Bulletin of the American Physical Society
50th Annual Meeting of the Division of Plasma Physics
Volume 53, Number 14
Monday–Friday, November 17–21, 2008; Dallas, Texas
Session JO4: Laser-Plasma Acceleration |
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Chair: Brad Shadwick, University of Nebraska Room: Reunion B |
Tuesday, November 18, 2008 2:00PM - 2:12PM |
JO4.00001: Frequency domain tomography of evolving laser-plasma accelerator structures Peng Dong, Stephen Reed, Serguei Kalmykov, Gennady Shvets, Mike Downer We recently reported detailed snapshots of quasi-static laser wakefield accelerating structures captured by Frequency Domain Holography (FDH) [1]. Here we demonstrate a generalization of FDH capable of recovering evolving laser-plasma structures. In its simplest form, analogous to a streak camera, we supplement the conventional collinear FDH probe-reference pulse pair with a second pair that propagates at angle A with respect to the pump. Simulations show that an evolving plasma bubble behind the drive pulse leaves an imprinted phase steak on the probe tilted at angle A/2 with respect to the probe phase front. Its recovered phase tracks bubble evolution. We will present preliminary experimental results using a 200TW pump. A comprehensive generalization, analogous to computer-aided tomography, uses probe-reference pairs propagating through the plasma at multiple angles. We will present simulations showing how complexity of the structure and its evolution determines the number of probe angles needed for accurate reconstruction. [1]N. H. Matlis et al., Nat. Phys. 2, 749(2006) [Preview Abstract] |
Tuesday, November 18, 2008 2:12PM - 2:24PM |
JO4.00002: Direct measurements of pulse-front steepening and erosion in a laser wakefield accelerator at laser powers up to 150 TW S.P.D. Mangles, J. Schreiber, C. Bellei, S. Kneip, S.R. Nagel, C.A.J. Palmer, Z. Najmdudin, T. Ibbotson, N. Bourgeois, S. Hooker, M. Streeter, D.R. Symes, P.P. Rajeev We report on the direct observation of pulse front erosion and compression due to the propagation of intense laser pulses (55 - 70 fs, 1 - 10 J) in centimeter scale plasmas at densities relevant for laser wakefield acceleration experiments. Pulse front erosion affects the group velocity of the pulse and ultimately the energy gain in the wakefield accelerator. The measurements were performed on the Astra Gemini laser at RAL using a frequency resolved optical gating technique. Particle-in-cell simulations are used to support the results. At high pulse energies (up to 10 J) the generation of a high-amplitude plasma wave leads to significant pulse compression and pulse front steepening, resulting in highly asymmetric laser pulses of sub-20 fs duration. Aspects of the pulse shape indicate that cavitation has occurred in the first wave period, i.e. that the bubble or blow out regime has been reached. [Preview Abstract] |
Tuesday, November 18, 2008 2:24PM - 2:36PM |
JO4.00003: Study of Pre-Pulse Effect on Generation of Quasi-Monoenergetic Electrons in Gas jets J.A. Chakera, Y. Tsui, N. Vafaei-Najafabadi, A. Ali, R. Fedosejevs Generation of quasi monoenergetic electrons in wakefield produced by high intensity fs laser pulses in gas jet has been a growing area of research. Reproducibility of the electron energy and beam stability is still an issue. Efforts are under way to achieve stable beams from such accelerators to be useful for practical application. In order to achieve a stable beam, it is important to study the plasma density profile and its evolution in time during the interaction. In most cases the shot to shot fluctuation may arises from the presence of pre-pulse, which varies from shot to shot, leading to variations in the gas jet density profile. Experiments were performed using the 10 TW laser beamline at ALLS facility. The 200 mJ, 32 fs laser pulses were focused into a 2mm diameter gas jet to a focal spot of 11 $\mu $m. The study has been carried out to correlate the high-energy electron generation and x-ray bremsstrahlung with the laser pre-pulse level. Electron energies in the range of 10-30 MeV for N$_{2 }$and 10-40 MeV for He have been observed. The characterization of plasma density was carried out using interferometric measurements. Measurements on side scattered and forward Raman Scattered light have also been carried out and the results obtained will be presented. [Preview Abstract] |
Tuesday, November 18, 2008 2:36PM - 2:48PM |
JO4.00004: Observation of large-angle quasi-monoenergetic electrons from a laser wakefield Dmitri Kaganovich, Daniel Gordon, Antonio Ting A relativistically intense laser pulse is focused into a gas jet and quasi-monoenergetic electrons emitted at a 40 degree angle with respect to the laser axis are observed. The average energy of the electrons was between 1 and 2 MeV and the total accelerated charge was about 1 nC emitted into a 10 degree cone angle. The electron characteristics were sensitive to plasma density. The results are compared with three dimensional particle-in-cell simulations. This electron acceleration mechanism might be useful as a source of injection electrons in a laser wakefield accelerator. [Preview Abstract] |
Tuesday, November 18, 2008 2:48PM - 3:00PM |
JO4.00005: Near GeV Laser Electron Beam Accelerator and Synchrotron Source S. Kneip, S.R. Nagel, C. Bellei, C. Palmer, J. Schreiber, S.P.D. Mangles, Z. Najmudin, T. Ibbotson, N. Bourgeois, S. Hooker, K. Ta Phuoc Electrons are accelerated to near GeV quasi-monoenergetic beams with a self-guided laser plasma wakefield accelerator. Experiments were carried out on the 250 TW Astra Gemini Laser at the Rutherford Appleton Laboratory. Up to 12 J of 55 fs, 800 nm laser light was focused with an $f/20$ parabolic mirror onto the front edge of circular gas plumes with 3 to 15 mm length. Interferometric probing reveals self generated plasma channels extending to 15 mm in length. Exit mode imaging of the laser light from the end of the gas jet indicates self-guiding over the full interaction length. Electron beams with $<3$ mrad divergence and $<5$ mrad RMS pointing stability are observed for a range of plasma densities and interaction lengths. At constant plasma density, the maximum achievable electron energy is found to scale linearly with the interaction length, consistent with accelerating fields of 0.8 GeV/cm. A bright source of 10 keV synchrotron radiation from electrons undergoing betatron oscillations in the plasma channel is observed in laser direction. These experiments illustrate that near GeV electron beams can now be produced without the need for an external guiding structure. [Preview Abstract] |
Tuesday, November 18, 2008 3:00PM - 3:12PM |
JO4.00006: Injection of electrons into a laser wakefield accelerator driven in a capillary discharge waveguide using an embedded gas jet Anthony Gonsalves, Dmitriy Panasenko, Kei Nakamura, Chen Lin, Eamonn Monaghan, Csaba Toth, Cameron Geddes, Carl Schroeder, Eric Esarey, Wim Leemans A key issue in laser wakefield accelerators (LWFAs) is injection of electrons into the accelerating region of the wake. Typically electron beams have been self-injected into the wake, requiring a higher plasma density than that for an optimized accelerating structure. This in turn limits the electron beam energy and quality that can be achieved. In this talk it is shown that this coupling of injection and acceleration can be addressed for LWFA in a capillary discharge waveguide with the use of a gas jet embedded into the capillary. Previous experiments without a gas jet have shown self-trapping and acceleration of electrons with energy up to 1 GeV [Leemans et al., Nature Phys. Vol. 2, 696, 2006]. The addition of a gas jet in this work has shown that injection can be turned on or off by a local density perturbation. Hence high-energy electrons can be produced for densities in the capillary lower than otherwise possible without the jet. Results will also be presented on the improvement of electron beam properties, as well as laser spectral modulation and pump depletion. [Preview Abstract] |
Tuesday, November 18, 2008 3:12PM - 3:24PM |
JO4.00007: Staging laser plasma accelerator using plasma mirrors Dmitriy Panasenko, Anthony J. Gonsalves, Kei Nakamura, Anthony J. Shu, Chen Lin, Nicholas Matlis, Guillaume Plateau, Cameron G.R. Geddes, Csaba Toth, Eric Esarey, Carl Schroeder, Wim P. Leemans One of the main challenges in staging plasma based Laser Wakefield Accelerators (LWFA) lies in incoupling laser energy into subsequent accelerating stages while preserving high acceleration gradient and without resorting to complicated e-beam transport. In this presentation we will describe a novel approach to laser incoupling based on reflection off supercritical plasma surface commonly referred to as plasma mirror. Using a plasma mirror as a last reflection surface before incoupling the laser into the accelerating stage will allow avoiding damage of conventional optics by an intense laser pulse and result in drastic reduction of distance between the accelerating stages. Here initial experimental results are presented on realizing this important concept for staging an LWFA and main challenges of this method are discussed such as practical realization of renewable surface for plasma mirror production, reflectivity, matching the reflected laser into plasma channel and effects on the emittance of the electron beam. [Preview Abstract] |
Tuesday, November 18, 2008 3:24PM - 3:36PM |
JO4.00008: The Interaction of an Ultra-short Laser Pulse and Relativistic Electron Beam in a Corrugated Plasma Channel T.M. Antonsen, J.P. Palastro, L. Divol Copropagation of a laser pulse and a relativistic electron beam in a corrugated plasma channel has been proposed for the direct laser acceleration of electrons [Palastro \textit{et al.} Phys. Rev. E (2008)]. The corrugated plasma channel allows for the guiding of laser pulses composed of subluminal spatial harmonics. Phase matching between the electron beam and the spatial harmonics results in acceleration, but for high beam densities the pulse energy can be rapidly depleted. This depletion can result in interaction times shorter than the waveguide length limited time or pulse length dephasing time. We present an analytic model and self-consistent simulations of the electron beam-laser pulse interaction. A linear dispersion relation is derived. The effect of the electron beam on the pulse after the occurrence of axial bunching is examined. Injection of axially modulated electron beams is also explored. In particular, we find that a properly phased electron beam can transfer energy to the laser pulse as an inverse process to acceleration. [Preview Abstract] |
Tuesday, November 18, 2008 3:36PM - 3:48PM |
JO4.00009: Proton acceleration from near critical density and underdense plasmas using ultra-intense laser pulses Stepan Bulanov, Vladimir Chvykov, Galina Kalinchenko, Takeshi Matsuoka, Pascal Rousseau, Victor Yanovsky, Karl Krushelnick, Dale Litzenberg, Anatoly Maksimchuk The propagation of ultra-intense laser pulses through plasma is connected with the generation of strong electric and magnetic fields and with electron and ion acceleration in the forward direction. Ion acceleration is more efficient in the region where the laser pulse exits the plasma. Since at the plasma-vacuum interface the magnetic field upon exiting the propagation channel redistributes plasma electrons thus forming a quasi-static charge separation electric field which accelerates and collimates ions. We present the results of 2D PIC simulation of the interaction of an intense laser pulse with underdense and near critical density plasmas. We show that the maximum ion energy can be controlled by matching the plasma density and its thickness to the laser pulse power and peak intensity. We show strong influence of the density gradients at the plasma-vacuum interface on ion acceleration. We performed simulations under the anticipated experimental conditions for the Hercules laser with pulse power of 300 TW, duration of 30 fs (FWHM), focused to a spot size of 0.8 $\mu $m FWHM onto a 60 $\mu $m, 2.25 n$_{cr}$ dense plasma slab which predict the maximum proton energy of 500 MeV. [Preview Abstract] |
Tuesday, November 18, 2008 3:48PM - 4:00PM |
JO4.00010: Towards GeV laser-driven ion acceleration B.M. Hegelich, L. Yin, B.J. Albright, K.A. Flippo, D.C. Gautier, R.P. Johnson, S. Letzring, R.C. Shah, T. Shimada, J.C. Fernandez, A. Henig, D. Kiefer, V. Liechtenstein, J. Schreiber, D. Habs, J. Meyer-ter-Vehn, S. Rykovanov, H.C. Wu Applications like ion-driven fast ignition (IFI) with heavy ions or laser-based hadron therapy require efficient laser-driven ion acceleration to $\sim $ 0.1 -- 1 GeV. The Break-Out Afterburner (BOA) [1] regime and the Phase-Stable Acceleration (PSA) [2] regime, also reported as Radiation Pressure Acceleration (RPA) [3], promise quasi-monoenergetic beams at such energies, with $\sim $ 10{\%} efficiency,. This talk summarizes our joint exploratory research program in this new and exciting area, emphasizing the realization of these mechanisms with today's lasers. The laser requirements are discussed, especially pulse contrast. The first experimental results are reported. [1] L. Yin et al., Laser {\&} Part. Beams \textbf{24}, 1-8 (2006) [2] X. Zhang et al., Phys. Plasmas \textbf{14}, 123108 (2007) [3] A. P. L. Robinson et al., New J. Phys. \textbf{10}, 013021 (2008) [Preview Abstract] |
Tuesday, November 18, 2008 4:00PM - 4:12PM |
JO4.00011: Multi-stage laser ion acceleration Jens Polz, Sebastian M. Pfotenhauer, Oliver Jaeckel, Hans-Peter Schlenvoigt, Jens Heymann, Malte C. Kaluza, Sven Steinke, Alex P.L. Robinson This abstract is not available. [Preview Abstract] |
Tuesday, November 18, 2008 4:12PM - 4:24PM |
JO4.00012: Quantum beam generations via the laser-cluster interactions Yuji Fukuda, Anatoly Faenov, Tania Pikuz, Motonobu Tampo, Akifumi Yogo, Masaki Kando, Yukio Hayashi, Takeshi Kameshima, Takayuki Homma, Alexander Pirozhkov, Yoshiaki Kato, Toshiki Tajima, Hiroyuki Daido, Sergei Bulanov The novel soft X-ray light source using the supersonic expansion of the mixed gas of He and CO$_{2}$, when irradiated by a femtosecond Ti:sapphire laser pulse, is observed to enhance the radiation of soft X-rays from the CO$_{2}$ clusters. Using this soft X-ray emissions, nanostructure images of 100-nm thick Mo foils in a wide field of view (mm$^{2}$ scale) with high spatial resolution (800 nm) are obtained with high dynamic range LiF crystal detectors. We also demonstrate the acceleration of charged particles via the laser-cluster interactions. [Preview Abstract] |
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