| 1. |
- Turcu, I. C. E., et al.
(författare)
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HIGH FIELD PHYSICS AND QED EXPERIMENTS AT ELI-NP
- 2016
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Ingår i: Romanian Reports on Physics. - 1221-1451 .- 1841-8759. ; 68, s. S145-S231
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Tidskriftsartikel (refereegranskat)abstract
- ELI-NP facility will enable for the first time the use of two 10 PW laser beams for quantum electrodynamics (QED) experiments. The first beam will accelerate electrons to relativistic energies. The second beam will subject relativistic electrons to the strong electromagnetic field generating QED processes: intense gamma ray radiation and electron-positron pair formation. The laser beams will be focused to intensities above 10(21) Wcm(-2) and reaching 10(22)-10(23) Wcm(-2) for the first time. We propose to use this capability to investigate new physical phenomena at the interfaces of plasma, nuclear and particle physics at ELI-NP. This High Power Laser System Technical Design Report (HPLS-TDR2) presents the experimental area E6 at ELI-NP for investigating high field physics and quantum electrodynamics and the production of electron-positron-pairs and of energetic gamma-rays. The scientific community submitted 12 commissioning runs for E6 interaction chamber with two 10 PW laser beams and one proposal for the CETAL interaction chamber with 1 PW laser. The proposals are representative of the international high field physics community being written by 48 authors from 14 European and US organizations. The proposals are classified according to the science area investigated into: Radiation Reaction Physics: Classical and Quantum; Compton and Thomson Scattering Physics: Linear and Non Linear Regimes; QED in Vacuum; Atoms in Extreme Fields. Two pump-probe colliding 10 PW laser beams are proposed for the E6 interaction chamber. The focused pump laser beam accelerates the electrons to relativistic energies. The accelerated electron bunches interact with the very high electro-magnetic field of the focused probe laser beam. We propose two main types of experiments with: (a) gas targets in which the pump laser-beam is focused by a long focal length mirror and drives a wakefield in which the electron bunch is accelerated to multi-GeV energies and then exposed to the EM field of the probe laser which is tightly focused; (b) solid targets in which both the pump and probe laser beams are focused on the solid target, one accelerating the electrons in the solid and the other, delayed, providing the high electric field to which the relativistic electrons are subjected. We propose four main focusing configurations for the pump and probe laser beams, two for each type of target: counter-propagating 10 PW focused laser beams and the two 10 PW laser beams focused in the same direction. For solid targets we propose an additional configuration with plasma-mirror on the pump laser beam: the plasma mirror placed between the focusing mirror and target. It is proposed that the 10 PW laser beams will have polarization control and focus control by means of adaptive optics. Initially only one 10 PW may have polarization control and adaptive optics. In order to accommodate the two laser beams and diagnostics the proposed interaction chamber is quasi-octagonal with a diameter of 4.5 m. A large electron-spectrometer is proposed for multi-GeV electrons. Other diagnostics are requested for: gamma-rays, electrons and positrons, protons and ions, plasma characterization, transmitted and reflected laser beam. Targets will be provided by the ELI-NP Target Laboratory or purchased. The E6 experiments and diagnostics will benefit from the ELI-NP Electronics Laboratory, the Workshop and the Optics Laboratory. In order to ensure radiation-protection, a large beam-dump is planned for both multi-GeV electrons and multi-100 MeV protons.
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| 2. |
- Dieckmann, Mark E, 1969-, et al.
(författare)
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Emergence of MHD structures in a collisionless PIC simulation plasma
- 2017
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Ingår i: Physics of Plasmas. - Melville, NY, United States : A I P Publishing LLC. - 1070-664X .- 1089-7674. ; 24:9
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Tidskriftsartikel (refereegranskat)abstract
- The expansion of a dense plasma into a dilute plasma across an initially uniform perpendicular magnetic field is followed with a one-dimensional particle-in-cell simulation over magnetohydrodynamics time scales. The dense plasma expands in the form of a fast rarefaction wave. The accelerated dilute plasma becomes separated from the dense plasma by a tangential discontinuity at its back. A fast magnetosonic shock with the Mach number 1.5 forms at its front. Our simulation demonstrates how wave dispersion widens the shock transition layer into a train of nonlinear fast magnetosonic waves.
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| 3. |
- Dieckmann, Mark E, 1969-, et al.
(författare)
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Expansion of a radially symmetric blast shell into a uniformly magnetized plasma
- 2018
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Ingår i: Physics of Plasmas. - : American Institute of Physics (AIP). - 1070-664X .- 1089-7674. ; 25:5
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Tidskriftsartikel (refereegranskat)abstract
- The expansion of a thermal pressure-driven radial blast shell into a dilute ambient plasma is examined with two-dimensional PIC simulations. The purpose is to determine if laminar shocks form in a collisionless plasma which resemble their magnetohydrodynamic counterparts. The ambient plasma is composed of electrons with the temperature of 2 keV and cool fully ionized nitrogen ions. It is permeated by a spatially uniform magnetic field. A forward shock forms between the shocked ambient medium and the pristine ambient medium, which changes from an ion acoustic one through a slow magnetosonic one to a fast magnetosonic shock with increasing shock propagation angles relative to the magnetic field. The slow magnetosonic shock that propagates obliquely to the magnetic field changes into a tangential discontinuity for a perpendicular propagation direction, which is in line with the magnetohydrodynamic model. The expulsion of the magnetic field by the expanding blast shell triggers an electron-cyclotron drift instability.
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| 4. |
- Moreno, Quentin, et al.
(författare)
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Failed self-reformation of a sub-critical fast magnetosonic shock in collisionless plasma
- 2019
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Ingår i: Plasma Research Express. - : Institute of Physics Publishing (IOPP). - 2516-1067. ; 1:3
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Tidskriftsartikel (refereegranskat)abstract
- We study with a 1D particle-in-cell (PIC) simulation the evolution of a subcritical perpendicular fast magnetosonic shock. The shock propagates at 1.5 times the fast magnetosonic speed. Some upstream protons are reflected by the shock's electric potential. They form a beam which carries less energy than those that are reflected magnetically by super-critical shocks. The beam triggers the growth of a fast magnetosonic solitary wave upstream of the shock, which reflects the beam protons back to the shock. Extracting the momentum and energy of this beam allows the solitary wave to grow into a proto-shock that is trailed by a short downstream region. Protons from the shock-reflected proton beam increase the density of the plasma between the shock and the proto-shock reducing its potential difference relative to both surrounding structures. Bulk protons, which cross the proto-shock, react to the decreased potential jump. The plasma behind the proto-shock accelerates and so does the shock. The trailing end of the proto-shock speeds up in order to continue reflecting the beam protons and eventually it catches up with its front; the proto-shock collapses and the self-reformation fails. A more energetic proton beam could decrease the potential jump across the shock, let it collapse and replace it with the proto-shock.
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| 5. |
- Moreno, Quentin, et al.
(författare)
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Impact of the electron to ion mass ratio on unstable systems in particle-in-cell simulations
- 2018
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Ingår i: Physics of Plasmas. - : American Institute of Physics (AIP). - 1070-664X .- 1089-7674. ; 25:6
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Tidskriftsartikel (refereegranskat)abstract
- The evolution of the Buneman and two-stream instabilities driven by a cold dilute mildly relativistic electron beam is studied as a function of the ion-to-electron mass ratio. The growth rates of both instabilities are comparable for the selected parameters if the realistic ion-to-electron mass ratio is used and the Buneman instability outgrows the two-stream instability for an artificially reduced mass ratio. Particle-in-cell simulations show that both instabilities grow independently during their linear growth phase. The much lower saturation amplitude of the Buneman instability implies that it saturates first even if the linear growth rates of both instabilities are equal. The electron phase space holes it drives coalesce. Their spatial size increases in time and they start interacting with the two-stream mode, which results in the growth of electrostatic waves over a broad range of wave numbers. A reduced ion-to-electron mass ratio results in increased ion heating and in an increased energy loss of the relativistic electron beam compared to that in a simulation with the correct mass ratio.
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| 6. |
- Moreno, Quentin, et al.
(författare)
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Quasi-perpendicular fast magnetosonic shock with wave precursor in collisionless plasma
- 2018
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Ingår i: Physics of Plasmas. - : American Institute of Physics (AIP). - 1070-664X .- 1089-7674. ; 25:7
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Tidskriftsartikel (refereegranskat)abstract
- A one-dimensional particle-in-cell simulation tracks a fast magnetosonic shock over time scales comparable with an inverse ion gyrofrequency. The magnetic pressure is comparable to the thermal pressure upstream. The shock propagates across a uniform background magnetic field with a pressure that equals the thermal pressure upstream at the angle 85° at a speed that is 1.5 times the fast magnetosonic speed in the electromagnetic limit. Electrostatic contributions to the wave dispersion increase its phase speed at large wave numbers, which leads to a convex dispersion curve. A fast magnetosonic precursor forms ahead of the shock with a phase speed that exceeds the fast magnetosonic speed by about ∼30%. The wave is slower than the shock, and hence, it is damped.
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| 7. |
- Moreno, Quentin, et al.
(författare)
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Shocks and phase space vortices driven by a density jump between two clouds of electrons and protons
- 2020
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Ingår i: Plasma Physics and Controlled Fusion. - : Institute of Physics Publishing (IOPP). - 0741-3335 .- 1361-6587. ; 62:2, s. 1-13
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Tidskriftsartikel (refereegranskat)abstract
- We study with 1D PIC simulations the expansion of a dense plasma into a dilute one for density ratios 2.5 ≤ α ≤ 20. Both are unmagnetized and consist of electrons and protons. Shocks form in all cases. We determine how α affects the speed of the shock, that of the trailing velocity plateau and the proton beam instabilities in its upstream region. The speed of the velocity plateau relative to the upstream plasma increases significantly with α. Faster shocks reflect more upstream protons and fewer protons make it downstream, which slows down the shock in the downstream frame. This slow-down reduces noticably the increase with α of the shock speed in the upstream frame. All simulations demonstrate that an ion acoustic instability develops between the shock-reflected proton beam and the ambient protons. We solve the linear dispersion relation for ion acoustic waves that have wave vectors which are parallel to the beam velocity vector. Upstream conditions, for which their growth rate is largest, lead to the most unstable upstream plasmas also in the simulation. Even though linear theory predicts the growth of sine waves, which reach a small amplitude in the simulations, solitary waves become the dominant ones upstream of the shock. They enforce the formation of new shocks and ion phase space vortices. We discuss the relevance of our findings to laser-plasma experiments.
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| 8. |
- Vallières, Simon, et al.
(författare)
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Enhanced laser-driven proton acceleration using nanowire targets
- 2021
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 11
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Tidskriftsartikel (refereegranskat)abstract
- Laser-driven proton acceleration is a growing field of interest in the high-power laser community. One of the big challenges related to the most routinely used laser-driven ion acceleration mechanism, Target-Normal Sheath Acceleration (TNSA), is to enhance the laser-to-proton energy transfer such as to maximize the proton kinetic energy and number. A way to achieve this is using nanostructured target surfaces in the laser-matter interaction. In this paper, we show that nanowire structures can increase the maximum proton energy by a factor of two, triple the proton temperature and boost the proton numbers, in a campaign performed on the ultra-high contrast 10 TW laser at the Lund Laser Center (LLC). The optimal nanowire length, generating maximum proton energies around 6 MeV, is around 1–2 μm. This nanowire length is sufficient to form well-defined highly-absorptive NW forests and short enough to minimize the energy loss of hot electrons going through the target bulk. Results are further supported by Particle-In-Cell simulations. Systematically analyzing nanowire length, diameter and gap size, we examine the underlying physical mechanisms that are provoking the enhancement of the longitudinal accelerating electric field. The parameter scan analysis shows that optimizing the spatial gap between the nanowires leads to larger enhancement than by the nanowire diameter and length, through increased electron heating.
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