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 QI2: Z-Pinch/ICF Physics |
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Chair: Gregory Moses, University of Wisconsin Room: Adam's Mark Hotel Plaza Ballroom EF |
Thursday, October 27, 2005 9:30AM - 10:00AM |
QI2.00001: Capsule implosions driven by dynamic hohlraum x-rays Invited Speaker: Dynamic hohlraum experiments at the Z facility already implode capsules with up to 80 kJ absorbed x-ray energy. However, many challenging issues remain for ICF. The present experiments use diagnostic capsules to address two of these issues: symmetry measurement and control and building understanding of the capsule/hohlraum implosion system. A suite of x-ray spectrometers record time and space resolved spectra emitted by Ar tracer atoms in the implosion core, simultaneously from up to three different quasi-orthogonal directions. Comparing the results with simulation predictions provide severe tests of understanding. These data also can used to produce a tomographic reconstruction of the time resolved core temperature and density profiles. X-ray and neutron diagnostics are used to examine how the implosion conditions change as the capsule design changes. The capsule design changes include variations in CH wall thickness and diameter, Ge-doped CH shells, and SiO$_{2}$ shells. In addition, a new campaign investigating Be capsule implosions is beginning. Be capsules may offer superior performance for dynamic hohlraum research and it may be possible to investigate NIF-relevant Be implosion issues such as the fill tube effects, sensitivity to columnar growth associated with sputtered Be capsule fabrication, and the effect of Cu dopants on implosion conditions. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the U.S. Dept. of Energy under contract No. DE-AC04-94AL85000. * In collaboration with G.A. Rochau, G.A. Chandler, S.A. Slutz, P.W. Lake, G. Cooper, G.S. Dunham, R.J. Leeper, R. Lemke, T.A. Mehlhorn, T.J. Nash, D.S. Nielsen, K. Peterson, C.L. Ruiz, D.B. Sinars, J. Torres, W. Varnum, Sandia; R.C. Mancini, T.J. Buris-Mog, UNR; I. Golovkin, J.J. MacFarlane, PRISM; A. Nikro, D. Steinman, J.D. Kilkenny, H. Xu, General Atomics; M. Bump, T.C. Moore, K-tech; D.G. Schroen, Schafer [Preview Abstract] |
Thursday, October 27, 2005 10:00AM - 10:30AM |
QI2.00002: Single and nested tungsten-wire-array dynamics and applications to inertial confinement fusion Invited Speaker: Wire array z-pinches show great promise as x-ray sources for indirect-drive inertial confinement fusion (ICF). The double z-pinch hohlraum, for example, has produced capsule radiation drive symmetric to within 3{\%}. This ICF concept will require that each of two 20-mm-diam arrays scale to x-ray powers $\sim $1 PW, to drive high-yield ($>$0.2 GJ) capsules to ignition. High-yield fusion will also require a temporally shaped radiation pulse to drive a low-entropy capsule implosion. Recently, improved understanding of high current (11-19 MA) single and nested wire-array dynamics has enabled significant progress towards these goals. As at lower currents, a single wire array (and both the outer and inner arrays of a nested system) shows a wire ablation phase, axial modulation of the ablation rate, a larger ablation rate for larger diameter wires, trailing mass and trailing current. These processes and others produce a broad mass profile that may impact the optimization of x-ray output for single and nested arrays. Our new insights into wire array physics have led to 20-mm-diam single and nested arrays with peak powers of 150-190 TW at implosion times of 55-90 ns, increased from 60-120 TW at 95-110 ns, improving power scaling. Radiation pulse shapes required for 3-shock isentropic compression of high-yield ICF capsules have also been demonstrated with nested wire arrays operating in current-transfer mode. In collaboration with: D.B. Sinars, R.A. Vesey, E.M. Waisman, W.A. Stygar, D.E. Bliss, S.V. Lebedev, J.P. Chittenden, P.V. Sasorov, R.W. Lemke, E.P. Yu, B.B. Afeyan, G.R. Bennett, M.G. Mazarakis, M.R. Lopez, M.E. Savage, J.L. Porter, T.A. Mehlhorn. [Preview Abstract] |
Thursday, October 27, 2005 10:30AM - 11:00AM |
QI2.00003: Measurement and modeling of the implosion of wire arrays with seeded instabilities Invited Speaker: Wire array z-pinches are powerful and efficient sources of soft x-rays used for inertial confinement fusion studies, radiation physics and other work. Understanding the origin and evolution of three-dimensional (3D) magneto-Rayleigh-Taylor instabilities in the imploding plasma is important for optimizing x-ray power and yield. In the research presented, the impact of 3D structure on wire array z-pinch dynamics is studied by controlled seeding of wire perturbations. Al wires were etched at Sandia, creating 20{\%} steps in radius with variable axial wavelength. With 9 mm periodicity, magnetic bubble formation at wire radius discontinuities is observed on the MAGPIE accelerator and in 3D magnetohydrodynamic (MHD) modeling due to non-uniformity in the current path and local \textbf{j} x \textbf{B} enhancement. Perturbations shorter than the 0.5 mm radial flare ablation mode dominate the evolution of the wire core and imprint the coronal plasma. The longer 0.5 mm natural mode is seen superimposed on these shorter scale length features, which offers insight into the physics of this mode and can constrain \textit{ad hoc} perturbations used in 3D MHD codes. Variation of the x-ray pulse shape due to seeded perturbations will be discussed. Experiments employing localized spectroscopic dopants to track turbulent particle flow in wire arrays will also be presented as a tool for diagnosing 3D structure. [Preview Abstract] |
Thursday, October 27, 2005 11:00AM - 11:30AM |
QI2.00004: Blast Wave Radiation Source Measurement Experiments on Z Invited Speaker: The Dynamic Hohlraum (DH) radiation on the Z facility at Sandia National Laboratories is a bright source of radiant energy that has proven useful for high energy density physics experiments. In this paper, we describe experiments that are designed to study the nature of this source through a unique mechanism using the high power and energy of the Z DH source. In these experiments, initially supersonic and diffusive radiation waves propagate into an unconstrained 40 mg/cm$^{3}$ SiO$_{2}$ foam cylinder. As this radiation wave propagates through the foam, it spreads out and the temperature drops, and as its temperature drops, so does the wave's speed. As long as the radiation is moving faster than the local shock speed, the foam cannot hydrodynamically respond in a significant way to the temperature and pressure gradients at the radiation front. However, once the speed of the radiation front reaches the shock speed, a shock wave begins to form. The density ridge at the shock front can be observed through x-ray radiography. Computer simulations have shown that the position of the shock front is sensitive to the time-integrated drive energy, thus acting as a radiation calorimeter. In the experiments on Z, radiation power is measured at the bottom of the pinch, and may be measured through a hole in the side of a foam-filled gold funnel that feeds the radiation into the sample foam. On a successful shot on Z in February of 2005 (Z1430), the peak radiant power measured out of the bottom of the pinch was roughly 12 to 13 TW and the power deduced to be radiating upward into the experiment was between 12.4 TW and 14.6 TW. The position of the shock in the foam is therefore a promising in-situ radiation source fluence diagnostic. [Preview Abstract] |
Thursday, October 27, 2005 11:30AM - 12:00PM |
QI2.00005: Stopping, Straggling, and Blooming of Directed Energetic Electrons in Hydrogenic and Arbitrary-Z Plasmas Invited Speaker: The interaction of directed energetic electrons with hydrogenic and arbitrary-Z plasmas is analytically modeled. These calculations reveal new features of the strong coupling between energy loss, straggling, and blooming, results which are important for fast ignition (FI), electron preheat in ICF, and electron penetration in relativistic astrophysical jets. Scattering enhances energy transfer along the initial electron direction and substantially reduces the penetration. Enhanced energy deposition occurs in the latter portion of the penetration and is inextricably linked to straggling and blooming. The Z dependence of these effects is very strong and electron scattering effects, ignored in previous calculations, are as important as scattering from the ions for DT plasmas; for higher Z plasmas, such as Be or CH in capsule ablators, scattering is dominated by ions. Penetration, blooming, and straggling are most easily parameterized and understood in terms of the \textit{total} $\rho $R through which the electrons propagate; little sensitivity is found on density or temperature gradients. As a concrete example for the case of electron preheat, 100 keV electrons are found to penetrate through 280 $\mu $m of DT, which is characteristic of proposed direct-drive ice thickness at the NIF. For astrophysical jets, for which n$\sim $10/cm$^{3}$, the penetration of 1 MeV electrons is of order 10,000 light years. For the case of FI in a 300 g/cm$^{3}$ DT plasma at 5 keV, 1 MeV electrons penetrate 14 $\mu $m with a lateral blooming of 5 $\mu $m. Such results will be important, among other reasons, for evaluating the requirements of fast ignition as well as determining tolerable levels of electron preheat. [Preview Abstract] |
Thursday, October 27, 2005 12:00PM - 12:30PM |
QI2.00006: High Energy Plasma Photonics Invited Speaker: Ultra-intense laser technologies are opening a variety of attractive fields of science and technology using high energy density plasmas. The critical issues in the applications are control of the intense light and the enormous current and energy densities of charged particles. These applications have been usually limited by high power laser technologies and their optics. However, if we have another device consisting of the 4$^{th}$ state of matter, plasma, higher energy density conditions can be more efficiently generated by this device allowing to explore the more extreme application possibilities. We denote this as ``high energy plasma photonic devices.'' One such attractive device has been demonstrated in the fast ignition scheme of the laser fusion, which is cone-guiding of ultra-intense laser light into high density regions.\footnote{R. Kodama et al., \textit{Nature} \textbf{412}, 798 (2001)~; R. Kodama et al., \textit{Nature} \textbf{418}, 933 (2002).} Another invention as a novel `photonic-like' device is a plasma fibre (5$\mu $m$\phi $/1mm) created on a hollow-cone target.\footnote{R. Kodama et al., \textit{Nature} \textbf{432}, 1005 (2004).} This device guides and collimates the high-density of MeV electrons generated by ultra-intense laser light in a manner akin to a light control by an optical fibre, enhancing the energy density by more than an order of magnitude and possibly generating of Giga-bar pressures. Such plasma devices hold rich promise for a range of applications utilizing enormous energy-densities of relativistic particles and will trigger a tremendous growth in high energy-density charged particle optics. [Preview Abstract] |
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