Bulletin of the American Physical Society
49th Annual Meeting of the Division of Plasma Physics
Volume 52, Number 11
Monday–Friday, November 12–16, 2007; Orlando, Florida
Session JO6: Short Pulse Laser-Plasma Interactions II |
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Chair: Stefano Atzeni, University of Roma Room: Rosen Centre Hotel Salon 5/6 |
Tuesday, November 13, 2007 2:00PM - 2:12PM |
JO6.00001: Stochastic Heating in High Intensity Laser-Plasma Interaction. Application to the Wake Field Acceleration Process Alain Bourdier, Xavier Davoine, Mathieu Drouin, Laurent Gremillet, Erik Lefebvre Recently, PIC simulations results published by Tajima et al. and Sheng et al. have shown that chaos can play an important role in the efficient electron heating observed in laser-plasma interaction at very high intensities. These results led us to investigate the conditions under which significant stochastic heating is likely to take place. First, we shall consider the dynamics of a single charged particle in the field of a high intensity wave propagating in an unmagnetized vacuum or plasma. In a second part, the effect of a constant homogeneous magnetic field will be discussed. Third, in the case of a plasma interacting with several electromagnetic waves, the use of Chirikov's criterion to predict the conditions favoring stochastic heating will be presented. Finally, it will be shown that when considering a low density plasma interacting with a high intensity wave perturbed by a low intensity counterpropagating wave, stochastic heating can provide electrons with the right momentum for trapping in the wake field and efficient acceleration. [Preview Abstract] |
Tuesday, November 13, 2007 2:12PM - 2:24PM |
JO6.00002: Enhanced Isochoric Heating in High Contrast Laser-Nano-Cone Interactions T.E. Cowan, J. Rassuchine, E. d'Humieres, Y. Sentoku, S. Baton, P. Gillou, M. Koenig, J. Fuchs, P. Audebert, R. Kodama, M. Nakatsutsumi, T. Norimatsu, D. Batani, A. Morace, R. Bedaello, L. Gremillet, C. Rousseaux, F. Dorchies, C. Fourment, J.J. Santos, S. Hansen We discuss the interaction of very high-contrast high-intensity laser pulses with sharp-tipped, nanofabricated Cu cone targets (see [1]), using frequency doubled light at the LULI 100 TW laser ($\lambda $=0.53 um, I=4x10$^{18}$ W/cm$^{2})$. Previous work at 1$\omega $ showed that pre-formed plasma, due to ASE, degraded the laser-cone coupling. At 2$\omega $, high-resolution spectroscopy of Cu K$_{\alpha }$ emission shows high charge states, implying peak temperatures of up to 400 eV, comparable to the smallest reduced mass targets (50 $\mu $m dia x 20 $\mu $m thick). This implies a new confinement mechanism which, from 2D collisional PIC simulations, is due to self-generated resistive magnetic fields (up to 10 MG) which confine the hot electrons to the tip region of the cone. Supported by Access to Research Infrastructures in the EU Sixth Framework Programme (contract RII3-CT-2003-506350, Laserlab Europe), and UNR DOE/NNSA grant DE-FC52-01NV14050. [1] Y. Sentoku \textit{et al.}, Phys. Plasmas, \textbf{11} 3083 (2004). [Preview Abstract] |
Tuesday, November 13, 2007 2:24PM - 2:36PM |
JO6.00003: Isochoric Heating of Reduced Mass Targets by Ultra-Intense Lasers S.C. Wilks, A.J. Kemp, D.S. Hey, P.K. Patel, S. LePape, M.M. Marinak, P. Neumayer, S. Glenzer, G. Gregori, S.N. Chen, F. Beg, W.L. Kruer Recent results using a novel target design that allows material high temperature ($\sim $ 1 keV) solid density plasmas to be created using ultra-intense laser pulses will be presented. Layered targets composed of titanium and tamped with aluminum were irradiated with 1$<$ E $<$ 200 Joules, 1 and 10 picosecond laser pulses. Significant increases in temperature over standard foil targets were observed. Using refined energy conservation arguments and coupling of PIC simulation results into a rad-hydro code, theoretical predictions of achievable temperatures are compared against temperatures inferred from experimental data. Predictions for plastic, titanium, and copper targets irradiated by a wide range of laser parameters will also be presented. [Preview Abstract] |
Tuesday, November 13, 2007 2:36PM - 2:48PM |
JO6.00004: Laser Heating of Solid Matter by Light Pressure-Driven Shocks at Ultra-Relativistic Intensities K.U. Akli, R.B. Stephens, A.J. MacKinnon, P.K. Patel, M.H. Key, S.B. Hansen, A.J. Kemp, R.R. Freeman, D. Clark, K. Highberger, N. Patel, L. Van Woerkom, R. Weber, F. Beg, T. Ma, D. Hey, K. Lancaster, C. Stoeckel, M. Storm, W. Theobald Heating by irradiation of a solid surface in vacuum with $5\times 10^{20}$ W$\mbox{cm}^{\mbox{-2}}$, 0.8 ps, 1.05 micron wavelength laser light is studied by x-ray spectroscopy of the K-shell emission from thin layers of Ni, Mo and V. A surface layer is heated to $\sim $5 keV with an axial temperature gradient of 0.6~$\mu \mbox{m}$ scale length. Images of Ni Ly$\alpha $ show the hot region has a $\sim $25~$\mu \mbox{m}$ diameter. Collisional particle-in-cell simulations based on density profiles from hydro-models suggest that light pressure compresses the preformed plasma and drives a shock into the solid. [Preview Abstract] |
Tuesday, November 13, 2007 2:48PM - 3:00PM |
JO6.00005: ABSTRACT HAS BEEN MOVED TO SESSION GP8 |
Tuesday, November 13, 2007 3:00PM - 3:12PM |
JO6.00006: ABSTRACT WITHDRAWN |
Tuesday, November 13, 2007 3:12PM - 3:24PM |
JO6.00007: Heating of buried layer targets by 1$\omega $ and 2$\omega $ pulses using the HELEN CPA laser Lee Thornton, David Hoarty Targets of plastic with a buried layer of aluminum at different depths were heated using the HELEN CPA laser which irradiated one surface. The emission spectra from the Al were used to infer the conditions in the target by comparing the measured spectra against those generated by the FLY code (whose input was the temperature and density history calculated by a radiation-hydrodynamics code iterated to achieve the best match to the experimental data). Measurements were taken at both a laser wavelength of 1.06 $\mu$m and after conversion to 0.53 $\mu$m. The laser irradiance was varied between 2 x 10$^{17}$ - 10$^{19}$ W/cm$^{2}$ by altering the laser pulselength, energy and wavelength. The data show the plastic target was heated above 200eV to a depth of about 4$\mu $m with 1.06 $\mu$m P-polarised light. The FLY comparisons indicate the buried layers heated with 0.53 $\mu$m light remained near solid density for the duration of the X-ray emission pulse and achieved a peak temperature of 500$\pm$50eV. In the case where the target was heated with 1.06 $\mu $m radiation, the density was an order of magnitude lower and the peak temperature achieved was also lower at 320$\pm $50eV. The depth to which the target was heated was similar at the two wavelengths for 0.5ps pulses. In further measurements using 0.53 $\mu$m light at similar energies (but using pulses with a FWHM of 2 ps), heating to greater than 200eV was observed to a depth of 8 $\mu$m. [Preview Abstract] |
Tuesday, November 13, 2007 3:24PM - 3:36PM |
JO6.00008: Experiments on Self-Guiding Mechanisms of High Power Laser Pulses in a Plasma Joseph Ralph, Arthur Pak, Kenneth Marsh, Christopher Clayton, Fang Fang, Chandrashekhar Joshi Recent 3D theory and PIC simulations in the blowout regime, wherein the pondermotive force of laser with a pulse length on the order of a plasma wavelength expels all electrons, has predicted a range of parameter space where stable laser propagation can occur [1]. In this theory, the density depression caused by electron blow out is the dominant mechism responsible for self-guiding. In this paper we examine experimentally and with PIC simulations laser beam guiding of a multi terwatt TiSapphire laser in a supersonic Helium gas jet. Gas jet density was varied from 2*E18 to to 2*E19 and the length of the plasma was varied from 2 to 5 mm using several gas jets with different diameters. Pondermotive and relativistic effects are considerd by varying laser and plasma parameters. Diagnostics include interferometric and Schlieren techniques. Images of the guided mode are taken at the exit of the gas jet. In addition, the forward images were sent to an imaging spectragraph to observe photon deceleration and deceleration [2]. \newline [1] W. Lu, C. Huang, M. Zhou, and M. Tzoufras, F. S. Tsung, W. B. Mori, and T. Katsouleas, Phys. Plasmas \textbf{13}, 056709 (2006) \newline [2] A. E. Pak, J. E. Ralph, K. A. Marsh , C. E. Clayton, F. Fang and C. Joshi, \textit{These Procedings} [Preview Abstract] |
Tuesday, November 13, 2007 3:36PM - 3:48PM |
JO6.00009: Ion Heating in Laser-Plasma Interaction J. Mendonca Ion instabilities due to relativistic electron beams in dense plasmas are considered. They can lead to anomalous heating and transport in inertial fusion plasmas. Results obtained using kinetic and fluid models are given. Significant ion growth rates are possible once the plasma electron drift velocity equals or exceeds the ion sound speed. An hybrid model, in which potential energies are introduced in addition to Temperatures, is also described. Energy is deposited into the electron potential energy which is converted to electron temperature by collisions and to ion potential energy by the ion instability, using integrated growth rates. Ion potential energy is then converted into ion temperature by collisions. The implications for fast ignition are discussed. [Preview Abstract] |
Tuesday, November 13, 2007 3:48PM - 4:00PM |
JO6.00010: Heating in short-pulse laser-driven cone-capped wire targets R.J. Mason, M. Wei, J. King, F. Beg, R.B. Stephens The 2-D implicit hybrid simulation code e-PLAS has been used to study heating in cone-capped copper wire targets. The code e-PLAS tracks collisional particle-in-cell (PIC) electrons traversing background plasma of collisional Eulerian cold electron and ion fluids. It computes $E-$ and \textit{B-fields} by the Implicit Moment Method [1,2]. In recent experiments [3] at the Vulcan laser facility, sub- picosecond laser pulses at 1.06 $\mu $m, and 4.0 x 10$^{20}$ W/cm$^{2}$ intensity were focused into thin-walled ($\sim $10 $\mu $m) cones attached to copper wires. The wire diameter was varied from 10-40 $\mu $m with a typical length of 1 mm. We characterize heating of the wires as a function of their diameters and length, and relate modifications of this heating to changes in the assumed laser-generated hot electron spectrum and directivity. As in recent nail experiments [4], the cones can serve as reservoirs for hot electrons, diverting them from passage down the wires. [1] R. J. Mason, and C. Cranfill, IEEE Trans. Plasma Sci. \textbf{PS-14}, 45 (1986). [2] R. J. Mason, J. Comp. Phys. \textbf{71,} 429 (1987). [3] J. King et al., to be submitted to Phys. Rev. Lett.. [4] R. J. Mason, M. Wei, F. Beg, R. Stephens, and C. Snell, in Proc. of ICOPS07, Albuquerque, NM, June 17-22, 2007, Talk 7D4. [Preview Abstract] |
Tuesday, November 13, 2007 4:00PM - 4:12PM |
JO6.00011: Transport of Energy by Laser-Generated Fast Electrons within Cone-wire Targets J. King, T. Ma, F. Beg, M. Key, J. Koch, A. Mackinnon, A. MacPhee, P. Patel, R. Stephens, K. Akli, R. Freeman, L. Van Woerkom, R. Heathcote, K. Lancaster, P. Norreys, R. Mason, W. Theobald Coupling of energy via laser accelerated electrons to 10 to 40$\mu $m diameter Cu wires attached to Al cones irradiated by a 500J, 1ps, f/3 focused laser is studied as a surrogate for fast ignition. Cu Ka images were recorded using a Bragg crystal imager. Ka yield was obtained with a single hit CCD and relative intensities in Cu K-shell spectra were recorded with a HOPG crystal spectrometer. Fitting 1D numerical modeling to axial profiles of Ka emission estimates the coupling efficiency and the average temperature of the electrons in the 1D Ohmically inhibited energy transport. [Preview Abstract] |
Tuesday, November 13, 2007 4:12PM - 4:24PM |
JO6.00012: Studies of Electron Transport Via Transition Radiation C. Bellei, S. Nagel, L. Willingale, S. Kneip, S.P.D. Mangles, A.E. Dangor, Z. Najmudin, K. Krushelnick, S. Kar, B. Dromey, K. Markey, P. Simpson, M. Zepf, R.J. Clark, J. Green, D. Neely, P. Norreys, D. Carroll, P. McKenna Measurements of electron transport through solid targets have been performed at the Vulcan Petawatt Laser Facility (Rutherford Appleton Laboratory, UK) by looking at the second harmonic of the laser frequency ($\lambda _{L}$=1054 nm) emitted at the rear side of the targets. The emission, that we mainly attribute to coherent transition radiation, is not compatible with a ballistic model of electron transport. The possibility of collimation and even coalescence of the relativistic electrons will be discussed. The radiation also exhibits a polarization dependence, consistent with the properties of transition radiation. The possibility of measuring the polarization state of the transition radiation in order to determine the direction of the fast electrons as they cross the plasma-vacuum interface will be further discussed. [Preview Abstract] |
Tuesday, November 13, 2007 4:24PM - 4:36PM |
JO6.00013: Hot electron coupling to dense plasma for fast ignition Andreas Kemp, Hartmut Ruhl, Yasuhiko Sentoku, Emmanuel Dhumieres, Max Tabak Critical issues for the fast ignition of inertial confinement fusion targets, where pre-compressed fuel is ignited by injection of an intense short laser pulse, are (i) the coupling efficiency of the short pulse to the hot electrons that heat the core and (ii) the transverse beam divergence of those electrons inside the dense plasma, i.e., determining the fraction of hot electron energy that will reach the core. We address these issues using one-, two- and three-dimensional kinetic computer models that include the effect of collisions. [Preview Abstract] |
Tuesday, November 13, 2007 4:36PM - 4:48PM |
JO6.00014: Measurement of distribution of x-ray polarization degrees caused by anisotropic hot electrons in ultra-high intensity laser produced plasma Y. Inubushi, Y. Okano, H. Nishimura, T. Kai, S. Fujioka, T. Kawamura, D. Batani, A. Morace, R. Redaelli, C. Fourment, J. Santos, G. Malka, A. Boscheron, A. Casner, M. Koenig, T. Nakamura, T. Johzaki, H. Nagatomo, K. Mima In fast-ignition, investigation of the velocity distribution function (VDF) of hot electrons is critical for clarifying energy transport in ultra-high intensity laser-produced plasmas. X-ray polarization spectroscopy is a useful diagnostic tool for measuring the VDF of electrons inside plasma [1, 2]. A new polarization measurement was performed using a laser pulse (10 J in $\sim$1 ps). Chlorinated triple-layer targets were irradiated, and polarization degrees of Cl-He$\alpha$ line were measured. Obtained distribution of polarization degrees indicates that the VDF is pancake-like shape at the target surface and cigar-like in deep region. Moreover, depolarizations due to isotropic excitation by bulk electrons and elastic collision of bulk electrons, which were predicted by a model calculation [3] and a time-dependent atomic kinetic code [4], was observed. [1] J. C. Kieffer, et al., Phys. Rev. Lett. $\textbf{68}$, 480 (1992), [2] Y. Inubushi, et al., JQSRT $\textbf{99}$, 305 (2006). [3] Y. Inubushi, et al., J. Plasma Fusion Res. $\textbf{2}$, 0013 (2007). [4] T. Kawamura, et al., submitted. [Preview Abstract] |
Tuesday, November 13, 2007 4:48PM - 5:00PM |
JO6.00015: Cross sections with magnetic sublevels of He-like ions for polarized x-ray spectroscopy T. Kai, T. Kawamura, S. Nakazaki, Y. Inubushi, H. Nishimura, Y. Okano, T. Nakamura, T. Johzaki, H. Nagatomo, S. Fujioka, K. Mima In fast-ignition plasma, energy transport in dense plasma is one of the critical issues. The fast-ignition plasma emits polarized x-rays since the VDF of generated fast electron is anisotropic VDF. Spectroscopy of polarized x-ray is a useful diagnostics for studying the VDF of fast electrons. The time- dependent collisional-radiative atomic kinetics model was developed to analyze the experimental results of polarized Cl-He $\alpha$ line [1]. To examine the model calculation, the cross sections with magnetic sublevels of He-like Cl and Cu ions were calculated [2]. The calculated cross sections with magnetic sublevels for He-like ions will be discussed for polarized x- ray spectroscopy in the ultrahigh-intense laser (10$^{17}$~10$^ {20}$ W/cm$^{2}$). \newline [1] T. Kai, et al., HEDP 3, 131 (2007); T. Kawamura et al., submitted. \newline [2] T. Kai, et al., PRA 75, 012703 (2007). ibit, 75, 062710 (2007). [Preview Abstract] |
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