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Weber, S

Publications and source records attributed to Weber, S.

11 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Dual harmonic Kelvin probe force microscopy at the graphene–liquid interface

Kelvin probe force microscopy (KPFM) is a powerful technique for the determination of the contact potential difference (CPD) between an atomic force microscope tip and a sample under ambient and vacuum conditions. However, for many energy storage and conversion systems, including graphene-based electrochemical capacitors, understanding electrochemical phenomena at the solid–liquid interface is paramount. Despite the vast potential to provide fundamental insight for energy storage materials at the nanoscale, KPFM has found limited applicability in liquid environments to date. Here, using dual harmonic (DH)-KPFM, we demonstrate CPD imaging of graphene in liquid. We find good agreement with measurements performed in air, highlighting the potential of DH-KPFM to probe electrochemistry at the graphene–liquid interface.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Possible experimental evidence for the presence of double octupole states in {sup 240}Pu

Excited states in the {sup 240}Pu nucleus have been studied by means of the (p,t) reaction using the Q3D spectrometer and the focal plane detector from Munich. The comparison between experimental angular distributions and the DWBA calculations allowed the extraction of relative two-neutron transfer strengths. These observables may reveal important information about the structure of different states. The experimental two neutron strength for the 0{sup +}{sub 2} and 0{sup +}{sub 3} states is found in good agreement with the predictions of the IBA model, confirming the double octupole nature for the 0{sup +}{sub 2} state proposed in the previous studies.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2012

Performance metrics for inertial confinement fusion implosions: Aspects of the technical framework for measuring progress in the National Ignition Campaign

The National Ignition Campaign (NIC) uses non-igniting 'tritium hydrogen deuterium (THD)' capsules to study and optimize the hydrodynamic assembly of the fuel without burn. These capsules are designed to simultaneously reduce DT neutron yield and to maintain hydrodynamic similarity with the DT ignition capsule. We will discuss nominal THD performance and the associated experimental observables. We will show the results of large ensembles of numerical simulations of THD and DT implosions and their simulated diagnostic outputs. These simulations cover a broad range of both nominal and off-nominal implosions. We will focus on the development of an experimental implosion performance metric called the experimental ignition threshold factor (ITFX). We will discuss the relationship between ITFX and other integrated performance metrics, including the ignition threshold factor (ITF), the generalized Lawson criterion (GLC), and the hot spot pressure (HSP). We will then consider the experimental results of the recent NIC THD campaign. We will show that we can observe the key quantities for producing a measured ITFX and for inferring the other performance metrics. We will discuss trends in the experimental data, improvement in ITFX, and briefly the upcoming tuning campaign aimed at taking the next steps in performance improvement on the path to ignition on NIF.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2011

Kinetic simulations of stimulated Raman backscattering and related processes for the shock-ignition approach to inertial confinement fusion

A detailed description of stimulated Raman backscattering and related processes for the purpose of inertial confinement fusion requires multi-dimensional kinetic simulations of a full speckle in a high-temperature, large-scale, inhomogeneous plasma. In particular for the shock-ignition scheme operating at high laser intensities, kinetic aspects are predominant. High- (I{lambda}{sub o}{sup 2}{approx}5x10{sup 15}W{mu}m{sup 2}/cm{sup 2}) as well as low-intensity (I{lambda}{sub o}{sup 2}{approx}10{sup 15}W{mu}m{sup 2}/cm{sup 2}) cases show the predominance of collisionless, collective processes for the interaction. While the two-plasmon decay instability and the cavitation scenario are hardly affected by intensity variation, inflationary Raman backscattering proves to be very sensitive. Brillouin backscattering evolves on longer time scales and dominates the reflectivities, although it is sensitive to the intensity. Filamentation and self-focusing do occur for all cases but on time scales too long to affect Raman backscattering.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2011

Laser plasma interaction studies in the context of shock ignition--Transition from collisional to collisionless absorption

The shock ignition concept implies laser pulse intensities higher than 10{sup 15} W/cm{sup 2} (at the wavelength of 351 nm), which is the commonly accepted limit where the inverse bremsstruhlung absorption dominates. The transition from collisional to collisionless absorption in laser plasma interactions at higher intensities is studied in the present paper with the help of large scale one-dimensional particle-in-cell simulations. The initial parameters are defined by the hydrodynamic simulations corresponding to recent experiments. The simulations predict that a quasi-steady regime of laser plasma interaction is attained where the total laser energy absorption stays on the level of {approx}65% in the laser intensity range 10{sup 15}-10{sup 16} W/cm{sup 2}. However, the relation between the collisional and collisionless processes changes significantly. This is manifested in the energy spectrum of electrons transporting the absorbed laser energy and in the spectrum of the reflected laser light.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗