C.G.R. Geddes

Bio: C.G.R. Geddes is an academic researcher from Lawrence Berkeley National Laboratory. The author has contributed to research in topics: Laser & Acceleration. The author has an hindex of 4, co-authored 7 publications receiving 1506 citations.

GeV electron beams from a centimetre-scale accelerator

Abstract: Gigaelectron volt (GeV) electron accelerators are essential to synchrotron radiation facilities and free-electron lasers, and as modules for high-energy particle physics. Radiofrequency-based accelerators are limited to relatively low accelerating fields (10–50 MV m−1), requiring tens to hundreds of metres to reach the multi-GeV beam energies needed to drive radiation sources, and many kilometres to generate particle energies of interest to high-energy physics. Laser-wakefield accelerators1,2 produce electric fields of the order 10–100 GV m−1 enabling compact devices. Previously, the required laser intensity was not maintained over the distance needed to reach GeV energies, and hence acceleration was limited to the 100 MeV scale3,4,5. Contrary to predictions that petawatt-class lasers would be needed to reach GeV energies6,7, here we demonstrate production of a high-quality electron beam with 1 GeV energy by channelling a 40 TW peak-power laser pulse in a 3.3-cm-long gas-filled capillary discharge waveguide8,9.

Application of the Reduction of Scale Range in a Lorentz Boosted Frame to the Numerical Simulation of Particle Acceleration Devices

Abstract: It has been shown [1] that it may be computationally advantageous to perform computer simulations in a boosted frame for a certain class of systems: particle beams interacting with electron clouds, free electron lasers, and laser-plasma accelerators. However, even if the computer model relies on a covariant set of equations, it was also pointed out that algorithmic difficulties related to discretization errors may have to be overcome in order to take full advantage of the potential speedup [2] . In this paper, we focus on the analysis of the complication of data input and output in a Lorentz boosted frame simulation, and describe the procedures that were implemented in the simulation code Warp[3]. We present our most recent progress in the modeling of laser wakefield acceleration in a boosted frame, and describe briefly the potential benefits of calculating in a boosted frame for the modeling of coherent synchrotron radiation.

Scaled simulation design of high quality laser wakefield accelerator stages

Abstract: Design of efficient, high gradient laser driven wakefield accelerator (LWFA) stages using explicit particle-incell simulations with physical parameters scaled by plasma density is presented. LWFAs produce few percent energy spread electron bunches at 0.1-1 GeV with high accelerating gradients. Design tools are now required to predict and improve performance and efficiency of future LWFA stages. Scaling physical parameters extends the reach of explicit simulations to address applications including 10 GeV stages and stages for radiation sources, and accurately resolves deep laser depletion to evaluate efficient stages.

Laser wakefield simulation using a speed‐of‐light frame envelope model

Abstract: Simulation of laser wakefield accelerator (LWFA) experiments is computationally intensive due to the disparate length scales involved. Current experiments extend hundreds of laser wavelengths transversely and many thousands in the propagation direction, making explicit PIC simulations enormously expensive and requiring massively parallel execution in 3D. We can substantially improve the performance of laser wakefield simulations by modeling the envelope modulation of the laser field rather than the field itself. This allows for much coarser grids, since we need only resolve the plasma wavelength and not the laser wavelength, and therefore larger timesteps. Thus an envelope model can result in savings of several orders of magnitude in computational resources. By propagating the laser envelope in a frame moving at the speed of light, dispersive errors can be avoided and simulations over long distances become possible. Here we describe the model and its implementation, and show simulations and benchmarking of laser wakefield phenomena such as channel propagation, self‐focusing, wakefield generation, and downramp injection using the model.

Application of the Reduction of Scale Range in a Lorentz Boosted Frame to the Numerical Simulation of Particle Acceleration Devices

Abstract: Application of the reduction of scale range in a Lorentz boosted frame to the numerical simulation of particle acceleration devices. ∗ J.-L. Vay † , W. M. Fawley, C. G. R. Geddes, E. Cormier-Michel, LBNL, Berkeley, CA, USA D. P. Grote, LLNL, Livermore, CA, USA Abstract It has been shown [1] that it may be computationally ad- vantageous to perform computer simulations in a boosted frame for a certain class of systems: particle beams inter- acting with electron clouds, free electron lasers, and laser- plasma accelerators. However, even if the computer model relies on a covariant set of equations, it was also pointed out that algorithmic difficulties related to discretization errors may have to be overcome in order to take full advantage of the potential speedup [2] . In this paper, we focus on the analysis of the complication of data input and output in a Lorentz boosted frame simulation, and describe the procedures that were implemented in the simulation code Warp[3]. We present our most recent progress in the mod- eling of laser wakefield acceleration in a boosted frame, and describe briefly the potential benefits of calculating in a boosted frame for the modeling of coherent synchrotron radiation. ratory frame. We explain in this paper how we handle this later complication into the accelerator PIC code Warp [3], present our latest results on the modeling of laser plasma wakefield acceleration in a boosted frame, and briefly de- scribe the potential benefits of calculating in a boosted frame for the modeling of coherent synchrotron radiation. INPUT AND OUTPUT OF DATA TO AND FROM A BOOSTED FRAME SIMULATION So far, it has been common practice to perform simu- lations in the laboratory frame, for direct comparison with experimental results, or in another frame (beam frame, cen- ter of mass frame, etc.) which offers an advantage of symmetry, simplification, or other convenience, in compar- ing the results to those of analytical theory or experiment. However, the analysis that was provided in [1] shows that the frame that will minimize the computational require- ments may not be any of the above. In this case, one may need to apply Lorentz transformations between the frame of calculation and the frame in which input data are known and/or the frame in which the output data are desired. Be- cause of the relativity of simultaneity that is inherent to the Lorentz transformation, this requires a process that goes beyond a mere algebraic manipulation of data. In the im- plementation of such process in the code Warp, we have found convenient to input data (particles of fields) through a plane, as well as to output data at series of planes, all of which are perpendicular to the direction of the relative ve- locity between the frame of calculation and the other frame of choice. For illustration purposes, we take as an example in this paper the test case that was presented in [1] of an ion beam interacting with a background of electrons, in an assumed continuous transverse focusing system, leading to a growing transverse instability. We present in this section in more detail the techniques that were used to input and output the data. We note that the careful implementation of these techniques was essential for the very high level of agreement that was obtained in [1] between a calculation in the laboratory frame and a calculation in a boosted frame. INTRODUCTION In [1], we have shown that the ratio of longest to shortest space and time scales of a system of two or more compo- nents crossing at relativistic velocities is not invariant un- der a Lorentz transformation. This implies the existence of a frame of reference minimizing an aggregate measure of the ratio of space and time scales. It was demonstrated that this translated into a reduction by orders of magnitude in computer simulation run times, using methods based on first-principles (e.g., Particle-In-Cell), for particle acceler- ation devices or problems such as: particle beams inter- acting with electron clouds, free electron lasers, and laser- plasma accelerators. In [2], we have shown that in order to take the full benefits of the calculation in a boosted frame, some of the standard numerical techniques needed to be re- vised, and proposed a new particle pusher which improves upon the standard Boris pusher [4] for the handling of rela- tivistic particles. An additional practical complication that is introduced by simulating in a boosted frame is that in- puts and outputs are often known, or desired, in the labo- ∗ This work was supported under the auspices of the U.S. DOE by Univ. of Calif., LBNL and LLNL under contracts DE-AC02-05CH11231 and DE-AC52-07NA27344, the U.S.-LHC Accelerator Research Program (LARP), and the U.S. Department of Energy, Office of Science grant of the SciDAC program, Community Petascale Project for Accelerator Sci- ence and Technology (ComPASS). This research used resources of the Na- tional Energy Research Scientific Computing Center, which is supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. † jlvay@lbl.gov Input Particles: In the laboratory frame, the electron back- ground is initially at rest and a moving window is used to follow the beam progression. Traditionally, the beam macroparticles are initialized all at once in the window, while background electron macroparticles are created con-

Extremely high-intensity laser interactions with fundamental quantum systems

Abstract: The field of laser-matter interaction traditionally deals with the response of atoms, molecules, and plasmas to an external light wave. However, the recent sustained technological progress is opening up the possibility of employing intense laser radiation to trigger or substantially influence physical processes beyond atomic-physics energy scales. Available optical laser intensities exceeding ${10}^{22}\text{ }\text{ }\mathrm{W}/{\mathrm{cm}}^{2}$ can push the fundamental light-electron interaction to the extreme limit where radiation-reaction effects dominate the electron dynamics, can shed light on the structure of the quantum vacuum, and can trigger the creation of particles such as electrons, muons, and pions and their corresponding antiparticles. Also, novel sources of intense coherent high-energy photons and laser-based particle colliders can pave the way to nuclear quantum optics and may even allow for the potential discovery of new particles beyond the standard model. These are the main topics of this article, which is devoted to a review of recent investigations on high-energy processes within the realm of relativistic quantum dynamics, quantum electrodynamics, and nuclear and particle physics, occurring in extremely intense laser fields.

X-Rays and Extreme Ultraviolet Radiation: Principles and Applications

Abstract: This self-contained, comprehensive book describes the fundamental properties of soft x-rays and extreme ultraviolet (EUV) radiation and discusses their applications in a wide variety of fields, including EUV lithography for semiconductor chip manufacture and soft x-ray biomicroscopy. The author begins by presenting the relevant basic principles such as radiation and scattering, wave propagation, diffraction, and coherence. He then goes on to examine a broad range of phenomena and applications. The topics covered include EUV lithography, biomicroscopy, spectromicroscopy, EUV astronomy, synchrotron radiation, and soft x-ray lasers. He also provides a great deal of useful reference material such as electron binding energies, characteristic emission lines and photo-absorption cross-sections. The book will be of great interest to graduate students and researchers in engineering, physics, chemistry, and the life sciences. It will also appeal to practicing engineers involved in semiconductor fabrication and materials science.

Controlled injection and acceleration of electrons in plasma wakefields by colliding laser pulses

Abstract: In laser-plasma-based accelerators, an intense laser pulse drives a large electric field (the wakefield) which accelerates particles to high energies in distances much shorter than in conventional accelerators. These high acceleration gradients, of a few hundreds of gigavolts per metre, hold the promise of compact high-energy particle accelerators. Recently, several experiments have shown that laser-plasma accelerators can produce high-quality electron beams, with quasi-monoenergetic energy distributions at the 100 MeV level. However, these beams do not have the stability and reproducibility that are required for applications. This is because the mechanism responsible for injecting electrons into the wakefield is based on highly nonlinear phenomena, and is therefore hard to control. Here we demonstrate that the injection and subsequent acceleration of electrons can be controlled by using a second laser pulse. The collision of the two laser pulses provides a pre-acceleration stage which provokes the injection of electrons into the wakefield. The experimental results show that the electron beams obtained in this manner are collimated (5 mrad divergence), monoenergetic (with energy spread <10 per cent), tuneable (between 15 and 250 MeV) and, most importantly, stable. In addition, the experimental observations are compatible with electron bunch durations shorter than 10 fs. We anticipate that this stable and compact electron source will have a strong impact on applications requiring short bunches, such as the femtolysis of water, or high stability, such as radiotherapy with high-energy electrons or radiography for materials science.

Femtosecond x rays from laser-plasma accelerators

Abstract: Relativistic interaction of short-pulse lasers with underdense plasmas has recently led to the emergence of a novel generation of femtosecond x-ray sources. Based on radiation from electrons accelerated in plasma, these sources have the common properties to be compact and to deliver collimated, incoherent, and femtosecond radiation. In this article, within a unified formalism, the betatron radiation of trapped and accelerated electrons in the so-called bubble regime, the synchrotron radiation of laser-accelerated electrons in usual meter-scale undulators, the nonlinear Thomson scattering from relativistic electrons oscillating in an intense laser field, and the Thomson backscattered radiation of a laser beam by laser-accelerated electrons are reviewed. The underlying physics is presented using ideal models, the relevant parameters are defined, and analytical expressions providing the features of the sources are given. Numerical simulations and a summary of recent experimental results on the different mechanisms are also presented. Each section ends with the foreseen development of each scheme. Finally, one of the most promising applications of laser-plasma accelerators is discussed: the realization of a compact free-electron laser in the x-ray range of the spectrum. In the conclusion, the relevant parameters characterizing each sources are summarized. Considering typical laser-plasma interaction parameters obtained with currently available lasers, examples of the source features are given. The sources are then compared to each other in order to define their field of applications.

Quasi-monoenergetic laser-plasma acceleration of electrons to 2 GeV

Abstract: Laser-plasma accelerators can produce high-energy electron bunches over just a few centimetres of distance, offering possible table-top accelerator capabilities. Wang et al. break the current 1 GeV barrier by applying a petawatt laser to accelerate electrons nearly monoenergetically up to 2 GeV.