| 1. |
- Johnson, Tomas, 1979, et al.
(författare)
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A finite volume method for electrostatic three species negative corona discharge simulations with application to externally charged powder bells
- 2015
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Ingår i: Journal of Electrostatics. - : Elsevier BV. - 0304-3886. ; 74, s. 27-36
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Tidskriftsartikel (refereegranskat)abstract
- A three species model for steady-state negative corona discharge is studied. Ionization, attachment, and recombination reactions are modeled. A novel unstructured finite volume algorithm to solve the equations is presented, using the secondary emission of electrons from the cathode to set boundary values for the electrons.To show the usefulness of the method for industrial applications it is used to characterize the electrostatic properties of an externally charged rotary powder bell used in the automotive industry. Experimental current density profiles are reconstructed with good accuracy, which validates the model and the method with real experimental data.
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| 2. |
- Siminos, Evangelos, 1979, et al.
(författare)
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Kinetic and finite ion mass effects on the transition to relativistic self-induced transparency in laser-driven ion acceleration
- 2017
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Ingår i: 3rd European Advanced Accelerator Concepts Workshop.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- We study kinetic effects responsible for the transition to relativistic self-induced transparency in the interaction of a circularly-polarized laser-pulse with an overdense plasma and their relation to hole-boring and ion acceleration. It is demonstrated using particle-in-cell simulations and an analysis of separatrices in single-electron phase-space, that ion motion can suppress fast electron escape to the vacuum, which would otherwise lead to transition to the relativistic transparency regime. A simple analytical estimate shows that for large laser pulse amplitude the time scale over which ion motion becomes important is much shorter than usually anticipated. As a result, the threshold density above which hole-boring occurs decreases with the charge-to-mass ratio. Moreover, the transition threshold is seen to depend on the laser temporal profile, due to the effect that the latter has on electron heating. Finally, we report a new regime in which a transition from relativistic transparency to hole-boring occurs dynamically during the course of the interaction. It is shown that, for a fixed laser intensity, this dynamic transition regime allows optimal ion acceleration in terms of both energy and energy spread.
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| 3. |
- Siminos, Evangelos, 1979, et al.
(författare)
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Kinetic and finite ion mass effects on the transition to relativistic self-induced transparency in laser-driven ion acceleration
- 2017
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 19:12, s. 123042-
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Tidskriftsartikel (refereegranskat)abstract
- We study kinetic effects responsible for the transition to relativistic self-induced transparency in the interaction of a circularly-polarized laser-pulse with an overdense plasma and their relation to hole-boring (HB) and ion acceleration. It is demonstrated using particle-in-cell simulations and an analysis of separatrices in single-electron phase-space, that ion motion can suppress fast electron escape to the vacuum, which would otherwise lead to transition to the relativistic transparency regime. A simple analytical estimate shows that for large laser pulse amplitude the time scale over which ion motion becomes important is much shorter than usually anticipated. As a result of enhanced ion mobility, the threshold density above which HB occurs decreases with the charge-to-mass ratio. Moreover, the transition threshold is seen to depend on the laser temporal profile, due to the effect that the latter has on electron heating. Finally, we report a new regime in which a transition from relativistic transparency to HB occurs dynamically during the course of the interaction. It is shown that, for a fixed laser intensity, this dynamic transition regime allows optimal ion acceleration in terms of both energy and energy spread.
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| 4. |
- Siminos, Evangelos, 1979, et al.
(författare)
-
Kinetic effects on the transition to relativistic self-induced transparency in laser-driven ion acceleration
- 2016
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Ingår i: 58th Annual Meeting of the APS Division of Plasma Physics. ; 61:18, s. TO6.00007-
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- We study kinetic effects responsible for the transition to relativistic self-induced transparency in the interaction of a circularly-polarized laser-pulse with an overdense plasma and their relation to hole-boring and ion acceleration. It is shown, using particle-in-cell simulations and an analysis of separatrices in single-particle phase-space, that this transition is mediated by the complex interplay of fast electron dynamics and ion motion at the initial stage of the interaction. It thus depends on the ion charge-to-mass ratio and can be controlled by varying the laser temporal profile. Moreover, we find a new regime in which a transition from relativistic transparency to hole-boring occurs dynamically during the course of the interaction. It is shown that, for a fixed laser intensity, this dynamic transition regime allows optimal ion acceleration in terms of both energy and energy spread.
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| 5. |
- Svedung Wettervik, Benjamin, 1990, et al.
(författare)
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A domain decomposition method for three species modeling of multielectrode negative corona discharge with applications to electrostatic precipitators
- 2015
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Ingår i: Journal of Electrostatics. - : Elsevier BV. - 0304-3886. ; 77, s. 139-146
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Tidskriftsartikel (refereegranskat)abstract
- The negative corona discharge problem for multi-electrode geometries is modeled by a three speciesmodel. The equations are solved using domain decomposition, by recognizing that multiple species areonly present in a small part of the domain, and hence only need to be incorporated locally in the model.The method is applied to an industrially relevant three wire electrostatic precipitator geometry. Thecalculated current density is in good agreement with experimental data. To further illustrate applicationsof the three species solution, it is used for coupled particle, fluid, and electrostatic simulations to analyzeparticle collection properties.
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| 6. |
- Svedung Wettervik, Benjamin, 1990, et al.
(författare)
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Laser-driven collisionless shock acceleration of protons
- 2016
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Ingår i: 43rd European Physical Society Conference on Plasma Physics, EPS 2016.
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Konferensbidrag (refereegranskat)abstract
- Experimental and numerical results have shown that collisionless shock acceleration is promis-ing for generation of high energy proton beams. There are many potential applications for suchbeams, for example: isotope generation for medical applications, ion therapy and proton radio-graphy. In this work, we use 1D1P Eulerian Vlasov-Maxwell simulations to study shock waveacceleration. Vlasov-Maxwell modeling allows for high resolution of the distribution functionand is highly suitable in cases where effects of low-density tails in the distribution function needto be resolved accurately.We find that combining collisionless shock acceleration with a strong, quasi-stationary sheath-field may be a way to reach even higher maximum proton energies and optimize the ion spec-trum. We show that a layered plasma target with a combination of light and heavy ions leads toa strong quasi-static sheath-field, which induces an enhancement of the energy of shock-waveaccelerated ions, without broadening their energy spectrum, if the heavy ion layer has highdensity.
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| 7. |
- Svedung Wettervik, Benjamin, 1990
(författare)
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Modelling of laser plasma interaction with applications
- 2018
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The development of laser systems with ultra-high intensities has both opened up prospects for compact particle accelerators, as well as probing QED-effects, which are present in the high intensity regime. To describe laser matter interaction, it is necessary to self-consistently account for the paths of a large number of particles and the corresponding electromagnetic fields, with the addition of stochastic effects at high laser intensities. The primary method for modelling laser plasma interaction is the Particle-In-Cell (PIC) method, a Monte-Carlo method which samples phase-space with macro-particles and allows for efficient modelling of high dimensional problems. However, for some applications, for example shock acceleration and instability growth, continuum methods, i.e. solving the Vlasov-Maxwell system of equations on a phase-space grid, may be preferable to accurately describe the plasma dynamics. In the first two papers in this thesis, we adress the problem of implementing efficient continuum methods for the Vlasov-Maxwell system of equations. Furthermore, we treat ion shock acceleration using continuum methods. This thesis also contains an investigation of the prospects for driving electron wakefield acceleration using coherent X-ray pulses. Recent advances in the theory for generation of high harmonics indicate the feasibility of relativistic amplitude coherent X-ray pulses, which could be used to drive a wakefield in a solid density plasma. We show by PIC-simulations, incorporating QED-effects, that similarity scaling laws hold for the wavelength 5 nm and moderate relativistic amplitudes in the range 10 to 100. The quantum parameter is shown to be enhanced, leading to comparable electron and photon energies already at modest relativistic amplitudes although with more infrequent emission of photons than at optical wavelengths, preventing radiation losses from becoming a roadblock for the acceleration process.
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| 8. |
- Svedung Wettervik, Benjamin, 1990
(författare)
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Modelling of laser plasma interaction with applications to particle acceleration and radiation generation
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The development of laser systems with ultra-high intensities has allowed the study of the relativistic interaction of laser light and ionized matter, plasmas, as well as opened up prospects for compact particle accelerators, generation of high intensity X-ray, XUV radiation, and probing QED-effects, which are present in the high intensity regime. To describe laser matter interaction, it is necessary to self-consistently account for the paths of a large number of particles and the corresponding electromagnetic fields, with the addition of stochastic effects at high laser intensities. Although analytical work can capture the essence of the dynamics in a range of situations, the rich dynamics in laser-plasma interaction results in that numerical modelling, and in particular the Particle-In-Cell (PIC) method, is critical to gain a detailed description of the dynamics. This is a stochastic method in which phase-space is sampled with macro-particles and allows for efficient modelling of high dimensional problems, but has limitations due to statistical noise. For some applications, for example shock acceleration and instability growth, continuum methods, i.e. solving the Vlasov-Maxwell system of equations on a phase-space grid, may be preferable to accurately describe the plasma dynamics. In the first two papers in this thesis, we address the problem of implementing efficient continuum methods for the Vlasov-Maxwell system of equations. Furthermore, we treat ion shock acceleration using continuum methods. In the following papers, we address scalings of the electron spectrum in the electron sheath, formed at the vacuum-plasma boundary through the interaction of a relativistic laser and moderately overdense plasma. This is important to determine the spectral properties of high harmonic radiation generated from the laser plasma interaction. We also explore electron wakefield acceleration driven by laser pulses with wavelength in the X-ray regime generated from laser plasma interaction in the moderately overdense regime. By reducing the wavelength, the quantum parameter is enhanced, leading to comparable electron and photon energies already at moderate relativistic amplitudes although with more infrequent emission of photons than at optical wavelengths, preventing radiation losses from becoming a roadblock for the acceleration process.
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| 9. |
- Svedung Wettervik, Benjamin, 1990, et al.
(författare)
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Physics of the laser-plasma interface in the relativistic regime of interaction
- 2019
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1089-7674 .- 1070-664X. ; 26:5
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Tidskriftsartikel (refereegranskat)abstract
- The reflection of intense laser radiation from solids appears as a result of relativistic dynamics of the electrons driven by both incoming and self-generated electromagnetic fields at the periphery of the emerging dense plasma. In the case of highly relativistic motion, electrons tend to form a thin oscillating layer, which makes it possible to model the interaction and obtain the temporal structure of the reflected radiation. The modeling reveals the possibility and conditions for producing singularly intense and short extreme ultraviolet (XUV) bursts of radiation, which are interesting for many applications. However, the intensity and duration of the XUV bursts, as well as the high-energy end of the harmonic spectrum, depend on the thickness of the layer and its internal structure which are not assessed by such macroscopic modeling. Here, we analyze the microscopic physics of this layer and clarify how its parameters are bound and how this controls the outlined properties of XUV bursts.
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| 10. |
- Svedung Wettervik, Benjamin, 1990, et al.
(författare)
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Prospects and limitations of wakefield acceleration in solids
- 2018
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1089-7674 .- 1070-664X. ; 25:1
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Tidskriftsartikel (refereegranskat)abstract
- Advances in the generation of relativistic intensity pulses with wavelengths in the X-ray regime, through high harmonic generation from near-critical plasmas, open up the possibility of X-ray driven wakefield acceleration. The similarity scaling laws for laser plasma interaction suggest that X-rays can drive wakefields in solid materials providing TeV/cm gradients, resulting in electron and photon beams of extremely short duration. However, the wavelength reduction enhances the quantum parameter χ, hence opening the question of the role of non-scalable physics, e.g., the effects of radiation reaction. Using three dimensional Particle-In-Cell simulations incorporating QED effects, we show that for the wavelength λ=5 nm and relativistic amplitudes a0=10-100, similarity scaling holds to a high degree, combined with χ∼1 operation already at moderate a0∼50, leading to photon emissions with energies comparable to the electron energies. Contrasting to the generation of photons with high energies, the reduced frequency of photon emission at X-ray wavelengths (compared with that at optical wavelengths) leads to a reduction in the amount of energy that is removed from the electron population through radiation reaction. Furthermore, as the emission frequency approaches the laser frequency, the importance of radiation reaction trapping as a depletion mechanism is reduced, compared with that at optical wavelengths for a 0 leading to similar χ.
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