Bulletin of the American Physical Society
59th Annual Meeting of the APS Division of Plasma Physics
Volume 62, Number 12
Monday–Friday, October 23–27, 2017; Milwaukee, Wisconsin
Session NO5: Z-pinch, X-pinch, Dense Plasma Focus, and Fast Ignition |
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Chair: Steve Richardson, Naval Research Laboratory Room: 202AB |
Wednesday, October 25, 2017 9:30AM - 9:42AM |
NO5.00001: Three Magnetized Noh Problems as Verification Tests for MHD Codes J.L. Giuliani, A.L. Velikovich, A. Beresnyak, S.T. Zalesak In a recent published work [1], the cylindrical version of the classical hydrodynamic Noh problem was generalized to the magnetohydrodynamic (MHD) realm through a self-similar solution that included an azimuthal magnetic field. We have extended this class of magnetized Noh verification tests to two new self-similar solutions that include both axial and azimuthal fields. Physical constraints on the azimuthal current density at the axis limit the ratio of specific heats to 1\textless $\gamma $ \textless 3/2 and $\gamma $ $=$2. Several MHD codes successfully match the $\gamma \quad =$2 case in cylindrical and 2D Cartesian coordinates. However, no MHD code tested so far has been able to reproduce the $\gamma \quad =$ 1.1 case in Cartesian geometry. This indicates either a difficulty in Cartesian grid modeling of Z-pinches or that the $\gamma \quad =$1.1 solution is physically unstable. We are investigating the stability of this MHD solution in r-phi coordinates with a numerical technique originally developed to analyze linear stability for compressible hydrodynamics [2]. Summarizing, we have developed a set of three magnetized Noh, self-similar solutions as verification tests for MHD codes. [1] Velikovich, et al., Phys. Plasmas, 19, 012707 (2012). [2] Zalesak, et al., Physics of Plasmas, 12, 056311, 2005. [Preview Abstract] |
Wednesday, October 25, 2017 9:42AM - 9:54AM |
NO5.00002: Three dimensional calculation of thermonuclear ignition conditions for magnetized targets Ross Cortez, Jason Cassibry, Michael Lapointe, Robert Adams Fusion power balance calculations, often performed using analytic methods, are used to estimate the design space for ignition conditions. In this paper, fusion power balance is calculated utilizing a 3-D smoothed particle hydrodynamics code (SPFMax) incorporating recent stopping power routines. Effects of thermal conduction, multigroup radiation emission and nonlocal absorption, ion/electron thermal equilibration, and compressional work are studied as a function of target and liner parameters and geometry for D-T, D-D, and $^{\mathrm{6}}$LI-D fuels to identify the potential ignition design space. Here, ignition is defined as the condition when fusion particle deposition equals or exceeds the losses from heat conduction and radiation. The simulations are in support of ongoing research with NASA to develop advanced propulsion systems for rapid interplanetary space travel. [Preview Abstract] |
Wednesday, October 25, 2017 9:54AM - 10:06AM |
NO5.00003: Streaked Thomson Scattering on Laboratory Plasma Jets Jacob Banasek, Tom Byvank, Sophia Rocco, Bruce Kusse, David Hammer Streaked Thomson scattering measurements have been performed on plasma jets created from a 15~$\mu$m thick radial Al or Ti foil load on COBRA, a 1~MA pulsed power machine. The goal was to measure the electron temperatures inside the center of the plasma jet created by the radial foil. The laser used for these measurements had a maximum energy of 10~J at 526.5~nm in a 3~ns duration pulse. Early experiments showed using the full energy significantly heats the 5$\times$10$^{18}$~cm$^{-3}$ jet by inverse bremsstrahlung radiation. Here we used a streak camera to record the scattered spectrum and measure the evolving electron temperature of this laser heated jet. Analysis of the streak camera image showed that the electron temperature of the Al jet was increased from about 25~eV to 80-100~eV within about 2~ns. The Ti jets showed even stronger interaction with the laser, being heated to over 150~eV, and showed some heating even when only 1~J of laser energy was used. Also, the ion-acoustic peaks in the scattered spectrum from the Ti jets were significantly narrower than those from Al jets. Initial results will also be presented with scattered spectra taken at two different times within a single experiment by splitting the probe beam. [Preview Abstract] |
Wednesday, October 25, 2017 10:06AM - 10:18AM |
NO5.00004: Simulations of a dense plasma focus on a high impedance generator Andrey Beresnyak, John Giuliani, Stuart Jackson, Steve Richardson, Steve Swanekamp, Joe Schumer, Robert Commisso, Dave Mosher, Bruce Weber, Alexander Velikovich We study the connection between plasma instabilities and fast ion acceleration for neutron production on a Dense Plasma Focus (DPF). The experiments will be performed on the HAWK generator (665 kA), which has fast rise time, 1.2 $\mu $s, and a high inductance, 607 nH. It is hypothesized that high impedance may enhance the neutron yield because the current will not be reduced during the collapse resulting in higher magnetization. To prevent upstream breakdown, we will inject plasma far from the insulator stack. We simulated rundown and collapse dynamics with Athena -- Eulerian 3D, unsplit finite volume MHD code that includes shock capturing with Riemann solvers, resistive diffusion and the Hall term. The simulations are coupled to an equivalent circuit model for HAWK. We will report the dynamics and implosion time as a function of the initial injected plasma distribution and the implications of non-ideal effects. We also traced test particles in MHD fields and confirmed the presence of stochastic acceleration, which was limited by the size of the system and the strength of the magnetic field. [Preview Abstract] |
Wednesday, October 25, 2017 10:18AM - 10:30AM |
NO5.00005: Advanced Design Concepts for Dense Plasma Focus Devices at LLNL Alexander Povilus, Yuri Podpaly, Christopher Cooper, Brian Shaw, Steve Chapman, James Mitrani, Michael Anderson, Aric Pearson, Enrique Anaya, Ed Koh, Steve Falabella, Tony Link, Andrea Schmidt The dense plasma focus (DPF) is a z-pinch device where a plasma sheath is accelerated down a coaxial railgun and ends in a radial implosion, pinch phase. During the pinch phase, the plasma generates intense, transient electric fields through physical mechanisms, similar to beam instabilities, that can accelerate ions in the plasma sheath to MeV-scale energies on millimeter length scales. Using kinetic modeling techniques developed at LLNL, we have gained insight into the formation of these accelerating fields and are using these observations to optimize the behavior of the generated ion beam for producing neutrons via beam-target interactions for kilojoule to megajoule-scale devices. Using a set of DPF’s, both in operation and in development at LLNL, we have explored critical aspects of these devices, including plasma sheath formation behavior, power delivery to the plasma, and instability seeding during the implosion in order to improve the absolute yield and stability of the device. [Preview Abstract] |
Wednesday, October 25, 2017 10:30AM - 10:42AM |
NO5.00006: Overview of pulsed-power-driven high-energy-density plasma research at the University of Michigan R.D. McBride, P.C. Campbell, S.M. Miller, J.M. Woolstrum, D.A. Yager-Elorriaga, A.M. Steiner, N.M. Jordan, Y.Y. Lau, R.M. Gilgenbach, A.S. Safronova, V.L. Kantsyrev, V.V. Shlyaptseva, I.K. Shrestha, C.J. Butcher, G.R. Laity, J.J. Leckbee, M.L. Wisher, S.A. Slutz, M.E. Cuneo The Michigan Accelerator for Inductive Z-pinch Experiments (MAIZE) is a 3-m-diameter, single-cavity Linear Transformer Driver (LTD) at the University of Michigan (UM). MAIZE supplies a fast electrical pulse (0--1 MA in 100 ns for matched loads) to various experimental configurations, including wire-array z-pinches and cylindrical foil loads. This talk will report on projects aimed at upgrading the MAIZE facility (e.g., a new power feed and new diagnostics) as well as various physics campaigns on MAIZE (e.g., radiation source development, power flow, implosion instabilities, and other projects relevant to the MagLIF program at Sandia). In addition to MAIZE, UM is constructing a second, smaller LTD facility consisting of four 1.25-m-diameter cavities. These cavities were previously part of Sandia's 21-cavity Ursa Minor facility. The status of the four Ursa Minor cavities at UM will also be presented. This research was funded in part by the University of Michigan, a Faculty Development Grant from the Nuclear Regulatory Commission, the NNSA under DOE grant DE-NA0003047 for UNR, and Sandia National Laboratories under DOE-NNSA contract DE-NA0003525. [Preview Abstract] |
Wednesday, October 25, 2017 10:42AM - 10:54AM |
NO5.00007: Implosion dynamics and radiative properties of W planar wire arrays influenced by Al wires on University of Michigan's LTD generator. A.S. Safronova, V.L. Kantsyrev, V.V. Shlyaptseva, I.K. Shrestha, C.J. Butcher, A. Stafford, P.C. Campbell, S. Miller, D.A. Yager-Elorriaga, N.M. Jordan, R.D. McBride, R.M. Gilgenbach The results of new experiments with W Double Planar Wire Arrays (DPWA) at the University of Michigan's Linear Transformer Driver (LTD) generator are presented that are of particular importance for future work with wire arrays on 40-60 MA LTDs at SNL. A diagnostic set similar to the previous campaigns comprised filtered x-ray diodes, a Faraday cup, x-ray spectrometers and pinhole cameras, but had an ultra-fast 12-frame self-emission imaging system. Implosion and radiative characteristics of two DPWAs of the same mass (60 $\mu $g/cm) and geometry (two planes with 8 wires each at the distance of 6 mm and an inter-wire gap of 0.7 mm) with one plane of W wires and another either of W wires (1) or of Al wires (2) were compared in detail. The substantial differences between two cases are observed: 1) precursor formation and intense hard x-ray characteristic emission of W (``cold'' L lines) caused by electron beams; 2) no precursor, standing shocks at the W plane side that lasted up to a hundred of ns, fast ablation and implosion of Al wires, and suppression of hard x-ray ``cold'' L lines of W. In addition, the evolution of self-emission in a broad period of time up to 400 ns is analyzed for the first time. [Preview Abstract] |
Wednesday, October 25, 2017 10:54AM - 11:06AM |
NO5.00008: First Results of the Comparison of Double Planar Foils and Wire Arrays on the Low Impedance Z-Pinch Michigan's LTD generator. V.L. Kantsyrev, A.S. Safronova, I.K. Shrestha, V.V. Shlyaptseva, C.J. Butcher, A. Stafford, K.A Schultz, P.C. Campbell, S. Miller, D.A. Yager-Elorriaga, N.M. Jordan, R.D. McBride, R.M. Gilgenbach The results of first experiments with Al double planar foil liners (DPFL) at the University of Michigan's low impedance Linear Transformer Driver (LTD) MAIZE generator are presented. The DPFL is a promising alternative load to wire arrays on future 40-60 MA generators. Last decade, there was a significant progress in efficient, repetitive Z-pinch generators such as the LTD for prospective ICF research. Though we have recently presented the results on the Planar Wires Arrays (PWAs) on MAIZE, there is no data collected yet for DPFLs on LTD machines. Diagnostics include x-ray Si-diodes, a Faraday cup, x-ray pinhole cameras and spectrometers, and an ultra-fast 12-frame self-emission imaging system. Implosion and x-ray radiative characteristics of Al DPFLs (two planes 1.8 \textmu m thick and 3.5 mm wide placed at 3 mm) are analyzed in detail and compared with data from Al double PWAs and results on Al DPFLs obtained early at high impedance generator. Experimental data demonstrate successful implosion of DPFL on LTD and therefore set the direction of the new work with thin foils. [Preview Abstract] |
Wednesday, October 25, 2017 11:06AM - 11:18AM |
NO5.00009: Shock ignition targets: gain and robustness vs ignition threshold factor Stefano Atzeni, Luca Antonelli, Angelo Schiavi, Silvia Picone, Gian Marco Volponi, Alberto Marocchino Shock ignition [1] is a laser direct-drive inertial confinement fusion scheme, in which the stages of compression and hot spot formation are partly separated. The hot spot is created at the end of the implosion by a converging shock driven by a final ``spike'' of the laser pulse. Several shock-ignition target concepts have been proposed and relevant gain curves computed (see, e. g. [2]). Here, we consider both pure-DT targets and more facility-relevant targets with plastic ablator. The investigation is conducted with 1D and 2D hydrodynamic simulations. We determine ignition threshold factors ITF's (and their dependence on laser pulse parameters) by means of 1D simulations [3]. 2D simulations indicate that robustness to long-scale perturbations increases with ITF. Gain curves (gain vs laser energy), for different ITF's, are generated using 1D simulations. [1] R. Betti et al., Phys. Rev. Lett. 98, 155001 (2007). [2] S. Atzeni et al., Nucl. Fusion 54, 054008 (2014). [3] S. Atzeni, A. Marocchino, A. Schiavi, Plasma Phys. Controll. Fusion 57, 014022 (2015). [Preview Abstract] |
Wednesday, October 25, 2017 11:18AM - 11:30AM |
NO5.00010: Laser plasma instabilities and hot electron generation from multi-kilojoule shock ignition relevant high-intensity IR and UV lasers S. Zhang, J. Li, F. N. Beg, C. M. Krauland, S. Muller, N. Alexander, C. Ren, W. Theobald, D. Turnbull, D. Haberberger, R. Betti, E. M. Campbell, D. Batani, J. Santos, P. Nicolai, M. S. Wei As an alternative ignition scheme, shock ignition uses a strong convergent shock driven by a high-intensity laser (\textasciitilde 10$^{\mathrm{16}}$ W/cm$^{\mathrm{2}})$ on a pre-compressed fuel to achieve ignition. Moderately energetic hot electrons (\textless 100 keV) generated from the laser plasma instabilities (LPI) can strengthen the ignition shock by depositing energy at the compressed outer shell increasing ablation pressure. In our previous experiments on OMEGA-EP, 90 keV collimated hot electrons were observed from a 100 ps, 2.5 kJ IR laser interacting with SI long scale length hot plasmas ($L_{\mathrm{n}}$ \textasciitilde 200 $-$ 500 \textmu m, $T_{\mathrm{e\thinspace \thinspace }}$\textgreater 1 keV, produced by low-intensity UV beams). To further characterize hot electron generation and investigate the related LPIs, we have extended the experiments with high-intensity, multi-kJ IR and UV lasers (both at normal incidence, up to 2\texttimes 10$^{\mathrm{16}}$ W/cm$^{\mathrm{2}})$. Two IR beams in co-propagation extend the pulse duration to 200 ps, closer to required ignition pulse duration. The scattered light is spectrally resolved to identify the LPI. Angular filter refractometer images from 4$\omega $ probe show the details of the laser propagation and interaction. The divergence, energy, and temperature of the hot electrons are diagnosed by measuring the bremsstrahlung and Cu K$\alpha $ emission. Details of the experimental results will be presented. [Preview Abstract] |
Wednesday, October 25, 2017 11:30AM - 11:42AM |
NO5.00011: Compact Fast Ignition experiments using Joule-class tailored drive pulses under counterbeam configuration Yoshitaka Mori, Ryohei Hanayama, Katsuhiro Ishii, Yoneyoshi Kitagawa, Takashi Sekine, Yasuki Takeuchi, Takashi Kurita, Yoshinori Katoh, Nakahiro Satoh, Norio Kurita, Toshiyuki Kawashima, Osamu Komeda, Tatsumi Hioki, Tomoyoshi Motohiro, Atsushi Sunahara, Yasuhiko Sentoku, Eisuke Miura, Akifumi Iwamoto, Hitoshi Sakagami Fast ignition (FI) is a form of inertial confinement fusion in which the ignition step and the compression step are separate processes resulting in a reduction of the symmetry requirement for hot spot generation. One of the problems of FI so far are the accessibility of an ignition laser pulse into the assembled core in which the driver energy is converted into relativistic electrons produced in the laser-plasma interaction. We have experimentally demonstrated that a tailored-pulse-assembled core with a diameter of 70 $¥mu$m, originally a deuterated polystyrene spherical shell of 500 $¥mu$m diameter, is flashed by directly counter irradiating 0.8 J/110 fs laser pulses [Y. MORI et al., PRL 2016]. This result indicates that once the assembled core is squeezed into the target center, the heating lasers can access the core’s edges and deposit their energy into the core. In this talk, we will discuss the heating effects in relation to formation of the assembled core. [Preview Abstract] |
Wednesday, October 25, 2017 11:42AM - 11:54AM |
NO5.00012: Two-colors-laser-plasma interaction for enhancing hot electron generation to drive strong shock in a dense matter Shinsuke Fujioka, Seungho Lee, Hidetaka Kishimoto, Hiroki Morita, Yuji Fukuyama, Syohei Sakata, Kazuki Matsuo, King Fai Farley Law, Yugo Ochiai, Keisuke Koga, Yasunobu Arikawa, Keisuke Shigemori, Akifumi Yogo, Hiroaki Nishimura, Kunioki Mima, Hiroshi Azechi, Natsumi Iwata, Takayoshi Sano, Hideo Nagatomo, Yasuhiko Sentoku, Ryosuke Kodama Localized heating of an overdense plasma by hot electrons is being studied as a scheme to drive strong shock in a matter. One of the challenges in this scheme is efficient energy conversion from laser light to hot electrons through laser-plasma interactions. Here we have demonstrated experimentally that mixture of 1.053 $\mu$m and 0.53 $\mu$m intense laser beams results in one order of magnitude enhancement of this efficiency. Number and energy distribution of hot electrons were measured by using two spectrometers of Bremsstrahlung X-ray and characteristic X-ray from Cu tracer embedded targets. Dependences of the energy conversion on laser intensity ratio and relative polarization were clearly observed. Spectrum of the backscattered light indicates change of electron plasma waves by the two-color lasers irradiation. Comparison between the experiment and simulation will also be presented. [Preview Abstract] |
Wednesday, October 25, 2017 11:54AM - 12:06PM |
NO5.00013: Diffusion of external magnetic fields into the cone-in-shell target in the fast ignition Atsushi Sunahara, Hiroki Morita, Tomoyuki Johzaki, Hideo Nagatomo, Shinsuke Fujioka, Ahmed Hassanein We simulated the diffusion of externally applied magnetic fields into~cone-in-shell target~in~the fast ignition. Recently, in the fast ignition scheme, the externally magnetic fields up to kilo-Tesla is used~to~guide~fast~electrons to the~high-dense~imploded core. In order to~study~the profile of the magnetic field, we have developed 2D~cylindrical~Maxwell equation solver with Ohm's law, and carried out simulations of diffusion of externally applied magnetic fields into~a~cone-in-shell target. We estimated the conductivity of the cone and shell target based on~the~assumption of Saha-ionization equilibrium.~Also, we calculated the temporal evolution of the target temperature heated by the eddy current driven by temporal variation of magnetic fields, based on the accurate equation of state. Both, the diffusion of magnetic field and the increase of target temperature interact with each other. We present our results of temporal evolution of the magnetic field and its diffusion into the cone and shell target. [Preview Abstract] |
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