Bulletin of the American Physical Society
51st Annual Meeting of the APS Division of Plasma Physics
Volume 54, Number 15
Monday–Friday, November 2–6, 2009; Atlanta, Georgia
Session TO4: Laser Wakefield Accelerators and Radiation Sources |
Hide Abstracts |
Chair: David Bruhwiler, Tech-X Corporation Room: Regency VI |
Thursday, November 5, 2009 9:30AM - 9:42AM |
TO4.00001: Injected wake field acceleration with a 40 MeV electron linac S. Kraft, A. Jochmann, C. Erler, A. Debus, M. Bussmann, R. Sauerbrey, U. Schramm, T.E. Cowan Over the last years multiple research groups achieved multi-MeV to GeV electron beams. Ultrashort bunches and a very low emittance combined with a high bunch charge offer a wide range of applications nevertheless the reproducibility of those beams is one of the main problems. External injection into a plasma wake is a promising concept to separate the influence of different input parameters from each other for more control of experimental results and to improve reproducibility. At the Research Center Dresden-Rossendorf the 150TW laser system DRACO was set up next to an superconducting electron accelerator. This will give the opportunity to study wake field acceleration in more detail. In this talk the present status of the experiment, ongoing upgrades and future plans will be described. [Preview Abstract] |
Thursday, November 5, 2009 9:42AM - 9:54AM |
TO4.00002: Injection and Trapping of Tunnel Ionized Electrons into Laser Produced Wakes A. Pak, K.A. Marsh, S.F. Martins, W. Lu, W.B. Mori, C. Joshi A method which utilizes the ionization potentials of gases as a mechanism for injecting electrons into a laser produced accelerating wakefields is presented. The properties of accelerated beams created via this injection method will be discussed for various experimental parameters. Experimental results will be supported by theory and simulations. [Preview Abstract] |
Thursday, November 5, 2009 9:54AM - 10:06AM |
TO4.00003: Ionization induced trapping in a laser wakefield accelerator William Schumaker, C. McGuffey, A.G.R. Thomas, T. Matsuoka, V. Chvykov, F.J. Dollar, G. Kalintchenko, V. Yanovsky, A. Maksimchuk, K. Krushelnick, V. Yu. Bychenkov, I.V. Glazyrin Experimental measurements of electrons accelerated in a laser wake?eld accelerator indicate trapping initiated by an ionization mechanism. By using a range of noble gases and nitrogen as a very small percentage contaminant in helium gas, it is found that tunneling ionization of inner shell electrons plays an important role in determining the trapped charge. Although there is a small increase in electron number density due to the higher Z contaminant, it is shown to be insufficient to account for the increase in charge in the trapped bunch. The behavior of the trapping with laser intensity is also consistent with the tunnel-ionization thresholds for the gases used. This mechanism is likely to allow lower power laser systems to be used to generate comparably high-energy and low-emittance monoenergetic electron beams than in pre-ionized gas configurations. 2D particle-in-cell simulations including an ADK ionization model were used to correlate with experimental results. [Preview Abstract] |
Thursday, November 5, 2009 10:06AM - 10:18AM |
TO4.00004: High-brightness near-GeV energy electron beams from a laser wakefield accelerator for long-standoff nuclear interrogation Nathan Powers, Sudeep Banerjee, Vidya Ramanathan, Nathaniel Cunningham, Nate Chandler-Smith, Donald Umstadter, Randy Vane, David Schultz, Shaun Clarke, Sara Pozzi High-brightness monochromatic electron beams are generated in a wakefield accelerator driven by a 100 TW laser. The energy can be varied from 20-800 MeV by varying laser and plasma parameters. Stable electron beams are obtained using self-injection and optical injection. The ability of these beams to penetrate large thicknesses of dense material and an angular spread of $<$5 mrad makes them suitable as active interrogation probes for long standoff nuclear activation of concealed nuclear materials. A series of ($\gamma $,xn) activation measurements were performed to demonstrate the viability of this technique. MCNP and GEANT Monte Carlo simulations are used to aid experiment design and interpretation. [Preview Abstract] |
Thursday, November 5, 2009 10:18AM - 10:30AM |
TO4.00005: Laser plasma generated electron beams for high resolution long range radiography Vidya Ramanathan, Sudeep Banerjee, Nathan Powers, Kun Zhao, Nate Chandler-Smith, Nathaniel Cunningham, Donald Umstadter, Shaun Clarke, Sara Pozzi Applications of tunable, collimated, high energy, monochromatic electron beams generated from a laser-plasma based accelerator are explored as active interrogation probes for long stand-off electron beam radiography. Besides being highly penetrating in nature the low-divergence of these electron beams, provides for an efficient delivery of the beam energy to a distant target. Laser wakefield accelerators are advantageous in that, they give rise to electron beams with micron-scale source size (comparable to the waist of the laser beam), which can provide superior image resolution. For the first time, electron beams are shown to resolve sub-millimeter (250 $\mu $m) structures that are embedded in thick and dense materials placed at a long standoff distance ($\sim $2m) from the source. Monte-Carlo simulations of the experimental results are also presented. [Preview Abstract] |
Thursday, November 5, 2009 10:30AM - 10:42AM |
TO4.00006: Generation and characterization of high-field, short-pulse THz emission from the Berkeley Laser Plasma Accelerator Nicholas Matlis, Guillaume Plateau, Jeroen van Tilborg, Carl Schroeder, Cameron Geddes, Csaba Toth, Wim Leemans We present progress on the generation of sub-ps THz pulses in the MV/cm regime from a Laser Plasma Accelerator (LPA) and their use as an accelerator diagnostic. The THz pulses serve the dual purpose of acting as a high-field short pulse source for pump-probe studies as well as a diagnostic of the bunch duration of electrons from the LPA. Characterization of the focused THz spatial and temporal mode properties was done using state-of-the-art electro-optic (EO) sampling methods. A new technique was also implemented which allows single-shot acquisition of the THz spatio-temporal waveform. Preliminary results showing spatio-temporal features of the THz pulses will be presented, as well as a preliminary demonstration of correlation between electron bunch properties and the THz spectrum. [Preview Abstract] |
Thursday, November 5, 2009 10:42AM - 10:54AM |
TO4.00007: Betatron radiation from the self-injected electrons in a laser wakefield Seok Won Hwang, Sang-Young Chung, Hae June Lee When self-injected electrons in a laser wakefield are accelerated to a hundred MeV or 1 GeV, the electrons also oscillate by the focusing fields of the wakefield which are composed of transverse electric field and azimuthal magnetic field. This oscillation is called betatron oscillation. The oscillating electrons emit betatron radiation per a half period of the oscillation. The number of oscillations is dependent on the propagation length and the strength of the wakefields. The radiation has a broad spectrum with an energy band from a few eV to several keV and a beam divergence of tens of mrad. In this presentation, the self-injected electrons are traced using a relativistic electromagnetic particle-in-cell (EM-PIC) code, and the radiaitons emitted from the electrons are calculated from the particle motion. The characteristics of the radiations are compared with the results from a single electron simulation which was calculated with an assumption that the wakfields did not change for the propagation of the electron. [Preview Abstract] |
Thursday, November 5, 2009 10:54AM - 11:06AM |
TO4.00008: Laser Plasma Wiggler S. Kneip, S.P.D. Mangles, C.A.J. Palmer, S.R. Nagel, C. Bellei, J. Schreiber, Z. Najmudin, C. McGuffey, V. Chvykov, F. Dollar, C. Huntington, G. Kalintchenko, G. Maksimchuk, T. Matsuoka, A.G.R. Thomas, V. Yanovsky, K. Krushelnick, J. Martins, S.F. Martins, R. Fonseca, S.O. Silva, K. Ta Phuoc A high quality beam of X-rays is measured when electrons perform transverse oscillations in a Laser-Wakefield Accelerator. The radiation is spatially coherent, originates from a micron-sized source, has mrad divergence, 10 to 100 keV energy range and a peak brightness comparable to 3rd generation conventional light sources. Radiation post-processing of electron trajectories obtained from PIC modeling is in excellent agreement with the experimental results. Electron trajectories resemble the scenario of an electron in a wiggler-type insertion device. This is an important step on a route to realize a single stage table-top all optical x-ray source with unique characteristics and interests over the whole spectrum of scientific studies. [Preview Abstract] |
Thursday, November 5, 2009 11:06AM - 11:18AM |
TO4.00009: Algorithm for calculating coherent radiation from many particles Alec Thomas An efficient algorithm for calculating coherent radiation in the far-field is described. Direct integration of the Lienard-Wiechert potentials for extremely high photon energies and many particles is made computationally feasible by a mixed analytic and numerical method. Exact integrals of spectral intensity are made between discretely sampled trajectories by assuming the space-time four-vector is a quadratic function of proper time. The integral of the trajectory with respect to time, the modulus squared of which comprises the spectral intensity, can then be formed by piecewise summation of exact integrals between discrete points. Because of this, the calculation is not restricted by discrete sampling bandwidth theory, and time- steps much larger than the inverse of the maximum frequency can be taken. The technique is incorporated into a radiation code {\it Radampeltrac}. Calculations of non-linear Thomson back-scattering of a 150 MeV electron bunch from the {\sc Hercules} laser system show angularly resolved spectral intensity photon distributions extending to 10~MeV in a well collimated beam. An experimentally measurable difference in the photon spectral distribution with and without radiation damping is demonstrated. [Preview Abstract] |
Thursday, November 5, 2009 11:18AM - 11:30AM |
TO4.00010: Spectral Analysis of Forward Scattered Radiation in a Laser Wakefield Acceleration Experiment Michael Helle, Dmitri Kaganovich, Daniel Gordon, Bahman Hafizi, Antonio Ting We have characterized the forward scattered radiation generated from a LWFA experiment at the U.S. Naval Research Laboratory. High-order, large amplitude, anti-Stokes radiation was produced from the interaction of an intense laser pulse propagating through an $\sim$1\% critical density plasma. Evidence of relativistic cross-phase modulation and previously unreported conical emission of Stokes radiation has also been observed. The Stokes radiation can be the consequence of a third order nonlinear mixing of two fundamental photons with an anti-Stokes photon. This nonlinear electromagnetic four wave mixing process is usually not permissible owing to phase matching considerations. However, the matching condition can become satisfied when modification of the plasma dispersion relation due to plasma channel guiding is considered. Discussion of these novel experimental results in relation to the underlying nonlinear effects will be presented. [Preview Abstract] |
Thursday, November 5, 2009 11:30AM - 11:42AM |
TO4.00011: Formation of optical bullets in laser-driven plasma bubble accelerators P. Dong, S.A. Reed, S. Yi, S. Kalmykov, G. Shvets, N.H. Matlis, W.P. Leemans, C. McGuffey, S.S. Bulanov, V. Chvykov, G. Kalintchenko, K. Krushelnik, A. Maksimchuk, T. Matsuoka, A.G.R. Thomas, V. Yanovsky We show that luminal velocity electron density bubbles produced by relativistically intense ultrashort drive laser pulses propagating through near-atmospheric-density plasma re-shape co-propagating probe pulses into optical ``bullets" that we reconstruct using frequency-domain interferometric techniques and use to visualize the spatio-temporal profile of the plasma bubble. A study of bubble-compressed bullets together with bubble-accelerated electrons reveals three regimes: (I) bullets of sub-plasma-wavelength (sub-$\lambda _{p})$ size, trapped and compressed inside plasma bubbles, appear at 1 $<$ n$_{e} \quad <$ 1.5 $\times $ 10$^{19}$ cm$^{-3}$ without production of relativistic electrons; (II) enlongated bullets spanning $\sim $2 $\lambda _{p}$, signifying temporary merging of sequential bubbles, are observed frequently at n$_{e} \quad >$ 2 $\times $ 10$^{19}$ cm$^{-3}$ together with poly-energetic relativistic electrons; (III) mono-energetic electrons are observed only in conjunction with intense sub-$\lambda _{p}$ bullets signifying stable or contracted bubbles, generally at n$_{e} \quad >$ 2.5 $\times $ 10$^{19}$ cm$^{-3}$. The results help to relate bubble structure to the properties of laser-wakefield-accelerated electrons in the blowout regime. [Preview Abstract] |
Thursday, November 5, 2009 11:42AM - 11:54AM |
TO4.00012: Laser Wakefield Simulation Using a Speed-of-Light Frame Envelope Model Benjamin Cowan, David Bruhwiler, Peter Messmer, Kevin Paul, Estelle Cormier-Michel, Eric Esarey, Cameron Geddes Simulation of laser wakefield accelerator (LWFA) experiments is computationally highly 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 FDTD/PIC simulations enormously expensive. We present a model which substantially improves the performance of LWFA 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 this also allows larger timesteps. We show that this envelope model has much lower numerical dispersion error than FDTD, while maintaining second-order convergence. We demonstrate a complete 3D simulation of a meter-scale LWFA stage with over $10^5$ speedup over explicit FDTD. In addition, we show studies of kinetic interpolation errors and simulations of particle trapping. [Preview Abstract] |
Thursday, November 5, 2009 11:54AM - 12:06PM |
TO4.00013: Modeling 10 GeV laser-plasma accelrators and conventional accelerators using boosted computational frames J.-L. Vay, W.M. Fawley, M.A. Furman, C.G. Geddes, E. Cormier-Michel, D.P. Grote It can be computationally advantageous to perform computer simulations in a Lorentz boosted frame for a certain class of particle acceleration devices or problems such as: free electron laser, laser-plasma accelerator, particle beams interacting with electron clouds [1]. Complications arising from calculating in a Lorentz boosted frame and respective solutions have now been further analyzed, supporting more successful applications of the method to these problems. Most notably, full PIC 3D simulations of 10 GeV laser acceleration stages were enabled, with demonstrated convergence at a few percent level at various gammas, with speed-ups of 1,000 or more. Such simulations are important to the design of next generation accelerators. We will present and discuss the latest developments of the method illustrated with various examples of its application. \\[4pt] [1] J.-L. Vay, Phys. Rev. Lett. \textbf{98}, 130405 (2007) [Preview Abstract] |
Thursday, November 5, 2009 12:06PM - 12:18PM |
TO4.00014: Laser Wakefield Acceleration with Shaped Laser Modes Estelle Cormier-Michel, Eric Esarey, Cameron G.R. Geddes, Carl B. Schroeder, David L. Bruhwiler, Ben Cowan, Kevin Paul, Wim P. Leemans LBNL is currently pursuing a collider design based on meter-long 10 GeV laser-plasma accelerator stages, and Thomson gamma source designs at $\sim$1 GeV, that will operate in the quasi-linear regime. This regime allows symmetric acceleration of electrons and positrons and has the property that the transverse fields are proportional to the transverse gradient of the laser intensity profile. We show that higher order laser modes can tailor this gradient and hence the focusing forces in the plasma, allowing control over the radius and the emittance of the accelerated bunch. We present simulations, using the VORPAL framework, of the design of 1-10 GeV stages. In particular, we show that, by using shaped laser modes, it is possible to increase the matched electron beam radius and hence the total charge in the bunch while preserving the low bunch emittance required for applications. [Preview Abstract] |
Thursday, November 5, 2009 12:18PM - 12:30PM |
TO4.00015: Plasma Wakefield Accelerator Driven by a Train of Electron Bunches Patric Muggli, Brian Allen, Vitaly Yakimenko, Jangho Park, Karl Kusche, Marcus Babzien We study experimentally the physics of the interaction between a train of electron bunches and a plasma whose density can be varied. The train of electron bunches consists of equidistant ($\sim $300 microns) drive bunches followed by a witness bunch ($\sim $450 microns from the last drive bunch). Each bunch length is about half the drive bunch spacing ($\sim $150 microns). The bunch train is produced using a masking technique recently demonstrated (P. Muggli et al., Phys. Rev. Lett. 101, 054801, 2008). The plasma density is varied by changing the arrival time of the bunch train with respect to the capillary discharge. At low density ($<$1e16/cc) the wakefields are driven by the envelope of the bunch train. At resonance, when the plasma density is such that the plasma wavelength is equal to the drive bunches spacing, large energy loss and energy gain is observed. The resonance also disappears at higher densities, or when the bunch train is replaced by a continuous electron bunch with a length equal to that of the train. Detailed experimental results will be presented. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700