Electron acceleration and generation of high-brilliance x-ray radiation in kilojoule, subpicosecond laser-plasma interactions (original) (raw)
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On the properties of synchrotron-like X-ray emission from laser wakefield accelerated electron beams
Physics of Plasmas, 2018
The electric and magnetic fields responsible for electron acceleration in a Laser Wakefield Accelerator (LWFA) also cause electrons to radiate x-ray photons. Such x-ray pulses have several desirable properties including short duration and being well collimated with tunable high energy. We measure the scaling of this x-ray source experimentally up to laser powers greater than 100 TW. An increase in laser power allows electron trapping at a lower density as well as with increased trapped charge. These effects resulted in an x-ray fluence that was measured to increase non-linearly with laser power. The fluence of x-rays was also compared with that produced from K-α emission resulting from a solid target interaction for the same energy laser pulse. The flux was shown to be comparable, but the LWFA x-rays had a significantly smaller source size. This indicates that such a source may be useful as a backlighter for probing high energy density plasmas with ultrafast temporal resolution.
Femtosecond x rays from laser-plasma accelerators
Reviews of Modern Physics, 2013
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 laseraccelerated 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.
The dynamics of plasma electrons in the focus of a petawatt laser beam are studied via measurements of their x-ray synchrotron radiation. With increasing laser intensity, a forward directed beam of x rays extending to 50 keV is observed. The measured x rays are well described in the synchrotron asymptotic limit of electrons oscillating in a plasma channel. The critical energy of the measured synchrotron spectrum is found to scale as the Maxwellian temperature of the simultaneously measured electron spectra. At low laser intensity transverse oscillations are negligible as the electrons are predominantly accelerated axially by the laser generated wakefield. At high laser intensity, electrons are directly accelerated by the laser and enter a highly radiative regime with up to 5% of their energy converted into x-rays.
Femtosecond X-ray generation through relativistic electron beam–laser interaction
Comptes Rendus de l'Académie des Sciences - Series IV - Physics, 2000
Methods for generating ultra-short X-rays using the interaction of intense laser pulses with relativistic electron beams, and their application to measuring ultra-fast phenomena in solid state materials, are reviewed. Two different methods that use a long electron bunch and short laser pulse are discussed: Thomson scattering and optical slicing which have been implemented on linac and storage ring beams, respectively. The possibility of generating ultrashort electrons bunches from laser-plasma injectors is discussed. © 2000 Académie des sciences/Éditions scientifiques et médicales Elsevier SAS X-ray / femtosecond / laser / electron beam / Thomson scattering / diffraction / laser wakefield acceleration Génération d'impulsion femtoseconde de rayon X par l'interaction de faisceau d'électron relativiste et laser Résumé. La génération d'impulsion de rayons X ultra-courts, par l'intermédiaire de l'interaction d'un faisceau d'electrons relativistes avec un laser intense, est discute, ainsi que leur utilisation pour la mesure des phénomènes ultra-rapides dans les matériaux solides. Deux dfférentes méthodes qui utilisent un paquet d'electron long avec un laser ultra-court seront presentés : la diffusion Thomson qui a été exécuté avec le faisceau d'un linac puis le « découpage » optique qui a été fait avec le faisceau d'un anneau de stockage. La possibilité d'obtenir des impulsion ultra-courtes par l'usage de paquets d'électrons, également ultra-courts, produit par l'effet sillage d'un laser dans un plasma, sera proposé.
Annular quasimonoenergetic electron beams with a mean energy in the range 200–400 MeV and charge on the order of several picocoulombs were generated in a laser wakefield accelerator and subsequently accelerated using a plasma afterburner in a two-stage gas cell. Generation of these beams is associated with injection occurring on the density down ramp between the stages. This well-localized injection produces a bunch of electrons performing coherent betatron oscillations in the wakefield, resulting in a significant increase in the x-ray yield. Annular electron distributions are detected in 40% of shots under optimal conditions. Simultaneous control of the pulse duration and frequency chirp enables optimization of both the energy and the energy spread of the annular beam and boosts the radiant energy per unit charge by almost an order of magnitude. These well-defined annular distributions of electrons are a promising source of high-brightness laser plasma-based x-rays.
Synchrotron x-ray radiation from laser wakefield accelerated electron beams in a plasma channel
Journal of Physics: Conference Series, 2010
Synchrotron x-ray radiation from laser wakefield accelerated electron beams was characterized at the HERCULES facility of the University of Michigan. A mono-energetic electron beam with energy up to 400 MeV was observed in the interaction of an ultra-short laser pulse with a super-sonic gas jet target. The experiments were performed at a peak intensity of 5×10 19 W/cm 2 by using an adaptive optic. The accelerated electron beam undergoes a so called "betatron" oscillation in an ion channel, where plasma electrons have been expelled by the laser ponderomotive force, and, therefore, emits synchrotron radiation. We observe broad synchrotron x-ray radiation extending up to 30 keV. We find that this radiation is emitted in a beam with a divergence angle as small as 12×4 mrad 2 and can have a source size smaller than 3 microns and a peak brightness of 10 22 photons/mm 2 /mrad 2 /second/0.1% bandwidth, which is comparable to currently existing 3 rd generation conventional light sources. This opens up the possibility of using laser-produced "betatron" sources for many applications that currently require conventional synchrotron sources.
Progress toward a laser-driven x-ray free-electron laser
SPIE Newsroom, 2009
The use of x-ray radiation has driven the development of synchrotron sources and, more recently, x-ray free-electron lasers (FELs). These microwave-based facilities are huge and expensive, yet governments are prepared to support them (usually one per nation) because of their great value to industry, academia, and society. However, laser-wakefield accelerators (LWFAs) are now advancing to the point where compact radiation sources could be developed into a new, complementary, or even disruptive technology. In addition to reductions in scale and cost-by a factor of up to 1000-x-ray pulse durations are significantly shorter than those of conventional lasers, which could facilitate probing of ultrafast dynamic processes. The Advanced Laser-Plasma High-Energy Accelerators towards X-rays (ALPHA-X) project, based at the University of Strathclyde, is developing laser-plasma accelerators as drivers of radiation sources. 1 The first demonstration of a compact synchrotron source based on an LWFA was recently demonstrated using a conventional undulator and a diverging electron beam. 2 Our challenge is to develop a compact x-ray FEL. Here we focus on developments to improve the electron-beam properties and discuss the suitability of LWFAs as drivers of FELs. Our work shows that the once-distant prospect of a compact x-ray FEL is now within reach. On the ALPHA-X accelerator beam line (see Figure 1), electrons are accelerated in a relativistically self-guiding plasma channel formed in a hydrogen-gas jet by a 35fs titaniumsapphire laser pulse with a power of 1J. Electrons are selfinjected from the background plasma into the density wake that trails behind the laser pulse (through the combined action
Physical Review Letters, 2017
We investigate a new regime for betatron x-ray emission that utilizes kilojoule-class, picosecond lasers to drive wakes in plasmas. When such laser pulses with intensities of ∼ 5 × 10 18 W/cm 2 are focused into plasmas with electron densities of ∼ 1 × 10 19 cm −3 , they undergo self-modulation and channeling, which accelerates electrons up to 200 MeV energies and causes those electrons to emit x-rays. The measured x-ray spectra are fit with a synchrotron spectrum with a critical energy of 10-20 keV, and 2D PIC simulations were used to model the acceleration and radiation of the electrons in our experimental conditions.
Ultra-short x-ray Radiation coming from a Laser Wakefield Accelerator
2008
A Laser Wakefield Accelerator (LWFA) is under development at Lawrence Livermore National Laboratory (LLNL) to produce electron bunches with GeV class energy and energy spreads of a few-percent. The ultimate goal is to provide a bright and compact photon source for high energy density physics. The interaction of a high power (200 TW), short pulse (50 fs) laser with neutral He gas can generate quasi-monoenergetic electrons beams at energies up to 1 GeV [1]. The laser pulse can be selfguided over a dephasing length of 1 cm (for a plasma density of 1.5 × 10 18 cm −3) overcoming the limitation of vacuum diffraction. Betatron radiation is emitted while the accelerated electrons undergo oscillations in the wakefield electrostatic field. Here we present electron spectrum measurements with a two screen spectrometer allowing to fix the ambiguities due to unknown angle at the plasma exit. We have measured monoenergetic electron beams at energies around 110 MeV. Furthermore a forward directed x-ray beam is observed. The peak energy of the measured synchrotron spectrum is reconstructed based on the energy deposited after different sets of filters, assuming x-ray radiation described in the synchrotron asymptotic limit (SAL) and is found around 6 keV.