Bulletin of the American Physical Society
54th Annual Meeting of the APS Division of Plasma Physics
Volume 57, Number 12
Monday–Friday, October 29–November 2 2012; Providence, Rhode Island
Session NO5: Intense Laser Plasma Interactions: Theory and Simulations |
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Chair: Paul Schmit, Princeton University Room: 552AB |
Wednesday, October 31, 2012 9:30AM - 9:42AM |
NO5.00001: Laser hosing in relativistically hot plasmas C. Ren, G. Li, W.B. Mori Electron response in an intense laser is studied in the regime where the electron temperature is relativistic, which is recently accessible in laboratory with kJ-class, short-pulse lasers. Equations for laser envelope and plasma density evolution, both in the electron plasma wave and ion acoustic wave regimes, are re-derived from the relativistic Vlasov equation to include the plasma temperature effect. They show that the mass of an electron fluid element increases relativistically from its thermal energy as well as its fluid motion. These equations are used to study short-pulse and long-pulse laser hosing instabilities using a variational method approach. The analysis shows that relativistic electron temperatures reduce the hosing growth rates and shift the fastest-growing modes to longer wavelengths. These results resolve a long-standing discrepancy between previous non-relativistic theory and simulations/experiments on hosing. This work was supported by DOE under Grant DE-FG02-06ER54879 and Cooperate Agreement No. DE-FC52-08NA28302, by NSF under Grant PHY-0903797, and by NSFC under Grant No. 11129503. The research used resources of NERSC. [Preview Abstract] |
Wednesday, October 31, 2012 9:42AM - 9:54AM |
NO5.00002: Strong radiation damping effects in a gamma-ray source generated by the interaction of a high intensity laser with a wakefield accelerated electron beam Alexander Thomas, Christopher Ridgers, Stepan Bulanov, Blake Griffin, Stuart Mangles We present numerical calculations of the angularly resolved radiation spectrum from a relativistic electron beam interacting with an ultrashort laser pulse. These calculations include the effect of semi-classical radiation reaction forces including a Gaunt factor for synchrotron radiation. For a laser of $5\times10^{21}$ Wcm$^{-2}$ intensity interacting with a 200 MeV electron beam with an emittance similar to that in laser wakefield acceleration experiments, radiation reaction does not produce a significant change in the angular and energy distribution of \emph{photons}. However the effects of radiation reaction are clear when observing the \emph{electron beam} properties. The result is that near-term experiments using such a counter-propagating beam-laser geometry should be able to measure the effects of quantum effects in radiation reaction. The calculations also show that the brilliance of this source is very high, with a peak spectral brilliance exceeding $10^{29}$ photons$\,$s$^{-1}$mm$^{-2}$mrad$^{-2}(0.1$\% bandwidth$)^{-1}$ with approximately 2\% efficiency and with a peak energy of 10 MeV. [Preview Abstract] |
Wednesday, October 31, 2012 9:54AM - 10:06AM |
NO5.00003: Angular distribution of high-harmonic emission in laser-solid interactions P.A. Norreys, W. Boekee-West, R. Trines, A.G. Machacek High harmonic generation in laser-solid interactions is important for the generation of sub-fs pulses having ultrahigh intensity [Baeva et al., Phys. Plasmas (2011)]. In order to maximise the efficiency of this process, a precise characterisation of the angular distribution of the emitted harmonic spectrum is indispensable. The results of particle-in-cell simulations indicate that the maximum intensity of the harmonics is found at angles close to the target surface, rather than close to the incident or reflected laser beam, for preformed plasma. This appears closely related to the deformation of the critical surface by the impact of the laser beam and laser-plasma instabilities in the area of impact. The effect of density gradient scale length, laser angle of impact and laser pulse intensity and duration on the angular distribution of the harmonics will be discussed. [Preview Abstract] |
Wednesday, October 31, 2012 10:06AM - 10:18AM |
NO5.00004: Phenomenological Quantum Model for Ionization in Strong, Time Dependent, Electric Fields T.C. Rensink, T.M. Antonsen, Jr., J.P. Palastro Laser pulse propagation simulations typically involve simplified ionization models where plasma generation is treated via rate laws following each ionization state. These models neglect the fact that the bound electronic response of the atom, ionization, and ionization damping are all part of one continuous process. In particular, the phase of an electron's dipole oscillation with respect to the electric field varies continuously from zero to pi depending on whether the electron is bound or free respectively. The rate law treatment neglects this transitional phase of the electron, treating the electron as either bound to its parent ion or free. For ultrashort laser pulses this transitional phase may play an important role in propagation. Here we present a phenomenological 3D quantum model of ionization. Based on the Schrodinger equation, this model uses a non-local binding potential in place of the Coulomb potential. By reducing the 3+1D Schrodinger equation into a set of 0+1D integral equations, the model promises to offer computational savings eventually leading to implementation in propagation simulations. [Preview Abstract] |
Wednesday, October 31, 2012 10:18AM - 10:30AM |
NO5.00005: Controlling Fast Electrons Divergence via Thin High-Z Layer Near Source Rohini Mishra, Mingsheng Wei, Yasuhiko Sentoku, Sugreev Chawla, Rich Stephens, Farhat Beg 2D collisional PICLS\footnote{Y. Sentoku, \textit{J Comput Phys} 227, 6846 (2008).} simulations are performed to study the effect of target material on fast electron transport in planer multilayer solid targets with common source layer (Al) and varying transport layers (Al, Au). Modeling shows that the strong self-generated resistive magnetic fields ($\sim $ 30 - 40 MG) are produced inside thin high-Z transport layer (e.g., Au). These fields suppress fast electron divergence and B-field channels guide the subsquent fast electron transport without much energy flux loss, which is consistent with the experimental observations.\footnote{S. Chawla \textit{et. al.} ``Effect of target material on fast electron transport and resistive collimation,'' submitted to Phys Rev Lett.''} Sensitivity of collimation and guiding on the offset distance of the high-Z layer from the source is examined and shown to be rather robust. We observed that the high-Z layer supplies hot return current via cumulative effects of resistive electro-magnetic fields produced inside Au, making the return current less collisional. Such return current can elongate the B-field channels, originally produced in Au layer, in backward direction and give positive feedback in the collimation of fast electrons. [Preview Abstract] |
Wednesday, October 31, 2012 10:30AM - 10:42AM |
NO5.00006: Simulations of MA current transport in conductor and insulator laser irradiated targets Philippe Leblanc, Yasuhiko Sentoku Prior research done by Stephens \textit{et al.} [PRE2004] has demonstrated that k-alpha emission patterns from the back side of a laser irradiated target are different for plastic and aluminum targets. Aluminum shows a more focused k-alpha image while plastic emissions exhibit larger scale modulations and lower emissions which indicates more electrons are stopped anomalously inside the target. To better understand the problem, we have conducted detailed 2D particle-in-cell simulations using a non-equilibrium ionization model to study electron and energy transport inside simulated aluminum conductor and plastic insulator targets. Analysis of the transport patterns reveal strong transverse modulations in electron transport in both materials. For insulators, the strong electric field at the ionization front slows hot electrons down and tightens their Larmor radius translating in shorter scale modulations which retain their shape through the entire thickness of the target. Conductors lack such a field which leads the hot electrons being focused more by the strong resistive magnetic field. For aluminum, modulations merge to form large scale transport patterns 100$\mu$m deep into the target while cold bulk electrons collisions smooth out inhomogeneities between transport channels. [Preview Abstract] |
Wednesday, October 31, 2012 10:42AM - 10:54AM |
NO5.00007: Role of preplasma for shortpulse laser-driven electron transport in mass-limited targets M. Schollmeier, A.B. Sefkow, M. Geissel, B. Atherton, S.E. Corwell, M.W. Kimmel, P. Rambo, J. Schwarz, A. Arefiev, B. Breizman, J.M. Koning, M.M. Marinak We report on experiments with the Z-Petawatt laser at Sandia National Labs using mm-sized foils and mass-limited targets of various thicknesses. Rear side accelerated proton beam measurements, in combination with simulation results, were used to infer hot electron transport in presence of preplasma. Full-scale, 3D radiation-hydrodynamics simulations of the ns to ps prepulse were performed. Preplasma properties (density profiles, temperatures, charge states) where then imported into a fully explicit and kinetic 2D particle-in-cell code to simulate, 10 ps of the main laser pulse interaction with the preplasma and target at full scale. A comparison of experimental data and numerical data shows outstanding agreement in all measured proton beam parameters, which gives confidence in the simulation results of hot electron transport. Sandia National Labs is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corp., for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. [Preview Abstract] |
Wednesday, October 31, 2012 10:54AM - 11:06AM |
NO5.00008: Higher Order Nonlocal Effects of Relativistic Ponderomotive Force in High Power Lasers Natsumi Iwata, Yasuaki Kishimoto, Kenji Imadera Recently, the intensity of high power lasers has reached $10^{21}W/cm^{2}$. Since such intensity is realized by tight focusing, the ponderomotive force becomes strong and plays an essential role in laser-matter interaction. The ponderomotive force has been derived by the averaging method, and explained as a force proportional to the field gradient under the first-order approximation with respect to $\epsilon$, the ratio between particle excursion length and scale length of field amplitude gradient. However, under strong focusing, the higher order terms neglected in the above method becomes important. Here, we introduce the noncanonical Lie perturbation theory based on the variational principle in phase space [1] and present an extended theory of relativistic ponderomotive force that includes nonlocal effects expressed by the higher order terms. By successfully finding suitable coordinates, we obtained a new formula of the relativistic ponderomotive force that involves second and third spatial derivatives of the field amplitude. We applied the formula to study particle confinement in a hollow-shaped laser field. The higher order terms are found to play a leading role regulating the betatron motion.\\[4pt] [1] N. Iwata, Y. Kishimoto and K. Imadera, Plasma Fusion Res. 6, 2404105 (2011) [Preview Abstract] |
Wednesday, October 31, 2012 11:06AM - 11:18AM |
NO5.00009: Post-Laser Radiation Pressure Acceleration: Coulomb Acceleration of Mono-Energetic Protons by Electron-Screened Carbon Ions in Laser Irradiated Multi-Ion Targets Chuan-Sheng Liu, Tung-Chang Liu, Xi Shao, Minqing He, Bengt Eliasson, Vipin Tripathi, Jao-Jang Su, Jyhpyng Wang, Shih-Hung Chen Laser acceleration of monoenergetic protons in a thin hydrocarbon target with protons as a minority species is studied theoretically and by simulation. We found there are two distinct stages of acceleration: radiation pressure acceleration of the target as a whole, followed by electron screened Coulomb repulsion of protons by carbon ions. The instabilities are largely suppressed, and the acceleration time with these combined mechanisms lasts ten times longer than with radiation pressure acceleration alone. We developed analytical theory, solved the proton equations of motion for the screened Coulomb acceleration, and compared with the simulation. Excellent agreement was obtained between the simulation result and the numerical solution. We found that the proton acceleration due to Coulomb repulsion in the second stage is effective. With 10\% protons, a proton beam of more than ten billion in number can be accelerated to close to 1 GeV for a laser with less than 7 petawatt power over two hundred laser periods. Novel schemes such as laser switching to further increase the energy of monoenergetic protons in this mechanism will also be discussed. [Preview Abstract] |
Wednesday, October 31, 2012 11:18AM - 11:30AM |
NO5.00010: Interaction between high power laser and clustered medium -propagation, acceleration, and radiation Y. Kishimoto, N. Iwata, Y. Suguyama, T. Uchida, Y. Fukuda A clustered medium has been found to exhibit prominent features in the interaction with a laser, e.g. the existence of polarization wave [1], high absorption efficiency of laser light, high energy particle acceleration, highly chaotic particle motions and associated emission of energetic radiation. Recently, signatures of high energy ion acceleration with 10-20 MeV per nucleon were observed in a clustered medium. A channeling over Rayleigh length was also detected. Here, we studied the characteristics of clustered medium irradiated by high power lasers using a particle based integrated code, EPIC3D, where key physical processes such as ionization, collisional relaxation, radiation damping, etc. are taken into account. The interaction is dominated not only by the averaged quantities, e.g. averaged cluster size and packing fraction, but also by their probabilistic configuration. The generation of high energy ions which range is the same order as the experiments [1] was observed. We also study the propagation dynamics of laser regulated by the cluster expansion and associated complex density profile with high fluctuation level. \\[4pt] [1] T. Tajima et al., Phys. Plasmas 6, 3759 (1999).\\[0pt] [2] Y. Kishimoto et al., Phys. Plasmas 9, 589 (2002) [Preview Abstract] |
Wednesday, October 31, 2012 11:30AM - 11:42AM |
NO5.00011: Relativistic laser interactions with near-critical density plasmas L. Willingale, K. Krushelnick, A.G.R. Thomas, F.J. Dollar, A. Maksimchuk, C. Zulick, H. Chen, A.U. Hazi, G.J. Williams, P.M. Nilson, R.S. Craxton, T.C. Sangter, V. Glebov, C. Stoeckl, W. Nazarov, J. Cobble, P.A. Norreys The Omega EP laser facility (LLE) and the Titan laser (LLNL) provide relativistic laser pulses for experiments to reach the extreme conditions relevant to fast ignition. We perform fundamental studies using very low-density foam targets, to generate a near-critical density plasma. The interactions are characterized and we investigate particle acceleration and channeling phenomena. In particular, the electron heating is measured and is shown to have strong dependance on target density. The effects of the density dependance on the accelerated proton beam and optical radiation measured from the interaction will be presented and discussed. Two dimensional particle-in-cell simulations give good agreement to these phenomenon. This work was supported by the National Laser Users' Facility (NLUF), DOE (Grant No.\ DE-NA000874). Work performed by LLNL under the auspices of U.S.\ DOE under contract DE-AC52-07NA27344. [Preview Abstract] |
Wednesday, October 31, 2012 11:42AM - 11:54AM |
NO5.00012: Dynamics of high-energy proton beam acceleration and focusing from advanced hemisphere-cone target by high-intensity lasers B. Qiao, M.E. Foord, R.B. Stephens, M.S. Wei, P. Patel, H. McLean, M. Key, F.N. Beg The ability to focus intense proton beam to higher intensities and smaller focal diameters makes it very attractive for the applications ranging from isochoric heating of plasma [1], imaging implosion dynamics [2], to proton fast ignition (FI) [3], opening a new avenue of research for high energy density physics (HEDP). The roles of the laser-heated electrons in determining conversion efficiency and focus have not been previously considered [4]. In this talk, we shall present the recent theoretical and numerical calculations that self-consistently describe the evolution of the proton beam starting with the laser-generation of electrons and continuing through to ballistic proton motion, 15ps later. An analytical model is given for the electrostatic field in the plasma during acceleration, which determines the focusing characteristics of the beam.\\[4pt] [1] P. K. Patel et al., PRL 91, 125004 (2003).\\[0pt] [2] M. Borghesi, et al., PPCF 43, A267 (2001).\\[0pt] [3] M. Roth et al., PRL 86, 436 (2001).\\[0pt] [4] T. Bartal et al., Nat. Phys. 8, 139 (2012). [Preview Abstract] |
Wednesday, October 31, 2012 11:54AM - 12:06PM |
NO5.00013: X-ray emission from femtosecond laser irradiation of vertically aligned nanowires Vyacheslav Shlyaptsev, Michael Purvis, Reed Hollinger, Clayton Bargsten, Amy Prieto, Alexander Noy, Jianfei Zhang, Alexander Pukhov, Jorge Rocca We are experimentally and theoretically studying the generation of bright x-ray pulses in volumetrically heated plasmas created by intense femtosecond laser pulse irradiation of vertically aligned nanowire arrays. The scheme we utilize allows us to achieve homogeneous volumetric heating of near-solid density targets to simultaneously achieve almost 100 percent laser absorption efficiency and low hydrodynamic losses, resulting in very hot plasmas at near-solid density which are strong x-ray emitters. Experiments conducted irradiating nickel nanowires 35-55 nm diameter with sub-100 fs duration laser pulses at intensities up to 7x10$^{18}$ Wcm$^{-2}$ show the generation of very hot plasmas in which the ionization reaches the He-like stage and strong x-ray emission. The experimental results are compared with PIC simulations and atomic physics calculations. [Preview Abstract] |
Wednesday, October 31, 2012 12:06PM - 12:18PM |
NO5.00014: Beat Wave Generation and Current Drive in Unmagnetized Plasmas Dale Welch, Scott Hsu, David Rose, Carsten Thoma, Thomas Genoni This work describes the scientific basis and associated simulation results for magnetization of an unmagnetized plasma via beat wave current drive. The technique could enable a variety of novel plasma experiments in which the use of magnetic coils is infeasible. Two-dimensional electromagnetic particle-in-cell simulations have been performed for a variety of angles between the injected waves to demonstrate beat wave generation in agreement with theoretical predictions of the beat-wave wavevector and saturation time. The simulations also clearly demonstrate electron acceleration by the beat waves and resultant current drive and magnetic field generation. The entire process depends on the angle between the parent waves and the ratio of the beat-wave phase velocity to the electron thermal velocity. The wave to magnetic energy conversion efficiency of the cases examined is as high as 0.2{\%}. [Preview Abstract] |
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