Abstract:Laser-plasma accelerators (LPAs) driven by picosecond-scale, kilojoule-class lasers can generate particle beams and x-ray sources that could be utilized in experiments driven by multi-kilojoule, high-energy-density science (HEDS) drivers such as the OMEGA laser at the Laboratory for Laser Energetics (LLE) or the National Ignition Facility at Lawrence Livermore National Laboratory. This paper reports on the development of the first LPA driven by a short-pulse, kilojoule-class laser (OMEGA EP) connected to a mul… Show more
“…Recent work has explored the study of the interplay between oblique and Weibeltype microinstabilities using either electron or electronpositron beams based on conventional RF accelerators (Shukla et al 2018;Arrowsmith et al 2021;San Miguel Claveria et al 2021). By considering configurations that would enable significantly denser and/or larger beams to be produced, such as those using picosecond kJ-class laser pulses (Shaw et al 2021), it may be possible to probe magnetic field amplification on the longer temporal and spatial scales associated with the cavitation instability. domain at the same time.…”
Plasma streaming instabilities play an important role in magnetic field amplification and particle acceleration in relativistic shocks and their environments. However, in the far shock precursor region where accelerated particles constitute a highly relativistic and dilute beam, streaming instabilities typically become inefficient and operate at very small scales when compared to the gyroradii of the beam particles. We report on a plasma cavitation instability that is driven by dilute relativistic beams and can increase both the magnetic field strength and coherence scale by orders of magnitude to reach near-equipartition values with the beam energy density. This instability grows after the development of the Weibel instability and is associated with the asymmetric response of background leptons and ions to the beam current. The resulting net inductive electric field drives a strong energy asymmetry between positively and negatively charged beam species. Large-scale particle-in-cell simulations are used to verify analytical predictions for the growth and saturation level of the instability and indicate that it is robust over a wide range of conditions, including those associated with pair-loaded plasmas. These results can have important implications for the magnetization and structure of shocks in gammaray bursts, and more generally for magnetic field amplification and asymmetric scattering of relativistic charged particles in plasma astrophysical environments.
“…Recent work has explored the study of the interplay between oblique and Weibeltype microinstabilities using either electron or electronpositron beams based on conventional RF accelerators (Shukla et al 2018;Arrowsmith et al 2021;San Miguel Claveria et al 2021). By considering configurations that would enable significantly denser and/or larger beams to be produced, such as those using picosecond kJ-class laser pulses (Shaw et al 2021), it may be possible to probe magnetic field amplification on the longer temporal and spatial scales associated with the cavitation instability. domain at the same time.…”
Plasma streaming instabilities play an important role in magnetic field amplification and particle acceleration in relativistic shocks and their environments. However, in the far shock precursor region where accelerated particles constitute a highly relativistic and dilute beam, streaming instabilities typically become inefficient and operate at very small scales when compared to the gyroradii of the beam particles. We report on a plasma cavitation instability that is driven by dilute relativistic beams and can increase both the magnetic field strength and coherence scale by orders of magnitude to reach near-equipartition values with the beam energy density. This instability grows after the development of the Weibel instability and is associated with the asymmetric response of background leptons and ions to the beam current. The resulting net inductive electric field drives a strong energy asymmetry between positively and negatively charged beam species. Large-scale particle-in-cell simulations are used to verify analytical predictions for the growth and saturation level of the instability and indicate that it is robust over a wide range of conditions, including those associated with pair-loaded plasmas. These results can have important implications for the magnetization and structure of shocks in gammaray bursts, and more generally for magnetic field amplification and asymmetric scattering of relativistic charged particles in plasma astrophysical environments.
“…Such systems, however, are rarely available at the same facilities as large HED drivers and cannot easily be installed for experiments because of cost and space constraints. Often these HED facilities have picosecond lasers available such as OMEGA EP, NIF-ARC (National Ignition Facility Advanced Radiograph Capability), PETAL, and Z-Petawatt lasers, which can be used for the efficient generation of relativistic electron beams via LPA techniques 18 . This method allows for electron beams to be generated for radiography without needing to add a rf linear accelerator to an HED facility.…”
Section: Introductionmentioning
confidence: 99%
“…For example, a laser-generated proton of 15 MeV will be fully stopped by ~ 2 mm of plastic at standard density and temperature, while a 15-MeV electron will require multiple centimeters of plastic to be fully stopped 20 . Far more electrons of similar energy or higher will also be generated for given laser conditions, providing a further advantage to laser-generated electrons over protons 5 , 18 . Figure 1 Areal density needed for a factor of 1/ e reduction in particle flux versus atomic number ( Z ) for average, mid-scale, and high-probe-energy laser-driven electron, X-ray, and proton probes.…”
Section: Introductionmentioning
confidence: 99%
“…Energies up to 1 GeV are shown corresponding to today’s high-performing electron LPA’s 23 , 32 and large proton LINACs 31 . LPA-generated electron beams are regularly created with energies as low as a few MeV 33 and as high as ~ 8 GeV 18 , 23 , 34 . This capability for large variation in energy makes for a customizable radiography tool that can provide insight into a wide variety of targets at areal densities ranging from mg/cm 2 to many g/cm 2 , integrated magnetic fields from 4.9 × 10 −3 to 28 T-m, and integrated electric fields from 0.9 to 1000 MV-m/m based on the above variation in electron energy.…”
Contact and projection electron radiography of static targets was demonstrated using a laser–plasma accelerator driven by a kilojoule, picosecond-class laser as a source of relativistic electrons with an average energy of 20 MeV. Objects with areal densities as high as 7.7 g/cm2 were probed in materials ranging from plastic to tungsten, and radiographs with resolution as good as 90 μm were produced. The effects of electric fields produced by the laser ablation of the radiography objects were observed and are well described by an analytic expression relating imaging magnification change to electric-field strength.
“…Direct laser acceleration is suitable for longer laser pulses interacting with slightly underdense plasma which results in nC-class electron bunches [20][21][22] with a duration comparable with the accelerating laser pulse duration [23]. Electron bunches carrying a charge up to µC level, but of the duration in the order of picoseconds or longer can be generated via the self-modulated laser wakefield acceleration regime employing high energy laser systems, as it was recently shown at OMEGA [24].…”
Ultrahigh-intensity laser-plasma physics provides unique light and particle beams as well as novel physical phenomena. A recently available regime is based on the interaction between a relativistic intensity few-cycle laser pulse and a sub-wavelength-sized mass-limited plasma target. Here, we investigate the generation of electron bunches under these extreme conditions by means of particle-in-cell simulations. In a first step, up to all electrons are expelled from the nanodroplet and gain relativistic energy from time-dependent local field enhancement at the surface. After this ejection, the electrons are further accelerated as they copropagate with the laser pulse. As a result, a few, or under specific conditions isolated, pC-class relativistic attosecond electron bunches are generated with laser pulse parameters feasible at state-of-the-art laser facilities. This is particularly interesting for some applications, such as generation of attosecond x-ray pulses via Thomson backscattering.
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