11,692 research outputs found
Tunable X-ray source by Thomson scattering during laser-wakefield acceleration
We report results on all-optical Thomson scattering intercepting the
acceleration process in a laser wakefield accelerator. We show that the pulse
collision position can be detected using transverse shadowgraphy which also
facilitates alignment. As the electron beam energy is evolving inside the
accelerator, the emitted spectrum changes with the scattering position. Such a
configuration could be employed as accelerator diagnostic as well as reliable
setup to generate x-rays with tunable energy
Probing electron acceleration and X-ray emission in laser-plasma accelerator
While laser-plasma accelerators have demonstrated a strong potential in the
acceleration of electrons up to giga-electronvolt energies, few experimental
tools for studying the acceleration physics have been developed. In this paper,
we demonstrate a method for probing the acceleration process. A second laser
beam, propagating perpendicular to the main beam is focused in the gas jet few
nanosecond before the main beam creates the accelerating plasma wave. This
second beam is intense enough to ionize the gas and form a density depletion
which will locally inhibit the acceleration. The position of the density
depletion is scanned along the interaction length to probe the electron
injection and acceleration, and the betatron X-ray emission. To illustrate the
potential of the method, the variation of the injection position with the
plasma density is studied
3D printing of gas jet nozzles for laser-plasma accelerators
Recent results on laser wakefield acceleration in tailored plasma channels
have underlined the importance of controlling the density profile of the gas
target. In particular it was reported that appropriate density tailoring can
result in improved injection, acceleration and collimation of laser-accelerated
electron beams. To achieve such profiles innovative target designs are
required. For this purpose we have reviewed the usage of additive layer
manufacturing, commonly known as 3D printing, in order to produce gas jet
nozzles. Notably we have compared the performance of two industry standard
techniques, namely selective laser sintering (SLS) and stereolithography (SLA).
Furthermore we have used the common fused deposition modeling (FDM) to
reproduce basic gas jet designs and used SLA and SLS for more sophisticated
nozzle designs. The nozzles are characterized interferometrically and used for
electron acceleration experiments with the Salle Jaune terawatt laser at
Laboratoire d'Optique Appliqu\'ee
Tuning the electron energy by controlling the density perturbation position in laser plasma accelerators
A density perturbation produced in an underdense plasma was used to improve
the quality of electron bunches produced in the laser-plasma wakefield
acceleration scheme. Quasi-monoenergetic electrons were generated by controlled
injection in the longitudinal density gradients of the density perturbation. By
tuning the position of the density perturbation along the laser propagation
axis, a fine control of the electron energy from a mean value of 60 MeV to 120
MeV has been demonstrated with a relative energy-spread of 15 +/- 3.6%,
divergence of 4 +/- 0.8 mrad and charge of 6 +/- 1.8 pC.Comment: 7 pages, 8 figure
A bremsstrahlung gamma-ray source based on stable ionization injection of electrons into a laser wakefield accelerator
Laser wakefield acceleration permits the generation of ultra-short,
high-brightness relativistic electron beams on a millimeter scale. While those
features are of interest for many applications, the source remains constraint
by the poor stability of the electron injection process. Here we present
results on injection and acceleration of electrons in pure nitrogen and argon.
We observe stable, continuous ionization-induced injection of electrons into
the wakefield for laser powers exceeding a threshold of 7 TW. The beam charge
scales approximately linear with the laser energy and is limited by beam
loading. For 40 TW laser pulses we measure a maximum charge of almost 1 nC per
shot, originating mostly from electrons of less than 10 MeV energy. The
relatively low energy, the high charge and its stability make this source
well-suited for applications such as non-destructive testing. Hence, we
demonstrate the production of energetic radiation via bremsstrahlung conversion
at 1 Hz repetition rate. In accordance with Geant4 Monte-Carlo simulations, we
measure a gamma-ray source size of less than 100 microns for a 0.5 mm tantalum
converter placed at 2 mm from the accelerator exit. Furthermore we present
radiographs of image quality indicators
Angular momentum evolution in laser-plasma accelerators
The transverse properties of an electron beam are characterized by two
quantities, the emittance which indicates the electron beam extend in the phase
space and the angular momentum which allows for non-planar electron
trajectories. Whereas the emittance of electron beams produced in laser- plasma
accelerator has been measured in several experiments, their angular momentum
has been scarcely studied. It was demonstrated that electrons in laser-plasma
accelerator carry some angular momentum, but its origin was not established.
Here we identify one source of angular momentum growth and we present
experimental results showing that the angular momentum content evolves during
the acceleration
Femtosecond x rays from laser-plasma accelerators
Relativistic interaction of short-pulse lasers with underdense plasmas has
recently led to the emergence of a novel generation of femtosecond x-ray
sources. Based on radiation from electrons accelerated in plasma, these sources
have the common properties to be compact and to deliver collimated, incoherent
and femtosecond radiation. In this article we review, within a unified
formalism, the betatron radiation of trapped and accelerated electrons in the
so-called bubble regime, the synchrotron radiation of laser-accelerated
electrons in usual meter-scale undulators, the nonlinear Thomson scattering
from relativistic electrons oscillating in an intense laser field, and the
Thomson backscattered radiation of a laser beam by laser-accelerated electrons.
The underlying physics is presented using ideal models, the relevant parameters
are defined, and analytical expressions providing the features of the sources
are given. Numerical simulations and a summary of recent experimental results
on the different mechanisms are also presented. Each section ends with the
foreseen development of each scheme. Finally, one of the most promising
applications of laser-plasma accelerators is discussed: the realization of a
compact free-electron laser in the x-ray range of the spectrum. In the
conclusion, the relevant parameters characterizing each sources are summarized.
Considering typical laser-plasma interaction parameters obtained with currently
available lasers, examples of the source features are given. The sources are
then compared to each other in order to define their field of applications.Comment: 58 pages, 41 figure
Concept of a laser-plasma based electron source for sub-10 fs electron diffraction
We propose a new concept of an electron source for ultrafast electron
diffraction with sub-10~fs temporal resolution. Electrons are generated in a
laser-plasma accelerator, able to deliver femtosecond electron bunches at 5 MeV
energy with kHz repetition rate. The possibility of producing this electron
source is demonstrated using Particle-In-Cell simulations. We then use particle
tracking simulations to show that this electron beam can be transported and
manipulated in a realistic beamline, in order to reach parameters suitable for
electron diffraction. The beamline consists of realistic static magnetic optics
and introduces no temporal jitter. We demonstrate numerically that electron
bunches with 5~fs duration and containing 1.5~fC per bunch can be produced,
with a transverse coherence length exceeding 2~nm, as required for electron
diffraction
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