Self Injection and Radiation Production in Laser Wakefield Accelerators PDF Download

Author: Matthew Philip Tooley
Publisher:
ISBN:
Category :
Languages : en
Pages : 0

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The laser wakefield accelerator (LWFA) is a nascent electron acceleration technology characterised by extremely large (100s GV/m) accelerating fields and compact (~ cm) scale. Self-injection is a key mechanism in the production of electron beams from the laser wakefield accelerator (LWFA), where background plasma electrons spontaneously enter the accelerating field region. Self-injection is routinely exploited but a fully self-consistent model for the process is still lacking,as are reliable methods for the control of the self-injection process. In this thesis a model for control of self-injection using plasma density gradients or laser intensity evolution is presented. The model is validated using particle-in-cell (PIC) simulations and injection of sub-femtosecond electron bunches is demonstrated. This control is further exploited to demonstrate injection of a train of multiple electron bunches into the LWFA.An additional characteristic of the LWFA is the strong transverse focusing fields, which cause electrons to undergo betatron motion and emit broadband XUV and X-ray radiation. The previously demonstrated bunching is investigated as a source of tuneable coherent emission. Analytic and numerical models demonstrate coherent enhancement at the bunching wavelength. Finally the stability of the scheme is considered with respect to energy and spatial bunch spreads and found to be viable for tuneable XUV radiation production with current state of the art LWFA bunch parameters.

Author: Deyun Li (M.A.)
Publisher:
ISBN:
Category :
Languages : en
Pages : 84

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Plasma-based wakefield accelerator is attractive for generating quasi-monoenergetic electron beams using the bubble regime. The bubble is formed by an intense driver, which propagates through the plasma and expels all electrons transversely, creating a cavity free of cold plasma electrons that trailing behind the driver. Self-injection is applicable in the bubble regime, which can produce bunches of quasi-monoenergetic electrons. (1) Such electron bunching structure can be diagnosed with coherent transition radiation and may be exploited to generate powerful high frequency radiation [16].This thesis focuses on electron bunching phenomenon through WAKE simulations and theoretical analysis. The simulation is completed under laser-driven field ionization wakefield acceleration. The code is improved by taking into consideration the high frequency property of laser driver in wakefield acceleration. Finer grid size is introduced to the ionization injection part of WAKE, for increasing simulation accuracy without much sacrifice of programming efficiency. Various conditions for optimal bunching in the trapped electrons are explored computationally and analytically.

Author: Asher Warren Davidson
Publisher:
ISBN:
Category :
Languages : en
Pages : 196

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In the pursuit of discovering the fundamental laws and particles of nature, physicists have been colliding particles at ever increasing energy for almost a century. Lepton (electrons and positrons) colliders rely on linear accelerators (LINACS) because leptons radiate copious amounts of energy when accelerated in a circular machine. The size and cost of a linear collider is mainly determined by the acceleration gradient. Modern linear accelerators have gradients limited to 20-100 MeV/m because of the breakdown of the walls of the accelerator. Plasma based acceleration is receiving much attention because a plasma wave with a phase velocity near the speed of light can support acceleration gradients at least three orders of magnitude larger than those in modern accelerators. There is no breakdown limit in a plasma since it is already ionized. Such a plasma wave can be excited by the radiation pressure of an intense short pulse laser. This is called laser wakefield acceleration (LWFA). Much progress has been made in LWFA research in the past 30 years. Particle-in-cell (PIC) simulations have played a major part in this progress. The physics inherent in LWFA is nonlinear and three-dimensional in nature. Three-dimensional PIC simulations are computationally intensive. In this dissertation, we present and describe in detail a new algorithm that was introduced into the Particle-In-Cell Simulation Framework. We subsequently use this new quasi three-dimensional algorithm to efficiently explore the parameter regimes of LWFA that are accessible for existing and near term lasers. This regimes cannot be explored using full three-dimensional simulations even on leadership class computing facilities. The simulations presented in this dissertation show that the nonlinear, self-guided regime of LWFA described through phenomenological scaling laws by Lu et al., in 2007 is still useful for accelerating electrons to energies greater than 10 GeV. Fortunately, in many situations the physics of LWFA is nearly azimuthally symmetric and the most salient three-dimensional physics is captured by the inclusion of only a few azimuthal harmonics. Recently, it was proposed by Lifschitz et al. [J. Comp. Phys. 228 (5) 2009] to model LWFA by expanding the fields and currents in azimuthal harmonics and truncating the expansion. The complex amplitudes of the fundamental and first harmonic for the fields were solved on an r-z grid and a procedure for calculating the complex current amplitudes for each particle based on its motion in Cartesian geometry was presented using a Marder's correction to maintain the validity of Gauss's law. In this dissertation, we describe in detail the implementation of this algorithm into OSIRIS using a rigorous charge conserving current deposition method to maintain the validity of Gauss's law. We show that this algorithm is a hybrid method which uses a particles-in-cell description in r-z and a gridless description in phi (which we have subsequently coined the 'quasi-3D' method). We include the ability to keep an arbitrary number of harmonics and higher order particle shapes. Examples for laser wakefield acceleration, plasma wakefield acceleration, and beam loading are also presented. In almost all of the recent experiments progress on LWFA the plasma wave wake has been excited in the nonlinear blowout regime. A phenomenological description of this regime was given by Lu et al. [PRSTAB, 10 (061301) 2007]. This included matching conditions for the laser spot size and pulse length so that the laser evolution and wake excitation would be stable and the laser would self-guide. Scaling laws for the electron electron energy (self or externally injected) in terms of the laser and plasma parameters was also given. The parameters for the supporting simulations were limited due to the computational demands for such simulations particularly for higher electron energy. The recent implementation of the quasi-3D algorithm into OSIRIS including the charge conserving current deposit, now make it possible to study these scaling laws and examine how well they still hold for higher laser intensities and laser energies. We have studied in detail how well the nonlinear, self-guided regime works for existing and near term 15-100 Joule lasers. We demonstrate that the scaling laws do capture the key phenomenological characteristics LWFAs under a wide range of different laser and plasma parameters, but are not meant to give exact predictions for a choice of parameters. The simulations indicate that the self-injected particles reach slightly higher energies than estimated by the scaling laws, although the evolution of the maximum energy looks similar when scaled to the dephasing time. We also find that shape of the evolution of the energy, spot size, and wake amplitude scales if the normalized vector potential, and transverse and axial profile shapes remain fixed. If the normalized vector potential is changed then the scaling laws are still useful but the shape of energy evolution curve changes. We also used the scaling laws to optimize the energy gain for a fixed laser energy. We then use the quasi-3D OSIRIS code to study study in detail how to optimize the energy gain for fixed laser energy including how to optimize the axial laser profile. We find that shortening the pulse length and reducing the plasma density is effective in producing a higher energy beam with a low energy spread, given a fixed laser energy.

Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 6

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A laser wakefield acceleration study has been performed in the matched, self-guided, blow-out regime where a 10 J, 60 fs laser produced 720 ± 50 MeV quasi-monoenergetic electrons with a divergence of [Delta][theta] = 2.85 ± 0.15 mRad. While maintaining a nearly constant plasma density (3 x 1018 cm−3), a linear electron energy gain was measured from 100 MeV to 700 MeV when the plasma length was scaled from 3 mm to 8 mm. Absolute charge measurements indicate that self-injection occurs when P/P{sub cr}> 4 and saturates around 100 pC for P/P{sub cr}> 12. The results are compared with both analytical scalings and full 3D particle-in-cell simulations.

Author: Jessica Shaw
Publisher:
ISBN:
Category :
Languages : en
Pages : 132

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In this dissertation, the direct laser acceleration (DLA) of ionization-injected electrons in a laser wakefield accelerator (LWFA) operating in the quasi-blowout regime has been investigated through experiment and simulation. In the blowout regime of LWFA, the radiation pressure of an intense laser pulse can push a majority of the plasma electrons out and around the main body of the pulse. The expelled plasma electrons feel the electrostatic field of the relatively-stationary ions and are thus attracted back towards the laser axis behind the laser pulse where they overshoot the axis and set up a wake oscillation. When ionization injection is used, the inner-shell electrons of higher-Z dopant atoms are tunnel ionized near the peak of the laser pulse. Those electrons slip back relative to the wake until they gain enough energy from the longitudinal wakefield to become trapped. Those electrons that are trapped off-axis will undergo betatron oscillations in response to the linear transverse focusing force of the ions. Through experiments and supporting simulations, this dissertation demonstrates that when there is a significant overlap between the drive laser and the trapped electrons in a LWFA cavity, the accelerating electrons can gain energy from the DLA mechanism in addition to LWFA. When laser pulse overlaps the trapped electrons, the betatron oscillations of the electrons in the plane of the laser polarization can lead to an energy transfer from the transverse electric field of the laser to the transverse momentum of the electrons. This enhanced transverse momentum can then be converted into increased longitudinal momentum via the v x B force of the laser. This process is known as DLA. In this experimental work, the properties of the electron beams produced in a LWFA where the electrons are injected by ionization injection and become trapped without escaping the laser field have been investigated. The maximum measured energy of the produced electron beams scales with the overlap between the electrons and the laser. Undispersed electrons beams are observed to be elliptical in the plane of the laser polarization, and the energy spectrum splits into a fork at higher energies when the electrons beams are dispersed orthogonal to the direction of the laser polarization. These characteristic features are reproduced in particle-in-cell (PIC) code simulations where particle tracking was used to demonstrate that such spectral features are signatures of the presence of DLA in LWFA. Further PIC simulations comparing LWFA with and without DLA show that the presence of DLA can lead to electron beams that have maximum energies that exceed the estimates given by the theory for the ideal blowout regime. The magnitude of the contribution of DLA to the energy gained by the electron was found to be on the order of the LWFA contribution. In the LWFAs studied here, both DLA and LWFA participate in accelerating the bulk of the electrons in the produced electron beam. The presence of DLA in a LWFA can also lead to enhanced betatron oscillation amplitudes and increased divergence in the direction of the laser polarization.

Author: Oliver Brning
Publisher: World Scientific
ISBN: 9814436402
Category : Science
Languages : en
Pages : 855

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"The past 100 years of accelerator-based research have led the field from first insights into the structure of atoms to the development and confirmation of the Standard Model of physics. Accelerators have been a key tool in developing our understanding of the elementary particles and the forces that govern their interactions. This book describes the past 100 years of accelerator development with a special focus on the technological advancements in the field, the connection of the various accelerator projects to key developments and discoveries in the Standard Model, how accelerator technologies open the door to other applications in medicine and industry, and finally presents an outlook of future accelerator projects for the coming decades."--Provided by publisher.

Author: Sunghwan Yi
Publisher:
ISBN:
Category :
Languages : en
Pages : 174

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Plasma-based accelerators aim to efficiently generate relativistic electrons by exciting plasma waves using a laser or particle beam driver, and "surfing" electrons on the resulting wakefields. In the blowout regime of such wakefield acceleration techniques, the intense laser radiation pressure or beam fields expel all of the plasma electrons transversely, forming a region completely devoid of electrons ("bubble") that co-propagates behind the driver. Injection, where initially quiescent background plasma electrons become trapped inside of the plasma bubble, can be caused by a variety of mechanisms such as bubble expansion, field ionization or collision between pump and injector pulses. This work will present a study of the injection phenomenon through analytic modeling and particle-in-cell (PIC) simulations. First, an idealized model of a slowly expanding spherical bubble propagating at relativistic speeds is used to demonstrate the importance of the bubble's structural dynamics in self-injection. This.

Author: Paul Gibbon
Publisher: World Scientific
ISBN: 1911298844
Category : Science
Languages : en
Pages : 328

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Book Description
This book represents the first comprehensive treatment of the subject, covering the theoretical principles, present experimental status and important applications of short-pulse laser-matter interactions.Femtosecond lasers have undergone dramatic technological advances over the last fifteen years, generating a whole host of new research activities under the theme of “ultrafast science”. The focused light from these devices is so intense that ordinary matter is torn apart within a few laser cycles. This book takes a close-up look at the exotic physical phenomena which arise as a result of this new form of “light-matter” interaction, covering a diverse set of topics including multiphoton ionization, rapid heatwaves, fast particle generation and relativistic self-channeling. These processes are central to a number of exciting new applications in other fields, such as microholography, optical particle accelerators and photonuclear physics.Repository for numerical models described in Chapter 6 can be found at www.fz-juelich.de/zam/cams/plasma/SPLIM/./a

Author: Emilien Guillaume
Publisher:
ISBN:
Category :
Languages : en
Pages : 228

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Author: National Research Council
Publisher: National Academies Press
ISBN: 030908637X
Category : Science
Languages : en
Pages : 177

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Book Description
Recent scientific and technical advances have made it possible to create matter in the laboratory under conditions relevant to astrophysical systems such as supernovae and black holes. These advances will also benefit inertial confinement fusion research and the nation's nuclear weapon's program. The report describes the major research facilities on which such high energy density conditions can be achieved and lists a number of key scientific questions about high energy density physics that can be addressed by this research. Several recommendations are presented that would facilitate the development of a comprehensive strategy for realizing these research opportunities.