emission of radiation from the produced plasma was carried out in the ABC facility of the ENEA Research Center in Frascati (Rome). Different targets have been used: plastic in solid or foam state and aluminium targets. The activated different diagnostics allowed to evaluate the plasma temperature, the density distribution, the fast particle spectrum and the yield of the X-Ray radiation emitted by the plasma for the different targets. These results confirm the foam homogenization action on laser-plasma interaction, mainly attributable to the volume absorption of the laser radiation propagating in such structured materials. These results were compared with simulation absorption models of the laser propagating into a foam target
Fast magnetic reconnection in laser-produced plasma bubbles
Recent experiments have observed magnetic reconnection in
high-energy-density, laser-produced plasma bubbles, with reconnection rates
observed to be much higher than can be explained by classical theory. Based on
fully kinetic particle simulations we find that fast reconnection in these
strongly driven systems can be explained by magnetic flux pile-up at the
shoulder of the current sheet and subsequent fast reconnection via two-fluid,
collisionless mechanisms. In the strong drive regime with two-fluid effects, we
find that the ultimate reconnection time is insensitive to the nominal system
Alfven time.Comment: 5 pages, 4 figures, accepted by Phys. Rev. Let
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