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 TO6: Laboratory Astrophysics |
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Chair: Bruce Remington, Lawrence Livermore National Laboratory Room: Hanover FG |
Thursday, November 5, 2009 9:30AM - 9:42AM |
TO6.00001: Super-Alfv\'{e}nic Expansion of a Laser-Plasma through an Ambient Magnetized Plasma Erik Everson, Carmen Constantin, Lucas Morton, Derek Schaeffer, Nathan Kugland, Walter Gekelman, Christoph Niemann In recent experiments on the Large Plasma Device (LAPD) several diagnostics have been implemented to investigate the super-Alfv\'{e}nic flows created by the rapid expansion of a high-density, energetic laser-plasma through the ambient magnetized, helium plasma of the LAPD. The laser-plasma is created by a $25$ J, $5$ ns FWHM laser pulse of $1064$ nm light incident on a graphite target and is allowed to expand a distance $>30$ cm across the magnetic field lines. With the laser-plasma expansion imparting enough energy to the low-density ambient plasma ($n\sim2\times10^{-12}$ cm$^{-3}$, $T_{e}\sim6$ eV, $T_{i}\sim1$ eV, $B_{o}=300$ G), super-Alfv\'{e}nic flows can be created. The magnetic structure of these flows has been measured using a $1$ mm, 3-axis differential magnetic probe (B-dot probe). A measurement of the energy distribution of ions has also been attempted using an energy analyzer. [Preview Abstract] |
Thursday, November 5, 2009 9:42AM - 9:54AM |
TO6.00002: Generation of intense magnetosonic waves by erupting laboratory simulations of solar coronal loops Shreekrishna Tripathi, Walter Gekelman Eruption of coronal loops in the ambient plasma of the sun is simulated in a laboratory experiment at UCLA. The laboratory plasma loops (simulations of coronal loops) are produced using an annular LaB$_6$ cathode and an annular anode mounted on two movable shafts in a large vacuum chamber. Two electromagnets produce a vacuum magnetic field along the arched axis of the plasma loop. Controlled flows of dense plasma are generated from the foot-points of the electrodes using laser beams that strike movable targets (C, LaB$_6$) placed behind the holes in the electrodes. This novel approach provides flexibility in independently controlling the timing and intensity of the flows. The vacuum chamber has an additional source to produce ambient magnetized plasma. In recent experiments, dramatic eruption of the loop plasma was observed following generation of super-Alfv\'{e}nic flows ($V_{flow} \sim 2-5$ $V_a$) from the foot-points. The erupting plasma loop sets up intense magnetosonic waves in the ambient plasma. We will present initial results on the loop eruption and excitation of the magnetosonic wave. [Preview Abstract] |
Thursday, November 5, 2009 9:54AM - 10:06AM |
TO6.00003: Episodic Magnetic Tower Jets in Laboratory Experiments F. Suzuki-Vidal, S.V. Lebedev, S.N. Bland, G. Burdiak, J.P. Chittenden, G.N. Hall, A.J. Harvey-Thompson, E. Khoory, L. Pickworth, G. Swadling, A. Ciardi, C. Stehle Results from laboratory astrophysics experiments showing the formation of episodic plasma jets will be presented. The jets are highly supersonic, radiatively cooled and driven by the pressure of the toroidal magnetic field in a `magnetic tower' configuration. The 1 MA, 250 ns current pulse from the MAGPIE generator is introduced into a radial foil, an aluminium disc held between two concentric electrodes. The ablation of plasma from the foil close to the central electrode forms a radial gap which triggers the formation of the jets. Several diagnostics including magnetic and inductive probes were used to study their dynamics, particularly their launching mechanism. The similarities with previous single-episode magnetic tower jets from radial wire arrays together with new measurements of dimensionless parameters such as the magnetic Reynolds number (Re$_{M}>$400) indicate that the experiments can be scaled to astrophysical jets. [Preview Abstract] |
Thursday, November 5, 2009 10:06AM - 10:18AM |
TO6.00004: Spike penetration in blast-wave-driven instabilities R.P. Drake Recent experiments by C. Kuranz and collaborators, motivated by structure in supernovae, have studied systems in which planar blast waves encounter interfaces where the density decreases. During the Rayleigh-Taylor (RT) phase of such experiments, they observed greater penetration of the RT spikes than tends to be seen in simulations. Here we seek to employ semi-analytic theory to understand the general nature and regimes of spike penetration for blast-wave-driven instabilities. This problem is not trivial as one must account for the initial vorticity deposition at the interface, for its time-dependent deceleration, for the expansion of the shocked material in time and space, and for the drag on the broadened tips of the spikes. One can hope that such models will increase our ability to interpret the behavior of simulations of such systems, in both the laboratory and astrophysics. Supported by the US DOE NNSA under the Predictive Sci. Academic Alliance Program by grant DE-FC52-08NA28616, the Stewardship Sci. Academic Alliances program by grant DE-FG52-04NA00064, and the Nat. Laser User Facility by grant DE-FG03--00SF22021. [Preview Abstract] |
Thursday, November 5, 2009 10:18AM - 10:30AM |
TO6.00005: Shock Wave Structure in a Fully Ionized Plasma Thomas Masser, John Wohlbier, Robert Lowrie We study the structure of planar shock waves in a two-temperature model of a fully ionized plasma that includes electron heat conduction and energy exchange between electrons and ions. For steady flow in a reference frame moving with the shock, the model reduces to an autonomous system of ordinary differential equations which can be numerically integrated. A phase space analysis of the ODEs provides additional insight into the structure of the solutions. For example, below a threshold mach number the model produces fully dispersed shocks; while above the threshold, the solutions contain embedded hydrodynamic shocks. We also find that the ion temperature may continue to increase after the shock and reaches a maximum near the isothermal sonic point. We summarize the methodology for solving for two-temperature shocks, and show results for several values of shock strength and material parameters to quantify the shock structure and explore the range of possible solutions. Such solutions may be used to verify hydrodynamic codes that use similar plasma physics models. [Preview Abstract] |
Thursday, November 5, 2009 10:30AM - 10:42AM |
TO6.00006: Accelerating aluminum foils for shock wave experiments Stephan Neff, Sandra Stein, David Martinez, Christopher Plechaty, Radu Presura The interaction of shock waves with inhomogeneous background media is ubiquitous in astrophysics, taking place for expample when supernova remnants move through interstellar gas clouds. Scaled experiments of such interactions are possible by launching shock waves into inhomogeneous low-density foam targets.Using a pulsed-power accelerator (Zebra) with a short-circuit load, we are currently developing the methods and diagnostics necessary for such experiments at the Nevada Terawatt Facility. So far, we have successfully accelerated flyers (50 micron thick, 6 mm in diameter) to velocities of up to 8 km/s with a 1 MA current. We have also impacted these flyers on transparent Plexiglas targets and imaged the resulting shock with shadowgraphy. We are currently implementing improvements to be ready for scaled experiments. These improvements include using a current-multiplier (currents of up to 1.6 MA) to achieve higher velocities and implementing velocity interferometry (VISAR) to obtain a more accurate and time-resolved velocity measurement. In addition, we are currently implementing x-ray backlighting using a 50 TW short-pulse laser. [Preview Abstract] |
Thursday, November 5, 2009 10:42AM - 10:54AM |
TO6.00007: Radiation effect and relaxation layer in electro-magnetically driven strong shock waves Kotaro Kondo, Mitsuo Nakajima, Tohru Kawamura, Kazuhiko Horioka Strong shock waves play a crucial role in many astrophysical phenomena. Ion-electron relaxation process and radiation affect the structure of strong shock waves. Since the non-linear nature of the relaxation process makes the plasma behavior extremely complicated, it requires well-defined shock wave formation to estimate the structure. We investigate electro-magnetically driven shock in laboratory experiments. The pulse power device with tapered electrodes can generate a quasi steady and 1-D shock [1], which allows for analysis of ion-electron relaxation and radiation processes. We will show results of electron temperature measurement by a line pair method and radiative cooling, which restricts the increase of electron temperature. \\[4pt] [1] K. Kondo, M. Nakajima, T. Kawamura and K. Horioka, Rev. Sci. Instr. \textbf{77}, 036104 (2006). [Preview Abstract] |
Thursday, November 5, 2009 10:54AM - 11:06AM |
TO6.00008: Structure in Radiative Shock Experiments F.W. Doss, R.P. Drake, H.F. Robey Astrophysical systems in which radiation transport across a shock front contributes substantially to the properties and dynamics of the system may be modeled in laboratory experiments under high-energy-density conditions. Recent experiments on the Omega laser facility have launched Be discs into shock tubes of Xe gas at atmospheric pressure, producing radiative shocks with speeds over 100 km/sec that are then diagnosed by x-ray pinhole radiography. These experiments are found to develop rich internal structure. First, heating and ablation of the shock tube material ahead of the radiative shock drives a secondary, inwardly directed radial shock, which we call a wall shock. Second, these radiating shock systems become susceptible to hydrodynamic instabilities of thin shocked layers. This research was supported by the DOE NNSA under the Predictive Science Academic Alliance Program by grant DE-FC52-08NA28616, the Stewardship Sciences Academic Alliances program by grant DE-FG52-04NA00064, the National Laser User Facility by grant DE-FG03-00SF22021, and by the Stewardship Science Graduate Fellowship program. [Preview Abstract] |
Thursday, November 5, 2009 11:06AM - 11:18AM |
TO6.00009: Measurements of Radiative Shock Properties using Thomson scattering A. Visco, R.P. Drake, M.J. Grosskopt, D.H. Froula, S.H. Glenzer, G. Gregori Radiative shocks are shock waves whose structure has been altered by radiation transport. Recent experiments have used the Omega laser to study radiative shock systems that are optically thin upstream and optically thick downstream. In these systems, a radiative precursor and high density cooling layer are formed in response to radiation. To create these shocks, a thin slab of berylium is driven into cylinder of argon gas at speeds $>$ 100 km/s, producing strong radiative effects. Thomson scattering is employed to measure the electron temperature and ionization in the system. The experiment used emission from a Mn x-ray source and the x-ray spectrum was detected using a crystal spectrometer and a gated, multi-strip, microchannel-plate detector. Measured results the will be shown, and the inferred properties will be compared with simulations and analytic estimates. [Preview Abstract] |
Thursday, November 5, 2009 11:18AM - 11:30AM |
TO6.00010: Laboratory Tests of Stellar Interior Opacity Models J.E. Bailey, G.A. Rochau, S.B. Hansen, P.W. Lake, T.J. Nash, D.S. Nielsen, R.D. Thomas, C.A. Iglesias, J. Abdallah Jr., M.E. Sherrill, J.J. MacFarlane, I.E. Golovkin, P. Wang, R.C. Mancini, C. Blancard, Ph. Cosse, G. Faussurier, F. Gilleron, J.C. Pain, A.K. Pradhan, S.N. Nahar, M. Pinsonneault The internal structure of stars depends on the radiative opacity of the stellar matter. However, opacity models have never been experimentally tested at the conditions that exist inside stars. Experiments at the Sandia Z facility are underway to measure the x-ray transmission of iron, an important stellar constituent, at temperature and density high enough to evaluate the physical underpinnings of stellar opacity models. Initial experiments provided information on the charge state distribution and the energy level structure for the iron ions that exist at the solar radiation/convection boundary. Data analysis and new experiments at higher densities and temperatures will be described. [Preview Abstract] |
Thursday, November 5, 2009 11:30AM - 11:42AM |
TO6.00011: Radiation from plasmas with sub-Larmor scale magnetic fields -- generalized jitter radiation Mikhail Medvedev Radiation produced by relativistic electrons in random magnetic fields of a sub-Larmor scale is referred to as the jitter radiation. It has been predicted to be produced from high- energy density environments which naturally generate such fields via Weibel-type (e.g., streaming) instabilities. Thus, it was argued to be a new diagnostic of Weibel turbulence in relativistic collisionless shocks, in reconnection in electron- positron plasmas and in laser-produced plasmas, the latter is of interest to both laser-plasma applications (e.g., Fast Ignition) and to Laboratory Astrophysics. The spectral characteristics of jitter radiation are markedly different from those of synchrotron and carry information about the magnetic fields structure (e.g., its spatial spectrum). Conventional treatment of jitter radiation assumes negligibly small deflections of particles in the magnetic fields, which is not always the case. Here we relax this assumption and discuss the transition between jitter and synchrotron regimes. Although the full treatment is model-dependent, certain important conclusions can be drawn. We will also address applications to both laboratory studies of the Weibel turbulence and astrophysical phenomena. [Preview Abstract] |
Thursday, November 5, 2009 11:42AM - 11:54AM |
TO6.00012: Fully relativistic form factor for Thomson scattering in umagnetized plasmas J.P. Palastro, J.S. Ross, B. Pollock, E.A. Williams, L. Divol, D.H. Froula, S. Glenzer We derive a fully relativistic form factor for Thomson Scattering in umagnetized plasmas valid to all orders in the normalized electron velocity, beta=v/c . The form factor is compared to a previously derived expression where the lowest order electron velocity, beta, corrections are included [J. Sheffield, ``Plasma scattering of electromagnetic radiation,'' Academic Press (1975)]. The beta expansion approach is sufficient for electro-static waves with small phase velocities such as ion-acoustic waves, but for electron plasma waves the phase velocities can be near luminal. At high phase velocities, the electron screening acquires relativistic corrections including effective electron mass, relative motion of the electrons and electromagnetic wave, and polarization rotation. These relativistic corrections alter the scattered emission of thermal plasma waves, which manifest as changes in both the peak and width of the observed Thomson scattered spectra. [Preview Abstract] |
Thursday, November 5, 2009 11:54AM - 12:06PM |
TO6.00013: Observation of relativistic, collective Thomson scattering from electron plasma waves James Ross, Siegfried Glenzer, Laurent Divol, John Palastro, Bradley Pollock, George Tynan, Dustin Froula We present collective Thomson-scattering measurements of light scattered from electron plasma fluctuations with relativistic phase velocities. Phase velocities (v/c) between 0.06 and 0.12 have been achieved in a N2 gas jet plasma by varying the gas jet backing pressure. These plasmas are heated by a 330 J, 527 nm laser beam resulting in plasmas with electron temperatures ranging from 200 to 700 eV and electron densities ranging from 1$\times $10$^{19}$ cm$^{-3}$ to 7$\times $10$^{19}$ cm$^{-3}$. For these conditions, the classical Thomson-scattering description is inadequate to analyze the measured spectra due to the large phase velocities. A fully relativistic treatment of the Thomson-scattering form factor has been developed and shows excellent agreement with the experimental data. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 and was partially funded by the Laboratory Directed Research and Development Program under project tracking code 08-LW-070. [Preview Abstract] |
Thursday, November 5, 2009 12:06PM - 12:18PM |
TO6.00014: Off-Hugoniot measurements for alpha-quartz Norimasa Ozaki, Takayoshi Sano, Tsutomu Mashimo, Tomoaki Kimura, Kohei Miyanishi, Tommaso Vinci, Francis Ree, Takashi Endo, Tatsuya Jitsui, Mihcel Koenig, Ryosuke Kodama In order to accurately obtain unknown material's EOS, off-Hugoniot information of standard material, including re-shock and release isentrope, is required. For this purpose, we performed sapphire EOS measurements with using quartz base, obtaining new sapphire data in TPa (10 Mbar) pressure regime. Moreover, a novel experimental scheme will be discussed to accurately determine quartz release curve for low-density, soft materials EOS experiments. [Preview Abstract] |
Thursday, November 5, 2009 12:18PM - 12:30PM |
TO6.00015: A New Candidate for Magnetic Energy Dissipation in Neutron Star Binary Systems Steven Bekhor Magnetic mountains, which build up against the confining stress of compressed equatorial magnetic fields through accretion over many Alfv\'{e}n times, in low-mass X-ray binary neutron stars are likely sources of gravitational waves. In spite of the susceptibility of magnetic mountains to transient, toroidal ideal inviscid magnetohydrodynamic (MHD) instabilities, none of these is sufficient to disrupt the confinement of accreted matter to the poles. Nonetheless, magnetic relaxation is believed to occur on time scales comparable to the fiducial accretion time scale on the order of 10$^{5}$ to 10$^{8}$ years. In this study, a new mechanism for the dissipation of magnetic fields in systems of neutron star binaries via the coupling of large-amplitude gravitational waves to the background plasma flow is postulated. The mechanism invokes power loss in the Alfv\'{e}n wave energy spectrum due to Joule heating as the waves accelerate upward in a gravitational potential field. This mechanism may account for much of the magnetic energy released by the stars without recourse to resistive effects. As a consequence, an analysis of the evolution of the global magnetic field's structure may provide some insight about the frequency and intensity of burst oscillations. [Preview Abstract] |
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