| 41. |
- Blackburn, Thomas, 1989, et al.
(författare)
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Self-absorption of synchrotron radiation in a laser-irradiated plasma
- 2021
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1070-664X .- 1089-7674. ; 28:5
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Tidskriftsartikel (refereegranskat)abstract
- Electrons at the surface of a plasma that is irradiated by a laser with intensity in excess of 1 0 23 W c m - 2 are accelerated so strongly that they emit bursts of synchrotron radiation. Although the combination of high photon and electron density and electromagnetic field strength at the plasma surface makes particle-particle interactions possible, these interactions are usually neglected in simulations of the high-intensity regime. Here we demonstrate an implementation of two such processes: photon absorption and stimulated emission. We show that, for plasmas that are opaque to the laser light, photon absorption would cause complete depletion of the multi-keV region of the synchrotron photon spectrum, unless compensated by stimulated emission. Our results motivate further study of the density dependence of quantum electrodynamics phenomena in strong electromagnetic fields.
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| 42. |
- Blackburn, Thomas, 1989, et al.
(författare)
-
Simulations of laser-driven strong-field QED with Ptarmigan: Resolving wavelength-scale interference and γ-ray polarization
- 2023
-
Ingår i: Physics of Plasmas. - 1070-664X .- 1089-7674. ; 30
-
Tidskriftsartikel (refereegranskat)abstract
- Accurate modeling is necessary to support precision experiments investigating strong-field QED phenomena. This modeling is particularly challenging in the transition between the perturbative and nonperturbative regimes, where the normalized laser amplitude a0 is comparable to unity and wavelength-scale interference is significant. Here, we describe how to simulate nonlinear Compton scattering, Breit-Wheeler pair creation, and trident pair creation in this regime, using the Monte Carlo particle-tracking code Ptarmigan. This code simulates collisions between high-intensity lasers and beams of electrons or γ rays, primarily in the framework of the locally monochromatic approximation. We benchmark our simulation results against full QED calculations for pulsed plane waves and show that they are accurate at the level of a few per cent, across the full range of particle energies and laser intensities. This work extends our previous results to linearly polarized lasers and arbitrary polarized γ rays.
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| 43. |
- 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.
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| 44. |
- Brenning, Nils, et al.
(författare)
-
Alfven's critical ionization velocity observed in high power impulse magnetron sputtering discharges
- 2012
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1070-664X .- 1089-7674. ; 19:9, s. 093505-
-
Tidskriftsartikel (refereegranskat)abstract
- Azimuthally rotating dense plasma structures, spokes, have recently been detected in several high power impulse magnetron sputtering (HiPIMS) devices used for thin film deposition and surface treatment, and are thought to be important for plasma buildup, energizing of electrons, as well as cross-B transport of charged particles. In this work, the drift velocities of these spokes are shown to be strongly correlated with the critical ionization velocity, CIV, proposed by Alfven. It is proposed as the most promising approach in combining the CIV and HiPIMS research fields is to focus on the role of spokes in the process of electron energization.
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| 45. |
- Brenning, Nils, et al.
(författare)
-
Conditions for plasmoid penetration across abrupt magnetic barriers
- 2005
-
Ingår i: Physics of Plasmas. - : AIP Publishing. - 1070-664X .- 1089-7674. ; 12:1
-
Tidskriftsartikel (refereegranskat)abstract
- The penetration of plasma clouds, or plasmoids, across abrupt magnetic barriers (of the scale less than a few ion gyro radii, using the plasmoid directed velocity) is studied. The insight gained earlier, from detailed experimental and computer simulation investigations of a case study, is generalized into other parameter regimes. It is concluded for what parameters a plasi-noid should be expected to penetrate the magnetic barrier through self-polarization, penetrate through magnetic expulsion, or be rejected from the barrier. The scaling parameters are n(e), upsilon(o), B-perpendicular to, m(i), T-i, and the width w of the plasmoid. The scaling is based on a model for strongly driven, nonlinear magnetic field diffusion into a plasma which is a generalization of the earlier laboratory findings. The results are applied to experiments earlier reported in the literature, and also to the proposed application of impulsive penetration of plasmoids from the solar wind into the Earth's magnetosphere.
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| 46. |
- Bret, Antoine, et al.
(författare)
-
Hierarchy of instabilities for two counter-streaming magnetized pair beams: Influence of field obliquity
- 2017
-
Ingår i: Physics of Plasmas. - : A I P Publishing LLC. - 1070-664X .- 1089-7674. ; 24:6
-
Tidskriftsartikel (refereegranskat)abstract
- The hierarchy of unstable modes when two counter-streaming pair plasmas interact over a flow-aligned magnetic field has been recently investigated [Phys. Plasmas 23, 062122 (2016)]. The analysis is here extended to the case of an arbitrarily tilted magnetic field. The two plasma shells are initially cold and identical. For any angle θ ∈ [0, π/2] between the field and the initial flow, the hierarchy of unstable modes is numerically determined in terms of the initial Lorentz factor of the shells γ0, and the field strength as measured by a parameter denoted σ. For θ = 0, four different kinds of mode are likely to lead the linear phase. The hierarchy simplifies for larger θ's, partly because the Weibel instability can no longer be cancelled in this regime. For θ > 0.78 (44°) and in the relativistic regime, the Weibel instability always govern the interaction. In the non-relativistic regime, the hierarchy becomes θ-independent because the interaction turns to be field-independent. As a result, the two-stream instability becomes the dominant one, regardless of the field obliquity.
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| 47. |
- Bret, Antoine, et al.
(författare)
-
How large can the electron to proton mass ratio be in particle-in-cell simulations of unstable systems?
- 2010
-
Ingår i: Physics of Plasmas. - : American Institute of Physics. - 1070-664X .- 1089-7674. ; 17:3, s. 032109-
-
Tidskriftsartikel (refereegranskat)abstract
- Particle-in-cell simulations are widely used as a tool to investigate instabilities that develop between a collisionless plasma and beams of charged particles. However, even on contemporary supercomputers, it is not always possible to resolve the ion dynamics in more than one spatial dimension with such simulations. The ion mass is thus reduced below 1836 electron masses, which can affect the plasma dynamics during the initial exponential growth phase of the instability and during the subsequent nonlinear saturation. The goal of this article is to assess how far the electron to ion mass ratio can be increased, without changing qualitatively the physics. It is first demonstrated that there can be no exact similarity law, which balances a change in the mass ratio with that of another plasma parameter, leaving the physics unchanged. Restricting then the analysis to the linear phase, a criterion allowing to define a maximum ratio is explicated in terms of the hierarchy of the linear unstable modes. The criterion is applied to the case of a relativistic electron beam crossing an unmagnetized electron-ion plasma.
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| 48. |
- Bret, Antoine, et al.
(författare)
-
Ions motion effects on the full unstable spectrum in relativistic electron beam plasma interaction
- 2008
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1070-664X .- 1089-7674. ; 15:1, s. 012104-1-12104-13
-
Tidskriftsartikel (refereegranskat)abstract
- A relativistic fluid model is implemented to assess the role of the ions motion in the linear phase of relativistic beam plasma electromagnetic instabilities. The all unstable wave vector spectrum is investigated, allowing us to assess how ion motions modify the competition between every possible instability. Beam densities up to the plasma one are considered. Due to the fluid approach, the temperatures must remain small, i.e., nonrelativistic. In the cold limit, ions motion affect the most unstable mode when the beam gamma factor bM/mi, being the beam to plasma density ratio, i the ion charge, M their mass, and m the electrons. The return current plays an important role by prompting Buneman-type instabilities which remain in the nonrelativistic regime up to high beam densities. Nonrelativistic temperatures only slightly affect these conclusions, except in the diluted beam regime where they can stabilize the Buneman modes.
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| 49. |
- Bret, Antoine, et al.
(författare)
-
Multidimensional electron beam-plasma instabilities in the relativistic regime
- 2010
-
Ingår i: Physics of Plasmas. - : AIP Publishing. - 1070-664X .- 1089-7674. ; 17:12, s. 120501-1-120501-36
-
Forskningsöversikt (refereegranskat)abstract
- The interest in relativistic beam-plasma instabilities has been greatly rejuvenated over the past two decades by novel concepts in laboratory and space plasmas. Recent advances in this long-standing field are here reviewed from both theoretical and numerical points of view. The primary focus is on the two-dimensional spectrum of unstable electromagnetic waves growing within relativistic, unmagnetized, and uniform electron beam-plasma systems. Although the goal is to provide a unified picture of all instability classes at play, emphasis is put on the potentially dominant waves propagating obliquely to the beam direction, which have received little attention over the years. First, the basic derivation of the general dielectric function of a kinetic relativistic plasma is recalled. Next, an overview of two-dimensional unstable spectra associated with various beam-plasma distribution functions is given. Both cold-fluid and kinetic linear theory results are reported, the latter being based on waterbag and Maxwell–Jüttner model distributions. The main properties of the competing modes (developing parallel, transverse, and oblique to the beam) are given, and their respective region of dominance in the system parameter space is explained. Later sections address particle-in-cell numerical simulations and the nonlinear evolution of multidimensional beam-plasma systems. The elementary structures generated by the various instability classes are first discussed in the case of reduced-geometry systems. Validation of linear theory is then illustrated in detail for large-scale systems, as is the multistaged character of the nonlinear phase. Finally, a collection of closely related beam-plasma problems involving additional physical effects is presented, and worthwhile directions of future research are outlined.
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| 50. |
- Bret, Antoine, et al.
(författare)
-
Oblique electromagnetic instabilities for a hot relativistic beam interacting with a hot and magnetized plasma
- 2006
-
Ingår i: Physics of Plasmas. - : AIP Publishing. - 1070-664X .- 1089-7674. ; 13:8, s. 082109-1-082109-8
-
Tidskriftsartikel (refereegranskat)abstract
- The temperature-dependent fluid model from Phys. Plasmas 13, 042106 (2006) is expanded in order to explore the oblique electromagnetic instabilities, which are driven by a hot relativistic electron beam that is interpenetrating a hot and magnetized plasma. The beam velocity vector is parallel to the magnetic-field direction. The results are restricted to nonrelativistic temperatures. The growth rates of all instabilities but the two-stream instability can be reduced by a strong magnetic field so that the distribution of unstable waves becomes almost one dimensional. For high beam densities, highly unstable oblique modes dominate the spectrum of unstable waves as long as omega(c)/omega(p)less than or similar to 2 gamma(3/2)(b), where omega(c) is the electron gyrofrequency, omega(p) is the electron plasma frequency, and gamma(b) is the relativistic factor of the beam. A uniform stabilization over the entire k space cannot be achieved.
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