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1.	Efimenko, E., et al. (författare) Extreme plasma states in laser-governed vacuum breakdown 2018 Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322 .- 2045-2322. ; 8:1 Tidskriftsartikel (refereegranskat)abstract Triggering vacuum breakdown at laser facility is expected to provide rapid electron-positron p air production for studies in laboratory astrophysics and fundamental physics. However, the density of the produced plasma may cease to increase at a relativistic critical density, when the plasma becomes opaque. Here, we identify the opportunity of breaking this limit using optimal beam configuration of petawatt-class lasers. Tightly focused laser fields allow generating plasma in a small focal volume much less than λ 3 and creating extreme plasma states in terms of density and produced currents. These states can be regarded to be a new object of nonlinear plasma physics. Using 3D QED-PIC simulations we demonstrate a possibility of reaching densities over 10 25 cm -3, which is an order of magnitude higher than expected earlier. Controlling the process via initial target parameters provides an opportunity to reach the discovered plasma states at the upcoming laser facilities.
2.	Gonoskov, Arkady, et al. (författare) Anomalous radiative trapping in laser fields of extreme intensity 2014 Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 113, s. 014801- Tidskriftsartikel (refereegranskat)abstract We demonstrate that charged particles in a suciently intense standing wave are compressed toward, and oscillate synchronously at, the antinodes of the electric eld. We call this unusualbehaviour `anomalous radiative trapping' (ART). We show using dipole pulses, which oer a pathto increased laser intensity, that ART opens up new possibilities for the generation of radiationand particle beams, both of which are high-energy, directed and collimated. ART also provides a mechanism for particle control in high-intensity quantum-electrodynamics experiments.
3.	Gonoskov, Arkady, et al. (författare) Probing Nonperturbative QED with Optimally Focused Laser Pulses 2013 Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 111:6 Tidskriftsartikel (refereegranskat)abstract We study nonperturbative pair production in intense, focused laser fields called e-dipole pulses. We address the conditions required, such as the quality of the vacuum, for reaching high intensities without initiating beam-depleting cascades, the number of pairs which can be created, and experimental detection of the created pairs. We find that e-dipole pulses offer an optimal method of investigating nonperturbative QED.
4.	Sergeev, Alexander M., et al. (författare) Generation of giant attosecond pulses at the plasma surface in the regime of relativistic electronic spring 2011 Ingår i: Diode-Pumped High Energy and High Power Lasers; ELI. - : SPIE - International Society for Optical Engineering. - 9780819486707 Konferensbidrag (refereegranskat)abstract The generation of attosecond pulses with an amplitude greatly exceeding the driving field of an ultrarelativistic laser pulse at oblique irradiation of a solid target is investigated. We develop a universal model of the process, the so-called relativistic electronic spring, which is different from the conventional concept of an oscillating mirror. It follows from the model that there exists a parameter region where the energy conversion from the femto- to the attosecond regime is maximal. Based on the study we propose a new concept of laser pulse interaction with a target having a groove-shaped surface, which opens up the potential to exceed an intensity level of 1026 W/cm(2) and observe effects due to nonlinear quantum electrodynamics with upcoming laser sources.
5.	Aurand, B., et al. (författare) Manipulation of the spatial distribution of laser-accelerated proton beams by varying the laser intensity distribution 2016 Ingår i: Physics of Plasmas. - : AIP Publishing. - 1089-7674 .- 1070-664X. ; 23:2 Tidskriftsartikel (refereegranskat)abstract We report on a study of the spatial profile of proton beams produced through target normal sheath acceleration using flat target foils and changing the laser intensity distribution on the target front surface. This is done by either defocusing a single laser pulse or by using a split-pulse setup and irradiating the target with two identical laser pulses with variable spatial separation. The resulting proton beam profile and the energy spectrum are recorded as functions of the focal spot size of the single laser pulse and of the separation between the two pulses. A shaping of the resulting proton beam profile, related to both an increase in flux of low-energy protons in the target normal direction and a decrease in their divergence, in one or two dimensions, is observed. The results are explained by simple modelling of rear surface sheath field expansion, ionization, and projection of the resulting proton beam.
6.	Bashinov, A. V., et al. (författare) New horizons for extreme light physics with mega-science project XCELS 2014 Ingår i: European Physical Journal: Special Topics. - : Springer Science and Business Media LLC. - 1951-6401 .- 1951-6355. ; 223:6, s. 1105-1112 Forskningsöversikt (refereegranskat)abstract A short review of the Russian mega-science project XCELS and scientific problems to be solved are presented. We discuss the origin of multi-beam design to attain the highest field magnitude at optimal focusing. Then, we formulate particular physical problems of fundamental interest that can be solved within this project.
7.	Bashinov, A. V., et al. (författare) Towards attosecond-scale highly directed GeV gamma-ray sources with multipetawatt-class lasers 2017 Ingår i: Journal of Optics. - : IOP Publishing. - 2040-8978 .- 2040-8986. ; 19:11 Tidskriftsartikel (refereegranskat)abstract We consider a possibility of constructing a gamma-ray source based on the multibeam configuration of a multipetawatt laser system which we simulate using a converging dipole wave. It is shown that such a configuration of fields allows the generation of gamma radiation with narrow directivity of about 1 mrad in the form of pulse trains or isolated pulses on the attosecond timescale. The influence of quantum electrodynamic cascade development on the parameters of generated gamma bursts is studied.
8.	Bastrakov, S., et al. (författare) Performance aspects of collocated and staggered grids for particle-in-cell plasma simulation 2017 Ingår i: Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics). - Cham : Springer International Publishing. - 1611-3349 .- 0302-9743. - 9783319629315 ; 10421, s. 94-100 Konferensbidrag (refereegranskat)abstract We present a computational comparison of collocated and staggered uniform grids for particle-in-cell plasma simulation. Both types of grids are widely used, and numerical properties of the corresponding solvers are well-studied. However, for large-scale simulations performance is also an important factor, which is the focus of this paper. We start with a baseline implementation, apply widely-used techniques for performance optimization and measure their efficacy for both grids on a high-end Xeon CPU and a second-generation Xeon Phi processor. For the optimized version the collocated grid outperforms the staggered one by about 1.5x on both Xeon and Xeon Phi. The speedup on the Xeon Phi processor compared to Xeon is about 1.9x.
9.	Bhadoria, Shikha, 1991, et al. (författare) Mapping the power-law decay of high-harmonic spectra from few-cycle laser-solid interactions 2022 Ingår i: Physics of Plasmas. - : AIP Publishing. - 1070-664X .- 1089-7674. ; 29 Tidskriftsartikel (refereegranskat)abstract Visible or near infrared light can be manipulated to produce bursts of coherent extreme ultraviolet or x rays via the relativistic high-order harmonic generation process when a laser irradiates a solid plasma target. The intensity of the spectral components of the reflected signal decays with the increase in harmonic order and the efficiency of this non-linear process largely hinges on how prompt this decay is. This is governed by the conditions of the laser-plasma interaction for which various models have been proposed. At relativistic intensities, a spectrum exhibiting a power-law decay with an exponent of 8/3 or 4/3 is often stated. Here, we analyze the dependence of this exponent on interaction parameters, including the angle of incidence, the carrier envelope phase, intensity of the laser, and the pre-plasma length, and discuss opportunities for optimization. Our simulations show that, rather than there being one universal exponent, the spectral decay is a continuous function of the laser-plasma interaction parameters.
10.	Blackburn, Tom, 1989, et al. (författare) Relativistically intense XUV radiation from laser-illuminated near-critical plasmas 2018 Ingår i: Physical Review A. - 2469-9934 .- 2469-9926. ; 98:2 Tidskriftsartikel (refereegranskat)abstract Pulses of extreme ultraviolet (XUV) light, with wavelengths between 10 and 100nm, can be used to image and excite ultrafast phenomena such as the motion of atomic electrons. Here we show that the illumination of plasma with near-critical electron density may be used as a source of relativistically intense XUV radiation, providing the means for novel XUV-pump-XUV-probe experiments in the nonlinear regime. We describe how the optimal regime may be reached by tailoring the laser-target interaction parameters and by the presence of preplasma. Our results indicate that currently available laser facilities are capable of producing XUV pulses with duration ∼10fs, brilliance in excess of 1023photons/s/mm2/mrad2 (0.1% bandwidth), and intensity Iλ21019Wcm-2μm2.
11.	Blanco, M., et al. (författare) Controlling the ellipticity of attosecond pulses produced by laser irradiation of overdense plasmas 2018 Ingår i: Physics of Plasmas. - : AIP Publishing. - 1089-7674 .- 1070-664X. ; 25:9 Tidskriftsartikel (refereegranskat)abstract The interaction of high-intensity laser pulses and solid targets provides a promising way to create compact, tunable, and bright XUV attosecond sources that can become a unique tool for a variety of applications. However, it is important to control the polarization state of this XUV radiation and to do so in the most efficient regime of generation. Using the relativistic electronic spring (RES) model and particle-in-cell simulations, we show that the polarization state of the generated attosecond pulses can be tuned in a wide range of parameters by adjusting the polarization and/or the angle of incidence of the laser radiation. In particular, we demonstrate the possibility of producing circularly polarized attosecond pulses in a wide variety of setups.
12.	Burza, Matthias, et al. (författare) Hollow microspheres as targets for staged laser-driven proton acceleration 2011 Ingår i: New Journal of Physics. - : Institute of Physics Publishing (IOPP). - 1367-2630. ; 13, s. 013030- Tidskriftsartikel (refereegranskat)abstract A coated hollow core microsphere is introduced as a novel targetin ultra-intense laser–matter interaction experiments. In particular, it facilitates staged laser-driven proton acceleration by combining conventional target normal sheath acceleration (TNSA), power recycling of hot laterally spreading electrons and staging in a very simple and cheap target geometry. During TNSA of protons from one area of the sphere surface, laterally spreading hot electrons form a charge wave. Due to the spherical geometry, this wave refocuses on the opposite side of the sphere, where an opening has been laser micromachined.This leads to a strong transient charge separation field being set up there, which can post-accelerate those TNSA protons passing through the hole at the right time. Experimentally, the feasibility of using such targets is demonstrated. A redistribution is encountered in the experimental proton energy spectra, as predicted by particle-in-cell simulations and attributed to transient fields set up by oscillating currents on the sphere surface.
13.	Burza, Matthias, et al. (författare) Laser wakefield acceleration using wire produced double density ramps 2013 Ingår i: Physical Review Special Topics. Accelerators and Beams. - 1098-4402. ; 16:1 Tidskriftsartikel (refereegranskat)abstract A novel approach to implement and control electron injection into the accelerating phase of a laser wakefield accelerator is presented. It utilizes a wire, which is introduced into the flow of a supersonic gas jet creating shock waves and three regions of differing plasma electron density. If tailored appropriately, the laser plasma interaction takes place in three stages: Laser self-compression, electron injection, and acceleration in the second plasma wave period. Compared to self-injection by wave breaking of a nonlinear plasma wave in a constant density plasma, this scheme increases beam charge by up to 1 order of magnitude in the quasimonoenergetic regime. Electron acceleration in the second plasma wave period reduces electron beam divergence by approximate to 25%, and the localized injection at the density downramps results in spectra with less than a few percent relative spread. DOI: 10.1103/PhysRevSTAB.16.011301
14.	Cardenas, Daniel, et al. (författare) Electron bunch evolution in laser-wakefield acceleration 2020 Ingår i: Physical Review Accelerators and Beams. - : American Physical Society. - 2469-9888. ; 23 Tidskriftsartikel (refereegranskat)abstract We report on systematic and high-precision measurements of the evolution of electron beams in a laser-wakefield accelerator (LWFA). Utilizing shock-front injection, a technique providing stable, tunable and high-quality electron bunches, acceleration and deceleration of few-MeV quasimonoenergetic beams were measured with cutting-edge technology sub-5-fs and 8-fs laser pulses. We explain the observations with dephasing, an effect that fundamentally limits the performance of LWFAs. Typical density dependent electron energy evolution with 57–300 μm dephasing length and 6–20 MeV peak energy was observed and is well described by a parabolic fit. This is a promising electron source for time-resolved few-fs electron diffraction.
15.	de Andres, Aitor, 1992-, et al. (författare) Dynamics of vacuum laser accelerated electrons from nanotips Annan publikation (övrigt vetenskapligt/konstnärligt)
16.	de Andres Gonzalez, Aitor, 1992-, et al. (författare) Vacuum laser acceleration of electrons injected from nanotips 2023 Ingår i: 2023 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference, CLEO/Europe-EQEC 2023. - : Institute of Electrical and Electronics Engineers (IEEE). - 9798350345995 - 9798350346008 Konferensbidrag (refereegranskat)abstract Vacuum laser acceleration (VLA) is a paradigm that utilizes the strong fields of focused laser light to accelerate electrons in vacuum. Despite its conceptual simplicity and a large existing collection of theoretical studies, realizing VLA in practice has proven remarkably challenging due to the difficulties associated with efficient injection: the electrons to be accelerated must be pre-energized and temporally compressed below an optical half-cycle before timely entering the rapidly oscillating fields of the laser. Therefore, only a handful of experiments have been published up to date, and a knowledge gap remains [1-3].
17.	Fuchs, J., et al. (författare) Plasma devices for focusing extreme light pulses 2014 Ingår i: European Physical Journal: Special Topics. - : Springer Science and Business Media LLC. - 1951-6401 .- 1951-6355. ; 223:6, s. 1169-1173 Tidskriftsartikel (refereegranskat)abstract Since the inception of the laser, there has been a constant push toward increasing the laser peak intensity, as this has lead to opening the exploration of new territories, and the production of compact sources of particles and radiation with unprecedented characteristics. However, increasing the peak laser intensity is usually performed by enhancing the produced laser properties, either by lowering its duration or increasing its energy, which involves a great level of complexity for the laser chain, or comes at great cost. Focusing tightly is another possibility to increase the laser intensity, but this comes at the risk of damaging the optics with target debris, as it requires their placement in close proximity to the interaction region. Plasma devices are an attractive, compact alternative to tightly focus extreme light pulses and further increase the final laser intensity.
18.	Giuffrida, L., et al. (författare) Manipulation of laser-accelerated proton beam profiles by nanostructured and microstructured targets 2017 Ingår i: Physical Review Accelerators and Beams. - 2469-9888. ; 20:8, s. 081301- Tidskriftsartikel (refereegranskat)abstract Nanostructured and microstructured thin foils have been fabricated and used experimentally as targets to manipulate the spatial profile of proton bunches accelerated through the interaction with high intensity laser pulses (6 x 1019 W/cm(2)). Monolayers of polystyrene nanospheres were placed on the rear surfaces of thin plastic targets to improve the spatial homogeneity of the accelerated proton beams. Moreover, thin targets with grating structures of various configurations on their rear sides were used tomodify the proton beam divergence. Experimental results are presented, discussed, and supported by 3D particle-in-cell numerical simulations.
19.	Giuffrida, L., et al. (författare) Nano and micro structured targets to modulate the spatial profile of laser driven proton beams 2017 Ingår i: Journal of Instrumentation. - 1748-0221. ; 12:3, s. article no C03040 - Tidskriftsartikel (refereegranskat)abstract Nano and micro structured thin (μ m-scale) foils were designed, fabricated and irradiated with the high intensity laser system operating at LLC (Lund Laser Centre, Sweden) in order to systematically study and improve the main proton beam parameters. Nano-spheres deposited on the front (laser irradiated) surface of a flat Mylar foil enabled a small enhancement of the maximum energy and number of the accelerated protons. Nano-spheres on the rear side allowed to modify the proton beam spatial profile. In particular, with nanospheres deposited on the rear of the target, the proton beam spatial homogeneity was clearly enhanced. Silicon nitride thin foils having micro grating structures (with different step dimensions) on the rear surface were also used as targets to influence the divergence of the proton beam and drastically change its shape through a sort of stretching effect. The target fabrication process used for the different target types is described, and representative experimental results are shown and discussed along with supporting 3D particle-in-cell simulations. © 2017 IOP Publishing Ltd and Sissa Medialab srl.
20.	Gonoskov, Arkady A., et al. (författare) Ultrarelativistic nanoplasmonics as a route towards extreme-intensity attosecond pulses 2011 Ingår i: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics. - Melville, N.Y. : American Physical Society through the American Institute of Physics. - 1539-3755 .- 1550-2376. ; 84:4, s. 046403- Tidskriftsartikel (refereegranskat)abstract The generation of ultrastrong attosecond pulses through laser-plasma interactions offers the opportunity to surpass the intensity of any known laboratory radiation source, giving rise to new experimental possibilities, such as quantum electrodynamical tests and matter probing at extremely short scales. Here we demonstrate that a laser irradiated plasma surface can act as an efficient converter from the femto- to the attosecond range, giving a dramatic rise in pulse intensity. Although seemingly similar schemes have been described in the literature, the present setup differs significantly from the previous attempts. We present a model describing the nonlinear process of relativistic laser-plasma interaction. This model, which is applicable to a multitude of phenomena, is shown to be in excellent agreement with particle-in-cell simulations. The model makes it possible to determine a parameter region where the energy conversion from the femto- to the attosecond regime is maximal. Based on the study we propose a concept of laser pulse interaction with a target having a groove-shaped surface, which opens up the potential to exceed an intensity level of 10(26) W/cm(2) and observe effects due to nonlinear quantum electrodynamics with upcoming laser sources.
21.	Gonoskov, Arkady, 1984 (författare) Agnostic conservative down-sampling for optimizing statistical representations and PIC simulations 2022 Ingår i: Computer Physics Communications. - : Elsevier BV. - 0010-4655. ; 271 Tidskriftsartikel (refereegranskat)abstract In particle-in-cell simulations and some other statistical computations, the representation of modelled distributions with tracked macro-particles can become locally excessive. Merging or resampling dense clusters or highly-populated phase space volumes may, however, remove or affect small-scale peculiarities in the modelled distribution or cause local changes of conserved quantities, such as energy and momenta. This may lead to additional noise, reduced accuracy or even unphysical effects. Here we describe a probabilistic algorithm for reducing the number of macro-particles in such clusters or volumes so that all the distribution functions are not affected on average and an arbitrary number of conservation laws, distribution central moments and contributions to the grid quantities (such as charge and current density) are preserved. (C) 2021 The Author. Published by Elsevier B.V.
22.	Gonoskov, Arkady, 1984, et al. (författare) Charged particle motion and radiation in strong electromagnetic fields 2022 Ingår i: Reviews of Modern Physics. - 0034-6861. ; 94:4 Forskningsöversikt (refereegranskat)abstract The dynamics of charged particles in electromagnetic fields is an essential component of understanding the most extreme environments in our Universe. In electromagnetic fields of sufficient magnitude, radiation emission dominates the particle motion and effects of quantum electrodynamics (QED) in strong fields are crucial, which triggers electron-positron pair cascades and counterintuitive particle-trapping phenomena. As a result of recent progress in laser technology, high-power lasers provide a platform to create and probe such fields in the laboratory. With new large-scale laser facilities on the horizon and the prospect of investigating these hitherto unexplored regimes, this review explores the basic physical processes of radiation reaction and QED in strong fields, how they are treated theoretically and in simulation, the new collective dynamics they unlock, recent experimental progress and plans, and possible applications for high -flux particle and radiation sources.
23.	Gonoskov, Arkady, 1984, et al. (författare) Employing machine learning for theory validation and identification of experimental conditions in laser-plasma physics 2019 Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322 .- 2045-2322. ; 9:1 Tidskriftsartikel (refereegranskat)abstract The validation of a theory is commonly based on appealing to clearly distinguishable and describable features in properly reduced experimental data, while the use of ab-initio simulation for interpreting experimental data typically requires complete knowledge about initial conditions and parameters. We here apply the methodology of using machine learning for overcoming these natural limitations. We outline some basic universal ideas and show how we can use them to resolve long-standing theoretical and experimental difficulties in the problem of high-intensity laser-plasma interactions. In particular we show how an artificial neural network can “read” features imprinted in laser-plasma harmonic spectra that are currently analysed with spectral interferometry.
24.	Gonoskov, Arkady, 1984 (författare) Explicit energy-conserving modification of relativistic PIC method 2024 Ingår i: Journal of Computational Physics. - 0021-9991 .- 1090-2716. ; 502 Tidskriftsartikel (refereegranskat)abstract The use of explicit particle-in-cell (PIC) method for relativistic plasma simulations is restricted by numerical heating and instabilities that may significantly constrain the choice of time and space steps. To partially eliminate these limitations we consider a possibility to enforce exact energy conservation by altering the standard time step splitting. Instead of updating particles in a given field and then the field using the current they produce, we consider subsystems that describe the coupling of a single particle and the field at the nearby nodes and solve them with enforced energy conservation sequentially for all particles, which is completed by the field update with zero current. Such an approach is compatible with various advances, ranging from accounting for additional physical effects to the use of numerical-dispersion-free field solvers, high-order weighting shapes and particle push subcycling. To facilitate further considerations and use, we provide a basic implementation in a 3D, relativistic, spectral code π-PIC, which we make publicly available. The method and its implementations are verified using simulations of cold plasma oscillations, Landau damping and relativistic two-stream instability. The capabilities of the method to deal with large time and space steps are demonstrated in the problem of plasma heating by intense incident radiation.
25.	Gonoskov, Arkady, 1984, et al. (författare) Extended particle-in-cell schemes for physics in ultrastrong laser fields : Review and developments 2015 Ingår i: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics. - 1539-3755 .- 1550-2376. ; 92:2 Tidskriftsartikel (refereegranskat)abstract We review common extensions of particle-in-cell (PIC) schemes which account for strong field phenomena in laser-plasma interactions. After describing the physical processes of interest and their numerical implementation, we provide solutions for several associated methodological and algorithmic problems. We propose a modified event generator that precisely models the entire spectrum of incoherent particle emission without any low-energy cutoff, and which imposes close to the weakest possible demands on the numerical time step. Based on this, we also develop an adaptive event generator that subdivides the time step for locally resolving QED events, allowing for efficient simulation of cascades. Further, we present a unified technical interface for including the processes of interest in different PIC implementations. Two PIC codes which support this interface, PICADOR and ELMIS, are also briefly reviewed.
26.	Gonoskov, Arkady, et al. (författare) Multicascade proton acceleration by a superintense laser pulse in the regime of relativistically induced slab transparency 2009 Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 102:18, s. 184801- Tidskriftsartikel (refereegranskat)abstract The regime of multicascade proton acceleration during the interaction of a 1021–1022 W=cm2 laserpulse with a structured target is proposed. The regime is based on the electron charge displacement under the action of laser ponderomotive force and on the effect of relativistically induced slab transparency which allows realization of the idea of multicascade acceleration. It is shown that a target comprising several thin foils properly spaced apart can optimize the acceleration process and give at the output aquasi-monoenergetic beam of protons with energies up to hundreds of MeV with an energy spread of just a few percent.
27.	Gonoskov, Arkady, 1984 (författare) Theory of relativistic radiation reflection from plasmas 2018 Ingår i: Physics of Plasmas. - : AIP Publishing. - 1089-7674 .- 1070-664X. ; 25:1 Tidskriftsartikel (refereegranskat)abstract We consider the reflection of relativistically strong radiation from plasma and identify the physical origin of the electrons' tendency to form a thin sheet, which maintains its localisation throughout its motion. Thereby, we justify the principle of relativistic electronic spring (RES) proposed in [Gonoskov et al., Phys. Rev. E 84, 046403 (2011)]. Using the RES principle, we derive a closed set of differential equations that describe the reflection of radiation with arbitrary variation of polarization and intensity from plasma with an arbitrary density profile for an arbitrary angle of incidence. We confirm with ab initio PIC simulations that the developed theory accurately describes laser-plasma interactions in the regime where the reflection of relativistically strong radiation is accompanied by significant, repeated relocation of plasma electrons. In particular, the theory can be applied for the studies of plasma heating and coherent and incoherent emissions in the RES regime of high-intensity laser-plasma interaction.
28.	Gonoskov, Arkady, 1984- (författare) Ultra-intense laser-plasma interaction for applied and fundamental physics 2013 Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract Rapid progress in ultra-intense laser technology has resulted in intensity levels surpassing 1022 W/cm2, reaching the highest possible density of electromagnetic energy amongst all controlled sources available in the laboratory. During recent decades, fast growth in available intensity has stimulated numerous studies based on the use of high intensity lasers as a unique tool for the initiation of nonlinear behavior in various basic systems: first molecules and atoms, then plasma resulting from the ionization of gases and solids, and, finally, pure vacuum. Apart from their fundamental importance, these studies reveal various mechanisms for the conversion of a laser pulse's energy into other forms, opening up new possibilities for generating beams of energetic particles and radiation with tailored properties. In particular, the cheapness and compactness of laser based sources of energetic protons are expected to make a revolution in medicine and industry. In this thesis we study nonlinear phenomena in the process of laser radiation interacting with plasmas of ionized targets. We develop advanced numerical tools and use them for the simulation of laser-plasma interactions in various configurations relating to both current and proposed experiments. Phenomenological analysis of numerical results helps us to reveal several new effects, understand the physics behind them and develop related theoretical models capable of making general conclusions and predictions. We develop target designs to use studied effects for charged particle acceleration and for the generation of attosecond pulses of unprecedented intensity. Finally, we analyze prospects for experimental activity at the upcoming international high intensity laser facilities and uncover a basic effect of anomalous radiative trapping, which opens up new possibilities for fundamental science.
29.	Gonoskov, Arkady, 1984, et al. (författare) Ultrabright GeV Photon Source via Controlled Electromagnetic Cascades in Laser-Dipole Waves 2017 Ingår i: Physical Review X. - 2160-3308. ; 7:4 Tidskriftsartikel (refereegranskat)abstract Electromagnetic cascades have the potential to act as a high-energy photon source of unprecedented brightness. Such a source would offer new experimental possibilities in fundamental science, but in the cascade process radiation reaction and rapid electron-positron plasma production seemingly restrict the efficient production of photons to sub-GeV energies. Here, we show how to overcome these energetic restrictions and how to create a directed GeV photon source, with unique capabilities as compared to existing sources. Our new source concept is based on a controlled interplay between the cascade and anomalous radiative trapping. Using specially designed advanced numerical models supported with analytical estimates, we demonstrate that the concept becomes feasible at laser powers of around 7 PW, which is accessible at soon-to-be-available facilities. A higher peak power of 40 PW can provide 10(9) photons with GeV energies in a well-collimated 3-fs beam, achieving peak brilliance 9 x 10(24) ph s(-1) mrad(-2) mm(-2)/0.1%BW.
30.	Harvey, Christopher, 1982, et al. (författare) Narrowing of the emission angle in high-intensity Compton scattering 2016 Ingår i: Physical Review A - Atomic, Molecular, and Optical Physics. - : American Physical Society. - 2469-9926 .- 2469-9934 .- 1050-2947 .- 1094-1622. ; 93:2 Tidskriftsartikel (refereegranskat)abstract We consider the emission spectrum of high-energy electrons in an intense laser field. At high intensities (a_0 \sim 200) we find that the QED theory predicts a narrower angular spread of emissions than the classical theory. This is due to the classical theory overestimating the energy loss of the particles, resulting in them becoming more susceptible to reflection in the laser pulse.
31.	Harvey, Christopher, 1982, et al. (författare) Quantum Quenching of Radiation Losses in Short Laser Pulses 2017 Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 118:10 Tidskriftsartikel (refereegranskat)abstract Accelerated charges radiate, and therefore must lose energy. The impact of this energy loss on particle motion, called radiation reaction, becomes significant in intense-laser matter interactions, where it can reduce collision energies, hinder particle acceleration schemes, and is seemingly unavoidable. Here we show that this common belief breaks down in short laser pulses, and that energy losses and radiation reaction can be controlled and effectively switched off by appropriate tuning of the pulse length. This "quenching" of emission is impossible in classical physics, but becomes possible in QED due to the discrete nature of quantum emissions.
32.	Korzhimanov, A. V., et al. (författare) Horizons of petawatt laser technology 2011 Ingår i: Physics-Uspekhi. - Russia/United Kingdom : Institute of Physics Publishing (IOPP). - 0042-1294. ; 54:1, s. 9-28 Tidskriftsartikel (refereegranskat)abstract Recent advances in the development of superpowerlasers are reviewed. A number of possibilities that the newly available petawatt-power level lasers open up in the physics of extreme light fields are discussed.
33.	Larin, Anton, et al. (författare) Load balancing for particle-in-cell plasma simulation on multicore systems 2018 Ingår i: Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics). - Cham : Springer International Publishing. - 1611-3349 .- 0302-9743. ; 10777 LNCS, s. 145-155 Konferensbidrag (refereegranskat)abstract Particle-in-cell plasma simulation is an important area of computational physics. The particle-in-cell method naturally allows parallel processing on distributed and shared memory. In this paper we address the problem of load balancing on multicore systems. While being well-studied for many traditional applications of the method, it is a relevant problem for the emerging area of particle-in-cell simulations with account for effects of quantum electrodynamics. Such simulations typically produce highly non-uniform, and sometimes volatile, particle distributions, which could require custom load balancing schemes. In this paper we present a computational evaluation of several standard and custom load balancing schemes for the particle-in-cell method on a high-end system with 96 cores on shared memory. We use a test problem with static non-uniform particle distribution and a real problem with account for quantum electrodynamics effects, which produce dynamically changing highly non-uniform distributions of particles and workload. For these problems the custom schemes result in increase of scaling efficiency by up to 20% compared to the standard OpenMP schemes.
34.	Mackenroth, Felix, 1984, et al. (författare) Chirped-Standing-Wave Acceleration of Ions with Intense Lasers 2016 Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 117:10 Tidskriftsartikel (refereegranskat)abstract We propose a novel mechanism for ion acceleration based on the guided motion of electrons from a thin layer. The electron motion is locked to the moving nodes of a standing wave formed by a chirped laser pulse reflected from a mirror behind the layer. This provides a stable longitudinal field of charge separation, thus giving rise to chirped-standing-wave acceleration of the residual ions of the layer. We demonstrate, both analytically and numerically, that stable proton beams, with energy spectra peaked around 100 MeV, are feasible for pulse energies at the level of 10 J. Moreover, a scaling law for higher laser intensities and layer densities is presented, indicating stable GeV-level energy gains of dense ion bunches, for soon-to-be-available laser intensities.
35.	Mackenroth, F., et al. (författare) Controlling laser-ion acceleration through pulse chirping 2017 Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9781510609822 ; 10240, s. Article no UNSP 102400B- Konferensbidrag (refereegranskat)abstract We present an in-depth study of the recently proposed novel laser-ion acceleration scheme Chirped-standing-wave acceleration. This scheme surpasses the scaling properties of previously studied thermal laser-based ion acceleration scheme while simultaneously offering unprecedented stability and control over the ion beam properties. In this work we elaborate on the possibilities of controlling ion beam properties such as ion energy and particle number collectively by tuning the laser's chirp and the target parameters in a consistent way. We provide quantitative estimates for the proposed scheme's capabilities and highlight its tunability.
36.	Mackenroth, Felix, 1984, et al. (författare) Reaching high flux in laser-driven ion acceleration 2017 Ingår i: European Physical Journal D. - : Springer Science and Business Media LLC. - 1434-6079 .- 1434-6060. ; 71:8 Tidskriftsartikel (refereegranskat)abstract Since the first experimental observation of laser-driven ion acceleration, optimizing the ion beams’ characteristics aiming at levels enabling various key applications has been the primary challenge driving technological and theoretical studies. However, most of the proposed acceleration mechanisms and strategies identified as promising, are focused on providing ever higher ion energies. On the other hand, the ions’ energy is only one of several parameters characterizing the beams’ aptness for any desired application. For example, the usefulness of laser-based ion sources for medical applications such as the renowned hadron therapy, and potentially many more, can also crucially depend on the number of accelerated ions or their flux at a required level of ion energies. In this work, as an example of an up to now widely disregarded beam characteristic, we use theoretical models and numerical simulations to systematically examine and compare the existing proposals for laser-based ion acceleration in their ability to provide high ion fluxes at varying ion energy levels.
37.	Magnusson, Joel, 1991, et al. (författare) Energy partitioning and electron momentum distributions in intense laser-solid interactions 2017 Ingår i: European Physical Journal D. - : Springer Science and Business Media LLC. - 1434-6079 .- 1434-6060. ; 71:9 Tidskriftsartikel (refereegranskat)abstract Producing inward orientated streams of energetic electrons by intense laser pulses acting on solid targets is the most robust and accessible way of transferring the laser energy to particles, which underlies numerous applications, ranging from TNSA to laboratory astrophysics. Structures with the scale of the laser wavelength can significantly enhance energy absorption, which has been in the center of attention in recent studies. In this article, we demonstrate and assess the effect of the structures for widening the angular distribution of generated energetic electrons. We analyse the results of PIC simulations and reveal several aspects that can be important for the related applications.
38.	Magnusson, Joel, 1991, et al. (författare) Laser-Particle Collider for Multi-GeV Photon Production 2019 Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 122:25 Tidskriftsartikel (refereegranskat)abstract As an alternative to Compton backscattering and bremsstrahlung, the process of colliding high-energy electron beams with strong laser fields can more efficiently provide both a cleaner and brighter source of photons in the multi-GeV range for fundamental studies in nuclear and quark-gluon physics. In order to favor the emission of high-energy quanta and minimize their decay into electron-positron pairs, the fields must not only be sufficiently strong, but also well localized. We here examine these aspects and develop the concept of a laser-particle collider tailored for high-energy photon generation. We show that the use of multiple colliding laser pulses with 0.4 PW of total power is capable of converting more than 18% of multi-GeV electrons passing through the high-field region into photons, each of which carries more than half of the electron initial energy. © 2019 authors. Published by the American Physical Society.
39.	Magnusson, Joel, 1991, et al. (författare) Multiple colliding laser pulses as a basis for studying high-field high-energy physics 2019 Ingår i: Physical Review A - Atomic, Molecular, and Optical Physics. - 2469-9926 .- 2469-9934. ; 100:6 Tidskriftsartikel (refereegranskat)abstract Apart from maximizing the strength of optical electromagnetic fields achievable at high-intensity laser facilities, the collision of several phase-matched laser pulses has been identified theoretically as a trigger of and way to study various phenomena. These range from the basic processes of strong-field quantum electrodynamics to the extraordinary dynamics of the generated electron-positron plasmas. This has paved the way for several experimental proposals aimed at both fundamental studies of matter at extreme conditions and the creation of particle and radiation sources. Because of the unprecedented capabilities of such sources, they have the potential to open up new opportunities for experimental studies in nuclear and quark-gluon physics. We perform here a systematic analysis of different regimes and opportunities achievable with the concept of multiple colliding laser pulses, for both current and upcoming laser facilities. We reveal that several distinct regimes could be within reach of multi-petawatt laser facilities.
40.	Magnusson, Joel, 1991, et al. (författare) Prospects for laser-driven ion acceleration through controlled displacement of electrons by standing waves 2018 Ingår i: Physics of Plasmas. - : AIP Publishing. - 1089-7674 .- 1070-664X. ; 25:5 Tidskriftsartikel (refereegranskat)abstract During the interaction of intense femtosecond laser pulses with various targets, the natural mechanisms of laser energy transformation inherently lack temporal control and thus commonly do not provide opportunities for a controlled generation of a well-collimated, high-charge beam of ions with a given energy of particular interest. In an effort to alleviate this problem, it was recently proposed that the ions can be dragged by an electron bunch trapped in a controllably moving potential well formed by laser radiation. Such standing-wave acceleration (SWA) can be achieved through reflection of a chirped laser pulse from a mirror, which has been formulated as the concept of chirped-standing-wave acceleration (CSWA). Here, we analyse general feasibility aspects of the SWA approach and demonstrate its reasonable robustness against field structure imperfections, such as those caused by misalignment, ellipticity, and limited contrast. Using this, we also identify prospects and limitations of the CSWA concept.
41.	Marklund, Mattias, 1970, et al. (författare) Towards critical and supercritical electromagnetic fields 2023 Ingår i: High Power Laser Science and Engineering. - : Cambridge University Press (CUP). - 2095-4719 .- 2052-3289. ; 11 Tidskriftsartikel (refereegranskat)abstract The availability of ever stronger, laser-generated electromagnetic fields underpins continuing progress in the study and application of nonlinear phenomena in basic physical systems, ranging from molecules and atoms to relativistic plasmas and quantum electrodynamics. This raises the question: how far will we be able to go with future lasers? One exciting prospect is the attainment of field strengths approaching the Schwinger critical field E-cr in the laboratory frame, such that the field invariant E-2 - c(2)B(2) > E-cr(2) is reached. The feasibility of doing so has been questioned, on the basis that cascade generation of dense electron-positron plasma would inevitably lead to absorption or screening of the incident light. Here we discuss the potential for future lasers to overcome such obstacles, by combining the concept of multiple colliding laser pulses with that of frequency upshifting via a tailored laser-plasma interaction. This compresses the electromagnetic field energy into a region of nanometre size and attosecond duration, which increases the field magnitude at fixed power but also suppresses pair cascades. Our results indicate that laser facilities with peak power of tens of PW could be capable of reaching Ecr. Such a scenario opens up prospects for the experimental investigation of phenomena previously considered to occur only in the most extreme environments in the universe.
42.	Meyerov, I., et al. (författare) Hybrid CPU + Xeon Phi implementation of the Particle-in-Cell method for plasma simulation 2016 Ingår i: Supercomputing Frontiers and Innovations. - : FSAEIHE South Ural State University (National Research University). - 2313-8734 .- 2409-6008. ; 3:3, s. 5-10 Tidskriftsartikel (refereegranskat)abstract This paper presents experimental results of Particle-in-Cell plasma simulation on a hybrid system with CPUs and Intel Xeon Phi coprocessors. We consider simulation of two relevant laserdriven particle acceleration regimes using the Particle-in-Cell code PICADOR. On a node of a cluster with 2 CPUs and 2 Xeon Phi coprocessors the hybrid CPU + Xeon Phi configuration allows to fully utilize the computational resources of the node. It outperforms both CPU-only and Xeon Phi-only configurations with the speedups between 1.36 x and 1.68 x.
43.	Muraviev, A. A., et al. (författare) Generation of current sheets and giant quasistatic magnetic fields at the ionization of vacuum in extremely strong light fields 2015 Ingår i: JETP Letters. - 1090-6487 .- 0021-3640. ; 102:3, s. 148-153 Tidskriftsartikel (refereegranskat)abstract The self-consistent dynamics of an electron–positron plasma, which is formed during the generation of quantum-electrodynamic cascades, in a superstrong field of counterpropagating linearly polarized waves is examined. It is shown that the formation of thin (on a wavelength scale) current sheets which generate quasistatic magnetic fields comparable to the corresponding fields of incident waves plays an important role in the dynamics of a cascade for fields above a certain threshold. The fraction of the laser energy transformed into the energy of quasistatic magnetic fields can exceed 20%.
44.	Muraviev, A., et al. (författare) Particle dynamics governed by radiation losses in extreme-field current sheets 2021 Ingår i: Physical Review E. - 2470-0045 .- 2470-0053. ; 104 Tidskriftsartikel (refereegranskat)abstract Particles moving in current sheets under extreme conditions, such as those in the vicinity of pulsars or those predicted on upcoming multipetawatt laser facilities, may be subject to significant radiation losses. We present an analysis of particle motion in model fields of a relativistic neutral electron-positron current sheet in the case when radiative effects must be accounted for. In the Landau-Lifshitz radiation reaction force model, when quantum effects are negligible, an analytical solution for particle trajectories is derived. Based on this solution, for the case when quantum effects are significant an averaged quantum solution in the semiclassical approach is obtained. The applicability region of the solutions is determined and analytical trajectories are found to be in good agreement with those of numerical simulations which account for radiative effects. Based on these results we demonstrate that radiation reaction itself can provide a mechanism of pinching even within a given field consideration.
45.	Muraviev, Alexander, et al. (författare) Strategies for particle resampling in PIC simulations 2021 Ingår i: Computer Physics Communications. - : Elsevier BV. - 0010-4655. ; 262 Tidskriftsartikel (refereegranskat)
46.	Olofsson, Christoffer, 1996, et al. (författare) Attaining a strong-field QED signal at laser-electron colliders with optimized focusing 2022 Ingår i: Physical Review A (PRA). - 2469-9926 .- 2469-9934. ; 106 Tidskriftsartikel (refereegranskat)abstract Colliding bunches of high-energy electrons with intense laser pulses provides a basis for studying strong-field QED processes enabled by high values of quantum nonlinearity parameter χ. Nevertheless, the signal deconvolution is intricate due to the probabilistic nature of the processes and shot-to-shot variation of the impact parameter, which disfavors the use of tight focusing. We propose a concept for distinguishing the signal of high-χ emissions that enables the use of optimal focusing to attain the highest χ≈5.25[ɛ/(1GeV)][P/(1PW)]^{1/2}[(1μm)/λ] for a given electron energy ɛ, laser power P, and wavelength λ. Reaching such a χ with f/2 focusing requires more than 10 times higher power.
47.	Olofsson, Christoffer, 1996, et al. (författare) Prospects for statistical tests of strong-field quantum electrodynamics with high-intensity lasers 2023 Ingår i: High Power Laser Science and Engineering. - 2095-4719. ; 11 Tidskriftsartikel (refereegranskat)abstract Exploiting high-energy electron beams colliding into high-intensity laser pulses brings an opportunity to reach high values of the dimensionless rest-frame acceleration $\chi$ and thereby invoke processes described by strong-field quantum electrodynamics (SFQED). Measuring deviations from the results of Furry-picture perturbation theory in SFQED at high $\chi$ can be valuable for testing existing predictions, as well as for guiding further theoretical developments. Nevertheless, such experimental measurements are challenging due to the probabilistic nature of the interaction processes, dominating signals of low-$\chi$ interactions and limited capabilities to control and measure the alignment and synchronization in such collision experiments. Here we elaborate a methodology of using approximate Bayesian computations for drawing statistical inferences based on the results of many repeated experiments despite partially unknown collision parameters that vary between experiments. As a proof-of-principle, we consider the problem of inferring the effective mass change due to coupling with the strong-field environment.
48.	Panova, E., et al. (författare) Optimized Computation of Tight Focusing of Short Pulses Using Mapping to Periodic Space 2021 Ingår i: Applied Sciences-Basel. - : MDPI AG. - 2076-3417. ; 11:3 Tidskriftsartikel (refereegranskat)abstract When a pulsed, few-cycle electromagnetic wave is focused by optics with f-number smaller than two, the frequency components it contains are focused to different regions of space, building up a complex electromagnetic field structure. Accurate numerical computation of this structure is essential for many applications such as the analysis, diagnostics, and control of high-intensity laser-matter interactions. However, straightforward use of finite-difference methods can impose unacceptably high demands on computational resources, owing to the necessity of resolving far-field and near-field zones at sufficiently high resolution to overcome numerical dispersion effects. Here, we present a procedure for fast computation of tight focusing by mapping a spherically curved far-field region to periodic space, where the field can be advanced by a dispersion-free spectral solver. In many cases of interest, the mapping reduces both run time and memory requirements by a factor of order 10, making it possible to carry out simulations on a desktop machine or a single node of a supercomputer. We provide an open-source C++ implementation with Python bindings and demonstrate its use for a desktop machine, where the routine provides the opportunity to use the resolution sufficient for handling the pulses with spectra spanning over several octaves. The described approach can facilitate the stability analysis of theoretical proposals, the studies based on statistical inferences, as well as the overall development and analysis of experiments with tightly-focused short laser pulses.
49.	Rodimkov, Yury, et al. (författare) ML-Based Analysis of Particle Distributions in High-Intensity Laser Experiments: Role of Binning Strategy 2021 Ingår i: Entropy. - : MDPI AG. - 1099-4300. ; 23:1 Tidskriftsartikel (refereegranskat)abstract When entering the phase of big data processing and statistical inferences in experimental physics, the efficient use of machine learning methods may require optimal data preprocessing methods and, in particular, optimal balance between details and noise. In experimental studies of strong-field quantum electrodynamics with intense lasers, this balance concerns data binning for the observed distributions of particles and photons. Here we analyze the aspect of binning with respect to different machine learning methods (Support Vector Machine (SVM), Gradient Boosting Trees (GBT), Fully-Connected Neural Network (FCNN), Convolutional Neural Network (CNN)) using numerical simulations that mimic expected properties of upcoming experiments. We see that binning can crucially affect the performance of SVM and GBT, and, to a less extent, FCNN and CNN. This can be interpreted as the latter methods being able to effectively learn the optimal binning, discarding unnecessary information. Nevertheless, given limited training sets, the results indicate that the efficiency can be increased by optimizing the binning scale along with other hyperparameters. We present specific measurements of accuracy that can be useful for planning of experiments in the specified research area.
50.	Rodimkov, Y., et al. (författare) Towards ML-Based Diagnostics of Laser-Plasma Interactions 2021 Ingår i: Sensors. - : MDPI AG. - 1424-8220. ; 21:21 Tidskriftsartikel (refereegranskat)abstract The power of machine learning (ML) in feature identification can be harnessed for determining quantities in experiments that are difficult to measure directly. However, if an ML model is trained on simulated data, rather than experimental results, the differences between the two can pose an obstacle to reliable data extraction. Here we report on the development of ML-based diagnostics for experiments on high-intensity laser-matter interactions. With the intention to accentuate robust, physics-governed features, the presence of which is tolerant to such differences, we test the application of principal component analysis, data augmentation and training with data that has superimposed noise of gradually increasing amplitude. Using synthetic data of simulated experiments, we identify that the approach based on the noise of increasing amplitude yields the most accurate ML models and thus is likely to be useful in similar projects on ML-based diagnostics.

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