Dissertations / Theses on the topic 'Laser-plasma interactions'
To see the other types of publications on this topic, follow the link: Laser-plasma interactions.
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Laser-plasma interactions.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Rae, Stuart Campbell. "Short-pulse laser-plasma interactions." Thesis, University of Oxford, 1991. http://ora.ox.ac.uk/objects/uuid:c429d2ee-64d4-415a-b799-f5436d19ccc9.
Full textAbstract:
This thesis deals with several theoretical aspects of the interaction of an intense femtosecond laser pulse with a plasma. A mechanism for the enhancement of the collisional absorption of light at high intensities is described, involving the direct excitation of collective modes of the plasma, and the importance of this mechanism for a solid-density laser-produced plasma is studied under a range of conditions. An intensity-dependent collision rate is used in a numerical calculation of the reflectivity of a steep-gradient plasma, such as might be produced by an intense femtosecond laser pulse, and the conditions required to maximize absorption at high intensities are determined. The relative contributions of field-induced ionization and collisional ionization in laser-produced plasmas are studied, and it is shown that the behaviour of a gaseous plasma is almost solely governed by the field-induced process. A model is developed to simulate the propagation of an intense femtosecond laser pulse through an initially neutral gas, and this model is used to make predictions about spectral modifications to the laser pulse. Under certain conditions the spectrum is significantly broadened and suffers an overall blue shift. Quantitative fitting of theoretical spectra to experimental results in the literature is attempted, but is complicated by associated defocusing effects in the plasma. Field-induced ionization can produce a gaseous plasma which is significantly colder, for the same degree of ionization, than a plasma produced by collisional ionization. One possible application for a cold highly-ionized plasma is in a recombination x-ray laser, and the propagation model allows the calculation of the plasma temperature, which is a crucial parameter in assessing the feasibility of such schemes.
2
Blackburn, Thomas George. "QED effects in laser-plasma interactions." Thesis, University of Oxford, 2015. http://ora.ox.ac.uk/objects/uuid:d026b091-f278-4fbe-b27e-bd6af4a91b7a.
Full textAbstract:
It is possible to reach the radiation-reaction–dominated regime in today’s high-intensity laser facilities, using the collision of a wakefield-accelerated GeV electron beam with a 30 fs laser pulse of intensity 1022 Wcm-2. This would demonstrate that the yield of high energy gamma rays is increased by the stochastic nature of photon emission: a beam of 109 electrons will emit 6300 photons with energy > 700 MeV, 60 times the number predicted classically. Detecting those photons, or a prominent low energy peak in the electron beam's post-collision energy spectrum, will provide strong evidence of quantum radiation reaction; we place constraints on the accuracy of timing necessary to achieve this. This experiment would provide benchmarking for the simulations that will be used to study the plasmas produced in the next generation of laser facilities. With focused intensities > 1023 Wcm-2, these will be powerful enough to generate high fluxes of gamma rays and electron-positron pairs from laser–laser and laser–solid interactions. It will become possible to test the physics of exotic astrophysical phenomena, such as pair cascades in pulsar magnetospheres, and explore fundamental aspects of quantum electrodynamics (QED). To that end we will discuss: classical theories of radiation reaction; QED processes in intense fields; and a Monte Carlo algorithm by which the latter may be included in particle-in-cell codes. The feedback between QED processes and classical plasma dynamics characterises a new regime we call QED-plasma physics.
3
Neil, Alastair John. "Quasilinear theory of laser-plasma interactions." W&M ScholarWorks, 1992. https://scholarworks.wm.edu/etd/1539623827.
Full textAbstract:
The interaction of a high intensity laser beam with a plasma is generally susceptible to the filamentation instability due to nonuniformities in the laser profile. In ponderomotive filamentation high intensity spots in the beam expell plasma by ponderomotive force, lowering the local density, causing even more light to be focused into the already high intensity region. The result--the beam is broken up into a filamentary structure.;Several optical smoothing techniques have been proposed to eliminate this problem. In the Random Phase Plates (RPS) approach, the beam is split into a very fine scale, time-stationary interference pattern. The irregularities in this pattern are small enough that thermal diffusion is then responsible for smoothing the illumination. In the Induced Spatial Incoherence (ISI) approach the beam is broken up into a larger scale but non-time-stationary interference pattern. In this dissertation we propose that the photons in an ISI beam resonantly interact with the sound waves in the wake of the beam. Such a resonant interaction induces diffusion in the velocity space of the photons. The diffusion will tend to spread the distribution of photons, thus if the diffusion time is much shorter than the e-folding time of the filamentation instability, the instability will be suppressed.;Using a wave-kinetic description of laser-plasma interactions we have applied quasilinear theory to model the resonant interaction of the photons in an ISI beam with the beam's wake field. We have derived an analytic expression for the transverse diffusion coefficient. The quasilinear hypothesis was tested numerically and shown to yield an underestimate of the diffusion rate. By comparing the quasilinear diffusion rate, {dollar}\gamma\sb{lcub}D{rcub}{dollar}, with the maximum growth rate for the ponderomotive filamentation of a uniform beam, {dollar}\gamma\sb{lcub}f\sb{lcub}max{rcub}{rcub}{dollar}, we have derived a worst case criterion for stability against ponderomotive filamentation: {dollar}{dollar}{lcub}\gamma\sb{lcub}f\sb{lcub}max{rcub}{rcub}\over \gamma\sb D{rcub} \sim .5 {lcub}\tilde f\sp5/\tilde D\sp5\over \vert \tilde E\vert\sp2 \tilde\omega\sbsp{lcub}0{rcub}{lcub}2{rcub}\tilde N\sp6{rcub}\ll 1.{dollar}{dollar}The tildaed quantities are scaled to the following fusion relevant reference values; laser intensity: {dollar}\vert E\vert\sp2{dollar} = 10{dollar}\sp{lcub}15{rcub}\vert\tilde E\vert{dollar} Watts cm,{dollar}\sp{lcub}-2{rcub}{dollar} focal length: {dollar}f = 30\tilde f{dollar}m, width of each ISI echelon: {dollar}D = .75\tilde D{dollar} cm, laser carrier frequency: {dollar}\omega\sb{lcub}0{rcub} = 7.5 \times 10\sp{lcub}15{rcub}\tilde\omega\sb0{dollar} s{dollar}\sp{lcub}-1{rcub}{dollar}, and the number of ISI echelons: {dollar}N = 20\tilde N{dollar}.
4
Kingham, Robert Joseph. "High intensity short-pulse laser-plasma interactions." Thesis, Imperial College London, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.267882.
Full text
5
Streeter, Matthew. "Ultrafast dynamics of relativistic laser plasma interactions." Thesis, Imperial College London, 2013. http://hdl.handle.net/10044/1/24854.
Full textAbstract:
This thesis documents the experimental and theoretical investigation of laser pulse evolution in relativistic laser-plasma interactions for plasma-wakefield acceleration and ion acceleration experiments. Power amplification of the Astra Gemini laser in a plasma was observed, with the compression of an initially 55 fs, 180 TW pulse down to 14 fs, with a peak power of 320 TW. This was achieved in a laser-driven plasma wakefield operating just below the self-injection threshold density for a propagation distance of 15 mm. Self-guiding of the laser pulse was observed, while pulse depletion was characterised as a function of density and propagation distance, showing that the pulse evolution scales equally with both. These measurements displayed good agreement with a depletion model based on pulse front etching. Particle-in-cell simulations were seen to closely reproduce the experimental results, which were concluded to be predominantly dependent on the longitudinal properties of the laser and wakefield. The simulations also revealed a new wakefield instability that is driven by the far red-shifted component of the laser pulse. In the case of high-contrast solid-density interactions, oscillations of the front surface of the plasma were seen to result in the generation of the second harmonic of the driving laser for a p-polarised interaction. Conversion efficiencies of 22% into the second harmonic were measured, while the total plasma reflectivity into the first and second harmonics remained relatively constant at 65% over the intensity range of 1E17 - 1E21 W/cm2. For normal incidence interactions with sub-micron thickness foils, the cycle-averaged surface motion was measured using a FROG diagnostic. Targets of a few nanometers in thickness underwent an acceleration away from the laser, but the measured surface velocities did not match the expected hole-boring velocities or the measured ion energies, due to the thermal expansion of the plasma. 2D simulations revealed that studying target motion in this way is affected by the scale length of the plasma and photon acceleration that can occur in the tenuous plasma in front of the laser-reflecting surface.
6
Quinn, Kevin Edward. "Plasma dynamics following ultraintense laser-solid interactions." Thesis, Queen's University Belfast, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.527919.
Full text
7
Tubman, Eleanor. "Magnetic field generation in laser-plasma interactions." Thesis, University of York, 2016. http://etheses.whiterose.ac.uk/16757/.
Full textAbstract:
The primary focus of this thesis is understanding the production of magnetic fields during laser-plasma experiments. Each chapter investigates a different mechanism of producing magnetic fields. The first is from the by-product of launching asymmetric shocks which drive Biermann battery generated magnetic fields. The second looks at the reconnection of magnetic fields between two laser focal spots and the third is from fields produced around a current carrying loop target. Blast waves are investigated in the laboratory using a fast framing camera to capture multiple images on a single shot. In analysing the images, the blast wave's trajectory is compared to a Sedov-Taylor solution and the coupling of the laser energy into the shock wave is calculated to be 0.5-2%. The evolution of the blast wave's shape is characterised by fitting an ellipse to the outer edge and is observed to progress into a more symmetrical shape. Calculations show that two shocks produced in the interaction cause the change in ellipticity. We experimentally demonstrate that when two laser spots are placed in close proximity reconnection occurs. Diagnostics, including proton radiography, X-ray detectors and an optical probe, record and diagnose the existence of a semi-collisional reconnection event. The experimental data and simulations show that both Nernst and anisotropic pressure effects need to be taken into account for understanding and predicting the correct plasma dynamics observed. Magnetic fields are produced by driving a current through a loop attached to two plates and new measurements recording the voltages induced are presented in this thesis. It is found that the predicted values for the resistance, capacitance and inductance do not match those extracted from the experimental data and reasons for these are presented. Ideas for furthering this research to enhance our understanding in this area are given.
8
Johnson, David A. "Some aspects of nonlinear laser plasma interactions." Thesis, University of St Andrews, 1995. http://hdl.handle.net/10023/14318.
Full textAbstract:
Recent advances in the development of high power short pulse laser systems has opened a new regime of laser plasma interactions for study. The thesis is presented in two parts. In Part I, we consider the implications of these high power laser pulses for the interaction with a uniform underdense plasma, with particular regard to plasma-based accelerators. We present a scheme for the resonant excitation of large electrostatic Wakefields in these plasmas using a train of ultra-intense laser pulses. We also present an analysis of the resonant mechanism of this excitation based on consideration of phase space trajectories. In Part II, we consider the transition from linear Resonance Absorption to nonlinear absorption processes in a linear electron density profile as the intensity of the incident radiation increases and the scale length of the density profile decreases. We find that the electron motion excited by an electrostatic field exhibits some extremely complicated dynamics with bifurcations to period doubling and chaotic motion as the strength of the driving field is increased or the density scale length is decreased. We also present some results obtained from particle simulations of these interactions.
9
Watts, Ian Frank. "Intense laser-plasma interactions : harmonics and other phenomena." Thesis, Imperial College London, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.271186.
Full text
10
Ramsay, Martin. "Short-pulse laser interactions with high density plasma." Thesis, University of Warwick, 2015. http://wrap.warwick.ac.uk/77583/.
Full textAbstract:
The constraints on particle-in-cell (PIC) simulations of short-pulse laser interactions with solid density targets severely limit the spatial and temporal scales which can be modelled routinely. Although recent advances in high performance computing (HPC) capabilities have rendered collisionless simulations at a scale and density directly applicable to experiments tractable, detailed modelling of the fast electron transport resulting from the laser interaction is often only possible by sampling the fast electron populations and passing this information to a separate, dedicated transport code. However, this approach potentially neglects phenomena which take place or are seeded near the transition between the two codes. Consequently there is a need to develop techniques capable of efficiently modelling fast electron transport in high density plasma without being subject to the usual grid-scale and time-step constraints. The approach employed must also be compatible with retaining the standard PIC model in the laser interaction regions in order to model laser absorption and charged particle acceleration processes. Such an approach, proposed by Cohen, Kemp and Divol [J. Comput. Phys., 229:4591, 2010], has been identified, adapted and implemented in EPOCH. The final algorithm, as implemented, is presented here. To demonstrate the ability of the adapted code to model high intensity laser-plasma interactions with peak densities at, and above, solid density, the results of simulations investigating filamentation of the fast electron population and heating of the bulk target, at high densities, are presented and compared with the results of recent experiments as well as other, similar codes.
11
Clark, Eugene Laurence. "Measurements of energetic particles from ultraintense laser plasma interactions." Thesis, Imperial College London, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.271738.
Full text
12
Mangles, Stuart Peter David. "Measurements of relativistic electrons from intense laser-plasma interactions." Thesis, Imperial College London, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.417730.
Full text
13
Mason, Philip. "Ultraintense laser-plasma interactions in one and two dimensions." Thesis, University of Essex, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.324248.
Full text
14
Evans, Peter John. "Laser plasma interaction for application to fusion energy /." View thesis, 2002. http://library.uws.edu.au/adt-NUWS/public/adt-NUWS20030724.133202/index.html.
Full text
15
Parfeniuk, Dean Allister. "Studies of dense plasmas in laser generated shock wave experiments." Thesis, University of British Columbia, 1987. http://hdl.handle.net/2429/27504.
Full textAbstract:
Shock waves generated by laser-driven ablation in solids have provided a great opportunity for the study of dense plasmas. The work presented in this thesis include measurements of Hugoniot curves and the reflectivity of shocked aluminum. In these experiments, planar aluminum targets were irradiated with a 0.53µm, 2ns (FWHM) laser pulse at irradiances up to ~ 10¹⁴/cm². Temporally and spectrally resolved measurements of the target rear surface luminous emission have yielded the shock speed and temperature Hugoniot curve which showed good agreement with equation of state predictions. In addition, temporally resolved reflectivity measurements of the shocked target rear surface compared well with a theoretical model for the electrical conductivity of a dense plasma. For copper and molybdenum targets, both the luminescence and the reflectivity measurements indicated that the heating of the dense target material was dominated by radiation transport from the coronal plasma rather than shock heating. An analysis of the molybdenum results indicate that x-ray shine-through may be the dominant energy transport mechanism to the target rear surface, whereas for the copper targets the transport process appears to be much more complex.Science, Faculty of
Physics and Astronomy, Department of
Graduate
16
Gremillet, Laurent Yvan André. "Etude théorique et expérimentale du transport des électrons rapides dans l'interaction laser-solide à très haut flux." Palaiseau, École polytechnique, 2001. http://www.theses.fr/2001EPXX0022.
Full text
17
Evans, Peter J., University of Western Sydney, of Science Technology and Environment College, and of Science Food and Horticulture School. "Laser plasma interaction for application to fusion energy." THESIS_CSTE_SFH_Evans_P.xml, 2002. http://handle.uws.edu.au:8081/1959.7/293.
Full textAbstract:
This thesis presents an investigation into inertial confinement fusion through mathematical models and computer simulations. Salient features affecting fusion are identified, in both energy absorption and fusion gains. Mathematical tools are applied to a directed investigation into plasma structure. Parameters such as these involved in electromagnetic energy absorption are identified first, and the next step is to model the immediate response of the plasma to this energy input, with a view to how this may be advantageous to initiating fusion. Models are developed that best suit plasma behaviour. The parameters are presented graphically against time and distance into a small plasma fuel pellet. It is noted how field density and ions form undulations through the plasma. Types of plasma fuels are discussed with regards to their key parameters. Computations are performed using the laser driven inertial energy option based on volume ignition with the natural adiabatic self-similarity compression and expansion hydrodynamics. The relative merits of each fuel are discussed against the parameters of density, volume and energy input versus fusion gains.Master of Science (Hons)
18
McKenna, RossAllan D. "A study of laser plasma interactions in a cylindrical cavity." Thesis, University of British Columbia, 1990. http://hdl.handle.net/2429/29588.
Full textAbstract:
A CO₂ laser system delivering a 12 J pulse with a FWHM of 2 ns on target was developed to serve as a driver for studies of laser plasma interactions within a cylindrical cavity. The system consisted of a hybrid oscillator, followed by an amplifier chain, and it achieved its design goals of delivering an intense CO₂ pulse, Gaussian in time and space, with a high contrast ratio on a reliable basis.
The targets in which the plasma was produced consisted of small rectangular plates of lucite, with holes drilled through one of the long axes. The holes were 350 μm to 600 μm in diameter, and 10 mm in length. These dimensions allowed the laser beam, focused at the entrance of the hole, to produce sufficient intensity on the inner walls of the cylindrical cavity for plasma formation, while allowing the beam, with a waist diameter of 100 μm at the focus to deliver most of its energy within the cavity. The beam propagated via multiple reflections from the plasma through the cavity.
Diagnostics were performed on the beam transmitted through the target. Streak camera
images were collected of the intensity of visible emission from the plasma along the axis of the target. Anomalous results were obtained with respect to the reproducible observation
of maximum visible light emission from regions at the far end cavity from where the laser beam is injected. Another unforseen but interesting result was the small divergence
of the beam transmitted through the cavity. Preliminary models were developed to attempt to explain the observations.Science, Faculty of
Physics and Astronomy, Department of
Graduate
19
González-Izquierdo, Bruno. "Collective charged particle dynamics in relativistically transparent laser-plasma interactions." Thesis, University of Strathclyde, 2016. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=27085.
Full textAbstract:
This thesis reports on experimental and numerical investigations of the collective response of electrons and ions to the interaction of ultra-intense (10²⁰ Wcm⁻²) laser with ultra-thin (nanometre scale) foils undergoing expansion and relativistic induced transparency. The onset of this relativistic mechanism is also characterised and studied in detail. This new insight into relativistic transparency is an important step towards optical control of charged particle dynamics in laser driven dense plasma sources and in its potential applications; including ion and radiation source development. The experimental and numerical investigations exploring the onset and the underpinning physics of the relativistic transparency have focused on its dependency on the target areal density, laser intensity and polarisation. The results show a maximum laser transmission for the thinnest targets investigated, which decreases exponentially with increasing target thickness. The same trend is obtained for linearly and circularly polarised laser light. However, for a given target thickness, the linear polarisation case exhibits a significantly higher transmission fraction, with respect to the circular polarisation case, due to additional electron heating and expansion. Moreover, it is shown that for the thinnest targets, once they become relativistically transparent, the transmitted light fraction increases rapidly as the laser intensity increases. The increasing rate is shown to be more pronounced in the thinnest targets investigated. This is diagnosed by measurement of both the fundamental and second harmonic wavelengths. An alternative approach, based on numerical measurement of the critical surface velocity, asa function of time, for various target thickness, and comparing it with corresponding analytical models is also proposed. The onset of relativistic induced transparency is found to curb the radiation pressure effciency of the charged particle acceleration mechanism. Investigations of the collective response of electrons in ultra-thin foils undergoing transparency show that a 'relativistic plasma aperture' is generated by intense laser light in this regime, resulting in the fundamental optical phenomenon of diffraction. It is numerically found that the plasma electrons collectively respond to the resulting laser near-field diffraction pattern, resulting in a beam of energetic electrons with spatial-intensity distribution, related to this diffraction structure, which can be controlled by variation of the laser pulse parameters,and in turn the onset of relativistic transparency. Additionally, it is shown that static electron beam, and induced magnetic field, structures can be made to rotate at fixed or variable angular frequencies depending on the degree of ellipticity in the laser polarisation. The predicted electron beam distributions using the 'relativistic plasma aperture' concept are verified experimentally. Understanding the collective response of plasma electrons to transparency and how this affects the subsequent acceleration of ions is highly important to the interpretation of experiments exploring ion acceleration employing ultra-thin foils. Control of this collective electron motion, and thus the resultant electrostatic fields, could enable unprecedented control over the spatial-intensity distribution of laser-driven ion acceleration. The results presented in this thesis show that in ultra-thin foils undergoing transparency the electron dynamics are mapped onto the beam of protons accelerated via strong charge-separation-induced electrostatic fields. It is demonstrated that the degree of ellipticity of the laser polarisation defines the spatial-intensity distribution of the proton beam profile and can therefore be used to control it. This demonstration of dynamic optical control of structures within the spatial-intensity distribution of the beam of laser accelerated ions opens a new route to optimising the properties of these promising ion sources.
20
Zhu, Wenxi. "Studies of spectral modification in intense laser pulse-plasma interactions." Thesis, University of Maryland, College Park, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=3611799.
Full textAbstract:
Laser pulses propagating through plasma undergo spectral broadening through local energy exchange with driven plasma waves. During propagation, a high power laser pulse drives large amplitude plasma waves, depleting the pulse energy. At the same time, the large amplitude plasma wave provides a dynamic dielectric response that leads to spectral shifting. The loss of laser pulse energy and the approximate conservation of laser pulse action imply that spectral red-shifts accompany the depletion. Here we examine the spectral shift and broadening, energy depletion, and action conservation of nonlinear laser pulses using the modified paraxial solver in WAKE. For pulses causing complete cavitation, large wavenumber shifts and action decay are observed at the distance where 40–50% of the pulse energy is depleted, consistent with theoretical prediction.
A tenuous plasma, enveloped, full wave solver was further implemented and compared to the modified paraxial solver through studying the University of Maryland laser-plasma system. The full wave solver has the advantage of better predicting the dispersion relation and eliminating the problematic divergence in the dispersion of the modified paraxial solver as wavenumber approaches zero, which is important especially when considering long wavelength generation.
Numerical analysis of the two propagation algorithms has been conducted via monitoring conservation laws. For large spectral shifts, numerical damping and convection of radiation out of the simulation domain result in action decay. Implementing a higher order evaluation of numerical derivatives and smaller spatial step have reduced numerical damping.
Spectral red-shifting of high power laser pulses propagating through underdensed plasma channel can be a source of ultrashort mid-infrared (MIR) radiation. Parametric dependence of MIR generation on laser pulse power, initial pulse duration, and plasma density is investigated through characteristic wavenubmer estimates and simulations.
21
Focia, Ronald J. "Investigation and characterization of single hot spot laser-plasma interactions." Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/87171.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, February 2002.Includes bibliographical references (p. 247-254).
Control of parametric laser-plasma interactions (LPI) is essential to the success of inertial confinement fusion (ICF). Through a research collaboration with the Los Alamos National Laboratory (LANL), we have had the opportunity to participate in world-class laser-plasma experiments. The goal of these experiments was to gain a fundamental understanding of LPI by studying the interaction of a single laser hot spot, or speckle, with a preformed, quasi-homogeneous, long scale-length plasma. Recent single hot spot experiments resulted in a wealth of data and the first definitive observation of two LPIs. Namely, the Langmuir decay instability (LDI) cascade and stimulated scattering off of an acoustic-like electron mode below the usual electron plasma wave frequency. The LDI is the result of the electron plasma wave (EPW) generated by stimulated Raman scattering (SRS) growing to a sufficient amplitude such that it exceeds a threshold (proportional to the damping of the LDI daughter waves) and undergoes parametric decay into another counter-propagating EPW and a co-propagating ion acoustic wave (IAW). Subsequent EPW decays due to LDI are possible and collectively more than one EPW generated by LDI is called LDI cascade. The LDI cascade can play a role in the saturation of SRS since wave energy from the SRS EPW couples into secondary waves that are non-resonant with the SRS process. Stimulated scattering from an electrostatic wave at a frequency and phase velocity (co 0.4cpe, vl1.4ve) between that of an EPW and LAW was also observed.
(cont.) In this thesis, a Vlasov-Maxwell code is used to numerically predict the time evolution of the electron distribution function for the experimental parameters. The resultant distribution function is then modeled as a bi-Maxwellian (one background and one beaming) to show that it exhibits linear modes that include the observed electron acoustic wave. A quasimode analysis of laser scattering off of this linear mode is presented as one possible explanation of the experimental observation.
by Ronald J. Focia.
Ph.D.
22
Snyder, Joseph Clinton. "Leveraging Microscience to Manipulate Laser-Plasma Interactions at Relativistic Intensities." The Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1483626346580096.
Full text
23
Green, James Simon. "Fast electron energy transport in high intensity laser-plasma interactions." Thesis, Imperial College London, 2008. http://hdl.handle.net/10044/1/7688.
Full textAbstract:
This thesis presents experimental measurements of fast electron energy transport made using optical probing, x-ray and XUV imaging techniques. Hydrodynamic and hybrid particlein- cell (PIC) simulations were used to interpret the results. Measurements of fast electron heating patterns were made using the Vulcan 100 Terawatt (TW) and Petawatt (PW) lasers. For the first (100 TW) experiment the laser power was increased from 10 TW to 70 TW and a transition was observed between collimated electron flow and an annular transport pattern. Hybrid modelling showed that a form of beam hollowing accounted for this. Using the PW laser, a comparison was made of different diagnostic techniques for measuring the fast electron beam divergence. Cu K-alpha and optical probing measurements were found to be consistent, with both measuring a divergence angle significantly larger than that measured before at lower intensities. Several different target geometries were used to investigate how energy coupling from the laser into the fast electron beam is affected by the presence of a laser guide cone. Using the Vulcan PW laser, a significant decrease in energy coupling was observed when using metallic cone-slab targets. The addition of a cone assembly to plastic I AI sandwich targets acted to reduce the fast electron heating pattern. Novel cone-wire target geometries revealed that heating of a cone-guided wire plasma is maximised close to the wire surface. Computational modelling revealed that this is due to enhanced Ohmic heating. Finally, measurements were made of the dependence of laser intensity on the fast electron beam divergence. Data taken at intensities relevant to fast ignition was combined with previous published measurements. It was found that the divergence angle increased with laser intensity and had little dependence on pulse duration. PIC modelling was performed to analyse the data and possible explanations for the intensity dependence are discussed.
24
Bellei, Claudio. "Measurements of optical radiation from high-intensity laser-plasma interactions." Thesis, Imperial College London, 2009. http://hdl.handle.net/10044/1/5372.
Full textAbstract:
This thesis presents experimental and theoretical results on the interaction of high-intensity lasers with solid and gaseous targets. All the measurements that are described belong to the optical region of the spectrum. The interaction with solid targets has been investigated for two different intensity regimes. Intensities of up to 10[21] Wcm-2 have been accessed on the VULCAN laser system at the Rutherford Appleton Laboratory whereas the JETI laser system at the Institut für Optik und Quantenelektronik in Jena allowed to reach intensities of up to 4x10[19] Wcm-2 . For both regimes, the transport of relativistic electrons generated in the interactions has been investigated through measurements of the optical radiation emitted from the rear surface of the solid targets. Polarimetry and angular distribution measurements indicate that the radiation presents a high degree of polarisation and is non-isotropically emitted. It is, therefore, mainly attributed to transition radiation. A theoretical model has been developed in order to interpret and validate the experimental observations. As a result, for the high intensity regime variation of the signal strength of the transition radiation with respect to the direction of observation is attributed to the presence of mm-scale filaments. The interaction with gaseous targets has been investigated at the Astra Gemini facility at the Rutherford Appleton Laboratory, for peak intensities of up to 3x10[19] Wcm-2 in a spot size of 20 [Mu]m FWHM. In this experiment the properties of the laser pulse were studied after interaction with the targets. For this purpose, a second harmonic generation FROG device was used. This allowed to determine both the pulse duration and the temporal phase of the pulse, giving an insight on the dependence of the pulse properties with respect to interaction length and electron number density. The experimental results show that the nonlinear evolution of the pulse can lead to compression from 45 fs before the interaction to a single pulse of below 20 fs duration, after propagating in the gaseous medium.
25
Nagel, Sabrina Roswitha. "Studies of Electron Acceleration Mechanisms in Relativistic Laser-Plasma Interactions." Thesis, Imperial College London, 2009. http://hdl.handle.net/10044/1/4639.
Full textAbstract:
Laser-plasma interactions have many potential applications, such as medical treatments,x-ray generation, particle acceleration and inertial confinement fusion (ICF).In all of these applications, understanding how laser energy is absorbed by the materialand converted into energetic electrons is very important. Therefore it is vitalto enhance the understanding of how these energetic electrons are created and whatmechanisms influence them. This Thesis comprises experimental studies of electron acceleration mechanismsin laser-plasma interactions, as well as simulations relevant to these experiments. The experiments described were conducted at the Rutherford Appleton Laboratoryutilising the VULCAN laser facility, and investigate laser interactions with both underdenseand overdense plasmas. In the underdense regime, the intensity dependence of the accelerated electronshas been studied experimentally, as well as the impact of the focusing geometry onthe generation of hot electrons. For high intensities, experimental measurementsshow a scaling of the temperature of the electrons with a0. Density and f-numberdependencies of the accelerated electrons are also observed. The effect of laser polarisation and target thickness on the escaping electronsis studied for laser interactions with solid targets, or overdense plasmas. It wasfound that the effective temperature of the electrons depends on both the laserpolarisation and the target thickness. The electron production from ultra-thin foils,and the effect of laser pre-pulse are also investigated.
26
Fang, Fang. "Some non-linear aspects of ultra-intense, laser-plasma interactions." Diss., Restricted to subscribing institutions, 2008. http://proquest.umi.com/pqdweb?did=1568414811&sid=1&Fmt=2&clientId=1564&RQT=309&VName=PQD.
Full text
27
Mollica, Florian. "Interaction laser-plasma ultra-intense à densité proche-critique pour l'accélération d'ions." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLX058/document.
Full textAbstract:
L'interaction d'un laser ultra-intense et ultra-court avec la matière donne naissance à une grande variété de processus issus du couplage des ondes électromagnétiques associées au laser avec les modes du plasma. Ce couplage hautement non-linéaire excite des phénomènes plasmas collectifs capables de produire des champs intenses pouvant atteindre le TV/m. Ces champs ouvrent la possibilité de réaliser des accélérateurs de particules compacts, aussi bien d'électrons que d'ions. Des sources laser-plasma d'ions de plusieurs dizaines de MeV ont été démontré au début des années 2000 et de nombreux mécanismes ont été suggérés depuis afin d'en améliorer les propriétés. Historiquement, les sources d'ions par laser ont été obtenues à partir de cibles solides dîtes sur-denses. L’innovation sur les cibles a été un moteur majeur de l’amélioration de ces sources. Dans la continuité de cette dynamique, l’utilisation de cibles gazeuses a été proposé afin d’alléger les contraintes de contraste laser et de taux de répétition. De récentes démonstrations expérimentales sont venus renforcer l’intérêt pour ces cibles, dîtes sous-denses ou proche critiques, dont la valeur est propice à la propagation, à l’absorption du laser et à la création de structures accélératrices que sont les chocs plasmas et les vortex magnétiques. Les travaux présentés dans cette thèse constituent une exploration expérimentale des paramètres plasmas nécessaires à l’accélération d’ions dans des cibles gazeuses de densité proche-critique. Pour la première fois ces régimes sont explorés avec un laser ultra-intense femtoseconde de 150TW. Une partie des travaux a été consacrée à la réalisation d’une cible innovante, adaptée aux contraintes de densité et de gradients plasma requises par ces régimes. Suivent, les travaux expérimentaux décrivant la propagation du laser et l’accélération d’électrons dans des cibles proche-critiques. Enfin une dernière partie décrit la production d’un faisceau d’atome issue d’une source d’ion laserInteraction of ultra-intense, ultra-short laser with matter gives rise to a wealth of phenomena, due to the coupling between the electromagnetic field and the plasma. The non-linear coupling excites collective plasma processes able to sustain intense electric fields up to 1TV/m. This property spurred early interest in laser accelerator as compact, next-generation source of accelerated electrons and ions. Laser-driven ion source of several MeV was demonstrated in early 2000 an various mechanisms had been suggest to improve the their properties. These first ion sources have been obtained on solid targets, called “overdense”. Target innovation has driven the improvement of these sources. In the continuity of this dynamic, new gaseous targets had been proposed in order to relax the constraints that solid targets impose on laser contrast and repetition rate. Recent experimental demonstrations of monoenergetic ion acceleration in gas renew the interest in such targets, called under-dense or near-critical because of their intermediate densities. At near-critical density the laser can propagate, but undergoes significant absorbtion, giving rise to the accelerating structures of plasma shocks and magnetic vortex.The work presented in this thesis is an experimental exploration of the plasma conditions required to drive ion acceleration in gaseous near-critical target. For the first time, these regimes are explored with an ultra-intense, femtosecond laser of 150TW. A part of this work has been dedicated to the design of an innovative gas target, suited for plasma density and gradient constraints set by these regimes. Then the experimental works describe laser propagation and electron acceleration in near-critical targets. Finally the last part report the efficient production of an atomic beam from a laser-driven ion source
28
Spark, Stephen N. "Pulsed mm-wave electron cyclotron maser experiments." Thesis, University of Strathclyde, 1988. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=21311.
Full textAbstract:
A pulsed Electron Cyclotron Maser (E. C. M.) was developed and used to generate high power mm-waves in the W-band (75-110GHz) and the G-band (150-220GHz) frequency ranges. The relativistic electron beam (R. E. B.) was produced from a field-immersed, field-emission, cold cathode. A shaped anode cavity was designed for the optimum cavity Q, resonant frequencies, relative mode density, reflection coefficients and mode conversion in the output coupler. Two pulsed conventional field coils were used; coil#1 (maximum B-field : 9T) produced the uniform intra-cavity magnetic field and coil#2 (maximum B-field : 1T) acted as a cathode field tuning coil. The addition of the cathode tuning coil increased the useful output energy in any pulse by a factor of =400. Four diagnostics were used to determine the characteristics of the maser; 1) direct uncalibrated power monitoring, 2) calibrated frequency measurements (made using a quasi-optical diffraction grating spectrometer), 3) near field radiation pattern measurements and 4) calibrated absolute power measurements (made using a thermopile calorimeter). The following characteristics of the maser oscillation were identified: in the W-band, single mode oscillation in the TE03 mode was observed, centred at 95.2GHz, with an output power of =50kW. The cavity was crudely step-tunable with the excitation of the TE13 mode at 81.4GHz and the TE12 mode at 88.OGHz. In the G-band, multi-mode oscillation was observed at all values of the intra-cavity magnetic field. With the increased mode density at these frequencies, the maser was quasi-continuously tunable and 200GHz oscillation was observed. These results proved to be self-consistent with the device-dependent calculations used to design the system and the general E. C. M. theory developed previously.
29
Wright, Warren. "The development and application of laser-induced fluorescence for the study of magnetically confined plasmas." Thesis, The University of Sydney, 1989. https://hdl.handle.net/2123/26237.
Full textAbstract:
Since its development nearly three decades ago, the laser has made an enormous contribution to science as an analytic and diagnostic tool. 'This is particularly true in the study of laboratory plasmas where measurements on plasmas are frequently required to be performed in a manner that does not alter the plasma characteristics.
This thesis is concerned with the development of the technique of laser-induced fluorescence for the investigation of plasma properties and its application. Laser-induced fluorescence (usually abbreviated to LIF in this thesis) may be briefly described as follows: a laser tuned to an atomic (or ionic) spectral transition of interest excites atoms (ions) from the lower energy level to the upper energy level of the transition thereby increasing the population density of the upper level. The increase in the amount of spontaneous emission from the upper level is then observed against the normal (no laser excitation) emission background with a suitable detection system. This observation is of a local region of the plasma, at the intersection of the laser beam with the optical axis of the detection system, and thus gives information about the local plasma conditions.
30
Neuville, Cedric. "Etude expérimentale des effets multi-faisceaux sur l'instabilité de diffusion Brillouin stimulée." Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLX046/document.
Full textAbstract:
Les installations laser dimensionnées pour réaliser des expériences de fusion thermonucléaire par confinement inertiel laser utilisent de nombreux faisceaux laser pour répondre à des contraintes de symétrie d'irradiation et pour déposer suffisamment d'énergie dans la matière. Malheureusement, le croisement des faisceaux laser dans un plasma impactent leurs propagations. Quand un faisceau laser se propage dans un plasma, il peut se coupler aux ondes acoustiques ioniques et diffuser une fraction importante de son énergie par diffusion Brillouin stimulée. Aussi bien les niveaux que les directions de ces diffusions sont profondément modifiés lorsque les faisceaux laser se croisent. Ce manuscrit présente l'étude expérimentale de deux types de modification multi-faisceaux :- en utilisant la flexibilité de l'installation laser LULI2000 (Laboratoire d'Utilisation des Lasers Intenses, Palaiseau, France), nous avons étudié le transfert d'énergie entre deux et trois faisceaux laser ;- les soixante faisceaux laser de l'installation OMEGA (Laboratory for Laser Energetics, Rochester, Etats-Unis) nous ont permis d'observer les diffusions produites par des instabilités Brillouin collectives dans des plasmas plans en géométrie ouverte et à l'entrée de cavités d'expériences de fusion.Ces deux mécanismes peuvent drastiquement redistribuer l'énergie laser incidente en échangeant jusqu’à 30% de l'énergie entre les faisceaux ou en diffusant plus de 10% de l'énergie laser dans des directions inhabituellesThe laser facilities designed to realize laser inertial confinement thermonuclear fusion experiments use numerous laser beams in order to meet irradiation symmetry constraints and to deposite enough energy in matter. Unfortunately, the crossing of laser beams in plasmas modifies their propagations. When a beam is propagating in plasmas, it can interact with ion acoustic waves and scatter its energy by stimulated Brillouin scattering. Not only the directions but also the levels of these scatterings are modified when beams are crossing one another in plasmas. This manuscript is about the experimental study of two kinds of multiple-beam modification:- the flexibility of the LULI2000 laser facility (Laboratoire d'Utilisation de Lasers Intenses, Palaiseau, France) enabled us to study crossed-beam energy transfer between two and three beams;- the sixty laser beams available on the OMEGA facility (Laboratory for Laser Energetics, Rochester, United-States) enabled us to observe scattering of collective Brillouin instabilities produced in planar geometries and at the entrance hole of cavities of fusion experiments.These two mecanisms can highly modify the initial laser irradiation by transferring up to 30% of the laser energy between beams and by scattering more than 10% of the laser energy in unusual directions
31
Sarri, Gianluca. "Investigations of laser-plasma interactions of relevance to inertial confinement fusion." Thesis, Queen's University Belfast, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.534604.
Full text
32
Willingale, Louise. "Ion acceleration from high intensity laser plasma interactions : measurements and applications." Thesis, Imperial College London, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.504795.
Full textAbstract:
This thesis presents measurements of high energy ion beams accelerated from high intensity laser interactions, with underdense through to near critical density plasmas, and also presents an application of laser generated ion beams. The first experimental measurements of longitudinally accelerated ion beams from high intensity (-1020 Wcm-2 ) laser interactions with an underdense (0.04 ne) helium plasma are presented. The ion beam was found to have a maximum energy for He2+ of 40+3 _8 MeV, with the highest energy ions being collimated to a cone of less than 10ø. Two dimensional particle-in-cell simulations show that additional effects, due to the time varying magnetic field associated with the fast electron current, enhance the accelerating electric field and provides a focusing mechanism on the ions. Very low density foam targets were used to investigate proton acceleration from near to critical density plasmas. Experimental results show a decrease in acceleration efficiency just above the critical density. Simulations of the interactions show the proton acceleration is very sensitive to the ability of the laser to propagate through the plasma. The lowest density foams allow the best laser propagation, thus enabling proton beams to be accelerated to energy and numbers comparable to those from a solid target. The suitability of a laser generated proton beam for the measurement of self-generated magnetic fields in laser generated plasma has been investigated. The technique was then used to study a novel magnetic reconnection geometry lIsing two laser beams. Proton probing provides evidence for the formation of the reconnection layer and the corresponding instabilities.
33
Ettlinger, Oliver. "Studies of near-critical density laser plasma interactions for ion acceleration." Thesis, Imperial College London, 2017. http://hdl.handle.net/10044/1/58099.
Full textAbstract:
This thesis presents experimental research, complemented by numerical particle-in-cell simulations, studying the interaction of a high power CO2 laser with near-critical density plasmas. The experiments all occurred around relativistic intensities, a0 ≃ 1, where radiation pressure effects are important. Experiments with a high intensity, 3.5 ps beam with peak intensities IL > 1016 Wcm−2, focussed on to a shaped, over-critical density hydrogen gas target were studied. The accelerated proton beams showed spectral peaking, indicative of radiation pressure or collisionless shock driven acceleration. Higher than previously observed proton energies for this laser system were observed, with peak energies > 1.8 MeV, and energy spreads as low as ∼ 5%. The peak proton energy showed good agreement with the predicted energy scaling for hole-boring RPA, with Ep ∝ IL/ni. Experiments were also conducted at lower intensities, with a 5 ps beam of peak intensity IL∼ 1015 Wcm−2 again focussed on to a shaped hydrogen gas target. Here, the unique laser and target conditions lead to a plasma grating structure being formed in the density ramp preceding the critical surface, from which radiation pressure driven acceleration could occur. The limited mass of these grating structures, along with the suppressed background density, results in enhanced acceleration when compared to that at the unmodified critical surface. Experimentally, a dependence on the peak proton energy compared with the scale length of the plasma preceding the critical surface was observed, attributed to an optimal density profile for the grating formation. Finally, using the same experimental conditions, an alternative method for producing thin gas targets was explored, through two colliding blast waves. Proton acceleration was studied for relative levels of separation between the shock fronts, with the optimal case being at the point of collision. Numerical simulations suggest that acceleration was again enhanced by the creation of grating structures in the sharpened density profile.
34
Lawrence-Douglas, Alistair. "Ionisation effects for laser-plasma interactions by particle-in-cell code." Thesis, University of Warwick, 2013. http://wrap.warwick.ac.uk/57465/.
Full textAbstract:
The particle-in-cell code EPOCH was extended to include field and collisional ionisation for use in simulating initially neutral or partially-ionised targets in laser-plasma inter- actions. The means by which particles ionise in the the field of an intense laser was described and physical models were included to determine the instantaneous ionisa- tion rate at particles within the simulation domain for multiphoton, tunnelling, barrier- suppression and electron-impact ionisation. The algorithms used to implement these models were presented and demonstrated to produce the correct ionisation statistics. A scheme allowing for modelling small amounts of ionisation for an arbitrarily low number of superparticles was also presented for comparison and it was shown that for sufficient simulation time the two schemes converge. The three major mechanisms of ionisation in laser-plasma interactions were described as being ionisation-induced defocussing, fast shuttering and ionisation injection. Simulations for these three effects were presented and shown to be in good agreement with theory and experiment. For fast-shuttering, plasma mirrors were simulated using the pulse profile for the Astra Gemini laser at the Central Laser Facility. Rapid switch-on and the theoretical maximum for contrast ratio was observed. For ionisation injection, simulations for laser wakefield acceleration in a helium gas were performed and the accelerated electron population was shown to be greatly increased through use of a 1% nitrogen dopant consistent with the experimental results of McGuffey et al. A study of the laser filamentation instability due to SRS backscatter at the relativistically corrected quarter critical surface (RCQCS) was per- formed in collaboration with C.S. Brady and T.D. Arber at the University of Warwick [1]. It was found that for hydrogen and plastic the instability was unaffected by the in- clusion of ionisation. Further study with argon revealed a attening of the RCQCS and it was demonstrated that for a material with multiple ionisation levels ionising strongly near the self-focussed intensities at the RCQCS, rapid ionisation caused an inversion of the RCQCS that suppressed the filamentation instability.
35
Link, Anthony John. "Specular Reflectivity and Suprathermal Electron Measurements from Relativistic Laser Plasma Interactions." The Ohio State University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=osu1268149986.
Full text
36
Williams, Brennig Elis Rhys. "Theory and modelling of fast electron transport in laser-plasma interactions." Thesis, Imperial College London, 2013. http://hdl.handle.net/10044/1/10974.
Full textAbstract:
The interaction of a high-intensity laser beam with a solid target generates a large number of fast electrons with long mean free paths. The study of these fast electrons is still the subject of active research, given their relevance to Tabak's [2] proposed fast-ignition approach to inertial confinement fusion. Conventional methods for simulating this system fall into two categories: kinetic and hybrid codes. Kinetic codes (Vlasov Fokker-Planck (VFP) and Particle in Cell (PIC) codes) provide an almost complete description of the system, but are often computationally expensive. Conventional hybrid codes simulate the fast-electrons well using a PIC code, but simplify the simulation of the background by using a rudimentary fluid model. In this thesis I present a new approach to modelling relativistic electrons propagating through a background plasma. This novel approach includes an improved classical transport description of the background plasma by using the VFP code IMPACT [21]. The fast electrons are modelled in two ways. Firstly, a 1D crude rigid beam model is used for the fast electrons. This gives rise to interesting transport effects in the background, such as transverse heat flow and non-local transport. It is found that the transverse heat flow is sufficient to reverse the `beam hollowing' effect of Davies et al [74] , allowing the reemergence of a fast electron collimating magnetic field over picosecond timescales. The second approach is to couple a PIC code into IMPACT to model the dynamic evolution of the fast electron beam. The scheme is tested against relevant beam-plasma phenomena. The code is used to model fast electron transport in 2D through a near-solid density background plasma. The significant result from this 2D investigation is the suppression of the filamentation instability by the resistively collimating field that surrounds the main beam.
37
Castan, Anaïs. "Propagation laser en plasma sous-dense et modélisation de déflectométrie protonique." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLX002/document.
Full textAbstract:
Dans le cadre de la Fusion par Confinement Inertiel, la maîtrise de la propagation des faisceaux laser intenses, qui se propagent dans le plasma sous-dense d'une cavité d'ignition, reste un enjeu majeur. En effet, durant leur propagation, les faisceaux vont modifier les paramètres du plasma, ces paramètres contrôlant eux-mêmes la propagation. Cette rétroaction entre le plasma et le laser est potentiellement instable et produit de l'autofocalisation, de la filamentation, etc. Ces mécanismes peuvent alors dégrader fortement la propagation et in fine l'uniformité du dépôt d'énergie recherché.Dans cette étude, expérimentale et numérique, nous nous intéressons à la propagation d'un filament laser (tache focale d'une dizaine de micromètres, impulsion de 1,5 ns et d'intensité variant de 1014 W.cm-2 à 1016 W.cm-2) dans un milieu très sous dense (quelques pour-cents de la densité électronique critique). Deux expériences ont été réalisées sur l'installation de puissance LULI2000 et ont permis à la fois d'observer la transmission laser et de caractériser les gradients de température. Ces gradients sont produits par le transport électronique et influencent la réponse du plasma au laser. Afin de modéliser le rôle des gradients de température dans les instabilités d'auto-focalisation et de filamentation, nous avons associé un code d'hydrodynamique-radiative (FCI2) à un code détaillé de propagation (Héra). Pour compléter les observables précédentes, nous avons aussi mis en œuvre un diagnostic de déflectométrie protonique. Ce diagnostic permet de mesurer les champs électriques présents dans le plasma, ces champs étant issus du chauffage et de l'interaction laser. Un nouvel outil, associant le code de propagation laser et un code Monte-Carlo de transport de protons, a donc été mis en place pour modéliser les déflexions des protons. Cet outil ouvre en plus de nouvelles perspectives pour discuter de l'influence des effets 3D dans l'exploitation de ce diagnostic. Les résultats obtenus confirment l'intérêt à sonder les champs électriques au cœur même du plasma pendant la propagation laserThe understanding and the control of high-power laser propagation into under-dense plasma is important to achieve inertial confinement fusion. During this process, the interaction of the laser with the plasma filling the hohlraum can lead to significant losses of laser energy which prevent ignition. Self-focusing or filamentation of the laser light is one of these phenomena which are desired to be mitigated since they also affect the uniformity of the laser illumination on the hohlraum wall.In order to improve our understanding of the laser-plasma interaction phenomena at play, we describe an experimental and numerical study involving an intense laser pulse between 1014 W.cm-2 and 1016 W.cm-2 , and which interacts with millimetric and under-dense plasma (having density of few % of the critical density). This work presents two experiments fielding a series of diagnostics aimed at well characterizing the laser propagation (Hisac camera) together with heat deposition in plasmas using Thomson scattering. Experimental results will be presented and discussed in the light of detailed simulations performed with the 3D laser propagation code Hera. In order to take into account the temperature gradients within the plasma during the laser propagation, Hera (laser propagation code) and FCI2 (radiation-hydrodynamic code) have been coupled. Besides, proton radiography has been used in order to access to electric fields. The measurements led to the implementation of a new and promising numerical tool using the Hera and Diane codes (Diane is a Monte Carlo particle tracing code). 3D proton radiography modelling opens new possibilities for users of this temporally and spatially resolved diagnostic
38
Li, Huayu. "Lattice Boltzmann simulation of laser interaction with weakly ionized plasmas." Diss., Connect to online resource - MSU authorized users, 2008.
Find full text
39
Wallace, Martin C. "Ion density fluctuations in plasma and their effects on hot electron generation /." Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2002. http://library.nps.navy.mil/uhtbin/hyperion-image/02Jun%5FWallace.pdf.
Full text
40
Krygier, Andrew. "On The Origin of Super-Hot Electrons in Intense Laser-Plasma Interactions." The Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1365724528.
Full text
41
Buffechoux, Sébastien. "Augmentation de l'énergie des faisceaux de proton accélérés par laser ultra-intense et étude des caractéristiques des faisceaux accélérés par laser ultra-court." Phd thesis, Université Paris Sud - Paris XI, 2011. http://tel.archives-ouvertes.fr/tel-00600647.
Full textAbstract:
De rapides avancées technologiques ont autorisé depuis le début des années 1980 un développement important des lasers de puissance et ont ouvert la voie aux régimes d'interaction laser-matière relativiste. L'accès aux intensités lumineuses supérieures à 1.1018 W.cm-2 a ainsi donné la possibilité à la communauté scientifique d'explorer une nouvelle physique riche d'applications. Bien que le principal moteur ait historiquement été constitué par les recherche sur la fusion par confinement inertiel, l'astrophysique de laboratoire, la génération de rayonnement (harmoniques, bétatron, X) ou la génération de particules énergétiques (électrons, ions) élargissent de plus en plus ce domaine d'étude.En effet, les très bonnes qualités des sources lumineuses et des sources d'ions créées par laser laissent fortement envisager qu'elles viendront un jour remplacer les sources conventionnelles comme les synchrotrons ou les accélérateurs qui sont des machines très coûteuses.Dans le cadre de cette thèse, une attention toute particulière a été portée à l'accélération d'ions qui a déjà montré son fort potentiel en termes de qualité des faisceaux accélérés. Malheureusement, ses applications sont encore limitées (radiographie, chauffage isochorique) à cause de paramètres limitants comme la divergence du faisceau, le spectre large ou l'énergie maximale atteinte par ces faisceaux. Au cours de ce travail de thèse, l'accent a plus particulièrement été mis sur l'augmentation de l'énergie maximale des faisceaux de protons dans le cadre des régimes à ultra haute intensité (supérieur à 1.1019W.cm-2). Cette recherche s'est orientée suivant deux axes principaux (impulsions longue et courtes), qui ont donné lieu à de nombreux échanges et au renforcement de la collaboration entre les laboratoires du LULI à l'École Polytechnique (France) et l'INRS-EMT (Canada).Dans le cadre des recherches menées au sein du LULI, des techniques innovantes ont pu être explorées afin de poursuivre la compréhension des mécanismes et d'améliorer les qualités de l'accélération d'ions à partir d'impulsion "longues" (entre 300 fs et 1,5 ps). Nous avons montré que l'utilisation de cibles ayant des dimensions transverses réduites permettait le confinement géométrique des électrons dans la zone d'impact du laser et augmentait ainsi significativement le taux de conversion de l'énergie laser vers les protons et l'énergie maximale atteinte par le faisceau. Par ailleurs, l'utilisation originale d'une optique plasma refocalisante a démontré son efficacité quant à réduire fortement la surface de focalisation du laser, conduisant à augmenter son intensité et donc l'énergie de coupure des faisceaux d'ions accélérés. Enfin, l'utilisation de deux impulsions laser a mis en évidence qu'une interaction entre les électrons accélérés par chaque impulsion était possible et qu'elle permet de modifier l'énergie et la typologie des faisceaux de protons.Les expériences réalisées au sein de l'INRS-EMT visaient quant à elle à améliorer la compréhension des régimes d'accélération femtoseconde, où peu d'études à ultrahaute intensité existaient au début de cette thèse, et à valider ou non la pertinence de ces régimes. Les nombreuses expériences menées ont clairement établi l'importance du contraste laser et la nécessité que ce derniers soit important pour que l'accélération de protons soit efficace dans ces régimes ultracourts. L'analyse systématique des faisceaux accélérés en face avant et en face arrière d'une cible mince montre que le processus d'accélération manifeste une certaine symétrie et prouve, qu'à énergie laser constante,l'accélération d'ions par laser n'est pas la plus efficace pour la plus courte durée d'impulsion.
42
Ibbotson, Thomas P. A. "An investigation of laser-wakefield acceleration in the hydrogen-filled capillary discharge waveguide." Thesis, University of Oxford, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.560930.
Full textAbstract:
This thesis describes a detailed investigation into the process of laser-wakefield acceleration (LWFA) for the generation of high-energy electron beams using the hydrogen-filled capillary discharge waveguide. In only the second experiment to be performed using the newly commissioned Astra-Gemini laser at the Rutherford Appleton Laboratory, electron beams were accelerated to energies greater than 0.5 GeV by laser pulses of energy 2.5J and peak power of 30T\~T. The injec- tion and acceleration of electron beams was seen to depend on the state of the plasma channel for axial electron densities less than 2.5 x 1018 cm -3. With the aid of simulations performed using the code WAKE it was found that the plasma channel allows the laser pulse to maintain its self-focussed spot size along the length of the capillary even below the critical power for self-guiding. It was found that the threshold laser energy required for the production of elec- tron beams was reduced by the use of an aperture placed early in the laser system. This was attributed to the increased energy contained in the central part of the focal spot of the laser. A short paper on this work was published in Physical Review Special Topics - Accelerators and Beams and a longer paper was published in the New Journal of Physics. Transverse interferometry was used to measure the electron density of the plasma channel used in the Astra-Gemini experiments. An imaging system was devised which used cylindrical optics to increase the field of view of the capillary longitudinally, whilst maintaining the trans- verse resolution. The measured properties were consistent with previous measurements made by Gonsalves et al. [J]. The observed longitudinal variations in the plasma channel parameters were not found to be significant enough to affect the injection process.
43
Soubacq, Stéphane. "Etude de la détente dynamique d'un plasma laser. : Influence du champ effectif laser." Pau, 2003. http://www.theses.fr/2003PAUU3022.
Full textAbstract:
Le premier objectif de cette thèse était d'analyser le claquage d'un intervalle d'air soumis à une haute tension et irradié par un laser Nd:YAG. Des mesures expérimentales des seuils de claquage montrent une dépendance envers la pression du gaz. L'introduction du champ effectif laser sur le temps de retard au claquage permet de rendre compte des mesures expérimentales. Le deuxième objectif comportait une modélisation du claquage optique du gaz. Pour la phase de préionisation on a simulé l'évolution de la densité et de la température électronique (ne1019cm-3, Te4×104K). La phase dynamique a été modélisée à l'aide d'un code aérodynamique 2D. Les résultats numériques concernant uniquement les neutres à l'ETL, décrivent correctement les phénomènes physiques (distribution ellipsoi͏̈dale, u104m/s, ne1018cm-3, T105K). Des mesures de vitesse d'expansion du plasma, ainsi que de densité électronique mesurée par interférométrie laser ont été réalisées et comparées aux résultats numériquesThe first objective of this thesis was to analyze the breakdown of an air gap subjected to an high voltage and irradiated by a Nd:YAG laser. Experimental measurements of the breakdown thresholds show a dependence on the gas pressure. The introduction of the effective laser field on the time lag to breakdown allows to render an account of the experimental measurements. The second objective concerned a modeling of the optical gas breakdown. For the preionization phase, we simulated the evolution of the electronic density and temperature (ne1019cm-3, Te4×104K). The dynamic phase was modelized using a 2D aerodynamic code. The numerical results relating to only the neutrals at the LTE, describe the physical phenomena correctly (ellipsoidal shape, u104m/s, ne1018cm-3, T105K). Measurements of plasma expansion velocity, as well as electronic density measured by laser interferometry were carried out and compared with the numerical results
44
Oubrerie, Kosta. "Amélioration de l'efficacité des accélérateurs laser-plasma." Electronic Thesis or Diss., Institut polytechnique de Paris, 2022. http://www.theses.fr/2022IPPAE002.
Full textAbstract:
Pour générer des faisceaux d'électrons à hautes énergies, les accélérateurs conventionnels utilisent des ondes radiofréquences pour accélérer des particules chargées à des vitesses relativistes. Cependant, le champ électrique accélérateur produit est limité à quelques dizaines de mégavolts par mètre, dû notamment à un phénomène de claquage. Il faut donc des installations de très grande taille pour atteindre des énergies suffisamment élevées. Ainsi, l'accélérateur linéaire de Stanford (SLAC), qui est l'accélérateur linéaire le plus long au monde, accélère des électrons jusqu'à 50GeV sur 3.2km. Les accélérateurs laser-plasma peuvent produire des champs électriques dépassant 100 GV/m, soit environ trois ordres de grandeur plus grands que ceux obtenus par les accélérateurs à cavités radiofréquences. Ils pourraient ainsi permettre une diminution drastique de la taille des accélérateurs pour des applications scientifiques, médicales et industrielles. Cependant, plusieurs verrous devront être levés avant que ces applications puissent voir le jour. Il sera notamment nécessaire de démontrer la production efficace de faisceaux d'électrons de haute qualité, à des énergies de plusieurs GeV et à un taux de répétition élevé.Le projet doctoral s’attaque à cette problématique en explorant de nouvelles méthodes pour augmenter l'énergie des faisceaux d'électrons grâce à des techniques qui sont compatibles avec des puissances laser et des taux de répétition élevés et qui peuvent être alliées avec des méthodes d'injection contrôlée. En effet, des faisceaux d'électrons à haute énergie ou avec une injection contrôlée ont été obtenus séparément durant les quinze dernières années, mais jamais de manière combinée. Cette thèse présente les travaux réalisés sur les techniques de guidage ainsi que sur celles d'injection des électrons qui ont permis d'obtenir expérimentalement des faisceaux de bonne qualité à hautes énergies. Ce travail s'est fait notamment au travers de l'optimisation d'une optique nouvellement conçue au Laboratoire d'Optique Appliquée, l'axiparabole, ainsi que sur le développement de jets de gaz spécifiques à l'accélération laser-plasmaTo generate high energy electron beams, conventional accelerators use radio frequency waves to accelerate charged particles to relativistic speeds. However, the accelerating electric field produced is limited to a few tens of megavolts per metre, mainly due to a breakdown phenomenon. Very large facilities are therefore needed to reach sufficiently high energies. For example, the Stanford Linear Accelerator (SLAC), which is the world's longest linear accelerator, accelerates electrons up to 50 GeV over a distance of 3.2 km. Laser-Plasma Accelerators can produce electric fields exceeding 100 GV/m, that are about three orders of magnitude larger than those obtained by radiofrequency-cavity accelerators. They could thus allow for a drastic decrease of the size of accelerators for scientific, medical and industrial applications. Yet, several bottlenecks have to be solved before these applications can be really implemented. It is notably necessary to demonstrate the efficient production of high-quality, multi-GeV electron beams at a high-repetition rate.The doctoral project tackles this problem by exploring new methods for increasing the energy of the electron beams thanks to techniques that are compatibles with arbitrarily high laser powers and repetition rates and that can be combined with controlled injection methods. Indeed, high energy or controlled injection electron beams have been obtained separately during the last fifteen years, but never combined. This thesis presents the work carried out on the guiding techniques as well as on the electron injection techniques which allowed to obtain experimentally good quality beams at high energies. This work was done in particular through the optimisation of a new optic designed at the Laboratoire d'Optique Appliquée, the axiparabola, as well as the development of gas jets specific to laser-plasma acceleration
45
Gaul, Erhard Werner. "Fully ionized helium waveguides for laser wakefield acceleration /." Full text (PDF) from UMI/Dissertation Abstracts International, 2000. http://wwwlib.umi.com/cr/utexas/fullcit?p3004269.
Full text
46
Bawa'aneh, Muhammad S. "Stimulated brillouin backscattering and magnetic field generation in laser-produced plasmas." Thesis, University of Essex, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.284583.
Full text
47
Layer, Brian David. "Structured plasma waveguides and deep EUV generation enabled by intense laser-cluster interactions." Thesis, University of Maryland, College Park, 2013. http://pqdtopen.proquest.com/#viewpdf?dispub=3557663.
Full textAbstract:
Using the unique properties of the interaction between intense, short-pulse lasers and nanometer scale van-der-Waals bonded aggregates (or 'clusters'), modulated waveguides in hydrogen, argon and nitrogen plasmas were produced and extreme ultraviolet (EUV) light was generated in deeply ionized nitrogen plasmas. A jet of clusters behaves as an array of mass-limited, solid-density targets with the average density of a gas.
Two highly versatile experimental techniques are demonstrated for making preformed plasma waveguides with periodic structure within a laser-ionized cluster jet. The propagation of ultra-intense femtosecond laser pulses with intensities up to 2 x1017 W/cm2 has been experimentally demonstrated in waveguides generated using both methods, limited by available laser energy. The first uses a 'ring grating' to impose radial intensity modulations on the channel-generating laser pulse, which leads to axial intensity modulations at the laser focus within the cluster jet target. This creates a waveguide with axial modulations in diameter with a period between 35 μm and 2 mm, determined by the choice of ring grating. The second method creates modulated waveguides by focusing a uniform laser pulse within a jet of clusters with ow that has been modulated by periodically spaced wire obstructions. These wires make sharp, stable voids as short as 50 μm with a period as small as 200 μm within waveguides of hydrogen, nitrogen, and argon plasma. The gaps persist as the plasma expands for the full lifetime of the waveguide. This technique is useful for quasi-phase matching applications where index-modulated guides are superior to diameter modulated guides. Simulations show that these 'slow wave' guiding structures could allow direct laser acceleration of electrons, achieving gradients of 80 MV/cm and 10 MV/cm for laser pulse powers of 1.9 TW and 30 GW, respectively.
Results are also presented from experiments in which a nitrogen cluster jet from a cryogenically cooled gas valve was irradiated with relativistically intense (up to 2 x 1018 W/cm2) femtosecond laser pulses. The original purpose of these experiments was to create a transient recombination-pumped nitrogen soft x-ray laser on the 2p3/2 → 1s1/2 (λ = 24.779 Å) and 2p1/2 → 1 s1/2 (λ = 24.785 Å) transitions in H-like nitrogen (N 6+). Although no amplification was observed, trends in EUV emission from H-like, He-like and Li-like nitrogen ions in the 15 –150 Åspectral range were measured as a function of laser intensity and cluster size. These results were compared with calculations run in a 1-D fluid laser-cluster interaction code to study the time-dependent ionization, recombination, and evolution of nitrogen cluster plasmas.
48
Rusby, Dean Richard. "Study of escaping electron dynamics and applications from high-power laser-plasma interactions." Thesis, University of Strathclyde, 2017. http://digitool.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=29265.
Full textAbstract:
In recent years, high intensity laser-matter interactions (> 1018 W/cm2) have been shown to produce bright, compact sources of many different particles. These include x-rays, neutrons, protons and electrons, which can be used in applications such as x-ray and electron radiography. The potential use of these sources for industrial applications is promising. However, the scalability and tuning of the sources needs to be understood at a fundamental level. This thesis reports on three aspects of the development and application of these sources; the first two discuss applications of laser-plasma interactions. Firstly, the generation, characterisation and tunability of high-energy x-rays (= 200 keV) produced by the hot-electrons generated inside a solid target for the application of x-ray radiography. The characterisation of the x-ray source is conducted using a novel scintillator based absorption spectrometer. This source of x-rays was then used to radiograph a high density test object. Secondly, a novel technique of x-ray backscatter is investigated numerically and demonstrated experimentally for the first time on a laser facility. This uses the high energy electrons generated via wakefield acceleration to probe deeper into materials than traditional backscatter techniques. Finally, an investigation is reported examining the fundamental dynamics of electrons escaping from solid targets under different irradiation conditions. Experimentally, the number of escaping electrons was shown to maximise for certain laser illumination conditions; this was also explored using PIC simulations. The new results discussed in these three sections produce important new understanding of laser-driven x-ray generation and its application to penetrative probing and imaging for possible future industrial applications as well as the understanding of escaping electron dynamics.
49
Chen, Cliff D. (Cliff Ding Yu). "Spectrum and conversion efficiency measurements of suprathermal electrons from relativistic laser plasma interactions." Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/53213.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2009.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 147-156).
Fast Ignition is an alternative scheme for Inertial Confinement Fusion (ICF) that uses a petawatt laser to ignite a hot spot in precompressed fuel. The laser delivers its energy into relativistic electrons at the critical surface of the blowoff plasma. These electrons must propagate to the fuel core and deliver their energy to a hot spot. Electrons of energies between 1 and 3 MeV have the appropriate range for efficient energy deposition. This thesis experimentally explores the coupling efficiency and spectrum of the laser produced electrons. The experiments make use of Bremsstrahlung and K-shell emission from planar foil targets to infer the electron distribution produced in the laser-plasma interaction. This thesis describes the development of a filter stack Bremsstrahlung spectrometer with differential sensitivity up to 500 keV. The spectrometer is used with a single photon counting camera for measuring K[alpha] emission in experiments on the Titan laser (1.06 [mu]m, 150 J, 0.7 ps) at Lawrence Livermore National Laboratories. The Bremsstrahlung and K-shell emission from 1 mm3 planar targets irradiated with intensities from 3x1018-8x1019 W/cm2 were measured. The target emission is modeled using the Monte Carlo code Integrated Tiger Series 3.0 in order to unfold the electron spectrum from the x-ray measurements. Conversion efficiencies into 1-3 MeV electrons of 12-28% were inferred, representing 35-60% total conversion efficiencies. Laser diagnostics were used to characterize the laser focal spot and pulselength in order to provide proper comparisons to intensity scaling laws.
(cont.) Comparisons to scaling laws show that the electron spectrum is colder than the laser ponderomotive potential derived from the peak intensity. For intensities above 2 x 1019 W/cm2, the spectrum is slightly hotter than widely used empirical scalings. More accurate comparisons to ponderomotive scaling using a synthetic energy spectra generated from the intensity distribution of the focal spot imply slope temperatures less than the ponderomotive potential, but is within the range of a correction due to the neglect of resistive transport effects. The impact of resistive transport effects were estimated using an analytic transport model and may lead to higher total conversion efficiencies but lower conversion efficiencies into 1-3 MeV electrons.
by Cliff D Chen.
Ph.D.
50
Kemp, Gregory Elijah. "Specular Reflectivity and Hot-Electron Generation in High-Contrast Relativistic Laser-Plasma Interactions." The Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1375386740.
Full text