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 FP1: Poster Session III |
Hide Abstracts |
Room: Adam's Mark Hotel Grand Ballroom I & II 9:30am |
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FP1.00001: ICF DIAGNOSTICS/LPI/HOHLRAUM PHYSICS |
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FP1.00002: The CVD Diamond Detector As A Neutron Spectrometer For ICF Implosions Thomas W. Phillips, L.S. Dauffy, J.A. Koch, M.J. Moran, G.J. Schmidt, V. Yu. Glebov, T.C. Sangster, C. Stoeckl, S.A. Wender, E.C. Morse Using CVD diamond in current mode to measure the neutron energy spectrum from ICF implosions is a challenge. The diamond sensitivity to neutrons varies with energy. The accuracy with which this variation is known will be presented. The limit which this places on measuring the down-scattered fraction of the fusion neutrons will be discussed. 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] |
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FP1.00003: White light parametric instabilities Jorge Santos, Luis Silva, Robert Bingham The Wigner formalism of quantum mechanics provides an alternative formulation to describe waves propagating in a dispersive medium. However the wave equation describes a two mode problem, and all previous theoretical models, based on the Wigner-Moyal equation, only deal with the single mode problem, where propagation is assumed to obey a Schr\"{o}dinger-like equation. We first present a formulation to describe the laser propagation in a cold plasma based on the Wigner formalism generalized to Klein-Gordon like-fields. We constructed a 2x2 Wigner matrix on the basis of the Hamiltonian form of the Klein-Gordon equation of a charged scalar particle field. The system of coupled transport equations governing the evolution of the photon densities in phase-space is then derived; this system is formally equivalent to the full wave equation. The system of transport equations for the photons is coupled with the relativistic fluid equations for the plasma. A general dispersion relation is obtained and, from first principles, the effect of a broadband radiation spectrum on stimulated Raman scattering is studied. [Preview Abstract] |
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FP1.00004: Non-Maxwellian effects in underdense plasmas heated by non-uniform laser beams Jean-Pierre Matte The collisionl heating of plasmas by intense laser beams is known to drive the electron distribution function into a super-Gaussian [1] or ``DLM'' [2] shape. This reduces the absorption [1], and the reduction is stronger if the beam is very non-uniform, for a given average intensity, as there is a depletion of slow electrons, compared to a Maxwellian of the same density and average energy. If the beam irradiates most or a good fraction of the plasma volume, these non-Maxwellian effects also imply a depletion of high energy electrons, with the resulting strong reduction of Landau damping of Langmuir waves [2], contrary to the results of Brunner and Valeo [3] which were obtained in the limit of a narrow beam heating a wide plasma. The depletion of fast electrons depends essentially on the average laser intensity. We will show how these two aspects vary with the laser and plasma parameters.\newline \newline [1] A.B. Langdon, Phys. Rev. Lett. \textbf{44}, 575 (1980) \newline [2] B.B. Afeyan, A.E. Chou, J.P. Matte et al., Phys. Rev. Lett. \textbf{80}, 2322 (1998). \newline [3] S. Brunner and E. Valeo, Phys. Plasmas \textbf{9}, 923 (2002). [Preview Abstract] |
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FP1.00005: Demonstration of beam propagation through hohlraum plasmas at NIF like temperatures Christoph Niemann, Laurent Divol, Dustin Froula, Gianluca Gregori, Ogden Jones, Robert Kirkwood, John Moody, James Ross, Charles Source, Laurence Suter, Siegfried Glenzer We have measured the propagation and backscatter of a 2$\omega$ (527 nm) high intensity ($\sim$5x10$^{14}$ W/cm$^2$) interaction beam through large-scale length plasmas at NIF like temperatures of up to 4 keV. The plasma is created by heating 2 mm x 1.6 mm diam. hohlraum targets with 37 defocused heater beams at 3$\omega$, delivering a total energy of 16 kJ in a 1 ns square pulse. A dedicated 2$\omega$ interaction beam probes the preformed plasma along the hohlraum axis. We have measured beam propagation and backscatter both in gas-filled and in foam-filled targets at 2$\omega$ NIF design densities around n$_e$/n$_c$=5\% (at 3$\omega$). We observe a beam transmission as high as 80\% with negligible SRS reflectivity and modest levels of SBS. Both 2$\omega$ and 3$\omega$ SBS spectra and Thomson scattering measurements are consistent with a plasma temperature above 3.5 keV, which is a factor of two higher than the temperatures in gasbag-plasmas that were studied previously. [Preview Abstract] |
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FP1.00006: Particle-In-Cell Simulations of the Two Plasmon Decay Instability in 2D and 3D F.S. Tsung, W.B. Mori, B.B. Afeyan A particle-in-cell code (OSIRIS) is used to investigate the two-plasmon decay instability in a nonuniform plasmas of various profiles. We find good agreement between the simulation and linear theory by Afeyan et al. (Phys. Plas. \textbf{4}, 3827, 1997.) By varying the lateral width of the laser drive, as would occur in a laser hot spot, the two-plasmon decay instability can be controlled and even suppressed and our simulations have verified this. As these plasmons grow, they can also accelerate electrons to relativistic energies. The temperature of the fast electrons appears to follows Coffey's wave breaking prediction. Additionally, we have also begun to look at the effect of oblique laser incidence. It can be shown that the most unstable modes are rotated by the angle of incidence. Hence, one plasmon is now more aligned with the density gradient while the other plasmon is now moves along the density gradient in a much shallower angle. The mode which is aligned to the density gradient becomes more stable because it spends less time in the resonant layer, and vice versa. While this trend can be obtained through simple geometric arguments, the quantitative theory for this effect had not been worked out until 1997 by Afeyan and Williams. [Preview Abstract] |
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FP1.00007: Dielectric Function and Nonlocal Transport in Two Component Plasmas A.V. Brantov, V. Yu. Bychenkov, W. Rozmus, Z. Zheng, C.E. Capjack A systematic procedure has been proposed [1] for finding the solution to a linearized kinetic equation for electrons with the Landau collision integral. Expressions for dielectric permittivity of a collisional plasma and nonlocal transport theory are obtained using this procedure for the entire range of frequencies, wave numbers, and the collision parameter. Our results reproduce well known limiting values in the strongly collisional and collisionless limits. In the present work we apply the method of Ref. [1] to the full set of linearized plasma kinetic equations which include ion dynamics and ion-ion, ion-electron collisions in the Landau form. The solution of the linearized ion kinetic equations parallels application of [1] to the low-Z plasmas as discussed in Ref. [2]. We have used this method to construct closure relations for ion transport theory and ion dielectric function. Thus we have derived the full set of nonlocal and nonstationary hydrodynamical equations in two component plasmas. They have been applied to study ion acoustic wave damping and dispersion. We have discussed ion effects on the zero frequency entropy mode. [1] A. V. Brantov, \textit{et al.}, Phys. Rev. Lett., \textbf{93}, 125002 (2004). [2] V. Yu. Bychenkov \textit{et al}, JETP \textbf{87}, 916 (1998). [Preview Abstract] |
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FP1.00008: Effects of Ion-ion Collisions and Inhomogeneity in Two-dimensional Simulations of Stimulated Brillouin Backscattering* B.I. Cohen, A.B. Langdon, L. Divol, E.A. Williams Two-dimensional simulations of stimulated Brillouin backscattering (SBBS) with the BZOHAR$^{1}$ code have been extended to include ion-ion collisions and spatial nonuniformity in the mean ion flow. BZOHAR hybrid simulations (particle-in-cell kinetic ions and Boltzmann fluid electrons) have shown$^{2}$ that SBBS saturation is dominated by ion trapping effects and secondary instability of the primary ion wave (decay into subharmonic ion waves and ion quasi-modes). Here we address the effects of ion collisions$^{3}$ on SBBS saturation and employ the efficient Langevin ion collision algorithm of Ref. 4 and the Fokker-Planck collision operator of Ref. 5. We also report simulations of SBBS with a linear gradient in the mean ion drift, which in conjunction with the nonlinear frequency shift due to ion trapping can introduce auto-resonance effects that may enhance reflectivities.$^{6}$ For SBBS in a high-gain limit with ion collisions or inhomogeneity, we find that ion trapping and secondary ion wave instabilities are robust saturation mechanisms. *Work performed for US DOE by UC LLNL under Contr. W-7405-ENG-48. $^{1}$B.I. Cohen, \textit{et al.,} Phys. Plasmas \textbf{4}, 956 (1997). $^{2}$B.I. Cohen, \textit{et al.}\textbf{, }Phys. Plasmas, \textbf{12}, 052703 (2005),. $^{ 3}$P.W. Rambo, \textit{et al.}, Phys. Rev. Lett. \textbf{79}, 83 (1997). $^{ 4}$M.E. Jones, \textit{et al.,} J. Comp. Phys. \textbf{123}, 169, (1996). $^{ 5}$W. M. Manheimer, \textit{et al}., J. Comp. Phys. \textbf{138}, 563 (1997). $^{ 6}$E.A. Williams, \textit{et al.}, Phys. Plasmas \textbf{11}, 231 (2004). [Preview Abstract] |
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FP1.00009: Laser Plasma Instability Reduction by Coherence Disruption and Other Techniques William Kruer, Peter Amendt, Nathan Meezan, Larry Suter Additional techniques to control laser plasma instabilities can enlarge the parameter space for ignition target designs on the National Ignition Facility. Recent experiments$^{1}$ on the Helen laser facility suggest that coherence disruption (in this case by modified electron distribution functions$^{2 }$ in higher Z targets) can significantly reduce the stimulated Brillouin reflectivity. We explore techniques to possibly engineer coherence disruptions in NIF hohlraums, say, by modulations in the liner composition or by manipulation of the plasma flow. Experiments to test these ideas in Omega experiments are outlined. We also explore other techniques for instability reduction, including conversion of plasma expansion energy into ion thermal energy. \begin{enumerate} \item R. M. Stevenson, \textit{et. al.,} Phys. Plasmas 11, 2709 (2004) \item B. B. Afeyan, \textit{et. al., }Phys. Rev. Lett. 80, 2322 (1998) \end{enumerate} This work was performed under the auspicies of the U.S. Department of Energy by the University of California Lawrence Livermore National Laboratory under Contract No. W-7405-Eng-48 [Preview Abstract] |
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FP1.00010: Beam Conditioning Mitigation of Laser Plasma Instabilities at the National Ignition Facility B. Langdon, E. Williams, D. Hinkel, S. Dixit, R. Kirkwood, D. Munro Several beam conditioning measures are planned for the National Ignition Facility. These include phase plates, smoothing by spectral dispersion (SSD), polarization smoothing (PS), and a color shift between inner and outer beam cones (``two color''). The latter reduces inter-cone power transfer in the plasma flowing out of the entrance hole in indirection drive ignition targets by introducing a frequency mismatch between the beam cones. We present simulation studies and analysis of the interaction of SSD and power transfer for beams smoothed by phase plates. In part, SSD effectively broadens the sonic resonances, eroding the mismatch, and we predict also that SSD also can introduce an oscillation in the power transfer at the modulator frequency of 17 GHz. However, a flexible span of ``two color'' wavelength shift minimizes power transfer. We also present analysis of effects of SSD on beam spray due to forward Brillouin scatter near the threshold for filamentation. [Preview Abstract] |
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FP1.00011: Aggregate model of backward stimulated Raman scattering in a random-phase-plate smoothed laser beam B.J. Albright, W. Daughton, Lin Yin, Q. Roper, K.J. Bowers, J.L. Kline, D.S. Montgomery, J.C. Fern\'{a}ndez Single-hot-spot experiments allow studies of dynamics in media that resemble hot spots of random-phase-plate (RPP) smoothed inertial confinement fusion (ICF) beams. Recently, a parametric coupling involving backward stimulated scattering of a laser and electron beam acoustic modes (BAM) has been described by theory and is observed in particle-in-cell (PIC) simulations where rapid increases in reflectivity with intensity occur with the emergence of BAM modes. This scaling is similar to that observed in the LANL Trident experiments. In this presentation, a discrete model is presented of the aggregate effects of a RPP-smoothed laser beam in which the individual elements are correlation lengths of the random laser field. The model is calibrated to reflectivities from 1D and 2D PIC simulations. In the linear gain regime, the backscatter intensity obeys a power-law. In long or strongly driven systems, nonlinear saturation ensues. [Preview Abstract] |
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FP1.00012: Two-Dimensional Particle-In-Cell Studies of Backward Stimulated Raman and Brillouin Scattering In Laser-Driven Hot Spots Lin Yin, W. Daughton, B.J. Albright, K.J. Bowers, J.L. Kline, D.S. Montgomery, J.C. Fern\'{a}ndez A parametric coupling involving backward stimulated scattering of a laser and electron beam acoustic modes (BAM) has been described by theory and is observed in 1-D Particle-In-Cell (PIC) simulations [L. Yin et al., Phys. Rev. Lett., submitted (2004)]. The BAM evolve from Langmuir waves as the electron velocity distribution is nonlinearly modified, resulting in reduced damping at the parametric resonance where enhanced reflectivity pulses are coupled to an electrostatic streak, as observed in the Trident single hot spot experiments at LANL [J. L. Kline et al., Phys. Rev. Lett., 94, 175003, 2005]. In this work, SRS is further examined using 2D PIC simulations, including processes in which the spectral streaking can be arrested by 2D effects, such as the transverse loss of hot electrons and filamentation of the laser speckle, and by the inclusion of the ion dynamics. Changes in ion composition that could result in a clear transition from an SRS- to SBS-dominated regime are also identified. [Preview Abstract] |
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FP1.00013: An Improved Model for Studying the Role Played by the Trapped Particle Instability in SRS Simulations Stephan Brunner, Ernest Valeo Simulations under laser-fusion conditions have shown the potential role played by the trapped-particle instability (TPI) in saturating the non-linear evolution of Stimulated Raman Scattering (SRS). The TPI may indeed act as a secondary instability by breaking-up the primary electron plasma wave [S. Brunner and E. Valeo, Phys. Rev. Lett. {\bf 93}, 145003-1 (2004)]. First analysis of simulation results were performed using the reduced model of Kruer for the TPI [W.~L.~Kruer {\it et al.}, Phys. Rev. Lett. {\bf 23}, 838 (1969)]. An improved analysis tool has now been developed which directly implements the general linear stability theory of large BGK-like plasma waves [M. Goldman, Phys. Fluids {\bf 13}, 1281 (1970)]. The implementation of this stability analysis tool, and its application to the SRS simulation results will be presented. [Preview Abstract] |
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FP1.00014: Models of the SRS-SBS coupling for NIF E.S. Dodd, D.F. DuBois, B. Bezzerides, H.X. Vu For about 20 years experimental and theoretical evidence has accumulated showing the anti-correlation of SRS and SBS backscatter reflectivity levels. Using reduced particle-in-cell (RPIC) methods, we study these instabilities in regimes where the temporal behavior is characterized by bursts of SRS and SBS reflectivity due to electron and ion trapping in the daughter electrostatic waves-Langmuir waves (LW) and ion acoustic waves (IAW), respectively. SRS is observed to die as soon as SBS begins to grow from low levels. The temporal envelope of the SRS LW obeys a Schrodinger equation where, for this problem, the potentialis the periodic electron density fluctuation, $n_{IAW}$, resulting from the SBS IAW. The LW in this case have a Bloch wave structure with a distorted frequency dispersion, including frequency band gaps at $k_{LW}~k_{IAW}/2~k_{l}$. This band structure is observed in RPIC $\omega$, k spectra of the LWs, which is functionally equivalent to experimental Thomson scatter spectra. The frequency distortion increases as $n_{IAW}$ increases in time, resulting in a time dependent frequency shift of the LW that detunes SRS. Simulations in laser and plasma parameter regimes typical of NIF targets and for Trident single hot spot experiments show similar behavior. This work can lead to a model of the SRS-SBS coupling for macroscopic simulations such as pF3d. [Preview Abstract] |
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FP1.00015: Simulations of Stimulated Raman Scattering in One and Two Dimensions B.J. Winjum, F.S. Tsung, W.B. Mori, A.B. Langdon Using the full-PIC code OSIRIS, we have studied stimulated Raman scattering (SRS) over a wide range of parameters relevant to NIF. In previous one-dimensional simulation studies using reduced PIC, Vlasov, or full PIC models, the modification of the electron distribution function and electron trapping effects are believed to play the dominant role in explaining the recurring behavior of SRS reflectivity. Vu et al., have proposed that a nonlinear frequency shift due to the trapped particles detunes the instability, Brunner and Valeo argue that the trapped-particle instability is the dominant saturation mechanism, while L. Yin et al., claim that electron beam acoustic modes are important. We will discuss the role played by each of these effects in OSIRIS simulations, as well as the importance of plasma wave convection on the recurrence of SRS reflectivity. In extending the simulations to two dimensions, we will discuss side-scattering and electron trapping by both forward and backward SRS. When the laser intensity is near-threshold for SRS and the laser is focused to a finite width, we find that the physics remains rather one-dimensional. On the other hand, for plane-wave lasers, as well as for higher-intensity lasers, the physics becomes multi-dimensional. Simulations performed on the Dawson Cluster under support of NSF grant NSF Phy-0321345. Work also supported by DE-FG02-03-NA00065. [Preview Abstract] |
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FP1.00016: Hot electron generation during ICF target compression Chuang Ren, Gang Li, Valeri Goncharov Yield degradation in ICF experiments is commonly attributed to hydrodynamic instabilities developed during shell implosion.. Preheating of the fuel shell due to the hot electrons generated by the drive laser could be a potential source of an additional yield reduction. A PIC code – OSIRIS is used to simulate the laser-plasma interactions and hot electron generation in two- dimensional space. For a typical run, the laser intensity is $3 \times 10^{15} W/cm^2$ ($\lambda=0.353 \mu m$) with a spot size of 3.4 $\mu m$. The density profile, taken from the simulations using hydrocode LILAC, changes from 0 to 0.3 $n_c$ in ~300 $\mu m$. The simulation box is 300 $\mu m$ in x direction and 12 $\mu m$ in y direction and the simulation time is up to 1.5 ps. Parametric instabilities such as Raman scattering and two-plasmon decay will be studied. Laser absorption and electron energy spectra in this regime will be presented. [Preview Abstract] |
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FP1.00017: Scaling of stimulated Raman scattering with laser irradiation conditions in high-temperature halfraums* Carmen Constantin, Hector Baldis, Marilyn Schneider, Denise Hinkel, Bruce Langdon, Wolf Seka, Raymond Bahr, Sylvie Depierreaux Measured stimulated Raman scattering in subcritical plasmas at electron temperature above 10 keV show the dependence of Raman instability temporal behavior and reflectivity on the irradiation incidence angle, target size and laser beam conditioning. These plasmas are created in reduced-scale, high-Z hohlraums that represent novel platforms for studying material properties in high radiation temperature environments. To reach an optimal radiation performance, the mitigation of parametric instabilities that reduce laser energy coupling to the target is of crucial importance. The targets were irradiated using the OMEGA laser beams at Laboratory for Laser Energetics (Rochester, NY), at intensities up to 1x10$^{16}$ W/cm$^{2}$, in 1 ns pulses of blue light (351 nm). The Raman spectra indicate the plasma is in regimes where the Bohm-Gross shifts are significant. Plasma parameters are inferred from these data and compared with simulations. **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 and grant number DE-FG52-2005NA26017 (NLUF) [Preview Abstract] |
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FP1.00018: Analytic Expressions for Cocktail Hohlraum Wall Losses Mordecai Rosen, Ogden Jones, Laurance Suter We apply recent analytic solutions [1] to the radiation diffusion equation to problems of interest for ICF hohlraums. The solutions provide quantitative values for absorbed energy which are of use for generating a desired radiation temperature vs. time within the hohlraum. In particular we use analytic fits to the rosseland mean opacity and to the specific heat of combinations of materials (``cocktails'') designed to maximize the former while minimizing the latter. By doing so we find good agreement with numerical simulations. In particular we find that the wall loss savings of cocktails vs. the standard gold walled hohlraums have both pulse-length and temperature dependencies. Due to those dependencies we predict that NIF cocktail hohlraums will perform better than present day cocktail experiments.\newline \newline [1] J.H. Hammer and M. D. Rosen, pop \textbf{10}, 1829 (2003). [Preview Abstract] |
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FP1.00019: Calculations of NIF Ignition Hohlraum at 1 MJ Laser Energy Norman Delamater, Paul Bradley, Doug Wilson, Glenn Magelssen Preliminary results of a 2-D design study using the LASNEX hydrodynamics code are presented for a SiO$_2$ foam filled hohlraum containing a Cu-doped Be ignition capsule. The hohlraum wall consists of a Au-U-Dy ``cocktail'' designed to maximize the amount of x-ray energy for the capsule to absorb, given the 1 MJ laser energy into the hohlraum. The foam fill acts to minimize wall expansion while maintaining symmetric drive on the capsule. Various foam densities and laser pointings for most efficient drive are considered. Sensitivities to drive asymmetries during the long ``foot'' portion of the laser drive are also considered as well as possible symmetry measurement techniques for NIF foot conditions, such as using a reemission ball. This work was performed under the auspices of the U.S. Department of Energy by the Los Alamos National Laboratory, under Contract No. W-7405-Eng-36. [LA-UR-05-5266] [Preview Abstract] |
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FP1.00020: Interpretation of symmetry experiments on Omega Laurence Lours, Marie-Christine Monteil, Franck Philippe, Jean-Paul Jadaud, Michel Naudy, Bruno Villette Since 1999, CEA has performed experiments on Omega in collaboration with LLNL. A summary of the symmetry shots with 3 cone LMJ-like irradiation (1999-2004) is presented here. The capsules used are Si foamballs, but a radiography test has also been performed with a 50 micron thick CHGe ablator capsule. Taking into account the measured backscattering, the radiation temperature can be compared to FCI2 calculations, as well as the evolution of the mean radius of the ablation front and the 2$^{nd}$ and 4$^{th}$ order distortions. The symmetry of foamballs is well predicted in FCI2 simulations, either with isotropic or anisotropic laser configuration. [Preview Abstract] |
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FP1.00021: Z-pinch double-ended hohlraum energetics, coupling, and symmetry modeling compared with Z data R.A. Vesey, M.E. Cuneo, G.R. Bennett, J.L. Porter, T.A. Mehlhorn Symmetry tuning in the pulsed-power driven double-ended vacuum hohlraum allows highly symmetric capsule implosions, aided by the separation of the capsule from the z-pinch and its associated instabilities, spatial variations, and non-thermal spectral components. X-ray backlit capsule experiments at Z have demonstrated the ability to predictably nullify and control time-integrated P$_{2}$ asymmetry [1], and have measured the sensitivity of P$_{2}$ and P$_{4}$ asymmetry to hohlraum geometric parameters (hohlraum length, case-to-capsule ratio, etc.). Detailed two-dimensional Lasnex hohlraum simulations of these experiments will be presented. These simulations include: hohlraum radiation transport, time-dependent asymmetry due to z-pinch source motion, hohlraum absorption/re-emission, wall plasma motion, and the capsule ablation and implosion process. The measured trends in P$_{2}$ and P$_{4}$ can be generally understood using these simulations, although quantitative uncertainties remain as to the precise sources of these modes within the hohlraum. [1] G. R. Bennett \textit{et al}., Phys. Plas. \textbf{10}, 3717 (2003), R. A. Vesey \textit{et al}., Phys. Plas. \textbf{10}, 1854 (2003). [Preview Abstract] |
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FP1.00022: Calculating and Measuring Self-Generated Magnetic Fields in Hohlraums R.P.J. Town, W.E. Alley, M.J. Edwards, J.H. Hammer, L.J. Suter, M. Tabak, G.B. Zimmerman, D.H. Froula, S.H. Glenzer, G. Gregori, A.J. Mackinnon, P.K. Patel, M.G. Haines, C.K. Li, R.D. Petrasso The spontaneous generation of magnetic fields in laser-produced plasmas has been observed experimentally and theoretically by many authors. The main generation term for these fields is the well-known $\nabla $n$_{e}\times \nabla $T$_{e}$ term, where n$_{e}$ is the density and T$_{e}$ is the temperature. For typical laser-plasma conditions Mega-gauss magnetic fields are predicted to be generated. It has previously been shown that the main effect of these magnetic fields for Nova-scale hohlraums is to modify the electron temperature around the laser entrance hole [1]. We will review these calculations and report on recent calculations of NIF design-1 ignition hohlraums. We will also report on simulations to directly measure the magnetic fields using proton deflectometry [2]. We will assess the effect that the magnetic fields have on electron transport, laser-plasma instabilities, and symmetry in ignition and OMEGA hohlraums. [1] S. H. Glenzer, Contrib. Plasma Phys. \textbf{40}, 36 (2000). [2] A. J. Mackinnon, \textit{et al}, Rev. Sci. Instrum. \textbf{75}, 3531 (2004). This work was performed under the auspices of the U.S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48. [Preview Abstract] |
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FP1.00023: The effect of nonuniformities induced by the magnetic Rayleigh-Taylor instability on the radiation producing shock in z-pinch dynamic hohlraums R.W. Lemke, J.E. Bailey, G.A. Chandler, T.J. Nash, S.A. Slutz, T.A. Mehlhorn Z-pinch experiments were conducted on the Z accelerator in which a nested array, tungsten wire plasma implodes onto a CH$_{2}$ foam converter to create a $\sim $135 eV dynamic hohlraum (DH). We present results of an investigation to determine the effect that the magnetic Rayleigh Taylor (MRT) instability has on the radiating shock in a DH, and the associated radiated power. X-ray power exiting the DH was measured using arrays of x-ray diodes and bolometers, and x-ray pinhole cameras viewing along the DH axis recorded time and space resolved images of emission produced by the radiating shock. Measured emission intensities are compared with synthetic x-ray images from 2D, radiation MHD simulations in which the amplitude of MRT perturbations is varied. These comparisons show that the axial uniformity of the shock is insensitive to the MRT amplitude for density perturbations up to 1{\%}. Comparison of measured and simulated x-ray power puts an upper limit on the MRT amplitude, and provides evidence for the validity of some of the assumptions used to measure the power. [Preview Abstract] |
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FP1.00024: BASIC PLASMA: NON-NEUTRAL, WAVES \& INSTABILITIES, NONLINEAR PHENOMENA |
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FP1.00025: The first experimental results from the Columbia Non-neutral Torus Jason Kremer, Thomas Pedersen, Remi Lefrancois, Quinn Marksteiner, Xabier Sarasola CNT is a new, simple stellarator designed to study non-neutral plasmas on magnetic surfaces. A detailed field line mapping effort was conducted and confirmed the existence of magnetic surfaces, an aspect ratio of 1.9 and good agreement with numerical predictions. The method and results of this field line mapping effort will be presented. The first electron plasma experiments have been conducted in CNT. Electron plasmas are made by thermionic emission from a negatively biased, heated tungsten filament inserted directly into the magnetic surfaces. The total number of electrons confined is estimated to be $10^{11}$. Confinement time has been estimated to be 20 ms and preliminary measurements indicate that this may be limited by the presence of the emitter and diagnostic arrays. Current-voltage characteristics of emitting and non-emitting floating probes have been measured and have been used to estimate a temperature of 5 - 15 eV. Through these measurements, it is believed that the plasma criterion has been met. The details of these measurements and the progress on refining them will be presented. [Preview Abstract] |
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FP1.00026: Creation of pure electron plasmas in a stellarator using internal, multifilament emitters Quinn Marksteiner, Thomas Sunn Pedersen, Jason P. Kremer, Remi Lefrancois Pure electron plasmas have been created by injecting electrons from a set of tungsten filaments held inside the magnetic surfaces of the CNT stellarator. By changing the negative bias on these emitters as well as the voltage drop across each filament, we can control the plasma potential profile, allowing us to explore its effects on plasma confinement, density profile, temperature, and stability. First results have shown that the physical design of the electron emitter also strongly affect the plasma parameters. By simply reducing the length of the tungsten filaments and the amount of exposed metal, we observed an increase by a factor of two in confinement time. The insulating ceramic rods contribute significantly, perhaps dominantly, to particle losses. An order of magnitude calculation shows that the rod charges up negative and becomes self-shielding on a microsecond timescale, and that the ExB drifts in the vicinity of the rod from this self-shielding leads to convective transport across the surfaces. We will present a detailed discussion of the importance of the emitter design and operation on plasma parameters, and discuss theoretical estimates and experimental measurements of the cross-field losses due to insulating rods penetrating deep into the plasma. [Preview Abstract] |
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FP1.00027: Design of a Retractable Electron Emitter for the Columbia Non-neutral Torus John Berkery, Jason Kremer, Remi Lefrancois, Quinn Marksteiner, Thomas Pedersen One goal of the Columbia Non-neutral Torus (CNT) research program is to investigate enhanced confinement in stellarators due to high electric fields. Non-neutral plasmas have high electric fields and consequently are predicted to have very long confinement times. Such plasmas have recently been created in the CNT stellarator. However, the presence of a probe array and an electron emitter in the plasma appears to dominate the losses of electrons. Although this setup allows a detailed study of the plasma equilibrium, it cannot be used to study the enhanced confinement due to the strong electric fields. Therefore, in order to realize the possible enhanced confinement times, a retractable electron emitter will be employed. The electron emitter must be able to retract from the core of the plasma to the edge in a fraction of a second. At the same time, the emitter must be robust enough to handle the stresses of acceleration and deceleration during retraction. A design of the retractable electron emitters that addresses all of these issues will be presented, and key elements of the relevant plasma physics will be discussed. [Preview Abstract] |
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FP1.00028: Observation of Non-Uniformity of Space Potential on Magnetic Surfaces in Helical Nonneutral Plasmas Hidenori Wakabayashi, Haruhiko Himura, Mitsutaka Isobe, Shoichi Okamura, Keisuke Matsuoka In a series of experiments on the helical non-neutral plasmas, it is observed that the space potential is non-uniform on magnetic surfaces. The electron plasmas are generated by continuous injection of electrons for 40ms into the vacuum magnetic surfaces of the Compact Helical System at NIFS. Electrons are launched out with the acceleration voltage ($V_ {acc}$) from 300V to 1kV. The potential non-uniformity is almost proportional to $V_{acc}$. Experimental errors such as misalignment of the measurement probe and the perturbing effect of probe insertion are carefully checked, and confirmed not to be the reason of the observed potential variation. By a dimensional analysis of the force balance equation, one can find that the potential variation along the magnetic field line of force can be on the order of the electron temperature $T_e$. In our experimental sitiation $T_e$ is not known properly so far. But it is estimated to be a few hundreds of eV, and seems to be consistent with the observed variation of the space potential. [Preview Abstract] |
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FP1.00029: Update on the design and construction of an ultra high vacuum, kiloGauss scale toroidal electron plasma experiment M.R. Stoneking, Bao Ha, D.P. Ryan A toroidal electron plasma experiment is under construction at Lawrence University, a four-year college in Wisconsin. The design of the experiment ($B_o=1$ kG, $R_o=18$ cm, $a=2$ cm) is informed by results and experience gained operating an existing toroidal device ($B_o=200$ G, $R_o=43$ cm, $a=4.5$ cm). \footnote{M.R. Stoneking \textit{et al.,} Phys. Rev. Lett. \textbf{92}, 095003 (2004)} We provide an update on the design and construction of the new experiment, and present recent results from the existing experiment that yield confinement times as long as 40 ms. These results encourage the expectation that the new device will achieve confinement times of the order of 1 second, permitting measurement of long timescale transport processes. This work is supported by NSF and USDOE. [Preview Abstract] |
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FP1.00030: Experimental determination of the radial temperature profile in a non-neutral plasma Grant W. Hart, Bryan G. Peterson In 1992 Eggleston, et al.$^{1}$ reported on a technique for measuring the radial temperature profile in a pure electron plasma by partially dumping the plasma onto a charge collector. Several of their assumptions do not apply to our plasma, and so last year$^{2}$ we reported on a modified method which uses a form of equilibrium calculation to determine the temperature. We applied the method to the results of a simulation and found that it gave the correct temperature distribution, but we had no experimental data to apply the method to. We have now applied it to real data and found that the method was extremely sensitive to experimental noise. We have modified the method to make it less sensitive to noise and compared it to the standard `evaporation' method. These experimental results will be presented. \\ $^{1}$D.L.Eggleston, C.F. Driscoll, B.R. Beck, A.W. Hyatt and J.H. Malmberg, Phys. Fluids B {\bf 4}, 3432 (1992).\\ $^{2}$Grant W. Hart and Bryan G. Peterson, Bull. Am. Phys. Soc. {\bf 49}, 320. [Preview Abstract] |
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FP1.00031: A numerical investigation of the effects of bounce-resonant and velocity-resonant particles on Landau damping in a non-neutral electron plasma Bryan G. Peterson, Grant W. Hart We are investigating the Landau damping mechanism for electrostatic oscillation modes in a non-neutral electron plasma in a Malmberg-Penning trap. In particular we are examining the effects of velocity-resonant particles where the particle velocity is very near the wave phase velocity and bounce-resonant particles where the particle bounce frequency in the trap is near the oscillation frequency of the mode.\footnote{M. E. Koepke, Bull. Am. Phys. Soc., 49, 40 (2004).} Because the particle turning points are generally not coincident with the end nodes in the electrostatic oscillations, a particle can be bounce-resonant but not velocity-resonant, and vice versa. RATTLE, a PIC simulation code for a non-neutral plasma is being used to evaluate the effects of particle velocity distributions which do or do not contain resonant particles. [Preview Abstract] |
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FP1.00032: Particle Dynamics in Asymmetry-Induced Transport: a Computational Study D.L. Eggleston We have developed a simple computer code as an aid to resolving the discrepanies between our experiments\footnote{D.L. Eggleston and B. Carrillo, Phys. Plasmas {\bf 10}, 1308 (2003).} and the theory\footnote{D.L. Eggleston and T.M. O'Neil, Phys. Plasmas {\bf 6}, 2699 (1999).} of asymmetry-induced transport. The code employs the fourth- order Runge-Kutta method to advance the particles in prescribed fields matching our experiment. For a single helical asymmety $\phi(r)\cos{(kz+l\theta-\omega t)}$, significant motion in the radial direction is restricted to those particles near the resonant velocity. Both the location and the width of this resonance are consistent with expectations. When a standing wave asymmetry is used (i.e., two counter-propagating helical waves), additional dynamical behaviors are observed. Stocastic motion occurs when the resonant regions of the two waves overlap, allowing a larger population of particles to undergo large radial excursions. There is also a class of particles with restricted axial motion, as in trapped particle modes\footnote{A.A. Kabantsev et al., Phys. Rev. Lett. {\bf 89}, 245001 (2002).}. These particles, which also make large radial excursions, are located near the radius where $\dot{\theta}= \omega/l$. Further progress in understanding asymmetry-induced transport may require inclusion of these effects. [Preview Abstract] |
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FP1.00033: The effects of extreme magnetic quadrupole and octupole fields on Malmberg Penning traps, and the consequences for anti-hydrogen trapping Joel Fajans, Will Bertsche, Korana Burke, Steve Chapman, Alon Deutsch, Patrick Ko, Dirk van der Werf Recently, the ATHENA and ATRAP collaborations produced slow antihydrogen atoms at CERN. The neutral antihydrogen atoms are not confined by the charged-particle Malmberg-Penning traps used to confine the positrons and antiprotons from which the antihydrogen is made, so the atoms quickly annihilate on the trap walls. The most commonly suggested scheme to confine antihydrogen employs a diamagnetic, minimum-B neutral trap, typically produced by adding quadrupole and mirror fields to the solenoid field. The quadrupole fields destroy the cylindrical symmetry that underlies the Penning trap's outstanding performance, and the positrons and antiprotons might be lost before they form antihydrogen. This contention has been quite controversial; several papers have been published with opposing conclusions. Recent measurements at Berkeley establish that strong quadrupoles are indeed unacceptable. Theory and simulations suggest that octupoles would not destroy the charged particle confinement. Experiments with octupoles are planned this summer. [Preview Abstract] |
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FP1.00034: The design and testing of a neutral antihydrogen trap Dirk P. van der Werf, Alon Deutsch, Joel Fajans, Jeffey S. Hangst, Paul Bowe, Brett Parker CPT conservation can be tested by comparing the 1S-2S electronic transition of hydrogen and anti-hydrogen. These transitions can only be accurately measured when the (anti)-atoms are trapped. In order to confine neutral anti-hydrogen, a multipole magnetic field is added to a conventional Malmberg-Penning trap. Previous measurements have shown that a quadrupolar field has a detrimental effect on the positron and antiproton plasmas needed to produce the anti-hydrogen. Therefore, we chose to use an octupolar field in combination with two mirror coils for trapping the neutral atoms. Using a 0.9:1 Cu/Superconductor cable and a technique developed by Brookhaven National Lab we have been able to design a trap with a well depth of about 1 T. We will report on a technical test of the quench properties of the cable and the magnet using a smaller version of the final trap. A study of the mirror field as a possible switch for dumping the anti-hydrogen out of the trap will be presented. Subsequently we will show the design for the final antihydrogen trap. [Preview Abstract] |
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FP1.00035: Warp simulations for anti-Hydrogen trap Katia Gomberoff, Jonathan Wurtele, Joel Fajans, David Grote, Jean-Luc Vay The 3D Particle-In-Cell code, Warp, is used to study positron confinement in anti-hydrogen traps. The magnetic geometry is close to that of an experiment conducted at UC Berkeley as part of the ALPHA collaboration. In order to confine neutral anti-Hydrogen, a multipole magnetic field is added to a conventional Malmberg-Penning trap. Simulations in which the positrons are injected into the trap reproduce numerically the analytical estimates for the ballistic loss of positrons. There is a critical radius for the plasma column for which the particles do not escape. The analytical estimate of the critical radius, as a function of the fraction of the multipole magnetic field and the axial field are reproduced. In the cases studied, comparisons between quadrupole and octupole fields have shown that while most of the positrons escape the trap with a quadrupole, it is easy to design an effective trap with an octupole. We also consider simulations for plasma that is initially in equilibrium, as well as finding the equilibrium under the presence of a multipole that is slowly turned on. The effect of the slow E$\times $B rotation drift is discussed. [Preview Abstract] |
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FP1.00036: High Voltage Pulsed Power Operation of Inertial Electrostatic Confinement Device at LANL J. Park, R.A. Nebel, M.R. Kostora, C.R. Mansfield The inertial electrostatic confinement (IEC) system provides a favorable development path for practical fusion applications for technical simplicity, compact size, and long target lifetime. In order to improve the efficiency of the IEC system, a novel plasma heating concept based on a periodically oscillating plasma sphere (POPS) was proposed theoretically. Following the recent experimental confirmation of POPS oscillation, a high voltage pulsed power system has been constructed to provide fusion relevant voltages up to 75 kV. In this poster, we will present initial results about the virtual cathode formation and its stability using this pulsed power system. Separately, we will discuss the conventional IEC operation based on glow discharges at LANL for nuclear assay applications. [Preview Abstract] |
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FP1.00037: Delta-f simulations of electron Bernstein modes Nong Xiang, John R. Cary, Daniel C. Barnes, Johan Carlsson Full-wave modeling provides an excellent description of wave propagation and absorption in the interior of a toroidal fusion plasma. However, in the coupling region, from the RF launch structure a few centimeters into the plasma, physics neglected by full-wave theory (such as parametric decay) can dominate. In principle, the particle-in-cell (PIC) algorithm provides a complete description of the RF coupling physics. An outstanding problem in PIC simulations of electron Bernstein modes is that particle noise may obscure the physical process being modeled. For instance, in full PIC simulations of the electron Bernstein waves (EBW) the incident wave field is required to be about $10^6$ V/m in order for the EBW field not to be noise dominated, even with 400 particles per cell, and this incident field is not only larger than typical wave fields in the experiments, but also gives rise to significant nonlinear effects. Hence, full PIC is not practical for simulating linear Bernstein modes. To overcome these difficulties, we implemented the delta-f method in VORPAL, a massive parallel, hybrid plasma modeling code. Consequently we are able to model much lower values of the incident field, as low as 100 V/m. This makes practical the simulations of linear plasma-wave interactions. The simulation results are in good agreement with the available (small $k_ {\perp} \rho_e$) linear theory. Moreover, with delta-f simulation, the effects of finite electron temperature on the linear mode conversion between the extraordinary (X) and electron Bernstein waves can be explored. [Preview Abstract] |
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FP1.00038: Electron Bernstein Wave Heating in the TCV Tokamak Anja Mueck, Heinrich P. Laqua, Stefano Coda, Basil Duval, Timothy P. Goodman, Igor Klimanov, Yves Martin, Antoine Pochelon, Laurie Porte In high density plasmas, the O-mode wave cut-off can be overcome by the O-X-B mode conversion process. To optimize the O-X conversion and to achieve central Electron Bernstein Wave (EBW) absorption, a high density H-mode target plasma is developed with densities over \hbox{$n_e$ = $1\cdot10^{20}$m$^{-3}$}. Measurements of the variation in the Electron Cyclotron (EC) stray radiation with the EC injection angle will be shown. The measured angular window of the O-X conversion is in good agreement with the calculated size and position with the ART code. Further on, EBW heating experiments will be presented with modulated ECRH at the experimentally determined optimum angle with variations in the magnetic field and the modulation frequency. For the first time in an overdense plasma in a classical aspect ratio tokamak, heating with EBW via O-X-B mode conversion could be demonstrated and its localized deposition identified by cross-correlating the soft X-ray signal with the stray radiation signal.\\ A. Mueck is supported by a EURATOM fellowship. [Preview Abstract] |
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FP1.00039: ICRH under spatially inhomogeneous wave amplitude Gunyoung Park, C.S. Chang Ion cyclotron resonance heating of plasma ions is studied both numerically and analytically under an RF wave which has spatially inhomogeneous amplitude. Test particle wave-particle interaction is rigorously simulated in 6-dimensional phase space using a Lorentz equation of motion. It is found that the usual quasilinear heating operator is valid when the wave amplitude is spatially homogeneous. However, as the variation of the wave amplitude over a gyro radius becomes non-negligible, the heating dynamics changes dramatically and the well-known quasilinear heating operator is no longer valid. Both uniform magnetic field and non-uniform tokamak magnetic field geometries are examined. It is observed that the torsion and curvature of the magnetic field, through modification of gyroangle dynamics, can also lead to a non-negligible correction to the heating rate. An analytic theory is developed together, using a spatially varying wave amplitude without a Fourier decomposition of the wave field. An improved quasilinear heating operator is derived. [Preview Abstract] |
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FP1.00040: Phase-space Path Integrals for Vector Wave Equations and Linear Mode Conversion A.S. Richardson, E.R. Tracy, N. Zobin, A.N. Kaufman The use of path integrals in quantum mechanics was pioneered by Feynman, though key ideas were anticipated by Wentzel [1] and Wiener [2]. The treatment of classical wave equations, such as those in plasma physics, by path integral methods is mathematically identical to the quantum case, with the classical limit corresponding to the ray or WKB limit. Berezin [3] has developed a general method for recasting wave equations as path integrals. We consider regions where WKB assumptions are invalid and mode conversion occurs, a situation not previously considered. This leads to a new normal form for the local 2x2 wave dispersion matrix in the conversion region. Here the diagonals are interpreted as uncoupled dispersion functions, there are no avoided crossings, and the location of conversion along a ray is unambiguous.\\ \\ 1] S. Antoci and D.-E. Liebscher, Intl J Theo Phys 37 (1998) 531\\ 2] N.Wiener, Acta Math 55 (1930) 117\\ 3] F. A. Berezin and M. A. Shubin, The Schr\"{o}dinger Equation (Kluwer, 1991) [Preview Abstract] |
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FP1.00041: Mode Conversion via Invariant Imbedding D. G. Swanson The method of invariant imbedding\footnote{R.~Bellman and G. M. Wing, {\bf An Introduction to Invariant Imbedding}, (John Wiley and Sons, 1975)} offers an alternative for calculating the scattering coefficients for mode conversion problems. The advantage is that the wave equation need not be solved at all, since the method provides a set of nonlinear first order coupled differential equations in the scattering coefficients themselves. For a second-order wave equation, the equations are of the form $dR/dx=f[R(x),k(x),k'(x)]$ and $dT/ dx=f[R(x),T(x),k(x),k'(x)]$ where $k(x)$ is the WKB solution of the wave equation. For a fourth-order system such as is appropriate for mode conversion near a resonance, there is a set of equations for $R(x)$, $T(x)$, $C_-(x)$, and $C_+(x)$ for incident fast waves and incident slow waves from each side. While the equations are more formidable than those for the second-order system, the solution involves only nonlinear first-order ordinary differential equations and avoids the problems associated with exponentially growing wave amplitudes. [Preview Abstract] |
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FP1.00042: Coherent multi-harmonic structures in an inhomogeneous current-free plasma Su-Hyun Kim, Robert Merlino High resolution observations with the FAST satellite in the upward current auroral region have revealed discreet electrostatic harmonic features at multiples of the proton gyrofrequency. The time series of the parallel electric field showed characteristic spiky waveform structures separated by the ion gyroperiod. These structures were associated with shear in the ion drift along the magnetic field. We have conducted laboratory experiments in a Q machine investigating the effects of ion flow shear on the excitation of EIC waves in a current-free plasma. A broadband white noise signal was applied to an antenna in the plasma which launched electrostatic waves into a region containing parallel velocity shear. Measurements of the wave amplitude in the shear region showed a discreet spectrum with multiharmonic features near the ion cyclotron frequency and several harmonics. These features were only observed when ion flow shear was present. The time series of these oscillations showed spiky features separated in time by the cyclotron period. These spiky structures appear to be due to a linear superposition of many phase-locked cyclotron harmonics. [Preview Abstract] |
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FP1.00043: Generation and propagation of instabilities in a magnetized linear plasma column Ashley Eadon, Michael Taylor, Joseph Senne, Edward Thomas Transverse and parallel sheared flows are important topics in both space and fusion plasmas, and have been the subjects of extensive study. For example, in fusion plasmas, sheared flows are a signature of enhanced confinement regimes. Investigations on the ALEXIS device use imposed radial potential structures to influence the axial and transverse flows and to modify the radial electric field. This presentation focuses on the generation of inhomogeneous energy density driven instabilities, starting from a pseudo-quiescent mode, which is characterized by a broadband reduction in low frequency plasma oscillations. Along with the generation of ion cyclotron waves, this poster will also present studies of the changes in launched wave propagation during the formation of the IEDDI, and the impact on other plasma parameters. [Preview Abstract] |
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FP1.00044: Effects of negative ions on instabilities driven by sheared magnetic-field-aligned positive-ion flow Ryuta Ichiki, Toshiro Kaneko, Rikizo Hatakeyama, Mark E. Koepke Using a Q-machine, we have observed low-frequency instabilities driven by sheared magnetic-field-aligned positive- ion flow in a plasma composed of K$^+$, SF$_6^-$, and electrons ($n_p \simeq 10^{-9}$ cm$^{-3}$, $T_e \simeq T_i \simeq 0.2$ eV, $\phi_s \simeq -4$V). Sheared K$^+$ ion flow is achieved with the combination of a concentrically segmented W hot plate (positive-ion source) at one end of a magnetized plasma column and a LaB$_6$-coated disk cathode (electron source) at the opposite end. The characteristics of fluctuations, attributed to the shear-modified drift instability, are found to change when negative ions are introduced into the plasma. First, the range of the shear strength that stabilizes the fluctuations extends to both larger and smaller values. Second, for sufficiently large concentration of negative ions, the frequency spectrum makes a transition from sharp to broad as the shear strength is increased. These trends may be related to negative-ion effects on the wave phase velocity which, in turn, modifies Landau damping and growth. We are interested in possible applications to structure formation in turbulent plasma that contain both negative ions and sheared positive-ion flow. [Preview Abstract] |
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FP1.00045: A wave absorption measurement of the electron distribution function Fred Skiff, Craig Kletzing, Derek Thuecks, Scott Bounds, Steven Vincena A new wave absorption technique for determining the electron distribution function parallel to the magnetic field in an overdense ($\omega_{pe} > \omega_{ce}$) magnetized plasma is tested in the LAPD device at UCLA. Previously, electron distribution functions have been determined in tokamak plasmas using electron cyclotron absorption (ECA) (1). In sufficiently overdense plasmas this is no longer possible because of the x-mode cut-off. Here we use the right-hand circularly polarized (whistler) wave. As in the previous experiments one can make use of reciprocity arguments to simplify the analysis in the case of determining the antisymmetric part of the distribution f(v$_{\parallel}$) -- f(-v$_{\parallel}$). However, since it is possible to calculate the coupling efficiency of the antenna structure one can determine the full distribution function with enough time resolution to measure fluctuations. Because the technique is based on wave-particle resonance it is both sensitive and selective. An explanation of the principles of the technique together with preliminary data from an instrument designed for the LAPD plasma (B$\sim $2kG, n$_e$$\sim $2x10$^{12}$ cm$^{-3}$, T$_e$$\sim $7eV) will be presented. The possibility of extending the technique to Lagrangian ``Vlasov tagging'' will also be discussed. (1) F. Skiff, D. A. Boyd, and J. A. Colborn, Phys. Fluids B5, 2445 (1993). [Preview Abstract] |
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FP1.00046: An alternative approach for the study of the linear Vlasov stability Enrico Camporeale, Gian Luca Delzanno, Giovanni Lapenta, William Daughton We present a technique for solving the linearized Vlasov-Maxwell set of equations, in which the perturbed distribution function is described as an infinite series of orthogonal functions, chosen as Hermite-Grad polynomials. The orthogonality properties of such functions allow us to decompose the Vlasov equation into a set of infinite coupled equations. This technique is based on solid but easy concepts, not attempting to evaluate the integration over the unperturbed trajectories and can be applied on any equilibrium. Although the solutions are approximate, because they neglect contributions of higher order coefficients of the series, the physical meaning of the low-order coefficients is clear. This allows us to know exactly on which assumptions the approximation is made and gives a snapshot on which quantites are dominant in the equilibrium. Furthermore the accuracy of solution, which depends on the number of terms taken in account in the Hermite series, appears to be merely a problem of computational power. The method has been tested setting an initial 1-D Harris equilibrium that is known to give rise to several instabilties, like tearing, drift-kink, lower hybrid. To comapre, the same problem has also been studied using particle-in-cell simulations. [Preview Abstract] |
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FP1.00047: Resonant and non resonant particle dynamics in Alfv\'{e}n Mode excitations Fulvio Zonca, Liu Chen \newcommand{\gaeq}{\raisebox{-.7ex}{$\stackrel{\textstyle>}{\sim}$}} The resonant excitations of Alfv\'{e}n Modes in toroidal plasmas by fast ions is considered in the present work, revisiting previous analyses that demonstrated in general the existence of two types of modes; {\it i.e.}, a discrete shear Alfv\'{e}n gap mode, or Alfv\'{e}n Eigenmode (AE), and an Energetic Particle continuum Mode (EPM)~[1]. Here, we demonstrate that the resonant fast ion dynamics in toroidal plasmas is dominated by the magnetic drift curvature coupling in the vorticity equation, while the non-resonant response has various contributions, whose relative weight depends on the ratio of the characteristic fast ion orbit width, $\rho_{LE}$, to the perpendicular mode wavelength, $\lambda_\perp$. Specifically, we demonstrate that the optimal wavelength ordering for analyzing energetic ion transport in burning plasmas is $\lambda_\perp\gaeq \rho_{LE}$, considered in [1], for which both resonant and non-resonant fast ion behaviors are dominated by the magnetic drift curvature coupling, that fully accounts for the energetic ion dynamics, including the {\it charge uncovering} effect~[2]. \newline --------------------------------- \newline \noindent [1] L. Chen, Phys. \ Plasmas {\bf 1}, 1519, (1994).\newline \noindent [2] M. N. Rosenbluth, Physica Scripta T2/1, 104 (1982). [Preview Abstract] |
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FP1.00048: Nonlinear dynamics of charged particle motion in Alfv\'{e}n waves Zehua Guo, Chris Crabtree, Liu Chen The nonlinear dynamics of charged particle motion in a uniform background magnetic field and obliquely propagating shear Alfv\'{e}n wave is investigated both numerically and analytically. Using Lie perturbation theory in the wave frame a resonance condition is found. In the lowest order one recovers the well-known linear resonance condition, when the particle completes $n$ full gyroperiods during it's traversal of the wavelength. That is, $n \Omega+v_z k_z=0$, where $v_z$ is the particle's velocity along the background field in the wave frame, $k_z$ is the parallel wave vector, and $\Omega$ is the gyrofrequency. In the second order, however, the resonance condition becomes $n \Omega + 2v_z k_z=0$. The analytical theory produces a resonance Hamiltonian which is directly compared to numerically computed Poincare surfaces of section. Detailed predictions on the location of fixed points, width of resonance, and resonance overlap criterion will be presented. [Preview Abstract] |
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FP1.00049: High-$\beta$ Alfv\'en Eigenmodes Excited by Energetic Particles in Toroidal Plasmas Shuanghui Hu, Liu Chen, Guoyong Fu We have further generalized the theoretical formalism of $\alpha$TAE [{\it Hu and Chen}, 2005] to the high-$\beta$ regime by including the energetic-particle compressional dynamics in the perpendicular Ampere's law. The $\alpha$TAEs are high-$n$ discrete Alfv\'en eigenmodes trapped by the $\alpha$-induced potential wells in high-$\beta$ second-balloning-mode stable toroidal plasmas and, hence, can exist independently of the toroidal Alfv\'en frequency gap; in contrast to the usual TAE (toroidicity-induced Alfv\'en eigenmode) [{\it Cheng, Chen, and Chance}, 1985]. Here, $\alpha$ denotes the ballooning drive due to pressure gradient and curvature, $\beta$ is the ratio of plasma to magnetic pressures, and $n$ is the toroidal wavenumber. Adopting the usual toroidal plasma orderings, we follow the standard linear gyrokinetic approach [{\it Chen and Hasegawa}, 1991] to obtain a set of equations for both the perpendicular and parallel magnetic perturbations along with the nonadiabatic response of energetic particles. While the sound waves are suppressed due to shortening of the parallel electric field by core electrons, both shear Alfv\'en and slow magnetic compressional modes ({\it e.g.}, mirror mode) are retained. Implications of $\alpha$TAE to advanced tokamaks with negative magnetic shear and ITER parameter regime will also be presented. [Preview Abstract] |
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FP1.00050: Modelling nonperturbative frequency sweeping of MHD modes in magnetic confinement fusion plasmas Roderick Vann, Richard Dendy, Mikhail Gryaznevich, Sergei Sharapov Frequency sweeping of magnetohydrodynamic modes for which the sweeping rate is approximately constant have been observed at the Mega-Amp Spherical Tokamak in the presence of heating by energetic particles. A fully nonlinear self-consistent numerical implementation of the Berk-Breizman augmentation of the Vlasov-Maxwell system is applied in the nonperturbative regime; frequency sweeping events phenomenologically comparable to experiment are observed. Experimental observations and simulation results are presented; the existence of a congruence between them is discussed. [Preview Abstract] |
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FP1.00051: Transport of Fast Ions Modulated by Shear Alfv\'en Waves Y. Zhang, H. Boehmer, W. Heidbrink, R. McWilliams, L. Zhao, B. Brugman, T. Carter, D. Leneman, S. Vincena Large-amplitude ($\delta B/B \sim 1$\%) shear Alf\'en waves (SAWs) can produce fast ion ($v_f\gg v_{thermal}$) deflections in addition to the classical spreading.\footnote{L. Zhao {\it et al.}, Phys. Plasmas {\bf12} (2005) 052108} The LArge Plasma Device (LAPD) at UCLA provides a vast space to fit fast ion orbits and SAWs in the kinetic regime. We developed a Li$^+$ ion source emitting $\sim1$~mA of Li$^+$ ions up to $\sim3000$~eV. The speed of fast ions is similar to the parallel phase speed of SAWs launched from loop antennas to modulate fast ion transport. Fast ion orbits are selected to coincide with maximum wave amplitude for the most deflections. A newly designed fast ion collimated analyzer has been employed to monitor fast ion orbits. First results are presented. [Preview Abstract] |
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FP1.00052: Measurements of Dispersion and Damping for Kinetic and Inertial Shear Alfv\'{e}n Waves D.J. Thuecks, C.A. Kletzing, S.R. Bounds, F. Skiff, S. Vincena, W. Gekelman Experiments to test the dispersion relation of shear Alfv\'{e}n waves as a function of $k_\bot $were performed using the Large Plasma Device at UCLA. The waves were launched using a 48 element antenna which allows good control over the perpendicular wave numbers of the wave. Amplified magnetic search coil probes placed along the length of the chamber are used to measure the wave across the center of the wave pattern. The measured signals are processed using an FFT transform and the signal for each individual perpendicular wave number is then reconstructed. Components at two different locations for the same wave number are cross correlated and the propagation time with the probe separation leads to a value of the parallel phase velocity for each wave number. Additionally, relative amplitudes of each wave number between two probes allow the damping to be calculated. The parallel phase velocity and the damping rate are then compared to the theoretical dispersion relation and damping for both the kinetic (V$_{Te}>$V$_{A})$ and inertial (V$_{Te}<$V$_{A})$ cases. [Preview Abstract] |
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FP1.00053: Nonlinear Alfv\'{e}n Wave Interactions on the Large Plasma Device Brian Brugman, Troy Carter The nonlinear dynamics of large amplitude Alfv\'{e}n waves is believed to play a major role in the evolution of the macroscopic properties of numerous laboratory plasmas and astrophysical systems. However, despite their importance the nonlinear dynamics of these fluctuations remains point of great controversy with few prior thorough experimental measurements. Nonlinear interactions between Alfv\'{e}n waves are being studied in the Large Plasma Device (LAPD) at UCLA, using large amplitude, $\delta B / B_{0} \sim 1 \%$, waves generated by LaPD's Alfv\'{e}n wave MASER or by antennas. In these experiments, two large amplitude shear Alfv\'{e}n waves are launched at different frequencies and beat against one another. The subsequent nonlinear generation of density fluctuations at the beat frequency along with the formation of numerous discrete Alfv\'{e}nic sidebands has been observed using both wave launching mechanisms over a broad range of plasma parameters and launch wave frequencies. Such interactions resemble a form of parametric decay, namely the modulational instability. In particular the spatial and temporal characteristics as well as amplitude scaling of the interaction as evident by its effects on magnetic, density, and potential fluctuations will be presented. [Preview Abstract] |
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FP1.00054: Kinetic Alfven Wave Turbulence Simulations Update Kate Despain, W. Dorland We present results for the numerical validation and verification of KAW, a 3D code designed to study the nonlinear interaction of kinetic Alfven waves. KAW employs an EMHD model, but is modified to include some kinetic effects by the electrons. Initial nonlinear results of interacting kinetic Alfen waves will also be presented. These results can be compared to experimental results from the Large Plasma Device (LAPD) at UCLA. [Preview Abstract] |
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FP1.00055: On the Transition from Hydrodynamic to MHD Cascade and the Breakdown of Vorticity Homogenization L.T. Katt, P.H. Diamond, L. Silvers, S.M. Tobias We adress the simple question of ``At what value of a weak uniform $B_0$ does a 2D hydrodynamic dual cascade (associated with enstrophy homogenization) convert to a 2D MHD forward energy cascade?" We approach this by calculating the gradient in vorticity within a cell or eddy (with closed streamlines) linked to an external magnetic field. Both a local and an averaged criterion are derived. The global criterion is in terms of an Hartmann nuber and is consistent with preliminary results of simulation. More interestingly, the degree of vorticity homogenization emerges as related to the topology of filed line to streamline linkage at the boundary of the cell, as well as the profile of current density on the boundary of the cell. A variety of stable configurations are shown to be possible and will be discussed. [Preview Abstract] |
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FP1.00056: Field-Aligned Currents due to Resonant Absorption in a Magnetized Plasma Dean Dauger, F.S. Tsung, J. Tonge, G.J. Morales A particle-in-cell code, OSIRIS is used to investigate the currents generated by the resonant absorption of an electromagnetic pulse (EMP) propagating across the magnetic field in a plasma with a cross-field density gradient. The electromagnetic pulse has finite extent along the magnetic field and can be excited with O or X-mode polarization. This situation is of interest in ionospheric modification studies, basic laboratory experiments, RF heating and it could lead to interesting particle acceleration scenarios. As expected, at the resonant layer the O-mode polarization is found to trigger strongly nonlinear processes. One such process consists of the carving of a cross-field density channel and the acceleration of electrons that stream out of the resonant region. The confinement magnetic field allows the development of a collimated current pulse that induces a coaxial return current. The self-consistent plasma response results in the radiation of whistlers as well as shear Alfv\'{e}n waves. The dependence of the current system on polarization and power of the EMP is investigated and the results are compared to on-going experiments at BaPSF. [Preview Abstract] |
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FP1.00057: Generation of Alfv\'en waves by high power pulse at the electron plasma frequency Bart Van Compernolle, Walter Gekelman, Patrick Pribyl A great deal of research has been done on the interaction of electron plasma waves in a density gradient at the resonant location ($\omega = \omega_{pe}$) in unmagnetized plasmas. The experiment at the LArge Plasma Device (LAPD) at UCLA takes this a step further, by focusing on the interaction with a fully magnetized plasma, capable of supporting Alfv\'en waves. The plasma is diagnosed with high frequency dipole probes, magnetic pickup loops and Mach probes. Both the ordinary mode (O-mode) and the extraordinary mode (X-mode) are studied. A pulse of high power microwaves is launched into a strongly magnetized plasma. The microwaves (f = 9 Ghz) are beamed across the magnetic field into a radial density gradient. Results show that the microwave interaction leads to heating and bulk ion flows, and generation of Alfv\'en waves. Data indicate that the Alfv\'en waves are radiated by the current systems generated by fast electrons in the resonant region. The Alfv\'en wave amplitude and frequency spectrum are studied for varying background magnetic field, varying input power of the microwaves and varying electron temperature, both in O-mode and X-mode. Studies of the damping mechanism are under way. \textit{This work is funded by the Department of Energy, and more recently by the National Science Foundation. It was performed at the UCLA Basic Plasma Science Facility.} [Preview Abstract] |
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FP1.00058: Kinetic shear Alfv\'{e}n waves in the presence of plasma flow. G.J. Morales, J. Tonge, F.S. Tsung The propagation of Alfv\'{e}n waves through regions where a transverse plasma flow exists relative to the wave source is a topic of interest to various space and laboratory studies. In the inertial regime, where the Alfven speed $V_{A}$ is much larger than the electron thermal velocity $v_{e}$ ,transverse flow above a critical speed gives rise to filamentation of currents associated with shear waves. The phenomenon arises from the competition between induction and electron inertia and is absent in MHD descriptions. In the kinetic regime ($v_{A} \sim v_{e}$) the wave-particle interaction increases the complexity of this competition. To explore this important regime, a parallel electromagnetic particle-in-cell code, PARSEC, is used. The effects of finite ion Larmor radius (kinetic Ion effects) and resonant electron damping (kinetic electron effects) are independently investigated. The major findings are: 1) the electron Landau damping experienced by launched shear-wave cones can be cancelled by the flow, thus resulting in collimated propagating structures; 2) finite ion Larmor radius gives rise to secondary, banded-structures that accompany the convection induced by the flow on the primary shear-wave cone. The dependence of these features on flow speed and wave frequency is analyzed. [Preview Abstract] |
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FP1.00059: Alfv\'{e}n Waves in Hall MHD and Gyrokinetics J. Pino, S.M. Mahajan It has been shown that the Hall MHD Linear dispersion relation can be obtained by taking the cold ion limit ($T_i\rightarrow 0$) in kinetic theory. We take the same limit in the gyrokinetic framework in order to investigate low frequency Alfv\'{e}n waves. This gives an estimate of electron Landau damping which was not present in the fluid model. Comparisons are made between HMHD, analytical gyrokinetic equations, and computational simulations using the GS2 code. An extension to nonlinear HMHD Alfv\'{e}n modes is made. [Preview Abstract] |
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FP1.00060: Ion heating due to Alfv\'{e}n waves in a helicon plasma C.S. Compton, C. Biloui, S. Houshmandyar, E.E. Scime Recent models for ion heating in the fast solar wind region of the Sun predict that the heating is due to MHD turbulence driven by counter propagating, low- frequency Alfv\'{e}n waves [Matthaeus et. al. 1999]. Experiments to test this theory will be conducted in the West Virginia University HELIX (Hot hELIcon eXperiment) device in argon and helium plasmas. It is argued that the counter-propagation is a result of the reflection of the waves off of a gradient in the Alfv\'{e}n speed. The HELIX device has a speed gradient similar to that found in the solar corona, a short region of high Alfv\'{e}n speed followed by an expansion region of lower Alfv\'{e}n speed. Alfv\'{e}n waves have been launched using an internal coil measuring 2 cm in length with 50 turns and received using a coil measuring 1 cm in length with 300 turns, both of radius 1.5 mm. The parallel wave number versus wave frequency of the waves and the ion response to the wave field (as determined by laser induced fluorescence in argon plasmas) will be presented. The ion response to the wave field will be compared to theoretical predictions for shear Alfv\'{e}n waves. The effect of moving the location of the reflection region (by varying the strength of the magnetic field in the expansion region) on the parallel wave number of the Alfv\'{e}n waves will also be reviewed. [Preview Abstract] |
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FP1.00061: Physical Mechanism for the Generation of Filaments and Alfv\'en Waves by Ion Beam-Plasma Interaction Xueyi Wang, Yu Lin, Liu Chen Our previous simulations found that filaments, frequently observed in space plasmas, can form via the interaction between an ion beam and a background plasma. In this study, the fundamental mechanism for the generation of the filaments is investigated by a 2-D hybrid simulation, in which a field-aligned ion beam with relative beam density $n_b=0.1$ and beam velocity $V_b=10V_A$ is initiated in a uniform plasma. Right-hand nonresonant ion beam modes are found to be dominant in the linear stage of the beam-plasma interaction, consistent with the linear theory prediction. In the later nonlinear stage, two types of shear Alfv\'en modes form, with one propagating along the background field ${\bf B_0}$ and the other obliquely propagating. Meanwhile, filaments corresponding to field-aligned structures of magnetic field $B$ and density are present. The filaments ( ${\bf k} \perp {\bf B}$) are nonlinearly generated in a prey-predator fashion by the parallel and oblique ion beam modes, which also lead to the Alfv\'en waves. In the filament mode, fluctuations in the background ion density and temperature and the beam density are in-phase with those in $B$, whereas the significantly enhanced beam temperature is anti-phase with $B$. Both the parallel and the oblique beam modes are crucial in the production of the filaments, and thus their generation mechanism is different from other mechanisms such as the stimulated excitation by the decay of an Alfv\'en wave. [Preview Abstract] |
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FP1.00062: Splitting of force-free EMHD current rings R.L. Stenzel, J.M. Urrutia, K.D. Strohmaier Tilting of boundary-free field-reversed configurations has been observed in a laboratory plasma in the regime of electron magnetohydrodynamics (EMHD) [R. ~L.\ Stenzel, J.~M.\ Urrutia, K.~D.\ Strohmaier, and M.~C.\ Griskey, Experiments on nonlinear EMHD fields, Physica Scripta \textbf{T107}, 163 (2004)]. Further investigations have revealed that the tilting is \textbf{not} due to magnetic forces, i.e., the torque on a magnetic dipole in an external field, because the magnetic force is balanced by the electric force in EMHD. The force-free current ring splits and moves slowly apart. Transverse gradients cause differences in propagation speed leading to an apparent tilt of the expanding current layer. The gradients are created in the early phase of the FRC creation. The propagation of EMHD fields depends primarily on magnetic field and density both of which are nonlinearly modified. The initially symmetric FRC relaxes into a spatially highly nonuniform field with multiple 3-D null points. Similar phenomena are seen during the interaction of two FRCs and also may occur in strong EMHD turbulence. [Preview Abstract] |
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FP1.00063: Ion acceleration in Hall electric fields K.D. Strohmaier, R.L. Stenzel, J.M. Urrutia Time-dependent magnetic fields are applied to a large laboratory plasma operating in the regime of electron magnetohydrodynamics (EMHD; magnetized electrons, unmagnetized but mobile ions). The fields are produced by pulsing currents through insulated magnetic loop antennas whose dipole axis is parallel or antiparallel to the uniform dc magnetic field. The magnetic $\mathbf{J} \times \mathbf{B}$ force on the electrons produces a space charge (Hall) electric field normal to the antenna coil. The unmagnetized ions are accelerated away leaving a density depletion around the coil. When the coil current is switched off, the induced image current flows outside the plasma void at a larger radius than the coil. Asymmetries in the ion expulsion may lead to the frequently observed asymmetries in the current rings. The current layer also produces strong electron heating. Thus, magnetic energy is transferred to both ions and electrons. [Preview Abstract] |
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FP1.00064: Radiation efficiency of nonlinear whistler wave antennas J.M. Urrutia, R.L. Stenzel, K.D. Strohmaier Time varying magnetic fields are applied with various antenna configurations in a laboratory plasma in the regime of low frequency whistler modes. In contrast to earlier work on antenna properties for linear whistler waves [R.~L.\ Stenzel, Antenna radiation patterns in the whistler wave regime measured in a large laboratory plasma, Radio Science \textbf{11}, 1045 (1976)], the present work deals with exciting whistlers whose wave magnetic field exceeds the ambient magnetic field. In this case, the propagation depends on the amplitude and direction of the wave magnetic field. When the two fields oppose each other, a field-reversed configuration arises which essentially prevents the excitation of propagating whistler waves. The field stagnates and dissipates. However, when the wave field adds to the ambient field a propagating whistler wave packet is excited. Thus, for a sinusoidal antenna current, only one half cycle produces radiation, the other leads to local dissipation. Rectified or pulsed currents produce optimum excitation of whistler waves. [Preview Abstract] |
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FP1.00065: Measurements of Dynamic Polarizabilities for Five Metal Atoms using Electrically Exploding Wires in Vacuum and Novel Integrated-Phase Technique Gennady Sarkisov, Izrael Beigman, Viatcheslav Shevelko, Ken Struve Accurate measurements within 10{\%} accuracy of the dipole dynamic polarizabilities for five non-refractory metal atoms Mg, Ag, Al, Cu and Au at laser wavelength 532nm and 1064nm are presented using electrical explosion of thin wires in vacuum and novel laser probing integrated-phase technique. The new technique is based on a single-wavelength interferometry and does not require an axial symmetry of the tested object. Theoretical prediction of dynamic polarizability for wavelengths 355, 532 and 1064 nm, as well as the static dipole polarizabilities, are also presented. An agreement within 20{\%} was obtained between calculated data, recommended static polarizabilities, and dynamic polarizabilities at 532nm and 1064nm, measured in the present work. [Preview Abstract] |
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FP1.00066: Parallel Implementation of Multi-Dimensional Spectral Code SPECT3D I.E. Golovkin, J.J. MacFarlane, P.R. Woodruff, P. Wang K-shell emission spectroscopy is commonly used to diagnose the core temperature and density of ICF plasmas. In particular, we will focus on the analysis of Ar doped capsule implosions and radiation driven doped foams. To this end, we utilize the multi-dimensional collisional-radiative, spectral analysis code SPECT3D. Comprehensive atomic models, including K-shell satellite and inner-shell transitions, are used so that very detailed spectra can be computed and compared with experimental spectra. Atomic level populations can be computed using time-dependent atomic kinetics, or a steady-state approximation. Calculations include the effects of bound-bound, bound-free, and free-free contributions to the plasma emission and opacity. Accurate accounting for radiation transport requires sophisticated atomic models that include a large number of energy levels and transitions. Additionally, the radiation field needs to be computed over a wide range of photon energies. Therefore, computational expense may push the limits of sequential computing. We will present a parallel implementation of the code and provide a scalability study performed on a Linux cluster. [Preview Abstract] |
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FP1.00067: Detection of Protons and Alpha Particles Using Charge Injection Devices (CIDs) Kurtis A. Fletcher, Benjamin Apker, Samantha Hammond, John Punaro, Frederic J. Marshall, Robert A. Forties, Benjamin L. Schmitt CID cameras, used for x-ray imaging on the University of Rochester's OMEGA laser system, can also be used to detect charged particles, such as those emitted in fusion reactions. We have demonstrated that CID cameras can be used to detect alpha particles from a radioactive source, and that the flux of alpha particles is identical to that measured using a surface barrier detector. In a series of experiments using the SUNY Geneseo 2~MV Van de Graaff accelerator, we have also determined the efficiency for detection of $^{2}$H(d,p)$^{3}$H protons by simultaneously detecting protons with a surface barrier detector and a CID placed at identical angles in the scattering chamber. In all cases the careful selection of appropriate energy-degrading foils is necessary to maximize the charged particle signal in the CID. Future work will focus on tests of the system using inertial confinement fusion products at the OMEGA laser facility. (Supported in part by the US Department of Energy through the University of Rochester's Laboratory for Laser Energetics.) [Preview Abstract] |
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FP1.00068: Magnetic Field Measurements in Wire-Array Z-Pinches Wasif Syed, David Hammer, Michal Lipson, Robert van Dover, Jon Douglass A method to determine the magnetic field in megampere level wire-array Z-pinches with high spatial and temporal resolution has not yet been developed. An ideal method would be passive and non-perturbing, such as Faraday rotation of laser light or emission spectroscopy. However, Faraday rotation measurements in Z-pinches suffer from severe difficulties, because density gradients are large and the plasma is magnetohydrodynamically turbulent inside the Z-pinches. Therefore, we are developing a method based on Faraday rotation through a sensing waveguide placed in the vicinity of, or perhaps in, a wire-array Z-pinch. We will also discuss emission spectroscopy methods based upon the Zeeman effect that are also under investigation. Finally, we will present a technique developed using magnetic CoPt thin films that measures a lower limit for the maximum magnetic field. [Preview Abstract] |
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FP1.00069: Improved signal-to-background utilizing coincidence counting of charged-particle tracks in CR-39 S. Volkmer, F.H. Seguin, J.A. Frenje, C.K. Li, J.R. Rygg, R.D. Petrasso, T.C. Sangster, V.Yu. Glebov, D.D. Meyerhofer, C. Stoekl CR-39 has proven invaluable for diagnosing implosions due to its EMP-insensitivity and compactness, but it is slightly sensitive to neutrons. While not a problem for many conventional nuclear diagnostics at OMEGA, this has to be dealt with for the Magnetic Recoil Spectrometer (MRS) and the Neutron Wedge Spectrometer that are currently being developed at OMEGA, and the MRS at the NIF. Orders-of-magnitude increased rejection of neutron induced events can be accomplished by performing coincidence counting of tracks on the front and back sides of CR-39: Since only signal protons will leave spatially coincident pairs of tracks on both sides of the CR-39, neutron-induced tracks can be discarded. We propose to develop this coincidence counting technique to lower the background level in CR-39 neutron spectrometry data. This poster will present the current status of this project. This work was supported in part by LLE, LLNL, the U.S. DoE, the Univ. of Rochester, and the N.Y. State Energy Research and Development Authority. [Preview Abstract] |
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FP1.00070: Characterization of a Fusion Product Source for ICF Diagnostic Development M.J. Canavan, J.A. Frenje, R. Leiter, C.K. Li, J.R. Rygg, F.H. Seguin, R.D. Petrasso, S. Roberts, K. Fletcher Characterization of the MIT fusion product source (FPS) has been extended through experimental and computational work, furthering the usefulness of this tool for many ICF applications. Additional hardware upgrades and the testing of various components have improved and allowed great control over fusion yields. Calculations and modeling have been performed to help understand the measured yields and to accurately characterize the energy and energy variations of emergent fusion products. ICF diagnostic development has begun, including testing of CR-39 nuclear track detectors and calibration of charged particle spectrometers. This work will be extended in the future to support the development of the Magnetic Recoil Spectrometer in addition to current ICF diagnostics. This work was supported in part by LLE, LLNL, the U.S. DoE, the Univ. of Rochester, and the N.Y.State Energy Research and Development Authority. [Preview Abstract] |
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FP1.00071: Shielding design for the Magnetic Recoil Spectrometer (MRS) at OMEGA and the NIF using TART2002 D.T. Casey, J.A. Frenje, C.K. Li, J.R. Rygg, F.H. Seguin, R.D. Petrasso, V.Yu. Glebov, D.D. Meyerhofer, T.C. Sangster, C. Stoekl, S. Haan, S. Hatchett, P. Amendt, D. Eder, N. Izumi, O. Landen, D. Lerche, D.C. Wilson, G. Kyala, R. Leeper, R. Olson A Magnetic Recoil Spectrometer (MRS) is currently being developed, at both OMEGA and the NIF, for measurements of down-scattered neutrons from which $\rho $R of cryogenic DT implosions can be inferred. As is the case for complementary methods to measure $\rho$R,\footnote{C. K. Li \textit{et al}, Phys. Plasmas \textbf{8}, 4902 (2001)} minimizing the effect of the background is critical for successful implementation. The established minimum S/B of 20, folded with CR-39 neutron response, determines the tolerable neutron fluence. The transport code TART2002 was used to calculate the neutron fluence at the MRS detector and provided input for design of the shielding for the MRS. This poster will present the current status of this project. This work was supported in part by LLE, LLNL, the U.S. DoE, the Univ. of Rochester, and the N.Y. State Energy Research and Development Authority. [Preview Abstract] |
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FP1.00072: Saturation study of a CVD diamond detection system Lucile S. Dauffy, Edward C. Morse, Jeffrey A. Koch, Aaron M. Tremaine, David J. Gibson, Jeremy S. Jacob Chemical Vapor Deposition (CVD) diamond detection systems are being tested to evaluate the feasibility of measuring areal density during the ignition campaign at the National Ignition Facility (NIF). The areal density of the compressed core, $\rho $R, is determined by the ratio of downscattered (scattered inside the target, 4-10 MeV) to primary neutrons (14 MeV). The 14 MeV peak intensity is several orders of magnitude larger than the downscattered neutron intensity. This large contrast presents a challenge, and detector saturation by the 14 MeV neutrons can lead to a nonlinear response to the downscattered neutrons. In order to quantify this non-linearity after a large pulse, the saturation of a CVD diamond detector and surrounding electronics is being studied. We are separately exploring saturation and recovery of the diamond wafer, the biasing electronics, and the data acquisition system, with the goal of demonstrating a capability to reliably measure a weak signal, hundreds of nanoseconds after saturation by a strong signal, with a contrast ratio of 1000 or more. Results from experiments and calculations will be presented. [Preview Abstract] |
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FP1.00073: Single-shot, high-resolution terahertz diagnostic and its applications to laser-plasma interactions Ki-Yong Kim, Balakishore Yellampalle, George Rodriguez, James Glownia We have developed a single-shot terahertz (THz) diagnostic capable of measuring free-space electromagnetic pulse fields in the THz frequency range with unprecedented temporal resolution. Using the chirped probe electro-optic sampling technique, combined with the Fourier retrieval algorithm that we recently developed, we have achieved the transform-limited temporal resolution (50 fs in case of our Ti:sapphire laser system). With our technique, the temporal resolution is mainly limited by the spectral bandwidth of the probe pulse, regardless of the probe chirp rate. The diagnostic can be used for many applications where single-shot laser operations are strongly demanded. As preliminary applications of the diagnostic, we have investigated the characterization of coherent THz radiation from laser-produced plasma ablation on solid targets and laser-induced shocked ionic crystals. We have also studied its application to laser-plasma-based electron accelerators in which we can measure the electron bunch length in a single-shot. High-field-strength THz sources can greatly benefit from these applications. This work was partially supported through the LANL LDRD program office. [Preview Abstract] |
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FP1.00074: ICF reaction rates using fusion gamma rays.$^{1}$ R.A. Lerche, R.L. Griffith, R.R. Berggren, S.E. Caldwell, C.R. Christensen, S.C. Evans, J.M. Mack, C.S. Young, V.Yu. Glebov The fusion reaction rate in ICF capsules has been measured with fusion neutrons for a dozen years. The 16.7-MeV gamma rays produced in DT fusion can be used for targets producing $>$10$^{15}$ neutrons. Gamma rays make the measurement independent of target-to-detector distance, but their low branching ratio ($<$10$^{-4})$ makes the task difficult at current ICF facilities where neutron yields are $<$10$^{14}$. A detector system based on a Cherenkov gas cell is being tested at the OMEGA laser facility. Incident gamma~rays produce forward-directed, relativistic electrons in a converter foil at the entrance to a high-pressure (100 psi) gas cell containing CO$_{2}$ gas. The electrons generate Cherenkov light when they travel faster than the speed of light through the CO$_{2}$ gas. Reflective lenses collect the light at the output of the cell and relay it to a streak camera several meters away. Fast, 130-ps fwhm signals have been recorded. Signal width and time correspond to the burn width and bang time recorded with neutrons for the same targets. The relative contribution of hard x rays and gamma rays to these fast signals is being investigated. $^{1}$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. [Preview Abstract] |
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FP1.00075: Diagnosing Asymmetry in Ignition Implosions with Neutron Imaging and Spectra C.K. Choi, D.C. Wilson, P.A. Bradley, R.D. Russell, J.E. Sweezy Simulations of NIF ignition hohlraums and capsule implosions with different laser pointings and identical laser pulse histories produce yields between 0.6 and 16 MJ. Simulations of temporal, spatial, and energy-dependent neutron images have been carried out. Images of the 14 MeV neutrons show an asymmetrical hot spot in capsules that fail to ignite. Images in the down-scattered neutrons show complementary asymmetries in the cold fuel. Images are obtained both along and normal to the hohlraum axis. The neutron spectra show the presence of the asymmetry visible in the energy gated images, as well as a variation with angle of observation with respect to the hohlraum axis. We compare neutron images and spectra from both failed and full yield NIF capsules. This work was sponsored by the US DOE. [Preview Abstract] |
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FP1.00076: Diagnostics for laser plasma interaction in the target chamber of the LIL C. Reverdin, E. Alozy, J.L. Bourgade, J.Y. Boutin, G. Charles, L. Disdier, A. Duval, A. Estadieu, D. Gontier, J.P. Le Breton, G. Lidove, Remy Marmoret, R. Rosch, G. Soullie, P. Stemmler, P. Troussel, B. Villette, R. Wrobel The main features of the diagnostics for laser plasma interaction in the target chamber of the LIL will be presented. The LIL facility (Ligne d'Int\'{e}gration Laser) is located at CEA CESTA near Bordeaux in France. Fist experiments were performed in 2004 with x-ray diagnostics. The remaining diagnostics will be available before the next experiments. The set of diagnostics to characterize the interaction of the quadruplet laser beam with the target includes the full aperture back scattering diagnostic called DRED, the full aperture transmitted laser light imaging camera, the near back scattering and the near forward scattering imaging cameras. Ten modules with UV, visible and x-ray diodes are installed on the target chamber for power measurements. X-ray imagery diagnostics include two multi-imagers with mirrors and framing camera, two mirror imagers with streak camera, a multi pinhole framing camera and a pinhole camera with film. For x ray spectrometry measurements, there is a broad band x ray spectrometer, similar to DMX now on OMEGA, LLE, a hard x ray broad band spectrometer and two crystal x-ray spectrometer. For equation of state measurements a VISAR diagnostic will be installed in 2006. [Preview Abstract] |
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FP1.00077: Collection Efficiency Measurements and Development of a Sample Analysis Station for the OMEGA Gas Sampling System Charles Freeman, Geoff Young, Rodney Engels, Mark Stoyer, G. Bryant Hudson, T. Craig Sangster, Jack Armstrong The OMEGA Gas Sampling System (OGSS) is a radiochemical diagnostic that can be used to study implosion parameters including shell areal density, mix, and neutron yield in inertial confinement fusion capsules. The OGSS is a prototype for a gas sampling diagnostic which may be installed at the National Ignition Facility. By doping the target capsule with appropriate detector nuclei, nuclear reactions between fusion products and the detector nuclei can produce noble gas isotopes. Following a capsule implosion, these gases are pumped out of the OMEGA chamber and are collected on a cryopump head. Upon regeneration of the cryopump, the OGSS turbopump pumps the gases into up to four 0.5 liter sample collection bottles. The composition of the sample collection bottles is analyzed using either mass spectroscopy or gamma ray spectroscopy. The results of preliminary measurements of the target chamber background and gas sample collection efficiency will be presented. The development of an auxiliary sample bottle analysis station using a residual gas analyzer will also be described. This work was funded in part by the US Department of Energy, the Laboratory for Laser Energetics, and Lawrence Livermore National Laboratory. [Preview Abstract] |
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FP1.00078: A Simple Model for Microchannel Plate Output E.C. Harding, R.P. Drake, J.L. Weaver Microchannel plates (MCPs) are an essential component in an imaging diagnostic known as an x-ray framing camera, which is currently used by NIF, Omega, Nike, and Z to image radiation imploded targets. An MCP is used to convert incident x-ray photons into electrons with gains of 10$^{2}$ to 10$^{4}$. These electrons are accelerated into a phosphor and the subsequent visible light is captured with a CCD. A variety of parameters, such as photocathode material type (Au, Ni, CsI), photocathode coating depth, and MCP bias angle, affect the gain and gain variations in the MCP electron output. This poster presents initial results of a simple 3D MCP computer model along with an experimental comparison. Several ideas for increasing MCP imaging performance by reducing gain variations and increasing MCP quantum efficiency are presented. Work supported by the Naval Research Laboratory, National Nuclear Security Administration under the Stewardship Science Academic Alliances program through DOE Research Grant DE-FG52-03NA00064, and through DE FG53 2005 NA26014, and Livermore National Laboratory. [Preview Abstract] |
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FP1.00079: Al Backlighter Characterization at the Omega Laser Jim Cobble, Tom Tierney, Joe Abdallah We have characterized He- and H-like Al emission for various laser illuminations at the Omega laser with the goal of optimizing the ability to backlight low-atomic-number (low-Z) materials such as beryllium for fusion ignition studies. The conversion efficiency to Lyman $\alpha $ at 1.73 keV has been determined for 1, 2, 4, and 7 laser beams, i.e., as a function of laser energy/power. Data is recorded by a time-integrating spectrometer and a streaked x-ray spectrograph and reveals that the line/continuum ratio improves when the laser turns off. The Al plasma is diagnosed by line ratios and line profiles to determine the temperature and density. Results are compared to 1-D hydrodynamic calculations and to detailed theoretical atomic physics models. Evidence points to the increasing plasma opacity as the laser flux is increased. [Preview Abstract] |
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FP1.00080: Streaked Backlighting with Double-Slit Imager for Laser-Accelerated Target Hydrodynamics Hiroyuki Shiraga, Norimitsu Mahigashi, Tatsuhiro Sakaiya, Keisuke Shigemori, Mitsuo Nakai, Hiroshi Azechi Trajectory and density profile of a laser-irradiated planer targets are usually observed with side-on x-ray backlighting. In such observation, three profiles are necessary to derive transmittance of the probing x-ray through the target: backlit target, backlighting x-ray source, and x-ray emission from the target. We have developed a double-slit imager to observe those three images simultaneously. A CH planer target was irradiated with 0.53-micron GEKKO-XII/HIPER laser beams, and such three separate images were obtained. Trajectory and the target density profile were clearly observed. [Preview Abstract] |
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FP1.00081: Data processing and analysis techniques of time and space resolved ICF capsule argon k-shell x-ray spectra Greg Dunham, J.E. Bailey, G.A. Rochau, P.N. Lake, R.C. Mancini, J.J. MacFarlane, I.E. Golovkin Spectroscopic measurements of Ar doped deuterium filled capsules driven by z pinch dynamic hohlraum x-rays provide insight into optimization and future potential of this ICF approach. Time- and space-resolved argon emission data were obtained using the suite of TREX instruments from three quasi-orthogonal lines of sight. Time and space resolution are of order 350 ps and 80 microns, respectively. Analysis of the argon spectra yield symmetry, $T_e$ $N_e$, and $\rho r$ measurements and these data provide tests of implosion system understanding. Novel techniques to process the raw spectral images have been developed. Difficulties such as image skew due to crystal defects have been overcome to produce argon spectra that is aligned to the plasma core center throughout the argon Lyman- and Helium-like emission range. This processing is challenging because of the large volume of information provided by multiple space resolved time gated spectrometers in each experiment. \newline \newline Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under contract DE-AC04-94AL85000. [Preview Abstract] |
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FP1.00082: An x-ray spectropolarimeter Nino Pereira, Elena Baronova Polarized x-rays are usually measured one polarization direction at the time, with techniques that suppress the other polarization direction such as Bragg reflection under 45 degrees. However, for many photon energies it is possible to see both polarization directions at the same time, by asymmetric reflections off specially cut Bragg crystals. This paper expands on the first publication of this approach by Baronova et al. in 2001, and highlights its possible use in diagnostics of vacuum spark, z-pinch and laser-produced plasmas. [Preview Abstract] |
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FP1.00083: Model-Based Analysis of an ICF Neutron Imaging System Carlos Barrera, Edward Morse, Steve Haan, Jeffrey Koch, Michael Moran A neutron imaging diagnostic is currently under development for the National Ignition Facility (NIF). The system should be capable of producing images from scattered neutrons in the 6 to 10 MeV energy range. In order to predict the spatial resolution and signal-to-noise ratios of the images, a model-based analysis has been implemented. The modeling calculations include appropriate fusion source distributions (in 1 MeV bins), a hypothetical pinhole camera system that includes the point-spread function of the neutron pinhole, the time of flight of the neutrons and the response of the detector, i.e., sensitivity and late-time decay ( $>$ 600 ns) characteristics of the neutron scintillator. The results show that a downscattered image can be recovered after careful subtraction of the 14 MeV afterglow and that a pinhole array is necessary in order to increase the image signal-to-noise ratio. Comparison of the modeling results for different system designs will make it possible to optimize and understand the performance of the diagnostic before a prototype is built. [Preview Abstract] |
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FP1.00084: WITHDRAWN--Performance Evaluation of Square Pore Microchannel Plates A. Visco, E.C. Harding, R.P. Drake, D.C. Lafferty, G.K. Rathore Microchannel Plates (MCP) are used in a variety of imaging systems as a means of amplifying the incident radiation. Using a microchannel plate mount, developed at the University of Michigan, we compare square and round pore MCPs. Using a characterized x-ray source, we investigate the differences in the pulse height distribution, modular transfer function, and Quantum efficiency of these two types. Using a metal grid, we create a potential difference above the MCP that forces ejected electrons back into the pores, which may prove to increase the quantum efficiency of the system. Measurements of the effect of the reflecting grid on the quantum efficiency are presented. Work supported by the Naval Research Laboratory, National Nuclear Security Administration under the Stewardship Science Academic Alliances program through DOE Research Grant DE-FG52-03NA00064, and through DE FG53 2005 NA26014, and Livermore National Laboratory. [Preview Abstract] |
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FP1.00085: Omega Dante Soft X-Ray Spectrometer Upgrade and Component Calibrations to 20 keV K.M. Campbell, J. Schein, F.W. Weber, D. Hargrove, D. Pellinen, C. Sorce, V. Rekow One key parameter in the design and optimization of ICF indirect drive experiments is the measurement of the absolute radiation drive flux inside the hohlraum. The Dante x-ray spectrometer is the core diagnostic for this measurement on Omega and a new version capable of measuring photon energies up to 10 keV will be installed. The upgrade will extend the spectral range and allow researchers to adjust their channel selection to better fit their experimental parameters. Each channel has a characteristic spectral response depending on the transmission of the filters, the reflectivity of the mirrors and the response of the x-ray diodes. Periodic calibrations of these three elements from 60 eV up to 6 keV have been performed at the National Synchrotron Light Source at Brookhaven National Lab. Now, we have performed calibrations on the x-ray diodes and filters up to 20 keV. This will allow Dante to more accurately measure the x-ray drive for higher hohlraum temperatures. The expanded capabilities will allow better comparison between our Omega hohlraum experiments and the NIF campaigns. [Preview Abstract] |
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FP1.00086: Measurements of the L-shell emission of a Laser--Heated Halfraum Using High-Resolution X-ray Spectroscopy Klaus Widmann, Marilyn Schneider, Mark May, Hyun Chung, Denise Hinkel, Greg Brown, Lynn James, Jim Emig, Peter Beiersdorfer, Carmen Constantin, Hector Baldis State--of--the--art 2D LASNEX simulations of the interaction between high--energy (kJ) laser pulses (ns) and gold halfraums predict plasma conditions with $T_e$ above 15 keV at $n_e \sim $ 10$^{22}$ cm$^{-3}$. At such temperatures the charge state distribution (CSD) of gold ions contains a significant fraction of Ne--like Au${69+}$ ions. Survey spectra from highly charged gold ions which have been measured at the Livermore SuperEBIT facility show that the emission lines from Au${69+}$ and its subsequent ionization stages are separated by 40 eV or more. Thus, the CSD can be determined spectroscopically by measuring the relative line intensities. We have developed a high--resolution transmission crystal spectrometer to observe the x--ray emission in the vicinity of the $3d_{5/2}$ --- $2p_ {3/2}$ transition of Au${69+}$ (10.5 keV), i.e., 1000 eV spectral range around 10.2 keV. We present survey spectra obtained at SuperEBIT/LLNL and x--ray emission spectra from a laser--heated halfraum experiment performed at OMEGA/LLE. [Preview Abstract] |
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FP1.00087: Developing a 9 keV zinc backlighter for use on the Z accelerator M.R. Lopez, J.L. Porter, G.R. Bennett, M.C. Jones, L.E. Ruggles, I.C. Smith, R.G. Watt, G.C. Idzorek, T.E. Tierney A 9 keV zinc point projection backlighter was recently brought online at Sandia's 20 MA Z accelerator. Using the Z-Beamlet laser system, less than 100 micron spatial resolution has been achieved with high contrast on the Z accelerator. Dynamic range, signal-to-noise, signal-to-background, and spatial resolution of the 9 keV backlighter system will be presented. Additionally, advanced image processing techniques are being investigated to further improve the quality of the image. Sandia is a multiprogram laboratory operated by the Sandia Corporation, a Lockheed Martin Company, for the U.S. Department of Energy under Contract No. DE-AC04-94AL85000. [Preview Abstract] |
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FP1.00088: Spectroscopic analysis of compressed-shell conditions in OMEGA direct-drive implosions using Ti line absorption H.M. Hill, R.C. Mancini, V.A. Smalyuk, J. Delettrez, S.P. Regan, B. Yaakobi The determination of temperature and density in the compressed shell of ICF implosions is important for diagnosing the shell at the collapse of the implosion. To this end, we have developed a Ti spectral model to analyze K-shell line absorption spectra produced by Ti-doped tracer layers embedded in the shell that are backlit by continuum radiation emitted in the core. Line absorption is observed in Ti ions from F- to Be-like Ti. Detailed modeling and analysis of these absorption line spectra can yield Ti ionization state, temperature, density, and areal-density in the tracer layer. The model includes collisional-radiative atomic kinetics and detailed Stark-broadened line shapes, as well as the effect of self-emission of the lines. Analysis results including and not including the self-emission effect are presented. [Preview Abstract] |
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