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 GO6: Laser Acceleration and Transport; Radiation and FELs |
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Chair: Carl Schroeder, Lawrence Berkeley National Laboratory Room: Hanover FG |
Tuesday, November 3, 2009 9:30AM - 9:42AM |
GO6.00001: Laser Proton acceleration from mass limited silicon foils K. Zeil, S. Kraft, T. Richter, J. Metzkes, M. Bussmann, U. Schramm, R. Sauerbrey, T.E. Cowan, J. Fuchs, S. Buffechoux We present recent studies on laser proton acceleration experiments using mass limited silicon targets. Small micro machined silicon foils with 2 $\mu $m thickness and 20x20 $\mu $m2 to 100x100$\mu $m2 size mounted on very tiny stalks were shot with the 100 TW LULI Laser (long pulse 150 fs) and with the new 150 TW DRACO Laser facility (short pulse 30 fs) of the Research Centre Dresden-Rossendorf. The experiments were carried out using high contrast levels. Proton spectra have been measured with magnetic spectrometers and radio chromic film stacks. [Preview Abstract] |
Tuesday, November 3, 2009 9:42AM - 9:54AM |
GO6.00002: First Laser-Accelerated Ion Observations From the Omega EP Laser at 1000 J in 10 ps K.A. Flippo, M.J. Schmitt, J.C. Cobble, D.C. Gautier, D. Offermann, T. Bartal, S. Chawla, F.N. Beg, P.M. Nilson, A. MacPhee, S. Le Pape, D. Hey, A. MacKinnon The efficient generation of ion beams using short intense laser pulses has many applications including active interrogation, providing a temporally-precise perturbation source for ICF capsule implosions, and providing a hot spot for ion fast ignition schemes. All applications benefit by improvements in the laser-to-ion conversion efficiency. For example, ion fast ignition fusion which promises order-of-magnitude reduction in laser driver energies, requires a conversion efficiency of order 10{\%} to avoid the short-pulse lasers from becoming impractically large and expensive. Presently, ion acceleration at the shortest pulse lengths (\textit{$\tau $}$_{pulse} \quad <$ 1 ps) has been limited. For integrated fast ignition experiments short-pulse laser energies in excess of 10's of kJ will be required necessitating longer pulse lengths on the order of \textit{$\tau $}$_{pulse} \quad \ge $ 10 ps. There is a lack of experimental data in this pulse length regime. For the first time the OMEGA EP laser has been focused onto small foils with 1000 J in 10 ps to produce proton beams up to nearly 50 MeV with high efficiencies. Results of ion energy and conversion efficiency as a function of target size, target thickness, and intensity will be presented. [Preview Abstract] |
Tuesday, November 3, 2009 9:54AM - 10:06AM |
GO6.00003: 65+ MeV Protons from Short-Pulse-Laser Micro-Cone-Target Interactions S.A. Gaillard, K.A. Flippo, D.C. Gautier, D.T. Offermann, J.B. Workman, F. Archuleta, R. Gonzales, T. Hurry, R.P. Johnson, S. Letzring, D.S. Montgomery, S.-M. Reid, T. Shimada, T. Lockard, Y. Sentoku, M.E. Lowenstern, J.E. Mucino, B.B. Gall, E. d'Humieres, M. Geissel, M. Schollmeier, M. Bussman, T.E. Cowan, T. Kluge, J.M. Rassuchine Two sets of laser-ion acceleration experiments at the LANL 200 TW Trident laser at $\sim $10$^{20}$ W/cm$^{2}$ (1 $\mu $m, 80 J, $\sim $600 fs) with high ($>$10$^{10})$ and low ($>$10$^{8})$ contrast are compared for regular size flat foils ($\sim $2x2 mm), reduced mass targets (RMT, 200-500 $\mu $m diameter) and new micro-cone targets in various geometries to elucidate the production of hot electrons and ions in these targets. Results from the latest experiment at high contrast show proton energies in excess of 65 MeV for flat-top cones, compared to $\sim $55 MeV for RMTs and $\sim $45 MeV for flat foils. Data from a Cu K$\alpha $ 2D imaging crystal, an electron spectrometer and an RCF stack are presented and compared, showing the importance of not just generating hot electrons, but efficiently propagating these hot electrons to the accelerating ``tip'', where they can then be converted to ion energy, as well as the importance of the micro-cones' supporting foil size. [Preview Abstract] |
Tuesday, November 3, 2009 10:06AM - 10:18AM |
GO6.00004: Experimental study of channel formation by 30 ps intense laser pulses in near-critical, mm-scale plasmas Gianluca Sarri, Peter Norreys, Kate Lancaster, Marco Borghesi, T. Tanimoto, E. Clark, S. Hassan, N. Kageiwa, Z. Najmudin, R. Scott, A. Rehman, K. Tanaka, Raoul Trines We will present results, obtained at the VULCAN laser (RAL, UK), of an experiment investigating channel creation in deuterium gasjets at different plasma densities (from 10$^{18} $cm$^{-3}$ up to 10$^{20}$cm$^{-3}$) using laser pulses with parameters of Fast Ignitor relevance (T$\approx$30ps, I$\approx$10$^{18}$ W/cm$^2$) and a range of diagnostics including optical and proton probing. For densities up to few times 10$^{18}$cm$^{-3}$, smooth and several mm long , strongly evacuated channels with sharp walls are created. For higher densities, the interaction appears to be more chaotic, with possible indication of unstable explosion of the channel walls. Soliton-like features are also observed in the channel vicinities. [Preview Abstract] |
Tuesday, November 3, 2009 10:18AM - 10:30AM |
GO6.00005: Tight focusing of ultra-intense laser pulses by innovative plasma optics toward extreme intensity M. Nakatsutsumi, A. Kon, J. Fuchs, S. Buffechoux, P. Audebert, R. Kodama With rapid advances in laser technology, laser beams are now available that can be routinely focused to intensities approaching $>$10$^{21}$ Wcm$^{-2}$. Enhancement of laser intensity is achieved by truncating the pulse width, increasing the laser-energy, or reducing the focal spot size. Although the reduction of the spot size is the simplest among those, by using low f-number optics, this method is not frequently employed because of the difficulty in avoiding damage from target debris or complexity of alignment procedure. We developed for the first time very compact ($<$1 cm$^{3}$) extremely low f-number (0.4) plasma-based, confocal ellipsoid focusing systems. Direct measurement of the laser focal spot using low-energy laser indicates 1/5 reduction of spot size compared to standard focusing (using a f/3 optics). Around tenfold enhancement of laser intensity by reduction of the spot size for high power shots is clearly evidenced by remarkable enhancement of proton energy. The experiment was performed at LULI 100TW laser facility. [Preview Abstract] |
Tuesday, November 3, 2009 10:30AM - 10:42AM |
GO6.00006: Charged particle dynamics and nano-target evolution in relativistic tightly focused electromagnetic fields Konstantin Popov, Valery Bychenkov, Wojciech Rozmus, Richard Sydora The electromagnetic field structure of a tightly focused laser pulse is calculated using Stratton-Chu integrals over the surface of a focusing mirror. The details of acceleration mechanisms and characteristic scalings of maximum attainable particle energy vs. maximum laser power and focusing optics were studied. The applicability of paraxial Gaussian beams is discussed. The 3D particle-in-cell (PIC) simulations of interaction between a tightly focused laser and nano-targets such as clusters and ultra-thin foils were performed with electromagnetic code SCPIC. In addition to the dynamical properties found in the test particle simulations, a new mechanism of Coulomb field assisted attosecond electron bunch formation has been identified. This basic mechanism includes the interplay between the laser and electrostatic fields of the partially evacuated target. Each bunch contains mono-energetic electrons. The length, density and average energy of the bunch are given in terms of simple analytical expressions. Electron acceleration and bunch formation have been also studied under more realistic conditions of the targets having a pre-plasma. [Preview Abstract] |
Tuesday, November 3, 2009 10:42AM - 10:54AM |
GO6.00007: THz Generation by Two Superposed Short Laser Pulses Anil Kumar Malik, Hitender Kumar Malik THz radiation generation is a subject of current interest due to its potential applications in various fields. The use of collective properties of laser-produced plasma underlies a number of methods of THz generation, particularly based on the phenomenon of nonlinear ponderomotive force induced excitation of plasma wake oscillations. A theoretical and simulation study has been done for THz generation based on tunnel - ionization of gas jet when two superposed short pulse lasers (circularly polarized and linearly polarized with same frequency while different amplitudes and phases) are focused on to it. In the proposed scheme a transverse transient current is caused by the presence of residual momentum after passing of the laser pulse. The effect of radial variation of electron density in the plasma channel on the frequency of plasma cylinder oscillation and hence on frequency of emitted THz radiations is examined. With optimum initial phase of the laser envelope and width of the channel, the mechanism seems to be much more efficient than some of other nonlinear phenomenon base mechanisms. [Preview Abstract] |
Tuesday, November 3, 2009 10:54AM - 11:06AM |
GO6.00008: Relativistic Spherical Wake Wave in Plasma. Relativistic focusing spherical mirror and Schwinger pair production Stepan Bulanov, Anatoly Maksimchuk, Alexei Zhidkov We report on the analytic and computer simulation study of a relativistic spherical wake wave. Such a wave in the breaking regime, traveling towards the center is able to reflect and focus the incoming radiation and up-shifting its frequency. The reflected and focused electromagnetic pulse can have such high intensity, that it is able to create $e^+e^-$ pairs via Schwinger process. [Preview Abstract] |
Tuesday, November 3, 2009 11:06AM - 11:18AM |
GO6.00009: Light scattering by a dense ionization plasma wave with a tunable velocity Alexei Zhidkov, Takashi Fujii, Timur Esirkepov, James Koga, Koshichi Nemoto, Sergei Bulanov An optically-dense ionization wave (\textit{IW}) produced by two
femtosecond laser pulses focused cylindrically and crossing each
other is shown to be an efficient coherent $x$-ray converter. The
resulting velocity of a quasi-plane \textit{IW} in the vicinity
of pulse intersection increases with the angle between the pulses
from the group velocity of ionizing pulses to infinity allowing an
easy tuning the wavelength of $x$-rays. We study the conversion
of a coherent light to x-rays by means of particle-in-cell
simulation and by solution of continuous equation with the
correct current. The x-ray spectra of a converted, lower
frequency coherent light change from the monochromatic to a high
order harmonic-like with the duration of ionizing pulses and the
intensity of scattered pulses; the spectrum are not symmetrical
at $V |
Tuesday, November 3, 2009 11:18AM - 11:30AM |
GO6.00010: Coherent radiation from the interaction of high-power femtosecond laser with a thin film target and the generation of attosecond pulses Sang-Young Chung, Kitae Lee, Dong Eon Kim, Seok Won Hwang, Hae June Lee The simulation studies about the generation of attosecond X-ray pulses have been reported from the relativistic nonlinear Thomson scattering (RNTS) of a single electron [Phys. Plasmas 12, 043107 (2005)]. However, even if one electron generates an ultrashort pulse, the radiation is summation from many electrons in a real experiment. The coherency among the RNTS radiation from each electron needs to be considered to confirm the generation of ultrashort pulse radiations. In this presentation, the coherent RNTS radiation from a thin film target is proposed and verified using a particle-in-cell simulation. The radiation from RNTS is squeezed in a narrow angular region and the specific angle is varied by the laser intensity. The coherence is controlled from the angular property of the radiation and attosecond pulses are generated. [Preview Abstract] |
Tuesday, November 3, 2009 11:30AM - 11:42AM |
GO6.00011: Underwater Laser Plasma Acoustic Source Directivity and Frequency Control Demonstration T.G. Jones, M. Hornstein, A. Ting, M. Nicholas A remote underwater laser acoustic source is under development at NRL. Sound is generated by intense laser pulses propagating through air and water, followed by underwater optical compression and laser-induced breakdown (LIB). Such an acoustic source would be useful for communications, navigation, and sonar imaging. Recent experiments demonstrated control of the shape of the LIB plasma volume, and thereby control of the acoustic frequency spectrum and sound pressure level as a function of acoustic propagation direction. Femtosecond and nanosecond lasers were used for lens-focused acoustic generation near the water surface. The LIB volume shape was controlled by varying laser pulse length, energy, optical bandwidth, and focusing angle. Aspherical LIB volumes produced strongly anisotropic acoustic sources. Initial results of acoustic propagation studies in a 30,000 gallon bubbly salt water tank suggest both ultrasonic and bubble-induced attenuation. Recent results will be discussed. [Preview Abstract] |
Tuesday, November 3, 2009 11:42AM - 11:54AM |
GO6.00012: Observation of Very High-order Electron-radiation Coupling in a 7$^{th}$ Harmonic IFEL Experiment Sergei Tochitsky, Oliver Williams, Pietro Musumeci, Chieh Sung, Daniel Haberberger, Alan Cook, James Rosenzweig, Chan Joshi FEL/IFELs based on the resonant interaction between laser and electron beams in an undulator would benefit from using efficient high-order resonances. The high-order harmonic FEL/IFEL interactions were considered theoretically as a technique for reduction of the beam energy without corresponding decrease in the undulator period and the magnetic field strength in a single-pass X-ray FEL. We demonstrate microbunching of the 12.3 MeV electrons in a 7$^{th}$ order IFEL interaction, where the seed radiation frequency is seven times higher then the undulator's fundamental frequency. Strong longitudinal modulation of the beam is inferred from the observation of the first, second and third harmonics of the seed radiation in a Coherent Transition Radiation spectrum. The highest CTR frequency is the 21$^{st}$ harmonic of the fundamental interaction. The level of seed power is comparable to that required for microbunching at the fundamental frequency in this undulator. This work was supported by DOE grant DE-FG03-92ER40727. [Preview Abstract] |
Tuesday, November 3, 2009 11:54AM - 12:06PM |
GO6.00013: High Transformer ratio PWFA for Applications on XFELs Wei Lu, Weiming An, Chengkun Huang, Chan Joshi, Warren B. Mori, Mark Hogan, T.O. Raubenheimer, A. Seryi, Patric Muggli , Tom Katsouleas Fourth generation of light sources (e.g.,LCLS and the XFEL) require high energy electron drivers (16-20GeV) of very high quality. We are exploring the possibility of using a high transformer ratio PWFA to meet these challenging requirements. This may have the potential to reduce the size of the electron drivers by a factor of 5 or more, therefore making these light source much smaller and more affordable. In our design, a high charge (5-10nC) low energy driver (1-3GeV) with an elongated current profile is used to drive a plasma wake in the blowout regime with a high transformer ratio (5 or more). A second ultra-short beam that has high quality and low charge beam (1nC) can be loaded into the wake at a proper phase and be accelerated to high energy (5-15GeV) in very short distances (10s of cms). The parameters can be optimized, such that high quality (0.1{\%} energy spread and 1mm mrad normalized emittance) and high efficiency (60-80{\%}) can be simultaneously achieved. The major obstacle for achieving the above goals is the electron hosing instabilities in the blowout regime. In this poster, we will use both theoretical analysis and PIC simulations to study this concept. [Preview Abstract] |
Tuesday, November 3, 2009 12:06PM - 12:18PM |
GO6.00014: The Generation of Transient Transparent Aluminum with Intense Femtosecond XUV Light Justin Wark Fourth generation light sources have spectral brightnesses ten orders of magnitude brighter than any synchrotron, and when their output is focussed down to small spots, they can create solid density, ``crystalline'' plasmas on femtosecond timescales, long before the atoms have had time to move. We report specifically on the first experiments performed using the FLASH XUV laser in Hamburg. This laser can produce 15 fsec pulses of XUV radiation containing tens of $\mu$J per pulse. Using a multi-layer-coated off-axis parabola, we have focused 13.5nm radiation to spots of order a few microns in diameter, corresponding to peak intensities in excess of 10$^{16}$Wcm$^{-2}$ - a region of intensity that had, until recently, been the domain of optical high power lasers. We discuss here some of the interesting absorption physics that takes place at this new frontier, where the intensity is so great that we can eject L-shell electrons from every atom in an aluminum target placed in the focal region of the laser,[1] and how the observed saturable absorption may impact on the creation and diagnosis of warm dense matter. \\[4pt] [1] Bob Nagler et al, Nature Physics, to be published [Preview Abstract] |
Tuesday, November 3, 2009 12:18PM - 12:30PM |
GO6.00015: Electronic Structure of a Photo-Generated Solid-Density Aluminum Plasma Sam Vinko Using high intensity radiation from the FLASH free electron XUV laser, we have created highly excited exotic states of matter in solid-density aluminum samples on time scales short compared with ion motion. The XUV intensity is sufficiently high to eject an inner-shell electron from every atom in the focal region. As the photo-excited electrons in this plasma recombine, the associated fluorescence signal provides information on the shape of the electronic density of states in the valence band, as well as the electron temperature. We demonstrate that the combination of normal and photo-ionized Al ion-cores alter the density of states in a very similar manner to that which would be expected in a binary alloy. Detailed calculations of the electronic structure, based on density functional theory, are in good agreement with the observed emission spectra. [Preview Abstract] |
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