131 research outputs found
Harmonic Generation by an Intense Laser Pulse in Neutral and Ionized Gases
Reported are the results of a harmonic generation experiment in a simple gas (hydrogen) using 1-ps, 1-pm laser pulses with a range of intensities extending from below to far above the laser ionization saturation threshold. The scaling with intensity above saturation of the third harmonic generated by a single laser-pulse in a filled gas cell is observed to not fit with a simple model that takes into consideration volume ionization effects alone. In another experiment, a pump-probe type, an upper limit on the conversion efficiency of third harmonic generation in a preformed plasma is determined. It is found to be in agreement with the efficiency predicted by a relativistic harmonic generation theory
Method for Generating a Plasma Wave to Accelerate Electrons
The invention provides a method and apparatus for generating large amplitude nonlinear plasma waves, driven by an optimized train of independently adjustable, intense laser pulses. In the method, optimal pulse widths, interpulse spacing, and intensity profiles of each pulse are determined for each pulse in a series of pulses. A resonant region of the plasma wave phase space is found where the plasma wave is driven most efficiently by the laser pulses. The accelerator system of the invention comprises several parts: the laser system, also called beam source, which preferably comprises photo cathode electron source and RF-LINAC accelerator; electron photo-cathode triggering system; the electron diagnostics; and the feedback system between the electron diagnostics and the laser system. The system also includes plasma source including vacuum chamber, magnetic lens, and magnetic field means. The laser system produces a train of pulses that has been optimized to maximize the axial electric field amplitude of the plasma wave, and thus the electron acceleration, using the method of the invention
Method for Generating a Plasma Wave to Accelerate Electrons
The invention provides a method and apparatus for generating large amplitude nonlinear plasma waves, driven by an optimized train of independently adjustable, intense laser pulses. In the method, optimal pulse widths, interpulse spacing, and intensity profiles of each pulse are determined for each pulse in a series of pulses. A resonant region of the plasma wave phase space is found where the plasma wave is driven most efficiently by the laser pulses. The accelerator system of the invention comprises several parts: the laser system, also called beam source, which preferably comprises photo cathode electron source and RF-LINAC accelerator; electron photo-cathode triggering system; the electron diagnostics; and the feedback system between the electron diagnostics and the laser system. The system also includes plasma source including vacuum chamber, magnetic lens, and magnetic field means. The laser system produces a train of pulses that has been optimized to maximize the axial electric field amplitude of the plasma wave, and thus the electron acceleration, using the method of the invention
Pulse evolution and plasma-wave phase velocity in channel-guided laser-plasma accelerators.
The self-consistent laser evolution of an intense, short-pulse laser exciting a plasma wave and propagating in a preformed plasma channel is investigated, including the effects of pulse steepening and energy depletion. In the weakly relativistic laser intensity regime, analytical expressions for the laser energy depletion, pulse self-steepening rate, laser intensity centroid velocity, and phase velocity of the plasma wave are derived and validated numerically
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Physics of Laser-driven plasma-based acceleration
The physics of plasma-based accelerators driven by short-pulse lasers is reviewed. This includes the laser wake-field accelerator, the plasma beat wave accelerator, the self-modulated laser wake-field accelerator, and plasma waves driven by multiple laser pulses. The properties of linear and nonlinear plasma waves are discussed, as well as electron acceleration in plasma waves. Methods for injecting and trapping plasma electrons in plasma waves are also discussed. Limits to the electron energy gain are summarized, including laser pulse direction, electron dephasing, laser pulse energy depletion, as well as beam loading limitations. The basic physics of laser pulse evolution in underdense plasmas is also reviewed. This includes the propagation, self-focusing, and guiding of laser pulses in uniform plasmas and plasmas with preformed density channels. Instabilities relevant to intense short-pulse laser-plasma interactions, such as Raman, self-modulation, and hose instabilities, are discussed. Recent experimental results are summarized
A compact, all-optical positron production and collection scheme
In this paper we discuss a compact, laser-plasma-based scheme for the
generation of positron beams suitable to be implemented in an all-optical
setup. A laser-plasma-accelerated electron beam hits a solid target producing
electron-positron pairs via bremsstrahlung. The back of the target serves as a
plasma mirror to in-couple a laser pulse into a plasma stage located right
after the mirror where the laser drives a plasma wave (or wakefield). By
properly choosing the delay between the laser and the electron beam the
positrons produced in the target can be trapped in the wakefield, where they
are focused and accelerated during the transport, resulting in a collimated
beam. This approach minimizes the ballistic propagation time and enhances the
trapping efficiency. The system can be used as an injector of positron beams
and has potential applications in the development of a future, compact,
plasma-based electron-positron linear collider
THE 13TH ADVANCED ACCELERATOR CONCEPTS WORKSHOP (AAC'8)
The Thirteenth Workshop on Advanced Accelerator Concepts (AAC) was held from July 27 to August 2, 2008 at the Chaminade Conference Center in Santa Cruz, California, USA, organized by the Lawrence Berkeley National Laboratory and the University of California at Berkeley. There were unprecedented levels of interest in the 2008 AAC Workshop, and participation was by invitation, with 215 workshop attendees, including 58 students. Reflecting the world-wide growth of the advanced accelerator community, there was significant international participation, with participants from twelve countries attending
Emittance-preserving acceleration of high-quality positron beams using warm plasma filaments
Preserving the quality of positron beams in plasma-based accelerators, where
wakefields are generated in electron filaments, is challenging. These
wakefields are characterized by transversely non-linear focusing fields and
non-uniform accelerating fields. However, a nonzero plasma temperature
linearizes the transverse wakefield within the central region of the electron
filament. In this study, we employ 3D particle-in-cell simulations with mesh
refinement to demonstrate that beams with emittances on the order of tens of
nanometers are contained within the linearized region of the transverse
wakefield. This enables emittance preservation to one percent, while positron
beams with the same charge and micrometer emittances, which sample the
non-linear part of the transverse wakefield, experience a relative emittance
growth of ten percent. Additionally, we observe a significant reduction in the
growth rate of the slice energy spread for the tens of nanometers emittance
beams in comparison to the micrometer emittance beams. The utilization of warm
plasmas in conjunction with low-emittance beams opens up new avenues for
enhancing the beam quality across various plasma-based positron acceleration
approaches.Comment: To be submitted as a proceedings for the 6th European Advanced
Accelerator Concepts worksho
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