Bulletin of the American Physical Society
2005 47th Annual Meeting of the Division of Plasma Physics
Monday–Friday, October 24–28, 2005; Denver, Colorado
Session FO2: Basic Plasma: Laser-Plasma, Beam-Plasma, and Other |
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Chair: John Kline, Los Alamos National Laboratory Room: Adam's Mark Hotel Governor's Square 11 |
Tuesday, October 25, 2005 9:30AM - 9:42AM |
FO2.00001: Hydrodynamics of Blast Waves in LPI Gasbags Shon Prisbrey, Larry Suter, Nathan Meezan Gasbags and gas-filled hohlraums utilizing thin membranes have been used extensively to study laser plasma interactions in ignition relevant regimes. A hydrodynamic feature of these targets is an inward traveling blast wave or density spike. These blast waves are perturbations that are important to the laser plasma interaction (LPI) physics. In the case of gasbags, they define an ever decreasing ``interaction'' region where the plasma conditions are relatively uniform. In higher density targets, they compromise the interpretation of Raman backscatter measurements since the density spikes tend to heavily absorb the longer-wavelength Raman light. In this paper we discuss the hydrodynamics of blast waves in LPI. We show the scaling, under fluid approximation, of blast wave density and velocity verses input parameters such as: laser intensity, skin density, gas density, Atwood number, etc. We present analytic modeling that simply explains the hydrodynamics and explore some ways in which to reduce the perturbations: pulse shaping and replacing the window with intermediate density closed cell foams. This work was performed under the auspices of the U.S. Department of Energy by University of California, Lawrence Livermore National Laboratory under Contract W-7405-Eng-48, UCRL-ABS-213751. [Preview Abstract] |
Tuesday, October 25, 2005 9:42AM - 9:54AM |
FO2.00002: Plasma filling in small, hot targets at the NIF and OMEGA lasers* M.B. Schneider, D.E. Hinkel, B.K. Young, J.P. Holder, A.B. langdon, L.J. Suter, O.L. Landen, D.H. Kalantar, R. Kirkwood, B.J. MacGowan, S.N. Dixit, A.J. Mackinnon, J.W. McDonald, M.J. May, C. Niemann, K.M. Campbell, J. Schein, F. Weber, K. Widmann, H.A. Baldis, C. Constantin, S. Ross, W. Seka, R. Bahr, C. Stoeckl, V. Glebov, G. Holland, J. Seely, J.F. Foster An experimental campaign to study radiation drive in small-scale hohlraums has been carried out at the NIF laser$^{1}$ and at the OMEGA laser.$^{2}$ Approximately 9.5kJ in 1nS of 351nm light in one on-axis beam (at NIF) or divided among 3 beam cones (at OMEGA) is used to heat 560 -- 600$\mu $m gold cans. The targets fill with plasma so quickly that, late in time, most of the laser energy is deposited at the laser entrance hole. The plasma filling and final radiation drive is a function of the geometry. The experimental results on x-radiation drive, laser backscatter, hard x-rays, hard x-ray imaging, and x-ray burnthrough versus geometry are discussed. \textbf{1.} Phys. Plasmas \textbf{12, }056305, (2005) 2. \textit{Inertial Fusion Sciences and Applications 2003 (IFSA03),} pp 242{\-}246 (2004). *Work performed under the auspices of the U.S. Department of Energy by the Lawrence Livermore National Laboratory under Contract No. W-7405-ENG-48 {\&} Grant Num DE-FG52-2005NA26017 (NLUF) [Preview Abstract] |
Tuesday, October 25, 2005 9:54AM - 10:06AM |
FO2.00003: The KL Mix Model Applied to Directly Driven Capsules on the Omega Laser Robert Tipton, Karnig Mikaelian, Hye-Sook Park, Guy Dimonte, J.R. Rygg, C.K. Li During the past few years the KL mix model has been applied to a variety of laser capsules with some success. Recently Guy Dimonte has found analytical solutions to the KL equations for the cases of Rayleigh-Taylor (RT) and Richtmyer-Meshkov (RM) instabilities. These analytical solutions not only increase our confidence in the value of the KL equations but also show how to set the seven coefficients of the model so as to match the RT and RM experiments and to maintain the condition of self-similarity$^{2}$. In this talk, results will be presented from the KL mix model applied to a variety of directly driven capsules fired on the Omega laser. The capsules studied include a range in laser drive energy, convergence ratio, ablator thickness and ablator type (CH or SiO$_{2})$. In general, the KL calculations using Dimonte's latest coefficients are able to match the DD primary neutron yields, the DT secondary neutron yields as well as the DHe3 proton yields on most of the capsules. $^{2}$See Guy Dimonte, ``K-L turbulence model for Rayleigh-Taylor and Richtmyer-Meshkov instabilities'' in this conference [Preview Abstract] |
Tuesday, October 25, 2005 10:06AM - 10:18AM |
FO2.00004: Self-Similar Evolution of Dense Plasmas into Nano-Clusters Yong W. Kim, Hedok Lee A dense laser-produced plasma (LPP) plume of aluminum atoms terminates in atomic clusters of nanometer dimensions. Their formation and growth process has been investigated by first determining the structure and its subsequent evolution of the LPP plume. To this end, a new robust method has been developed for reconstruction of the 3-D structure of a LPP plume as a function of time.[Kim, Lee, \textit{Rev. Sci. Instr. }\textbf{75}, 3953 (2004)] From the reconstructed structure, we follow the paths of plasma cooling to super-saturation below the gas-liquid critical point of aluminum. More than 100,000 cells of the plasma plume have been followed in time. Nano-cluster formation by atom-atom and atom-cluster collisions in each cell is then computed. The resulting clusters grow larger in size and broader in distribution over time but in a manner that is strikingly self-similar. This self-similarity is utilized to transform the clustering computation in each of the 100,000 cells into the scaling of the maximal population and size with the initial cellular atom density at large times. The computed cluster size distribution is in excellent agreement with the histogram of nano-clusters sampled from laboratory LPP experiments. [Preview Abstract] |
Tuesday, October 25, 2005 10:18AM - 10:30AM |
FO2.00005: Ion Temperature Measurements Behind a Normal Ionizing Shock Wave Chavis Raynor, Joseph Johnson III, Nirmol Podder It is generally accepted that thermodynamic properties like density, velocity, temperature, and pressure are important to our understanding of turbulent plasmas. It is also generally accepted that the understanding and manipulation of turbulent plasmas is paramount to the operation of a successful fusion device. Some of these thermodynamic properties can be measured directly, while others are derived indirectly. For example, the ion temperature in high temperature plasmas are usually either assumed to be equal to the electron temperature, or derived from equations that relate it to other thermodynamic properties of the plasma that can be directly measured. However, direct measurement of the ion temperature may provide deeper insight into the role of turbulent parameters. To investigate this, Doppler broadening of the H$_{\beta }$ line profile behind a normal ionizing shock wave in a Hydrogen-Argon mixture is used. A comparison of these measurements with standard thermodynamic properties and turbulent parameters will be done. [Preview Abstract] |
Tuesday, October 25, 2005 10:30AM - 10:42AM |
FO2.00006: Nonlinear generation of ion-acoustic harmonics by stimulated Brillouin scattering Dustin Froula, L. Divol, C. Rousseaux, S. Ross, N. Meezan, D. Price, S. Dixit, S. Glenzer Thomson-scattering experiments in well-characterized laser-produced plasmas have directly observed the primary ion acoustic wave driven by stimulated Brillouin scattering (SBS) together with its harmonics. This work introduced a novel technique to first characterize the dispersion of thermal ion-acoustic fluctuations by applying Thomson-scattering at multiple probe wavelengths. This technique has provided accurate data on both the local electron density and temperature with high temporal and spatial resolution under which we have studied the generation of harmonics. The amplitudes of the second and third harmonics at wave-numbers 4k$_{o}$, and 6k$_{o}$ indicate strong saturation of the primary ion-acoustic wave that itself is driven at 2k$_{o}$. The accurate knowledge of the plasma conditions further allows comparisons with modeling of the fluid nonlinear processes that lead to the generation of harmonics. These processes limit the SBS reflectivity in underdense inertial confinement fusion plasmas and are important for the simulation of laser-plasma interactions in ignition targets for the National Ignition Facility. This work was performed under the auspices of the U.S. Department of Energy by University of California Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48. [Preview Abstract] |
Tuesday, October 25, 2005 10:42AM - 10:54AM |
FO2.00007: Detrapping accelerations in a strong electron-beam Tsuyoshi Takeda, Keiichiro Yamagiwa Modulation instabilities and particle-trapping have been observed in space plasmas, and thus it is important to simulate such phenomena in laboratory experiments. In our previous works, electron-beam holes induced by self-trapping were experimentally turned up in phase-space in a weak electron-beam, and their behaviors from emergences to collapses were exhibited [1]. In this work, the self-trapping is further investigated in a strong electron-beam. It is observed that electron-beam branches are formed next to the holes in the high velocity side, and expand with time. These imply that the beam-electrons are detrapped from potential wells of a wave packet. It is confirmed with plotting velocity tips of the branches that the square velocities are proportional to the positions. This proves that accelerations for the beam occur as a result of taking away the wave energy. The holes may play an important role in the accelerations.\newline \newline [1] T. Takeda and K. Yamagiwa, Phys. lett. A, \textbf{339}, 118-122 (2005). [Preview Abstract] |
Tuesday, October 25, 2005 10:54AM - 11:06AM |
FO2.00008: 3D Instability and Subsequent Saturation of an Electron Beam Penetrating an Overdense Plasma A.G. Sgro When an electron beam encounters an over dense plasma, the beam is quickly destabilized and dispersed. However, it was shown previously\footnote{A. G. Sgro and T. J. T. Kwan, Phys. Plasmas 10, 849 (2003)} by means of 2D simulations that over long time scales the beam ejects background electrons from the region where the beam is propagating, leaving background ions to neutralize the beam charge, thus stabilizing the beam propagation. The present paper extends these simulations to 3D. It is shown that 3D modes, including non axial kink modes, grow and disperse the beam to the diameter of the simulation box, and just as in the 2D simulations, over long time scales the beam also ejects background electrons from the region where the beam is propagating, thereby stabilizing the propagation in 3D also. These simulations thus show that the stable beam propagation at longer times that was found in the 2D simulations is also found when 3 dimensional perturbations are excited. [Preview Abstract] |
Tuesday, October 25, 2005 11:06AM - 11:18AM |
FO2.00009: Stochastization as a cause of fast reconnection of neoclassical tearing modes Olgierd Dumbrajs, Valentin Igochine, Dana Constantinescu, Hartmut Zohm We analyze the role of stochastization of magnetic field lines in fast reconnection phenomena occurring in a magnetized fusion plasma. We use a mapping technique for the field lines of a toroidally confined plasma where the perturbation parameter is expressed in terms of experimental perturbation amplitudes determined from the ASDEX Upgrade tokamak. It is found that fast reconnection observed during amplitude drops of the neoclassical tearing mode instability in the frequently interrupted regime can be related to stochastization [Preview Abstract] |
Tuesday, October 25, 2005 11:18AM - 11:30AM |
FO2.00010: Elliptic and hyperelliptic magnetohydrodynamic equilibria Henri Tasso, George Throumoulopoulos We construct three classes of axisymmetric equilibria with incompressible flow nonaligned with the magnetic field reducible to elliptic integrals and having similar magnetic field characteristics. They are restricted by appropriate side conditions like ``isothermal'' magnetic surfaces, ``isodynamicity'' or $P+B^{2}/2$ constant on magnetic surfaces. The third class is closely related to recent equilibria found in Schief, Phys. Plasmas 10, 2677 (2003). In contrast to field aligned flows, all solutions found here have nonzero toroidal magnetic field on and elliptic surfaces near the magnetic axis. [Preview Abstract] |
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