Publications

Results 1401–1425 of 2,290

Search results

Jump to search filters

Design and testing of a magnetically driven implosion peak current diagnostic

Physics of Plasmas

Hess, Mark H.; Peterson, Kyle J.; Ampleford, David A.; Hutsel, Brian T.; Jennings, Christopher A.; Gomez, Matthew R.; Laros, James H.; Robertson, Grafton K.; Payne, Sheri L.; Stygar, William A.; Martin, Matthew; Sinars, Daniel S.

We report that a critical component of the magnetically driven implosion experiments at Sandia National Laboratories is the delivery of high-current, 10s of MA, from the Z pulsed power facility to a target. In order to assess the performance of the experiment, it is necessary to measure the current delivered to the target. Recent Magnetized Liner Inertial Fusion (MagLIF) experiments have included velocimetry diagnostics, such as PDV (Photonic Doppler Velocimetry) or Velocity Interferometer System for Any Reflector, in the final power feed section in order to infer the load current as a function of time. However, due to the nonlinear volumetrically distributed magnetic force within a velocimetry flyer, a complete time-dependent load current unfold is typically a time-intensive process and the uncertainties in the unfold can be difficult to assess. In this paper, we discuss how a PDV diagnostic can be simplified to obtain a peak current by sufficiently increasing the thickness of the flyer. This effectively keeps the magnetic force localized to the flyer surface, resulting in fast and highly accurate measurements of the peak load current. Additionally, we show the results of experimental peak load current measurements from the PDV diagnostic in recent MagLIF experiments.

More Details
TYPE Journal Article YEAR 2018
DOIOSTI

Tunable dual-band graphene-based infrared reflectance filter

Optics Express

Goldflam, Michael G.; Ruiz, Isaac R.; Howell, Stephen W.; Wendt, J.R.; Sinclair, Michael B.; Peters, D.W.; Laros, James H.

We experimentally demonstrated an actively tunable optical filter that controls the amplitude of reflected long-wave-infrared light in two separate spectral regions concurrently. Our device exploits the dependence of the excitation energy of plasmons in a continuous and unpatterned sheet of graphene on the Fermi-level, which can be controlled via conventional electrostatic gating. The filter enables simultaneous modification of two distinct spectral bands whose positions are dictated by the device geometry and graphene plasmon dispersion. Within these bands, the reflected amplitude can be varied by over 15% and resonance positions can be shifted by over 90 cm-1. Electromagnetic simulations verify that tuning arises through coupling of incident light to graphene plasmons by a grating structure. Importantly, the tunable range is determined by a combination of graphene properties, device structure, and the surrounding dielectrics, which dictate the plasmon dispersion. Thus, the underlying design shown here isapplicable across a broad range of infrared frequencies.

More Details
TYPE Journal Article YEAR 2018
DOIOSTIScopusDOIOSTIScopus

Exploiting Geometric Partitioning in Task Mapping for Parallel Computes

Deveci, Mehmet D.; Devine, Karen D.; Laros, James H.; Taylor, Mark A.; Rajamanickam, Sivasankaran R.; Catalyurek, Umit V.

We present a new method for mapping applications' MPI tasks to cores of a parallel computer such that applications' communication time is reduced. We address the case of sparse node allocation, where the nodes assigned to a job are not necessarily located in a contiguous block nor within close proximity to each other in the network, although our methods generalize to contiguous allocations as well. The goal is to assign tasks to cores so that interdependent tasks are performed by "nearby' cores, thus lowering the distance messages must travel, the amount of congestion in the network, and the overall cost of communication. Our new method applies a geometric partitioning algorithm to both the tasks and the processors, and assigns task parts to the corresponding processor parts. We also present a number of algorithmic optimizations that exploit specific features of the network or application. We show that, for the structured finite difference mini-application MiniGhost, our mapping methods reduced communication time up to 75% relative to MiniGhost's default mapping on 128K cores of a Cray XK7 with sparse allocation. For the atmospheric modeling code E3SM/HOMME, our methods reduced communication time up to 31% on 32K cores of an IBM BlueGene/Q with contiguous allocation.

More Details
TYPE Other Report YEAR 2018
DOIOSTI
Results 1401–1425 of 2,290
Results 1401–1425 of 2,290