In Situ Measurement of Electron Energy Evolution in a Laser-Plasma Accelerator
Simon BohlenT. BrümmerF. GrünerC. A. LindstrømMartin MeiselTheresa StauferM. J. V. StreeterMatthew C. VealeJonathan WoodRichard D’ArcyKristjan PõderJens Osterhoff
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We report on a novel, noninvasive method applying Thomson scattering to measure the evolution of the electron beam energy inside a laser-plasma accelerator with high spatial resolution. The determination of the local electron energy enabled the in-situ detection of the acting acceleration fields without altering the final beam state. In this Letter we demonstrate that the accelerating fields evolve from (265±119) GV/m to (9±4) GV/m in a plasma density ramp. The presented data show excellent agreement with particle-in-cell simulations. This method provides new possibilities for detecting the dynamics of plasma-based accelerators and their optimization.Keywords:
Thomson scattering
Plasma acceleration
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Plasma window
Temporal resolution
The effect of a fine-scale plasma variations on the acceleration of electrons by a wake wave excited by a short laser pulse is investigate analytically and numerically. A criterion is derived under which the effect of small plasma density variations on the acceleration process can be neglected. Electron transmission through a nonuniform plasma layer is considered. 14 refs., 4 figs.
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Plasma wakefield accelerators (PWFA) or laser wakefield accelerators (LWFA) are new technologies of particle accelerators that are particularly promising, as they can provide accelerating fields of hundreds of Gigaelectronvolts per meter while conventional facilities are limited to hundreds of Megaelectronvolts per meter. In the Plasma Wakefield Acceleration scheme (PWFA) and the Laser Wakefield Acceleration scheme (LWFA), a bunch of particles or a laser pulse propagates in a gas, creating an accelerating structure in its wake: an electron density wake associated to electromagnetic fields in the plasma. The main achievement of this thesis is the very first demonstration and experimental study in 2016 of the Plasma Wakefield Acceleration of a distinct positron bunch. In the scheme considered in the experiment, a lithium plasma was created in an oven, and a plasma density wave was excited inside it by a first bunch of positrons (the drive bunch) while the energy deposited in the plasma was extracted by a second bunch (the trailing bunch). An accelerating field of 1.36 GeV/m was reached during the experiment, for a typical accelerated charge of 40 pC. In the present manuscript is also reported the feasibility of several regimes of acceleration, which opens promising prospects for plasma wakefield accelerator staging and future colliders. Furthermore, this thesis also reports the progresses made regarding a new scheme: the use of a LWFA-produced electron beam to drive plasma waves in a gas jet. In this second experimental study, an electron beam created by laser-plasma interaction is refocused by particle bunch-plasma interaction in a second gas jet. A study of the physical phenomena associated to this hybrid LWFA-PWFA platform is reported. Last, the hybrid LWFA-PWFA scheme is also promising in order to enhance the X-ray emission by the LWFA electron beam produced in the first stage of the platform. In the last chapter of this thesis is reported the first experimental realization of this last scheme, and its promising results are discussed.
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A plasma beam dump uses the collective oscillations of plasma electrons to absorb the kinetic energy of a particle beam. In this paper, a modified passive plasma beam dump scheme is proposed using either a gradient or stepped plasma profile to maintain a higher decelerating gradient compared with a uniform plasma. The improvement is a result of the plasma wavelength change preventing the re-acceleration of low energy particles. Particle-in-cell simulation results show that both stepped and gradient plasma profiles can achieve improved energy loss compared with a uniform plasma for an electron bunch of parameters routinely achieved in laser wakefield acceleration.
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Collective Thomson scattering is widely used to measure bulk plasma parameters in high density, laser-produced plasmas, and is used to detect plasma waves from instabilities. However, inhomogeneity in these small plasmas often leads to a spectrum with insufficient resolution to discern phenomena such as wave damping and nonlinear wave effects. Two techniques are discussed for laser-produced plasmas to overcome these limitations, and provide details of wave damping and nonlinear behavior. First, imaging Thomson scattering is used to obtain spatially resolved plasma wave profiles in a 100–200 eV plasma, and allows us to infer ion-ion collisional damping rates. Second, a diffraction-limited laser beam is used to drive stimulated Raman scattering in a hot plasma, generating large amplitude Langmuir waves. The comparatively small interaction volume permits sufficient spectral resolution to observe nonlinear wave behavior previously unresolved in other experiments.
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An overview is given of the physics issues relevant to the plasma wakefield accelerator, the plasma beat-wave accelerator, the laser wakefield accelerator, including the self-modulated regime, and wakefield accelerators driven by multiple electron or laser pulses. Basic properties of linear and nonlinear plasma waves are discussed, as well as the trapping and acceleration of electrons in the plasma wave. Formulas are presented for the accelerating field and the energy gain in the various accelerator configurations. The propagation of the drive electron or laser beams is discussed, including limitations imposed by key instabilities and methods for optically guiding laser pulses. Recent experimental results are summarized.
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The nonlinear blowout regime of the plasma Wakefield acceleration has been the subject of considerable interest due to its potential use as a next accelerator generation in high energy Physics. Much of the analytical work and simulations in this regime has been restricted to scenarios of cold background plasma in one dimension. This paper addresses the phenomenon of hot Plasma in two dimensions. We simulate beam-driven plasma Wakefield using object oriented particle-in-cell (OOPIC) code. The number density of the electron bunch was considered to be greater than the plasma density and so all of the Plasma electrons were expelled from the axis, which causes blowout of the plasma electrons. It is found that at a position where the blown out electrons return to the axis, the electron Plasma density was increased by almost 2 orders of magnitude, which further creates a strong spike in the electric field component E z within the tail of the electron beam. These blowouts remain static throughout the simulation period. Key Words : Beam-driven plasma wave, OOPIC and Plasma Wakefield Accelerators.
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The authors of this work discuss the impact of varying laser shape pulses on laser Wakefield acceleration. Researchers have identified a relativistic plasma wave with an extraordinarily high electric field, which has the potential to be used to accelerate plasma particles in general, as well as for particle acceleration in general, according to the researchers. The acceleration process is fueled by a massive accelerating field gradient created by plasma wave, which acts as the primary motivator for acceleration process to take place and accelerate the plasma wave. A plasma wave provides the energy for the acceleration process. To ignite this kind of plasma wave, it is possible to produce an ionizing wakefield with a single laser, and the plasma wave will then interact with the laser itself. A wiggler magnetic field is utilized in this article to illustrate that augmentation of electron acceleration created by plasma wave may be investigated by deploying a plasma wave generator, which is described in detail elsewhere. A faster forward motion is required to make use of the higher resonance provided by the wiggler field, thus, electrons caught in the plasma wave are propelled forward at a faster pace. As a consequence, the amount of energy that the electrons accumulate throughout their acceleration increases dramatically.
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This work describes the physics of plasma waves and plasma accelerators. The superiority of plasma accelerators over conventional accelerators has generated renewed interest in these devices with the advent of ultra-fast laser technology. The ponderomotive force produced by ultra short laser pulses interacting with the plasma is considered and the resulting acceleration gradient is derived from first principles. Electron injection is described. Beam driven, including electron beam and proton beam, plasma waves are proposed as the future of high energy plasma accelerators.
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Optimum operation of a plasma beat-wave or wakefield accelerator requires an injected beam consisting of a train of electron bunches separated by the plasma wavelength, with each bunch in the train having a length much shorter than the plasma wavelength, and the capability of controlling the relative phase of the electron bunches and plasma wave. The typical plasma wavelength is about 0.1 mm, requiring a bunch length of about 10 to 20 /spl mu/m, which is difficult to achieve with conventional RF based injectors. In this paper we describe an electron accelerator-buncher system based on a photoinjector and an FEL, which can satisfy the plasma accelerator requirements.
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