Bulletin of the American Physical Society
58th Annual Meeting of the APS Division of Plasma Physics
Volume 61, Number 18
Monday–Friday, October 31–November 4 2016; San Jose, California
Session KI2: Rosenbluth Award and Magnetized High Energy Density PhysicsInvited
|
Hide Abstracts |
Chair: Arati Dasgupta, Naval Research Laboratory Room: 210 CDGH |
Tuesday, November 1, 2016 3:00PM - 3:30PM |
KI2.00001: Demonstration of Ion Kinetic Effects in Inertial Confinement Fusion Implosions and Investigation of Magnetic Reconnection Using Laser-Produced Plasmas Invited Speaker: M.J. Rosenberg Shock-driven laser inertial confinement fusion (ICF) implosions have demonstrated the presence of ion kinetic effects in ICF implosions and also have been used as a proton source to probe the strongly driven reconnection of MG magnetic fields in laser-generated plasmas. Ion kinetic effects arise during the shock-convergence phase of ICF implosions when the mean free path for ion--ion collisions $\left( {\lambda_{\mbox{ii}} } \right)$ approaches the size of the hot-fuel region $\left( {R_{\mbox{fuel}} } \right)$ and may impact hot-spot formation and the possibility of ignition. To isolate and study ion kinetic effects, the ratio of $N_{\mbox{K}} ={\lambda_{\mbox{ii}} } \mathord{\left/ {\vphantom {{\lambda_{\mbox{ii}} } {R_{\mbox{fuel}} }}} \right. \kern-\nulldelimiterspace} {R_{\mbox{fuel}} }$ was varied in D$^{\mathrm{3}}$He-filled, shock-driven implosions at the Omega Laser Facility and the National Ignition Facility, from hydrodynamic-like conditions $\left( {N_{\mbox{K}} {\kern 1pt}\sim 0.01} \right)$ to strongly kinetic conditions $\left( {N_{\mbox{K}} \sim 10} \right).$ A strong trend of decreasing fusion yields relative to the predictions of hydrodynamic models is observed as $N_{\mathrm{K}}$ increases from $\sim 0.1$ to 10. Hydrodynamics simulations that include basic models of the kinetic effects that are likely to be present in these experiments---namely, ion diffusion and Knudsen-layer reduction of the fusion reactivity---are better able to capture the experimental results. This type of implosion has also been used as a source of monoenergetic 15-MeV protons to image magnetic fields driven to reconnect in laser-produced plasmas at conditions similar to those encountered at the Earth's magnetopause. These experiments demonstrate that for both symmetric and asymmetric magnetic-reconnection configurations, when plasma flows are much stronger than the nominal Alfv\'{e}n speed, the rate of magnetic-flux annihilation is determined by the flow velocity and is largely insensitive to initial plasma conditions. This work was supported by the Department of Energy Grant Number DE{\-}NA0001857. [Preview Abstract] |
Tuesday, November 1, 2016 3:30PM - 4:00PM |
KI2.00002: Diagnosing the Stagnation Conditions of MagLIF Implosions Using High-Resolution Spectroscopy Invited Speaker: Eric Harding An inertial fusion concept known as Magnetized Liner Inertial Fusion (MagLIF) is currently being pursued on the Z-machine at Sandia National Laboratory. Electrical current from the Z-machine is directly coupled onto the outside surface of a beryllium tube known as a ``liner'' causing it to implode. The liner contains gaseous deuterium (D$_{\mathrm{2}})$ fuel, which is pre-magnetized, pre-heated, and then compressed by the imploding walls of the liner. Target implosions of this type have produced thermonuclear plasmas that generated 2e12 DD neutrons [M.R. Gomez et al., PRL 113, 155003 (2014)]. For the first time we have accurately measured the space-dependent, fuel conditions at the time of stagnation. In addition, the state of the compressed Be liner was determined. This was accomplished by the simultaneous use of high-resolution, x-ray spectroscopic and imaging diagnostics. These new measurements relied on the observation of K-shell spectra emitted by microscopic iron and nickel impurities that naturally occur in the Be. The measurements currently indicate that the non-uniformity of the x-ray emission from the fuel is due to variations in the fuel conditions. Ultimately, the data provides critical insight into the performance of the MagLIF target and will further enable us to enhance the target design. [Preview Abstract] |
Tuesday, November 1, 2016 4:00PM - 4:30PM |
KI2.00003: Extended MHD Effects in High Energy Density Experiments Invited Speaker: Charles Seyler The MHD model is the workhorse for computational modeling of HEDP experiments. Plasma models are inheritably limited in scope, but MHD is expected to be a very good model for studying plasmas at the high densities attained in HEDP experiments. There are, however, important ways in which MHD fails to adequately describe the results, most notably due to the omission of the Hall term in the Ohm's law (a form of extended MHD or XMHD). This talk will discuss these failings by directly comparing simulations of MHD and XMHD for particularly relevant cases. The methodology is to simulate HEDP experiments using a Hall-MHD (HMHD) code based on a highly accurate and robust Discontinuous Galerkin method, and by comparison of HMHD to MHD draw conclusions about the impact of the Hall term. We focus on simulating two experimental pulsed power machines under various scenarios. We examine the MagLIF experiment on the Z-machine at Sandia National Laboratories and liner experiments on the COBRA machine at Cornell. For the MagLIF experiment we find that power flow in the feed leads to low density plasma ablation into the region surrounding the liner. The inflow of this plasma compresses axial magnetic flux onto the liner. In MHD this axial flux tends to resistively decay, whereas in HMHD a force-free current layer sustains the axial flux on the liner leading to a larger ratio of axial to azimuthal flux. During the liner compression the magneto-Rayleigh-Taylor instability leads to helical perturbations due to minimization of field line bending. Simulations of a cylindrical liner using the COBRA machine parameters can under certain conditions exhibit amplification of an axial field due to a force-free low-density current layer separated by some distance from the liner. This results in a configuration in which there is predominately axial field on the liner inside the current layer and azimuthal field outside the layer. We are currently attempting to experimentally verify the simulation results. [Preview Abstract] |
Tuesday, November 1, 2016 4:30PM - 5:00PM |
KI2.00004: Laser-Driven Magnetized Liner Inertial Fusion on OMEGA Invited Speaker: D.H. Barnak Magneto-inertial fusion (MIF) is an approach that combines the implosion and compression of fusion fuel (a hallmark of inertial fusion) with strongly magnetized plasmas that suppress electron heat losses (a hallmark of magnetic fusion). It is of interest because it could potentially reduce some of the traditional velocity, pressure, and convergence ratio requirements of inertial confinement fusion (ICF). The magnetized liner inertial fusion (MagLIF) concept being studied at the Z Pulsed-Power Facility is a key target concept in the U.S. ICF Program. Laser-driven MagLIF is being developed to enable a test of the scaling of MagLIF over a range of absorbed energy from of the order of 20 kJ (on OMEGA) to 500 kJ (on Z). It is also valuable as a platform for studying the key physics of MIF. An energy-scaled point design has been developed for the Omega Laser Facility that is roughly $10\times $ smaller in linear dimensions than Z MagLIF targets. A 0.6-mm-outer-diam plastic cylinder filled with 2.4 mg/cm$^{\mathrm{3}}$ of D$_{\mathrm{2}}$ is placed in a 10-T axial magnetic field, generated by MIFEDS (magneto-inertial fusion electrical discharge system), the cylinder is compressed by 40 OMEGA beams, and the gas fill is preheated by a single OMEGA beam propagating along the axis. Preheating to \textgreater 100 eV and axially uniform compression over a 0.7-mm height have been demonstrated, separately, in a series of preparatory experiments that meet our initial expectations. Preliminary results from the first integrated experiments combining magnetization, compression, and preheat will be reported for the first time. The scaling of laser-driven MagLIF from OMEGA up to the 1800 kJ available on the NIF (National Ignition Facility) will also be described briefly. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700