Bulletin of the American Physical Society
57th Annual Meeting of the APS Division of Plasma Physics
Volume 60, Number 19
Monday–Friday, November 16–20, 2015; Savannah, Georgia
Session BO8: Laser and Plasma Wakefield Accelerators |
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Chair: Sven Steinke, Lawrence Berkeley National Laboratory Room: 103/104 |
Monday, November 16, 2015 9:30AM - 9:42AM |
BO8.00001: Electron acceleration with advanced injection methods at the ASTRA laser Kristjan Poder, Nelson Carreira-Lopes, Jonathan Wood, Jason Cole, Bucker Dangor, Peta Foster, Ram Gopal, Christos Kamperidis, Olena Kononenko, Stuart Mangles, Halil Olgun, Charlotte Palmer, Daniel Symes, Rajeev Pattathil, Zulfikar Najmudin Recent electron acceleration results from the \uppercase{ASTRA} laser facility are presented. Experiments were performed using both the 40~TW ASTRA and the 350~TW ASTRA-Gemini laser. Fundamental electron beam properties relating to its quality were investigated both experimentally and with PIC simulations. For increased control over such parameters, various injection mechanisms such as self-injection and ionization injection were employed. Particular interest is given to the dynamics of ionization injected electrons in strongly driven wakes. [Preview Abstract] |
Monday, November 16, 2015 9:42AM - 9:54AM |
BO8.00002: Effect of the laser wavefront in a laser-plasma accelerator Aline Vernier, B. Beaurepaire, M. Bocoum, F. B\"ohle, A. Jullien, J.-P. Rousseau, T. Lefrou, G. Iaquaniello, R. Lopez-Martens, A. Lifschitz, J. Faure Laser-plasma accelerators are a promising alternative as they can currently provide short (down to a few fs), relativistic (from a few MeV up to a few GeV) electron beams over millimeter distances. In such devices, an intense laser pulse drives a plasma wave in which self-injected electrons can be accelerated. The quality, in terms of emittance, of such electron beams is known to strongly depend on the laser focal spot, but very little attention is generally given to the laser transverse distribution on either side of the focal plane. Our recent experimental results and PIC simulations quantify the role of the wavefront at the focus on the acceleration of eletrons: distortions of the laser wavefront cause spatial inhomogeneity of the out-of-focus laser intensity distribution and consequently, the laser pulse drives a transversely inhomogenous wakefield whose focusing/defocusing properties affect the electron distribution. [Preview Abstract] |
Monday, November 16, 2015 9:54AM - 10:06AM |
BO8.00003: MeV electron acceleration by sub-terawatt laser pulses in near critical density plasmas Andy Goers, George Hine, Linus Feder, Bo Miao, Fatholah Salehi, Howard Milchberg We demonstrate laser-plasma acceleration of high charge electron beams to the 10 MeV scale using ultrashort laser pulses with as little energy as 10 mJ. This result is made possible by an extremely dense and thin hydrogen gas jet where even sub-terawatt laser pulses are well above the critical power for relativistic self-focusing, and the 10 mJ pulses can drive a self-modulated wakefield accelerator. Total charge up to 0.5 nC is measured for energies \textgreater 1 MeV. Acceleration is correlated to the presence of an intense, coherent, broadband light flash, associated with wavebreaking, which can radiate more than 3{\%} of the laser energy in a sub-femtosecond bandwidth consistent with half-cycle optical emission. Our results enable truly portable applications of laser-driven acceleration, such as low dose radiography, ultrafast probing of matter, and isotope production. [Preview Abstract] |
Monday, November 16, 2015 10:06AM - 10:18AM |
BO8.00004: Direct Laser Acceleration of Electrons in a Laser Wakefield Accelerator with Ionization Injection Jessica Shaw, Nuno Lemos, Kenneth Marsh, Frank Tsung, Navid Vafaei-Najafabadi, Warren Mori, Chan Joshi We show through experiments and supporting simulations the role of direct laser acceleration (DLA) of electrons in a plasma accelerator when ionization injection of electrons is employed to inject charge into the laser-produced wake. If the laser pulse is intense enough to expel most of the plasma electrons but is nevertheless long enough to overlap the electrons trapped in the first accelerating potential well (bucket) of the wakefield, then the betatron oscillations of the electrons in the plane of the laser polarization in the presence of an ion column can lead to an energy transfer from the laser pulse to the electrons. By measuring the electron properties over a range of laser and plasma parameters, we show that DLA can be a major contributor to the maximum electron energy and that the energy gain due to DLA can exceed that due to laser wakefield acceleration for certain laser and plasma parameters. [Preview Abstract] |
Monday, November 16, 2015 10:18AM - 10:30AM |
BO8.00005: Non-Maxwellian electron distributions by direct laser acceleration in near-critical plasmas T. Toncian, C. Wang, A. Arefiev, E. McCary, A. Meadows, J. Blakeney, C. Chester, R. Roycroft, H. Fu, X.Q. Yan, J. Schreiber, I. Pomerantz, H. Quevedo, G. Dyer, E. Gaul, T. Ditmire, B.M. Hegelich The irradiation of few nm thick targets by a finite-contrast high-intensity short-pulse laser results in a strong pre-expansion of these targets at the arrival time of the main pulse. The targets will decompress to near and lower than critical electron densities plasmas extending over lengths of few micrometers. The laser-matter interaction of the main pulse with such a highly localized but inhomogeneous the target leads to the generation of a channel and further self focussing of the laser beam. As measured in a experiment conducted with the GHOST laser system at UT Austin, 2D PIC simulations predict Direct Laser Acceleration of non-Maxwellian electron distribution in the laser propagation direction for such targets. The hereby high density electron bunches have potential applications as injector beams for a further wakefield acceleration stage. This work was supported by NNSA cooperative agreement DE-NA0002008, the DARPA's PULSE program (12-63-PULSE-FP014) and the AFOSR (FA9550-14-1-0045). [Preview Abstract] |
Monday, November 16, 2015 10:30AM - 10:42AM |
BO8.00006: A spectral, quasi-cylindrical and dispersion-free Particle-In-Cell algorithm Remi Lehe, Manuel Kirchen, Igor Andriyash, Brendan Godfrey, Jean-Luc Vay Particle-In-Cell (PIC) codes are widely used today for laser-wakefield acceleration and other laser-plasma interactions. However, these codes remain very computationally intensive and still suffer from a number of numerical artifacts, especially due to numerical dispersion. These two short-comings have been addressed in two separate manner, in the context of laser-wakefield acceleration. On the one hand, the computational time can be strongly reduced in the situations with close-to-cylindrical symmetry, by using a quasi-cylindrical computational grid. On the other hand, some numerical artifacts can be suppressed by the use of pseudo-spectral analytical PIC codes, which have no numerical dispersion at all. Here we present a PIC code that combines these two advantages. The code uses of a quasi-cylindrical grid to strongly reduce the computational time, and solves the Maxwell equations in spectral space, through the use of Hankel and Fourier transforms. We show that this type code performs better than standard finite-difference PIC codes in a number of physical situations. [Preview Abstract] |
Monday, November 16, 2015 10:42AM - 10:54AM |
BO8.00007: Performance evaluation of OSIRIS EM-PIC on a Xeon Phi cluster Ricardo Fonseca The quest towards exascale computing has lead to the development of hybrid systems with add-on accelerator cards such as the Xeon Phi accelerators powering for example the Tianhe-2 system in China (currently the {\#}1 system in the world) and the SuperMIC at LZR in Germany. In this work we report on our efforts on deploying the OSIRIS electromagnetic particle-in-cell code on the latter system, focusing not only on algorithm details and single card performance but also on multiple card use. Our benchmarks show code performance of $\sim$ 600(2D) / 300(3D) million particle pushes per second on a single board, and above 74{\%} (strong)/ 94{\%} (weak) scaling efficiency up to 32 boards. \\[4pt] [1]~R. A. Fonseca et al., Lecture Notes in Computer Science \textbf{2331}, 342-351 (2002) [Preview Abstract] |
Monday, November 16, 2015 10:54AM - 11:06AM |
BO8.00008: Wakefield structure of plasma hollow channels self-driven by tightly focused beams Ligia D. Amorim, Jorge Vieira, Ricardo A. Fonseca, Luis O. Silva Plasma based wakefield accelerators (PWFA) are promising alternatives to conventional configurations due to the high accelerating gradients they can sustain. For future linear colliders, however, PWFAs need to overcome the challenge of efficiently accelerating positrons. PWFAs regimes with high acceleration gradients typically defocus positron bunches. Several techniques have tried to solve this challenge [1]. Here we explore how tightly focused positron bunches sent through homogeneous plasmas can radially expel the plasma ions generating a hollow channel with high accelerating and focusing fields. We modeled the hollow channel accelerating and focusing wakefields structures analytically, and found good agreement with 3D numerical simulations performed with the PIC code OSIRS [2]. We demonstrated that this scheme could accelerate positrons to high energies. Furthermore, we analyzed the impact of the key drive bunch properties on the formation of the hollow channel, finding that bunches with short fall times (compared to electron bubble radius) and small transverse sizes (compared to plasma skin depth) maximize both accelerating and focusing fields. We also studied hollow channels driven by laser beams.\\[4pt] [1] J. Vieira, J.T. Mendon\c{c}a, PRL 112, 215001 (2014)\\[0pt] [2] R. A. Fonseca et al., Lect. Notes Comput. Sci. 2331, 342 (2002) [Preview Abstract] |
Monday, November 16, 2015 11:06AM - 11:18AM |
BO8.00009: Intrinsic phase space discretization of charge in laser-triggered ionization injection in plasma accelerators Xinlu Xu, Wei Lu, Warren Mori, Chan Joshi Ionization injection is attractive as a controllable injection scheme for generating high quality electron beams in plasma wakefield acceleration. Due to the phase dependent tunneling ionization rate and the ultra-high accelerating fields, the discrete injection of electrons within the wake is nonlinearly mapped to the final phase space of the beam where the electrons are relativistic. This unique phase space structure is theoretically analyzed and examined by three-dimensional particle-in-cell simulations. The period of the modulation varies from $> 2k_0$ to about $5k_0$ depending on the initial range of phases of ionization and the final phases where the electrons become trapped, where $k_0$ is the wavenumber of the injection laser. Such a pre-bunched beam can be diagnosed through coherent transition radiation upon its exit from the plasma and may find use in generating high-power ultraviolet radiation upon passage through a resonant undulator. Work supported by NSF and DOE. [Preview Abstract] |
Monday, November 16, 2015 11:18AM - 11:30AM |
BO8.00010: Understanding and optimizing the LWFA in the nonlinear self-guided blowout regime Asher Davidson, Peicheng Yu, Xinlu Xu, Frank Tsung, Thamine Dalichaouch, Wei Lu, Weiming An, Warren Mori We report on recent results on LWFA in the nonlinear, self-guided, blowout regime, where the normalized vector potential is larger than 4. In the work of Lu et al. [Phys. Rev. Spec. Top. Accel. Beams 10, 061301 (2007)], matching conditions for the laser spot size were presented as well as scaling laws for the accelerated electron energy in terms of laser and plasma parameters. Recent advances in PIC modeling, including the quasi-3D and boosted frame techniques now make it possible to study these scaling laws for higher laser energies. The quasi-3D algorithm uses a PIC algorithm on an r-z grid and a girdless description in the azimuthal angle. The fields are expanded in azimuthal harmonics that are truncated at a chosen number. We have implemented this algorithm in OSIRIS and here we use it to examine the nonlinear regime for existing and future 15-100 Joule lasers. Excellent agreement with the scaling laws in Lu et al. was found. In addition, we study adjustments to the laser profile characteristics in which the electron beam is optimized for a fixed energy laser. [Preview Abstract] |
Monday, November 16, 2015 11:30AM - 11:42AM |
BO8.00011: Simulation of free-space optical guiding structure based on colliding gas flows Dmitri Kaganovich, John Palastro, Yu-hsin Chen, Daniel Gordon, Michael Helle, Antonio Ting Preformed plasma channels with parabolic radial density profiles enable the extended and stable optical guiding of high intensity laser pulses. High voltage discharge capillaries, commonly used for channel formation, have limited guiding length and opaque walls, complicating diagnosis of the plasma within. We propose a unique free-space gas channel produced by the collision of several gas flows. The collision of the gas flows forms an on-axis density depression surrounded by higher density walls. By offsetting the flows, we demonstrate the creation of a novel vortex structure exhibiting a long-lived parabolic density profile. Once ionized, the resulting plasma density profile has a near-parabolic dependence appropriated for guiding. Detailed 2-D fluid dynamics simulations are performed to examine the properties and stability of the guiding structure. Simple physical model and experimental perspectives will be presented. [Preview Abstract] |
Monday, November 16, 2015 11:42AM - 11:54AM |
BO8.00012: Observation of the self-modulation of electron and positron bunches in plasmas Patric Muggli Relativistic, charged particle bunches with length longer that the electron plasma wavelength are subject to the transverse self-modulation instability (SMI). The instability arises from the interplay between the low level transverse wakefields (focusing/defocusing) and the bunch density that drives the wakefields. As a result, the bunch density becomes periodically modulated with a period approximately equal to the electron plasma wavelength. The modulated bunch can then resonantly drive wakefields to large amplitudes. Measurements with the SLAC-FACET electron and positron bunches show clear signs of the occurrence of the SMI. The experimental setup as well as the results obtained to date will be presented. [Preview Abstract] |
Monday, November 16, 2015 11:54AM - 12:06PM |
BO8.00013: Recent results from optical probe measurements of PWFA at FACET Rafal Zgadzaj, M.C. Downer, Zhengyan Li, Spencer Gessner, James Allen, Mike Litos, Erik Adli, Christine Clark, Selina Green, Mark Hogan, Vitaly Yakimenko We report first MOPI (multi object plane imaging,[1]) optical probe measurements of plasma structures in electron beam driven plasma acceleration (PWFA) experiments performed at the FACET facility in SLAC. Experiments were performed in hydrogen and Argon, using FACET's 20.35 GeV electron beam. Plasma structures were observed with laser pre-ionization and electron beam self-ionization, and at densities as low as $\sim$ 2 10$^{17}$ cm$^{-3}$. Under some conditions instabilities imprint a transverse structure in the plasma column whose evolution is directly observable. The measurements also allow the study of long term evolution of the plasma column, which is an important factor limiting the maximum operating rate of possible future PWFA based colliders. \\[4pt] [1] Z. Li, et al., ``Single-shot visualization of evolving, light-speed structures by multi object plane phase-contrast imaging,'' Opt. Lett. 38, 5157-5160 (2013). [Preview Abstract] |
Monday, November 16, 2015 12:06PM - 12:18PM |
BO8.00014: Non-linear Ion-Wake Excitation by Plasma Electron Wakefields of an Electron or Positron Beam for Positron Acceleration Thomas Katsouleas, Aakash Sahai The excitation of a non-linear ion-wake by a train of non-linear electron wake of an electron and a positron beam is modeled and its use for positron acceleration is explored. The ion-wake is shown to be a driven non-linear ion-acoustic wave in the form of a cylindrical ion-soliton similar to the solution of the cKdV equation. The phases of the oscillating radial electric fields of the slowly-propagating electron wake are asymmetric in time and excite time-averaged inertial ion motion radially. The radial field of the electron compression region sucks-in the ions and the field of space-charge region of the wake expels them, driving a cylindrical ion-soliton structure with on-axis and bubble-edge density-spikes. Once formed, the channel-edge density-spike is driven radially outwards by the thermal pressure of the thermalized wake energy. Its channel-like structure due to the flat-residue left behind by the propagating ion-soliton, is independent of the energy-source driving the non-linear electron wake. We explore the use of the partially-filled channel formed by the cylindrical ion-soliton for a novel regime of positron acceleration. PIC simulations are used to study the ion-wake soliton structure, its driven propagation and its use for positron acceleration (arXiv:1504.03735). [Preview Abstract] |
Monday, November 16, 2015 12:18PM - 12:30PM |
BO8.00015: Quantitative single shot and spatially resolved plasma wakefield diagnostics Muhammad Kasim, James Holloway, Luke Ceurvorst, Matthew Levy, Naren Ratan, James Sadler, Robert Bingham, Philip Burrows, Raoul Trines, Matthew Wing, Peter Norreys Plasma wakefield detections and diagnostics can give valuable information for optimizing plasma accelerator experiments. However, there are only a few techniques to do the plasma wakefield diagnostics. Here we introduce a method to diagnose the plasma wakefield's parameters using photon acceleration. In this technique, a laser pulse that could cover several plasma wavelengths is fired into the wakefield. Inverting the measured frequency modulation profile of the pulse yields the density profile of the wakefield at the interaction point. By introducing a crossing angle, the interaction point can be chosen and thus make it possible to diagnose the wakefield at the chosen point in the plasma. We performed simulations to check the accuracy between the measured wakefield amplitude and the actual amplitude. These results agree qualitatively and quantitatively with a relative error less than 10{\%} for various wakefield amplitudes, probe's wavelengths, and crossing angles. Theoretical model with its computational method are presented as well as several limitations that could spoil the measurements. This technique opens up new possibilities of qualitative and quantitative diagnose of plasma wakefield density at known positions. [Preview Abstract] |
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