159 research outputs found
Particle acceleration using intense laser produced plasmas
Recent results from high intensity (up to 5 × 10 20 W/cm 2 ) laser plasma interaction experiments at Imperial College London have shown that the plasmas produced during such interactions can be efficient sources of relativistic electron beams and also of high quality beams of non-relativistic ions. These beams may be important for the development of compact sources of energetic particles for applications in science, medicine and technology. (© 2007 by Astro Ltd., Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA)Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/57406/1/847_ftp.pd
Measurement of Magnetic-Field Structures in a Laser-Wakefield Accelerator
Experimental measurements of magnetic fields generated in the cavity of a
self-injecting laser-wakefield accelerator are presented. Faraday rotation is
used to determine the existence of multi-megagauss fields, constrained to a
transverse dimension comparable to the plasma wavelength and several plasma
wavelengths longitudinally. The fields are generated rapidly and move with the
driving laser. In our experiment, the appearance of the magnetic fields is
correlated to the production of relativistic electrons, indicating that they
are inherently tied to the growth and wavebreaking of the nonlinear plasma
wave. This evolution is confirmed by numerical simulations, showing that these
measurements provide insight into the wakefield evolution with high spatial and
temporal resolution
High Repetition-Rate Wakefield Electron Source Generated by Few-millijoule, 30 femtosecond Laser Pulses on a Density Downramp
We report on an experimental demonstration of laser wakefield electron
acceleration using a sub-TW power laser by tightly focusing 30-fs laser pulses
with only 8 mJ pulse energy on a 100 \mu m scale gas target. The experiments
are carried out at an unprecedented 0.5 kHz repetition rate, allowing "real
time" optimization of accelerator parameters. Well-collimated and stable
electron beams with a quasi-monoenergetic peak in excess of 100 keV are
measured. Particle-in-cell simulations show excellent agreement with the
experimental results and suggest an acceleration mechanism based on electron
trapping on the density downramp, due to the time varying phase velocity of the
plasma waves.Comment: 4 pages, 5 figures, submitted to Phys. Rev. Let
Longitudinal Ion Acceleration from High-Intensity Laser Interactions with Underdense Plasma
Longitudinal ion acceleration from high-intensity (I ~ 10^20 Wcm^-2) laser
interactions with helium gas jet targets (n_e ~ 0.04 n_c) have been observed.
The ion beam has a maximum energy for He^2+ of approximately 40 MeV and was
directional along the laser propagation path, with the highest energy ions
being collimated to a cone of less than 10 degrees. 2D particle-in-cell
simulations have been used to investigate the acceleration mechanism. The time
varying magnetic field associated with the fast electron current provides a
contribution to the accelerating electric field as well as providing a
collimating field for the ions. A strong correlation between the plasma density
and the ion acceleration was found. A short plasma scale-length at the vacuum
interface was observed to be beneficial for the maximum ion energies, but the
collimation appears to be improved with longer scale-lengths due to enhanced
magnetic fields in the ramp acceleration region.Comment: 18 pages, 6 figure
Dynamic Control of Laser Produced Proton Beams
The emission characteristics of intense laser driven protons are controlled
using ultra-strong (of the order of 10^9 V/m) electrostatic fields varying on a
few ps timescale. The field structures are achieved by exploiting the high
potential of the target (reaching multi-MV during the laser interaction).
Suitably shaped targets result in a reduction in the proton beam divergence,
and hence an increase in proton flux while preserving the high beam quality.
The peak focusing power and its temporal variation are shown to depend on the
target characteristics, allowing for the collimation of the inherently highly
divergent beam and the design of achromatic electrostatic lenses.Comment: 9 Pages, 5 figure
Laser-Plasma Interactions Enabled by Emerging Technologies
An overview from the past and an outlook for the future of fundamental
laser-plasma interactions research enabled by emerging laser systems
Characterisation of Laser Wakefield Acceleration Efficiency with Octave Spanning Near-IR Spectrum Measurements
We report on high efficiency energy transfer in a GeV-class laser wakefield
accelerator. Both the transfer of energy from the laser to the plasma
wakefield, and from the plasma to the accelerated electron beam were diagnosed
experimentally by simultaneous measurement of the deceleration of laser photons
and the accelerated electrons as a function of acceleration length. The
extraction efficiency, which we define as the ratio of the energy gained by the
electron beam to the energy lost by the self-guided laser mode, was maximised
at % by tuning of the plasma density, plasma length and incident laser
pulse compression. At higher densities, the laser was observed to fully
redshift over an entire octave, from 800~nm to 1600~nm.Comment: 7 pages, 5 figure
Experimental Evidence of Radiation Reaction in the Collision of a High-Intensity Laser Pulse with a Laser-Wakefield Accelerated Electron Beam
The dynamics of energetic particles in strong electromagnetic fields can be heavily influenced by the energy loss arising from the emission of radiation during acceleration, known as radiation reaction. When interacting with a high-energy electron beam, today's lasers are sufficiently intense to explore the transition between the classical and quantum radiation reaction regimes. We present evidence of radiation reaction in the collision of an ultrarelativistic electron beam generated by laser-wakefield acceleration (μ 500 MeV) with an intense laser pulse (a0>10). We measure an energy loss in the postcollision electron spectrum that is correlated with the detected signal of hard photons (γ rays), consistent with a quantum description of radiation reaction. The generated γ rays have the highest energies yet reported from an all-optical inverse Compton scattering scheme, with critical energy >30 MeV
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