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Thermal effects in plasma-based accelerators

Description: Finite plasma temperature can modify the structure of thewake field, reduce the wave-breaking field, and lead to self-trappedelectrons, which can degrade the electron bunch quality in a plasma-basedaccelerator. A relativistic warm fluid theory is used to describe theplasma temperature evolution and alterations to the structure of anonlinear periodic wave exited in a warm plasma. The trapping thresholdfor a plasma electron and the fraction of electrons trapped from athermal distribution are examined using a single-particle model.Numerical artifacts in particle-in-cell models that can mimic the physicsassociated with finite momentum spread are discussed.
Date: January 9, 2007
Creator: Esarey, E.; Schroeder, C.B.; Michel, E.; Shadwick, B.A.; Geddes,C.G.R. & Leemans, W.P.
Partner: UNT Libraries Government Documents Department

Modeling of 10 GeV-1 TeV laser-plasma accelerators using Lorentz booster simulations

Description: Modeling of laser-plasma wakefield accelerators in an optimal frame of reference [J.-L. Vay, Phys. Rev. Lett. 98 130405 (2007)] allows direct and e#14;fficient full-scale modeling of deeply depleted and beam loaded laser-plasma stages of 10 GeV-1 TeV (parameters not computationally accessible otherwise). This verifies the scaling of plasma accelerators to very high energies and accurately models the laser evolution and the accelerated electron beam transverse dynamics and energy spread. Over 4, 5 and 6 orders of magnitude speedup is achieved for the modeling of 10 GeV, 100 GeV and 1 TeV class stages, respectively. Agreement at the percentage level is demonstrated between simulations using different frames of reference for a 0.1 GeV class stage. Obtaining these speedups and levels of accuracy was permitted by solutions for handling data input (in particular particle and laser beams injection) and output in a relativistically boosted frame of reference, as well as mitigation of a high-frequency instability that otherwise limits effectiveness.
Date: December 1, 2011
Creator: Vay, J.-L.; Geddes, C.G.R.; Esarey, E.; Esarey, E.; Leemans, W.P.; Cormier-Michel, E. et al.
Partner: UNT Libraries Government Documents Department

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

Description: 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.
Date: September 8, 2008
Creator: Cowan, B.; Bruhwiler, D.L.; Cormier-Michel, E.; Esarey, E.; Geddes, C.G.R.; Messmer, P. et al.
Partner: UNT Libraries Government Documents Department

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

Description: 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.
Date: May 1, 2009
Creator: Vay, J.-L.; Fawley, W.M.; Geddes, C.G.R.; Cormier-Michel, E. & Grote, D.P.
Partner: UNT Libraries Government Documents Department

Modeling laser wakefield accelerators in a Lorentz boosted frame

Description: Modeling of laser-plasma wakefield accelerators in an optimal frame of reference is shown to produce orders of magnitude speed-up of calculations from first principles. Obtaining these speedups requires mitigation of a high-frequency instability that otherwise limits effectiveness in addition to solutions for handling data input and output in a relativistically boosted frame of reference. The observed high-frequency instability is mitigated using methods including an electromagnetic solver with tunable coefficients, its extension to accomodate Perfectly Matched Layers and Friedman's damping algorithms, as well as an efficient large bandwidth digital filter. It is shown that choosing the frame of the wake as the frame of reference allows for higher levels of filtering and damping than is possible in other frames for the same accuracy. Detailed testing also revealed serendipitously the existence of a singular time step at which the instability level is minimized, independently of numerical dispersion, thus indicating that the observed instability may not be due primarily to Numerical Cerenkov as has been conjectured. The techniques developed for Cerenkov mitigation prove nonetheless to be very efficient at controlling the instability. Using these techniques, agreement at the percentage level is demonstrated between simulations using different frames of reference, with speedups reaching two orders of magnitude for a 0.1 GeV class stages. The method then allows direct and efficient full-scale modeling of deeply depleted laser-plasma stages of 10 GeV-1 TeV for the first time, verifying the scaling of plasma accelerators to very high energies. Over 4, 5 and 6 orders of magnitude speedup is achieved for the modeling of 10 GeV, 100 GeV and 1 TeV class stages, respectively.
Date: June 15, 2010
Creator: Vay, J.-L.; Geddes, C.G.R.; Cormier-Michel, E. & Grotec, D. P.
Partner: UNT Libraries Government Documents Department

Modeling laser wakefield accelerators in a Lorentz boosted frame

Description: Modeling of laser-plasma wakefield accelerators in an optimal frame of reference [1] is shown to produce orders of magnitude speed-up of calculations from first principles. Obtaining these speedups requires mitigation of a high frequency instability that otherwise limits effectiveness in addition to solutions for handling data input and output in a relativistically boosted frame of reference. The observed high-frequency instability is mitigated using methods including an electromagnetic solver with tunable coefficients, its extension to accomodate Perfectly Matched Layers and Friedman's damping algorithms, as well as an efficient large bandwidth digital filter. It is shown that choosing theframe of the wake as the frame of reference allows for higher levels of filtering and damping than is possible in other frames for the same accuracy. Detailed testing also revealed serendipitously the existence of a singular time step at which the instability level is minimized, independently of numerical dispersion, thus indicating that the observed instability may not be due primarily to Numerical Cerenkov as has been conjectured. The techniques developed for Cerenkov mitigation prove nonetheless to be very efficient at controlling the instability. Using these techniques, agreement at the percentage level is demonstrated between simulations using different frames of reference, with speedups reaching two orders of magnitude for a 0.1 GeV class stages. The method then allows direct and efficient full-scale modeling of deeply depleted laser-plasma stages of 10 GeV-1 TeV for the first time, verifying the scaling of plasma accelerators to very high energies. Over 4, 5 and 6 orders of magnitude speedup is achieved for the modeling of 10 GeV, 100 GeV and 1 TeV class stages, respectively.
Date: September 15, 2010
Creator: Vay, J.-L.; Geddes, C.G.R.; Cormier-Michel, E. & Grote, D.P.
Partner: UNT Libraries Government Documents Department

Speeding Up Simulations of Relativistic Systems using an Optimal Boosted Frame

Description: It can be computationally advantageous to perform computer simulations in a Lorentz boosted frame for a certain class of systems. However, even if the computer model relies on a covariant set of equations, it has been pointed out that algorithmic difficulties related to discretization errors may have to be overcome in order to take full advantage of the potential speedup. We summarize the findings, the difficulties and their solutions, and show that the technique enables simulations important to several areas of accelerator physics that are otherwise problematic, including self-consistent modeling in three-dimensions of laser wokefield accelerator stages at energies of 10 GeV and above.
Date: January 27, 2009
Creator: Vay, J.-L.; Fawley, W.M.; Geddes, C.G.R.; Cormier-Michel, E. & Grote, D.P.
Partner: UNT Libraries Government Documents Department

Effects of Hyperbolic Rotation in Minkowski Space on the Modeling of Plasma Accelerators in a Lorentz Boosted Frame

Description: Laser driven plasma accelerators promise much shorter particle accelerators but their development requires detailed simulations that challenge or exceed current capabilities. We report the first direct simulations of stages up to 1 TeV from simulations using a Lorentz boosted calculation frame resulting in a million times speedup, thanks to a frame boost as high as gamma = 1300. Effects of the hyperbolic rotation in Minkowski space resulting from the frame boost on the laser propagation in the plasma is shown to be key in the mitigation of a numerical instability that was limiting previous attempts.
Date: September 21, 2010
Creator: Vay, J.-L.; Geddes, C. G. R.; Cormier-Michel, E. & Grote, D. P.
Partner: UNT Libraries Government Documents Department

Plasma density gradient injection of low absolute momentum spread electron bunches

Description: Plasma density gradients in a gas jet were used to control the wake phase velocity and trapping threshold in a laser wakefield accelerator, producing stable electron bunches with longitudinal and transverse momentum spreads more than ten times lower than in previous experiments (0.17 and 0.02 MeV/c FWHM, respectively) and with central momenta of 0.76 +- 0.02 MeV/c. Transition radiation measurements combined with simulations indicated that the bunches can be used as a wakefield accelerator injector to produce stable beams with 0.2 MeV/c-class momentum spread at high energies.
Date: December 22, 2007
Creator: Geddes, C.G.R.; Nakamura, K.; Plateau, G.R.; Toth, Cs.; Cormier-Michel, E.; Esarey, E. et al.
Partner: UNT Libraries Government Documents Department

High Quality Electron Bunches up to 1 GeV from Laser WakefieldAcceleration at LBNL

Description: Experiments at the LOASIS laboratory of LBNL havedemonstrated production of 100 MeV to 1 GeV electron bunches with lowenergy spread and low divergence from laser wakefield acceleration. Theradiation pressure of a 10 TW laser pulse, guided over 10 diffractionranges by a few-mm long plasma density channel, was used to drive anintense plasma wave (wakefield), producing electron bunches with energieson the order of 100 MeV and acceleration gradients on the order of 100GV/m. Beam energy was increased from 100 MeV to 1 GeV by using a few-cmlong guiding channel at lower density, driven by a 40 TW laser,demonstrating the anticipated scaling to higher beam energies. Particlesimulations indicate that the low energy spread beams were produced fromself-trapped electrons through the interplay of trapping, loading, anddephasing. Other experiments and simulations are also underway to controlinjection of particles into the wake, and hence improve beam quality andstability further.
Date: July 1, 2006
Creator: Esarey, E.; Nagler, B.; Gonsalves, A.J.; Toth, Cs.; Nakamura, K.; Geddes, C.G.R. et al.
Partner: UNT Libraries Government Documents Department

Stable Electron Beams With Low Absolute Energy Spread From a LaserWakefield Accelerator With Plasma Density Ramp Controlled Injection

Description: Laser wakefield accelerators produce accelerating gradientsup to hundreds of GeV/m, and recently demonstrated 1-10 MeV energy spreadat energies up to 1 GeV using electrons self-trapped from the plasma.Controlled injection and staging may further improve beam quality bycircumventing tradeoffs between energy, stability, and energyspread/emittance. We present experiments demonstrating production of astable electron beam near 1 MeV with hundred-keV level energy spread andcentral energy stability by using the plasma density profile to controlselfinjection, and supporting simulations. Simulations indicate that suchbeams can be post accelerated to high energies,potentially reducingmomentum spread in laser acceleratorsby 100-fold or more.
Date: June 25, 2007
Creator: Geddes, Cameron G.R.; Cormier-Michel, E.; Esarey, E.; Leemans,W.P.; Nakamura, K.; Panasenko, D. et al.
Partner: UNT Libraries Government Documents Department

Laser-PlasmaWakefield Acceleration with Higher Order Laser Modes

Description: Laser-plasma collider designs point to staging of multiple accelerator stages at the 10 GeV level, which are to be developed on the upcoming BELLA laser, while Thomson Gamma source designs use GeV stages, both requiring efficiency and low emittance. Design and scaling of stages operating in the quasi-linear regime to address these needs are presented using simulations in the VORPAL framework. In addition to allowing symmetric acceleration of electrons and positrons, which is important for colliders, this regime has the property that the plasma wakefield is proportional to the transverse gradient of the laser intensity profile. We demonstrate use of higher order laser modes to tailor the laser pulse and hence the transverse focusing forces in the plasma. In particular, we show that by using higher order laser modes, we can reduce the focusing fields and hence increase the matched electron beam radius, which is important to increased charge and efficiency, while keeping the low bunch emittance required for applications.
Date: June 1, 2010
Creator: Geddes, C.G.R.; Cormier-Michel, E.; Esarey, E.; Schroeder, C.B.; Mullowney, P.; Paul, K. et al.
Partner: UNT Libraries Government Documents Department

SCALED SIMULATION DESIGN OF HIGH QUALITY LASER WAKEFIELD ACCELERATOR STAGES

Description: 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.
Date: May 4, 2009
Creator: Geddes, C.G.R.; Cormier-Michel, E.; Esarey, E.; Schroeder, C.B.; Leemans, W.P.; Bruhwiler, D.L. et al.
Partner: UNT Libraries Government Documents Department

New Developments in the Simulation of Advanced Accelerator Concepts

Description: Improved computational methods are essential to the diverse and rapidly developing field of advanced accelerator concepts. We present an overview of some computational algorithms for laser-plasma concepts and high-brightness photocathode electron sources. In particular, we discuss algorithms for reduced laser-plasma models that can be orders of magnitude faster than their higher-fidelity counterparts, as well as important on-going efforts to include relevant additional physics that has been previously neglected. As an example of the former, we present 2D laser wakefield accelerator simulations in an optimal Lorentz frame, demonstrating>10 GeV energy gain of externally injected electrons over a 2 m interaction length, showing good agreement with predictions from scaled simulations and theory, with a speedup factor of ~;;2,000 as compared to standard particle-in-cell.
Date: September 10, 2008
Creator: Paul, K.; Cary, J.R.; Cowan, B.; Bruhwiler, D.L.; Geddes, C.G.R.; Mullowney, P.J. et al.
Partner: UNT Libraries Government Documents Department

Betatron radiation from density tailored plasmas

Description: In laser wakefield accelerators, electron motion is driven by intense forces that depend on the plasma density. Transverse oscillations in the accelerated electron orbits produce betatron radiation. The electron motion and the resulting betatron radiation spectrum can therefore be controlled by shaping the plasma density along the orbit of the electrons. Here, a method based on the use of a plasma with a longitudinal density variation (density depression or step) is proposed to increase the transverse oscillation amplitude and the energy of the electrons accelerated in a wakefield cavity. For fixed laser parameters, by appropriately tailoring the plasma profile, the betatron radiation emitted by these electrons is significantly increased in both flux and energy.
Date: April 11, 2009
Creator: Ta Phuoc, Kim; Esarey, E.; Leurent, V.; Cormier-Michel, E.; Geddes, C.G.R.; Schroeder, C.B. et al.
Partner: UNT Libraries Government Documents Department

Automated detection and analysis of particle beams in laser-plasma accelerator simulations

Description: Numerical simulations of laser-plasma wakefield (particle) accelerators model the acceleration of electrons trapped in plasma oscillations (wakes) left behind when an intense laser pulse propagates through the plasma. The goal of these simulations is to better understand the process involved in plasma wake generation and how electrons are trapped and accelerated by the wake. Understanding of such accelerators, and their development, offer high accelerating gradients, potentially reducing size and cost of new accelerators. One operating regime of interest is where a trapped subset of electrons loads the wake and forms an isolated group of accelerated particles with low spread in momentum and position, desirable characteristics for many applications. The electrons trapped in the wake may be accelerated to high energies, the plasma gradient in the wake reaching up to a gigaelectronvolt per centimeter. High-energy electron accelerators power intense X-ray radiation to terahertz sources, and are used in many applications including medical radiotherapy and imaging. To extract information from the simulation about the quality of the beam, a typical approach is to examine plots of the entire dataset, visually determining the adequate parameters necessary to select a subset of particles, which is then further analyzed. This procedure requires laborious examination of massive data sets over many time steps using several plots, a routine that is unfeasible for large data collections. Demand for automated analysis is growing along with the volume and size of simulations. Current 2D LWFA simulation datasets are typically between 1GB and 100GB in size, but simulations in 3D are of the order of TBs. The increase in the number of datasets and dataset sizes leads to a need for automatic routines to recognize particle patterns as particle bunches (beam of electrons) for subsequent analysis. Because of the growth in dataset size, the application of machine learning techniques for ...
Date: May 21, 2010
Creator: Ushizima, Daniela Mayumi; Geddes, C.G.; Cormier-Michel, E.; Bethel, E. Wes; Jacobsen, J.; Prabhat, , et al.
Partner: UNT Libraries Government Documents Department

Low energy spread 100 MeV-1 GeV electron bunches from laserwakefiel d acceleration at LOASIS

Description: Experiments at the LOASIS laboratory of LBNL recentlydemonstrated production of 100 MeV electron beams with low energy spreadand low divergence from laser wakefield acceleration. The radiationpressure of a 10 TW laser pulse guided over 10 diffraction ranges by aplasma density channel was used to drive an intense plasma wave(wakefield), producing acceleration gradients on the order of 100 GV/m ina mm-scale channel. Beam energy has now been increased from 100 to 1000MeV by using a cm-scale guiding channel at lower density, driven by a 40TW laser, demonstrating the anticipated scaling to higher beam energies.Particle simulations indicate that the low energy spread beams wereproduced from self trapped electrons through the interplay of trapping,loading, and dephasing. Other experiments and simulations are alsounderway to control injection of particles into the wake, and henceimprove beam quality and stability further.
Date: August 1, 2006
Creator: Geddes, C.G.R.; Esarey, E.; Michel, P.; Nagler, B.; Nakamura, K.; Plateau, G.R. et al.
Partner: UNT Libraries Government Documents Department

Simulating relativistic beam and plasma systems using an optimal boosted frame

Description: It was shown recently that it may be computationally advantageous to perform computer simulations in a Lorentz boosted frame for a certain class of systems. However, even if the computer model relies on a covariant set of equations, it was pointed out that algorithmic difficulties related to discretization errors may have to be overcome in order to take full advantage of the potential speedup. In this paper, we summarize the findings, the difficulties and their solutions, and review the applications of the technique that have been performed to date.
Date: May 1, 2009
Creator: Vay, J.-L.; Bruhwiler, D. L.; Geddes, C. G. R.; Fawley, W. M.; Martins, S. F.; Cary, J. R. et al.
Partner: UNT Libraries Government Documents Department

Progress on laser plasma accelerator development using transverselyand longitudinally shaped plasmas

Description: A summary of progress at Lawrence Berkeley National Laboratory is given on: (1) experiments on down-ramp injection; (2) experiments on acceleration in capillary discharge plasma channels; and (3) simulations of a staged laser wakefield accelerator (LWFA). Control of trapping in a LWFA using plasma density down-ramps produced electron bunches with absolute longitudinal and transverse momentum spreads more than ten times lower than in previous experiments (0.17 and 0.02 MeV Ic FWHM, respectively) and with central momenta of 0.76 +- 0.02 MeV Ic, stable over a week of operation. Experiments were also carried out using a 40 TW laser interacting with a hydrogen-filled capillary discharge waveguide. For a 15 mm long, 200 mu m diameter capillary, quasi-monoenergetic bunches up to 300 MeV were observed. By detuning discharge delay from optimum guiding performance, self-trapping was found to be stabilized. For a 33 mm long, 300 mu m capillary, a parameter regime with high energy bunches, up to 1 Ge V, was found. In this regime, peak electron energy was correlated with the amount of trapped charge. Simulations show that bunches produced on a down-ramn and iniected into a channel-guided LWFA can produce stable beams with 0.2 MeV Ic-class momentum spread at high energies.
Date: March 31, 2009
Creator: Leemans, Wim P.; Esarey, E.; Geddes, C.G.R.; Toth, Cs.; Schroeder, C.B.; Nakamura, K. et al.
Partner: UNT Libraries Government Documents Department

Benchmarking the codes VORPAL, OSIRIS, and QuickPIC with Laser Wakefield Acceleration Simulations

Description: Three-dimensional laser wakefield acceleration (LWFA) simulations have recently been performed to benchmark the commonly used particle-in-cell (PIC) codes VORPAL, OSIRIS, and QuickPIC. The simulations were run in parallel on over 100 processors, using parameters relevant to LWFA with ultra-short Ti-Sapphire laser pulses propagating in hydrogen gas. Both first-order and second-order particle shapes were employed. We present the results of this benchmarking exercise, and show that accelerating gradients from full PIC agree for all values of a0 and that full and reduced PIC agree well for values of a0 approaching 4.
Date: September 8, 2008
Creator: Paul, Kevin; Huang, C.; Bruhwiler, D.L.; Mori, W.B.; Tsung, F.S.; Cormier-Michel, E. et al.
Partner: UNT Libraries Government Documents Department

Recent results and future challenges for large scale Particle-In-Cell simulations of plasma-based accelerator concepts

Description: The concept and designs of plasma-based advanced accelerators for high energy physics and photon science are modeled in the SciDAC COMPASS project with a suite of Particle-In-Cell codes and simulation techniques including the full electromagnetic model, the envelope model, the boosted frame approach and the quasi-static model. In this paper, we report the progress of the development of these models and techniques and present recent results achieved with large-scale parallel PIC simulations. The simulation needs for modeling the plasma-based advanced accelerator at the energy frontier is discussed and a path towards this goal is outlined.
Date: May 1, 2009
Creator: Huang, C.; An, W.; Decyk, V.K.; Lu, W.; Mori, W.B.; Tsung, F.S. et al.
Partner: UNT Libraries Government Documents Department