166 research outputs found
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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
Low transverse emittance electron bunches from two-color laser-ionization injection
A method is proposed to generate low emittance electron bunches from two
color laser pulses in a laser-plasma accelerator. A two-region gas structure is
used, containing a short region of a high-Z gas (e.g., krypton) for ionization
injection, followed by a longer region of a low-Z gas for post-acceleration. A
long-laser-wavelength (e.g., 5 micron) pump pulse excites plasma wake without
triggering the inner-shell electron ionization of the high-Z gas due to low
electric fields. A short-laser-wavelength (e.g., 0.4 micron) injection pulse,
located at a trapping phase of the wake, ionizes the inner-shell electrons of
the high-Z gas, resulting in ionization-induced trapping. Compared with a
single-pulse ionization injection, this scheme offers an order of magnitude
smaller residual transverse momentum of the electron bunch, which is a result
of the smaller vector potential amplitude of the injection pulse
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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Laser and electron deflection from transverse asymmetries in laser-plasma accelerators.
We report on the deflection of laser pulses and accelerated electrons in a laser-plasma accelerator (LPA) by the effects of laser pulse front tilt and transverse density gradients. Asymmetry in the plasma index of refraction leads to laser steering, which can be due to a density gradient or spatiotemporal coupling of the laser pulse. The transverse forces from the skewed plasma wave can also lead to electron deflection relative to the laser. Quantitative models are proposed for both the laser and electron steering, which are confirmed by particle-in-cell simulations. Experiments with the BELLA Petawatt Laser are presented which show controllable 0.1-1 mrad laser and electron beam deflection from laser pulse front tilt. This has potential applications for electron beam pointing control, which is of paramount importance for LPA applications
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