Bulletin of the American Physical Society
57th Annual Meeting of the APS Division of Plasma Physics
Volume 60, Number 19
Monday–Friday, November 16–20, 2015; Savannah, Georgia
Session YO4: Z-Pinches and Dense Plasma Focus |
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Chair: George Swadling, Lawrence Livermore National Laboratory Room: 105/106 |
Friday, November 20, 2015 9:30AM - 9:42AM |
YO4.00001: The Largest Multi-Planar Wire Arrays on Zebra with LCM and their Applications. A.S. Safronova, V.L. Kantsyrev, M.E. Weller, V.V. Shlyaptseva, I.K. Shrestha, M.Y. Lorance, A. Stafford, K.A. Schultz, C.A. Coverdale, A.S. Chuvatin Two new approaches of i) simultaneous study of implosion and radiative characteristics of different materials in wire array Z-pinch plasma in one shot [Safronova et al, PoP 21, 031205 (2014)] and ii) investigation of larger sized wire arrays (to enhance energy coupling to plasmas and provide better diagnostic access) were further developed in experiments with 1.7 MA Zebra with a Load Current Multiplier. In particular, the largest multi-Planar Wire Arrays with two outer planes from alloyed Al wires placed as far from each other as at 19 mm (compare with 6 and 9 mm studied before) and with a modified central plane from Ni-60 (mostly Cu), were investigated. Though K-shell Al and L-shell Cu plasmas have similar temperatures and densities, the ablation dynamics and radiation of Al and Cu planes is somewhat different, which was investigated in detail using the full set of diagnostics and modeling. Advantages of using such wire arrays at higher currents to study plasma flow and radiation from different materials and jets are highlighted. This work was supported by NNSA under DOE Cooperative Agreement DE-NA0001984 and in part by DE-NA0002075. SNL is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Company, for the U.S. DOE under Contract DE-AC04-94AL85000. [Preview Abstract] |
Friday, November 20, 2015 9:42AM - 9:54AM |
YO4.00002: Diagnosing Pulsed Power Produced Plasmas with X-ray Thomson Scattering at the Nevada Terawatt Facility J.C. Valenzuela, C. Krauland, D. Mariscal, I. Krasheninnikov, F.N. Beg, P. Wiewior, A. Covington, R. Presura, T. Ma, C. Niemann, P. Mabey, G. Gregori We present experimental results on X-ray Thomson scattering (XRTS) at the Nevada Terawatt Facility (NTF) to study current driven plasmas. Using the Leopard laser, $\sim$ 30 J and pulse width of 0.8 ns, we generated He-$\alpha $ emission (4.75 keV) from a thin Ti foil. Initial parameter scans showed that the optimum intensity is $\sim$ 10$^{15} $W/cm$^{2}$ with a foil thickness of 2 $\mu $m for forward X-ray production. Bandwidth measurements of the source, using a HAPG crystal in the Von Hamos configuration, were found to be $\Delta $E/E $\approx $ 0.01. Giving the scattering angle of our experimental setup of 129 degrees and X-ray probing energy, the non-collective regime was accessed. The ZEBRA load was a 3 mm wide, 500 $\mu $m thick, and 10 mm long graphite foil, placed at one of the six current return posts. Estimates of the plasma temperature, density and ionization state were made by fitting the scattering spectra with dynamic structure factor calculations based on the random phase approximation for the treatment of charged particle coupling. [Preview Abstract] |
Friday, November 20, 2015 9:54AM - 10:06AM |
YO4.00003: Interaction of laser radiation with plasma under the MG external magnetic field V.V. Ivanov, A.V. Maximov, A.M. Covington, P.P. Wiewior, A.L. Astanovitskiy, V. Nalajala, O. Chalyy, O. Dmitriev A strong magnetic field can dramatically change the properties of plasmas. Studies of plasmas in the magnetic field are important for basic physics, astrophysics, and controlled fusion. A series of shots was carried out at the 1 MA pulsed power generator coupled with a 50-TW laser. A 2-2.5 MG magnetic field was generated on the surface of the Al 1 mm rod load by 1 MA current. A sub-nanosecond laser pulse with intensity of 3x10$^{15}$ W/cm$^{2}$ was focused on the load surface. A collimated plasma jet 1-3 mm long was observed propagating back from the focal spot with a speed of 240 km/s. Another plasma jet was seen on the rear side of the rod load. Both jets on the front and rear sides were also seen in shots with the 0.8 mm Cu load. The front plasma jet may be linked to the \textbf{E}x\textbf{B} drift observed elsewhere at smaller $B$-fields. The enhanced temperature and keV x-ray radiation of laser plasma in the magnetic field were found with x-ray spectroscopy. [Preview Abstract] |
Friday, November 20, 2015 10:06AM - 10:18AM |
YO4.00004: Stark Broadening Analysis Using Optical Spectroscopy of the Dense Plasma Focus Patrick Ross, Nikki Bennett, Eric Dutra, E. Chris Hagen, Scott Hsu, Gene Hunt, Jeff Koch, Tom Waltman To aid in validating numerical modeling of MA-class dense plasma focus (DPF) devices, spectroscopic measurements of the Gemini Dense Plasma Focus (DPF) were performed using deuterium and deuterium/dopant (argon/krypton) gas. The spectroscopic measurements were made using a fiber-coupled spectrometer and streak camera. Stark line-broadening analysis was applied to the deuterium beta emission (486 nm) in the region near the breakdown of the plasma and during the run-down and run-in phases of the plasma evolution. Densities in the range of 1e17 to low 1e18 cm$^{-3}$ were obtained. These values are in agreement with models of the DPF performed using the LSP code. The spectra also show a rise and fall with time, indicative of the plasma sheath passing by the view port. Impurity features were also identified in the spectra which grew in intensity as the gas inside the DPF was discharged repeatedly without cycling. Implications of this impurity increase for D-T discharges (without fresh gas fills between every discharge) will be discussed. This work was done by National Security Technologies, LLC, under Contract No. DE-AC52-06NA25946, and by Los Alamos National Laboratory, under Contract no. DE-AC52-06NA25396 with the U.S. Department of Energy. DOE/NV/25946-- 2515 [Preview Abstract] |
Friday, November 20, 2015 10:18AM - 10:30AM |
YO4.00005: Magnetic Field Measurements using Zeeman splitting on the SMP Diode at Sandia National Laboratories Sonal Patel, Mark Johnston, Timothy Webb, Yitzhak Maron, David Muron, Mark Keifer, Ronald Gilgenbach Self-Magnetic Pinch (SMP) diode experiments are in progress at the RITS-6 accelerator (5-11 MV, 100-200 kA) at Sandia National Laboratories. A hollow cathode emits electrons through an approximately 1-cm vacuum A-K gap onto a high-Z material. The high current compresses the electron beam to a few mm spot for use in flash x-ray radiography.\footnote{K. Hahn, N. Bruner, M. D. Johnston, B.V. Oliver, et. al., IEEE Trans. Plasma Sci. 38 (2010) 2652-62.} Visible spectra of the diode plasma have been taken during the radiation pulse using a high resolution (0.6 A) spectrometer and a lens coupled fiber array focused across the anode surface of the diode. Zeeman splitting measurements of CIV and Al III suggest magnetic fields of 3-4 T a few mm off the diode axis. These measurements yield current density profiles near the target surface. [Preview Abstract] |
Friday, November 20, 2015 10:30AM - 10:42AM |
YO4.00006: Acceleration of Deuterons to Multi-MeV Energies in Deuterium Gas-Puff Z-Pinch D. Klir, J. Cikhardt, B. Cikhardtova, J. Kravarik, P. Kubes, K. Rezac, O. Sila, A. Shishlov, R. Cherdizov, F. Fursov, V. Kokshenev, B. Kovalchuk, N. Kurmaev, A. Labetsky, N. Ratakhin, J. Krasa, K. Turek A novel configuration of a deuterium gas-puff z-pinch has been used to generate a short (approx. 20 ns) pulse of multi-MeV ions and neutrons. Even though ion acceleration in z-pinches has not been researched to such an extent as in laser-based sources, obtained results show that z-pinches can reach values comparable to those of state-of-the-art lasers. On the 3 MA GIT-12 generator, the peak neutron yield was 3.6x10$^{\mathrm{12}}$. When a neutron-producing sample was placed onto the axis below a cathode mesh, the neutron yield was increased up to 10$^{\mathrm{13}}$. The emission time of 20 ns implied the neutron production rate of 5x10$^{\mathrm{20}}$ n/s. Neutron energies reached the maximum value of 33 MeV. The comprehensive set of ion diagnostics provided unique information about ion acceleration mechanism. The ion emission was highly anisotropic. Deuterons were trapped in the radial direction whereas a lot of fast ions escaped the z-pinch along the axis. On the axis, the total number of \textgreater 1 MeV and \textgreater 25 MeV deuterons was 10$^{\mathrm{16}}$ and 5x10$^{\mathrm{12}}$, respectively. Utilizing these ions offers a real possibility of various applications including the production of short-lived isotopes or fast neutron radiography. [Preview Abstract] |
Friday, November 20, 2015 10:42AM - 10:54AM |
YO4.00007: Gas puff Z-pinches with deuterium-krypton gas mixtures Timothy Darling, Erik McKee, Aaron Covington, Vladimir Ivanov, Frank Wessel, Hafiz Rahman We discuss experiments with single-shell, pure and mixed-gas loads on the zebra pulsed-power generator at the Nevada Terawatt Facility (NTF). These experiments are modeled using the MACH2 code and provide input and benchmarking for further models and experiments on upcoming staged Z-pinch (SZP) studies under an ARPA-E program. The 1MA-70ns rise time discharge of Zebra produces bursts of both high and low energy X-rays and neutrons if deuterium gas is present. The gas is injected from the (grounded) anode to cathode as an expanding cylindrical shell of approximately 4cm diameter. A pulsed valve and a flow-forming nozzle determine the details of the gas target geometry which is imaged as a density map using a UV excited fluorescent tracer (LIF). The gases imaged are pure Kr and D2 and binary mixtures thereof. A pure D2 pinch produces a (yet to be optimized) neutron yield in the 1e10 regime. Additional diagnostics include a 2-frame Schlieren 1064nm IR imaging diagnostic, which provides information on the implosion dynamics of the pinch. [Preview Abstract] |
Friday, November 20, 2015 10:54AM - 11:06AM |
YO4.00008: Temperature Evolution of a 1 MA Triple-Nozzle Gas-Puff Z-Pinch Philip de Grouchy, Jacob Banasek, Joey Engelbrecht, Niansheng Qi, Levon Atoyan, Tom Byvank, Adam Cahill, Hannah Moore, William Potter, Lauren Ransohoff, David Hammer, Bruce Kusse Mitigation of the Rayleigh-Taylor instability (RTI) plays a critical role in optimizing x-ray output at high-energy $\sim$ 13 keV using the triple-nozzle Krypton gas-puff at Sandia National Laboratory [1]. RTI mitigation by gas-puff density profiling [1] using a triple-nozzle gas-puff valve has recently been recently demonstrated on the COBRA 1MA z-pinch at Cornell University [2]. In support of this work we investigate the role of shell cooling in the growth of RTI during gas-puff implosions. Temperature measurements within the imploding plasma shell are recorded using a 527 nm, 10 GW Thomson scattering diagnostic for Neon, Argon and Krypton puffs. The mass-density profile is held constant at 22 microgram per centimeter for all three puffs and the temperature evolution of the imploding material is recorded. In the case of Argon puffs we find that the shell ion and electron effective temperatures remain in equilibrium at around 1keV for the majority of the implosion phase. In contrast scattered spectra from Krypton are dominated by of order 10 keV effective ion temperatures. [1] C. Jennings et al. Phys. Plasmas, accepted (2015)\ [2] A. Velikovich et al. Phys. Rev. Lett. 77 853-856 (1996) [3] P. de Grouchy et al. IEEE Trans. Plasma Sci. Invited and Plenary Speakers of ICOPS 2015 [Preview Abstract] |
Friday, November 20, 2015 11:06AM - 11:18AM |
YO4.00009: Relativistic Modeling Capabilities in PERSEUS Extended-MHD Simulation Code for HED Plasmas Nathaniel Hamlin, Charles Seyler We discuss the incorporation of relativistic modeling capabilities into the PERSEUS extended MHD simulation code for high-energy-density (HED) plasmas, and present the latest simulation results. The use of fully relativistic equations enables the model to remain self-consistent in simulations of such relativistic phenomena as hybrid X-pinches and laser-plasma interactions. We have overcome a major challenge of a relativistic fluid implementation, namely the recovery of primitive variables (density, velocity, pressure) from conserved quantities at each time step of a simulation. Our code recovers non-relativistic results along with important features of published Particle-In-Cell simulation results for a laser penetrating a super-critical hydrogen gas with Fast Ignition applications. In particular, we recover the penetration of magnetized relativistic electron jets ahead of the laser. Our code also reveals new physics in the modeling of a laser incident on a thin foil. [Preview Abstract] |
Friday, November 20, 2015 11:18AM - 11:30AM |
YO4.00010: ABSTRACT WITHDRAWN |
Friday, November 20, 2015 11:30AM - 11:42AM |
YO4.00011: ABSTRACT WITHDRAWN |
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