Bulletin of the American Physical Society
56th Annual Meeting of the APS Division of Plasma Physics
Volume 59, Number 15
Monday–Friday, October 27–31, 2014; New Orleans, Louisiana
Session JO6: Intense Laser Plasma Physics, and Technology Applications of Plasmas |
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Chair: Tony Ting, Naval Research Laboratory Room: Galerie 3 |
Tuesday, October 28, 2014 2:00PM - 2:12PM |
JO6.00001: Quantum radiation reaction in laser--electron-beam collisions T.G. Blackburn, C.P. Ridgers, J.G. Kirk, A.R. Bell The ever-increasing intensity produced by high power, short pulse lasers has led to substantial interest into how radiation reaction and QED processes such as pair production will affect the plasma physics studied in future laser facilities. It is likely that the interaction of a laser pulse of intensity $> 10^{23}$Wcm$^{-2}$ with another laser pulse\footnote{A.R. Bell and J.G. Kirk, Phys. Rev. Lett. 101, 200403 (2008)} or with a solid density target\footnote{C.P. Ridgers \textit{et al.}, Phys. Rev. Lett. 108, 165006 (2012)} will produce copious high energy gamma rays and critical density electron-position pair plasmas. Recently we have shown\footnote{T.G. Blackburn \textit{et al.}, Phys. Rev. Lett 112, 015001 (2014)} how an experiment that could be accomplished in today's high intensity laser facilities, the collision of a GeV electron beam with a laser pulse of intensity $> 10^{21}$Wcm$^{-2}$, could provide clear signatures of quantum radiation reaction. These are the increased yield of the highest energy gamma rays and the broadening in energy of the electron beam, caused by the stochastic nature of photon emission. [Preview Abstract] |
Tuesday, October 28, 2014 2:12PM - 2:24PM |
JO6.00002: The generation of tens kT magnetic fields by transport instability of laser generated electrons in a near critical preformed plasma Toma Toncian, Bjorn Manuel Hegelich, Oswald Willi, Goetz Lehmann First direct measurements of the electron transport along extended wire targets by Quinn et al [PRL \textbf{102} (2009)] revealed a charging current and associated magnetic field moving close to the speed of light away from focal volume of the employed heating laser. The motion of the electrons is bound electrostatic to the proximity of the solid. A return current compensating the escaping charge is formed at the surface of the solid, the overall current loop sustaining kT magnetic fields, with traversal decay lengths of $\mu$m. In our study we show by means of numerical 2 dimensional particle in cell simulations that the motion of the hot electrons and dynamic of the charge compensating return current can be dramatically affected by a preformed $\mu$m scale length plasma gradient on the solid surface. In particularly the two velocities distribution and two antiparallel currents developing in the near critical plasma are unstable in respect of two stream and Kevin Helmholtz instability. The particle motion becomes locally magnetized resulting in current eddies trapping particles and localized magnetic and electric fields with values of tens of kT and TV/m sustained on $\mu$m scales and with characteristic decay times of ps. [Preview Abstract] |
Tuesday, October 28, 2014 2:24PM - 2:36PM |
JO6.00003: Amplification of ultra-short laser pulses via strongly-coupled Brillouin backscattering Goetz Lehmann, Friedrich Schluck, Karl-Heinz Spatschek Plasma based amplification of laser pulses is currently discussed as a key component for the next generation of high-intensity laser systems, possibly enabling the generation of ultra-short pulses in the exawatt-zetawatt regime [1]. In these scenarios the energy of a long pump pulse (several ps to ns of duration) is transferred to a short seed pulse via a plasma oscillation. Strongly-coupled Brillouin (sc-SBS) backscattering is identified as a potential candidate for robust amplification scenarios [2]. With the help of three-wave interaction models, we investigate the multi-dimensional dynamics the seed pulse undergoes during amplification. The influences of filamentation and self-focusing are analyzed and mitigation strategies are discussed. \\[4pt] [1] G.A. Mourou, N.J. Fisch, V.M. Malkin, Z. Toroker, E.A. Khazanov, A.M. Sergeev, T. Tajima, and B. Le Garrec, \textit{Optics Communications }285, 720 (2012), \\[0pt] [2] G. Lehmann and K.H. Spatschek, \textit{Phys. Plasmas} 20, 073112 (2013) [Preview Abstract] |
Tuesday, October 28, 2014 2:36PM - 2:48PM |
JO6.00004: Deploying electromagnetic particle-in-cell (EM-PIC) codes on Xeon Phi accelerators boards Ricardo Fonseca The complexity of the phenomena involved in several relevant plasma physics scenarios, where highly nonlinear and kinetic processes dominate, makes purely theoretical descriptions impossible. Further understanding of these scenarios requires detailed numerical modeling, but fully relativistic particle-in-cell codes such as OSIRIS [1] are computationally intensive. The quest towards Exaflop computer systems has lead to the development of HPC systems based on add-on accelerator cards, such as GPGPUs and more recently the Xeon Phi accelerators that power the current number 1 system in the world. These cards, also referred to as Intel Many Integrated Core Architecture (MIC) offer peak theoretical performances of \textgreater 1 TFlop/s for general purpose calculations in a single board, and are receiving significant attention as an attractive alternative to CPUs for plasma modeling. In this work we report on our efforts towards the deployment of an EM-PIC code on a Xeon Phi architecture system. We will focus on the parallelization and vectorization strategies followed, and present a detailed performance evaluation of code performance in comparison with the CPU code. \\[4pt] [1] R. A. Fonseca et al., LNCS 2331, 342, (2002) [Preview Abstract] |
Tuesday, October 28, 2014 2:48PM - 3:00PM |
JO6.00005: High angular momentum density physics of intense laser Baifei Shen, Yin Shi, Lingang Zhang, Xiaomei Zhang, Wenpeng Wang, Zhizhan Xu Relativistic laser pulse has been used as an important research tool in well known high energy density physics as well as in ultrahigh momentum density which has many important applications like radiation pressure acceleration. But another important character of relativistic laser, orbital angular momentum (OAM) effect was ignored. When a relativistic laser pulse with a high photon density interacts with a specially tailored thin foil target, a strong torque is exerted on the resulting spiral-shaped foil plasma, or ``light fan.'' Because of its structure, the latter can gain significant orbital angular momentum (OAM), and the opposite OAM is imparted to the reflected light, creating a twisted relativistic light pulse. Such an interaction scenario is demonstrated by particle-in-cell simulation as well as analytical modeling, and should be easily verifiable in the laboratory. As an important characteristic, the twisted relativistic light pulse has a strong torque and ultrahigh OAM density. Relativistic light has opened new research fields in high-field physics, including laser acceleration and relativistic high-order harmonics, because it has a high energy density. Now, relativistic twisted light has high angular momentum density, which may result in many new physical phenomena. \\[4pt] [1] Yin Shi, Baifei Shen et al., PRL 112, 235001 (2014).\\[0pt] [2] http://phys.org/news/2014-06-spiral-shaped-fan-laser-driven-plasma.html [Preview Abstract] |
Tuesday, October 28, 2014 3:00PM - 3:12PM |
JO6.00006: Propagation of high power, quasi-radially polarized TEM$_{01}$ modes in a plasma waveguide Andrew Goers, George Hine, Jennifer Elle, Linus Feder, Howard Milchberg The longitudinal electric field of a tightly focused radially polarized laser pulse has been proposed and investigated as a compact means of accelerating femtosecond scale electron bunches. However, generation of high power, short pulse lasers with radial polarization has presented a significant technical challenge. We present a simple method of generating quasi-radial polarization by creating a pi-phase delay between two halves of a linearly polarized laser. When focused, the quasi-radially polarized pulse creates an approximately TEM$_{01}$ mode. We investigate guiding of the TEM$_{01}$ mode in a plasma waveguide over a range of intensities approaching $a_{0} =1$. [Preview Abstract] |
Tuesday, October 28, 2014 3:12PM - 3:24PM |
JO6.00007: The aero-optical performance of inductively-coupled plasma adaptive lenses Javier Urzay, Milad Mortazavi, Ali Mani In this presentation, we address the optical performance of a plasma adaptive lens for ground-surveillance applications by using three-dimensional numerical simulations and scaling analyses. The principle of operation of a plasma lens consists of controlling the refractive-index distribution, or equivalently, the electron-density field in an ionized-gas environment. A closed cylindrical chamber filled with Argon plasma is used as a model lens. In principle, scaling analyses show that increasing the input electric power increases the optical performance of the plasma lens. However, the numerical simulations reveal that this design shift makes the plasma lens more susceptible to buoyant and centrifugal hydrodynamic instabilities, which are caused by gravity-driven thermal convection and cycle-averaged Lorentz forces. This destabilization effect, in turn, breaks the initial axisymmetry and leads to the occurrence of discrete electron-rich spots, which degrade the optical performance of the plasma lens. [Preview Abstract] |
Tuesday, October 28, 2014 3:24PM - 3:36PM |
JO6.00008: Absolute Instability in Coupled-Cavity TWTs D.M.H. Hung, I.M. Rittersdorf, Peng Zhang, Y.Y. Lau, D.H. Simon, R.M. Gilgenbach, D. Chernin, T.M. Antonsen, Jr. This paper will present results of our analysis of absolute instability in a coupled-cavity traveling wave tube (TWT). The structure mode at the lower and upper band edges are respectively approximated by a hyperbola in the (omega, k) plane. When the Briggs-Bers criterion is applied, a threshold current for onset of absolute instability is observed at the upper band edge, but not the lower band edge. The nonexistence of absolute instability at the lower band edge is mathematically similar to the nonexistence of absolute instability that we recently demonstrated for a dielectric TWT. The existence of absolute instability at the upper band edge is mathematically similar to the existence of absolute instability in a gyroton traveling wave amplifier. These interesting observations will be discussed, and the practical implications will be explored. [Preview Abstract] |
Tuesday, October 28, 2014 3:36PM - 3:48PM |
JO6.00009: TWT Driven by a Large Diameter Annular Electron Beam in a Disk-on-Rod Slow-Wave Structure P. Wong, D.H. Simon, Peng Zhang, Y.Y. Lau, R.M. Gilgenbach, B. Hoff This paper studies the viability of a high-power traveling wave tube (TWT) using a disk-on-rod slow-wave structure (SWS), which admits a large diameter, high current, annular electron beam. The annular electron beam would achieve much higher current than a pencil beam. The cold-tube as well as the hot-tube dispersion relations are analytically studied and compared to numerical simulations. The Pierce gain parameter, $C, $is calculated by two very different methods: the exact formulation of the space-charge wave on the disk-on-rod SWS, and the calculation of the action of the beam on the operating circuit mode. Both methods yield identical results of $C$. The so-called Pierce AC space charge effect parameter, \textit{QC}, is calculated rigorously for the first time for the disk-on-rod SWS TWT. Proof-of-principle experiment is designed based on the combined analytic and simulation studies. [Preview Abstract] |
Tuesday, October 28, 2014 3:48PM - 4:00PM |
JO6.00010: Experiments and Simulations on a Prototype Recirculating Planar Magnetron G. Greening, N. Jordan, R. Gilgenbach, S. Exelby, P. Zhang, D. Simon, M. Franzi, Y.Y. Lau The Multi-Frequency Recirculating Planar Magnetron (MFRPM) is a type of Recirculating Planar Magnetron, a crossed-field, high power microwave source, with the added benefit of simultaneous oscillation at more than one primary frequency.\footnote{R.M. Gilgenbach et al., ``Crossed Field Device'', U.S. 2011/0204785 A1, Aug. 25, 2011, Patent Pending.} Prior research focused on the design of a dual L/S-band MFRPM prototype to demonstrate simultaneous operation at 1~GHz and 2~GHz. Dual frequency microwave emission on this prototype was recently demonstrated on the Michigan Electron Long Beam Accelerator with a ceramic insulator (MELBA-C), which drives the MFRPM by applying a -300~kV, 0.3--1.0~$\mu$s pulse to the cathode. Experiments are underway to characterize operation of the MFRPM prototype. Microwave power extraction and different cathode designs are also being explored to improve operation.\footnote{M. Franzi et al., Phys. Plasmas 20, 033108 (2013).} Results are compared to simulations of the experimental setup using the MAGIC particle-in-cell and HFSS finite-element codes. [Preview Abstract] |
Tuesday, October 28, 2014 4:00PM - 4:12PM |
JO6.00011: Microwave Power Measurements on the Recirculating Planar Magnetron N.M. Jordan, M. Franzi, G.B. Greening, R.M. Gilgenbach, D.H. Simon, Y.Y. Lau, B.W. Hoff, J.W. Luginsland The recirculating planar magnetron (RPM)\footnote{R.M. Gilgenbach, et. al., IEEE Trans. Plasma Sci., V39, p980-987 (2011)} is a high power microwave generator that recirculates the beam in two-coupled, planar magnetrons. Experiments on the first L-band prototype\footnote{M.A. Franzi, et. al., IEEE Trans. Plasma Sci., V41, p639-645 (2013)} have successfully produced 50-200 $\mu$s, 30-130 MW microwave pulses with instantaneous electronic efficiencies of up to 30{\%} at approximately 1 GHz. The device is driven using MELBA-C, with parameters of: -300 kV for 0.3-1.0 $\mu$s, and 0.15-0.3 T axial magnetic fields. Recent RPM experiments have explored the effect of cathode surface treatment on the extracted microwave power, efficiency, and pulse width. This work utilized a proof of principle extraction system with antennas on the center vane of each oscillator to couple RF power into two, coaxial transmission lines. An advanced design, the Coaxial All Cavity Extractor, is in fabrication and will be discussed. [Preview Abstract] |
Tuesday, October 28, 2014 4:12PM - 4:24PM |
JO6.00012: Impedance Dynamics in the Self-Magnetic Pinch (SMP) Diode on the RITS-6 Accelerator* Timothy Renk, Mark Johnston, Joshua Leckbee, Timothy Webb, Michael Mazarakis, Mark Kiefer, Nichelle Bennett The RITS-6 inductive voltage adder (IVA) accelerator (3.5-8.5 MeV) at Sandia National Laboratories produces high-power (TW) focused electron beams (\textless 3mm diameter) for flash x-ray radiography applications. The Self-Magnetic Pinch (SMP) diode utilizes a hollowed metal cathode to produce a pinched focus onto a high Z metal converter. The electron flow from the IVA driver into the load region complicates understanding of diode evolution. There is growing evidence that reducing cathode size below some ``optimum'' value in order to achieve desired spot size reduction results in pinch instabilities leading to either reduced dose-rate, early radiation power termination, or both. We are studying evolving pinch dynamics with current and x-ray monitors, optical diagnostics, and spectroscopy, as well as with LSP [1] code simulations. We are also planning changes to anode-cathode materials as well as changes to the diode aspect ratio in an attempt to mitigate the above trends and improve pinch stability while achieving simultaneous spot size reduction. Experiments are ongoing, and latest results will be reported. [1] LSP is a software product of ATK Mission Research, Albuquerque, NM. *Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. De-partment of Energy's National Nuclear Security Adminis-tration under contract DE-AC04-94AL85000. [Preview Abstract] |
Tuesday, October 28, 2014 4:24PM - 4:36PM |
JO6.00013: ABSTRACT WITHDRAWN |
Tuesday, October 28, 2014 4:36PM - 4:48PM |
JO6.00014: ABSTRACT WITHDRAWN |
Tuesday, October 28, 2014 4:48PM - 5:00PM |
JO6.00015: A nonlinear plasma retroreflector for single pulse Compton backscattering J.P. Palastro, D. Kaganovich, D. Gordon, B. Hafizi, J. Penano, M. Helle, A. Ting A long laser pulse focused onto the edge of a gas jet nozzle launches a shock wave. The shock wave and gas jet flow collide forming a density spike [1]. The leading edge of an incident ultrashort laser pulse ionizes the gas, while the bulk undergoes a nonlinear Poynting flux reversal from the ionized spike. The resulting counterpropagating field can Compton backscatter from electrons accelerated in the ultrashort pulse's wakefield, upshifting the frequency. We examine the reversal mechanism and properties of the counterpropagating field to optimize the Compton scattered radiation. \\[4pt] [1] D. Kaganovich \textit{et al.}, Phys. Plasmas 18, 120701 (2011). [Preview Abstract] |
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