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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,549 records · Page 86
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

ACCELERATION OF LOW-ENERGY IONS AT PARALLEL SHOCKS WITH A FOCUSED TRANSPORT MODEL

We present a test particle simulation on the injection and acceleration of low-energy suprathermal particles by parallel shocks with a focused transport model. The focused transport equation contains all necessary physics of shock acceleration, but avoids the limitation of diffusive shock acceleration (DSA) that requires a small pitch angle anisotropy. This simulation verifies that the particles with speeds of a fraction of to a few times the shock speed can indeed be directly injected and accelerated into the DSA regime by parallel shocks. At higher energies starting from a few times the shock speed, the energy spectrum of accelerated particles is a power law with the same spectral index as the solution of standard DSA theory, although the particles are highly anisotropic in the upstream region. The intensity, however, is different from that predicted by DSA theory, indicating a different level of injection efficiency. It is found that the shock strength, the injection speed, and the intensity of an electric cross-shock potential (CSP) jump can affect the injection efficiency of the low-energy particles. A stronger shock has a higher injection efficiency. In addition, if the speed of injected particles is above a few times the shock speed, the produced power-law spectrum is consistent with the prediction of standard DSA theory in both its intensity and spectrum index with an injection efficiency of 1. CSP can increase the injection efficiency through direct particle reflection back upstream, but it has little effect on the energetic particle acceleration once the speed of injected particles is beyond a few times the shock speed. This test particle simulation proves that the focused transport theory is an extension of DSA theory with the capability of predicting the efficiency of particle injection.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

A direct measurement of the forward shock speed in supernova remnant 0509–67.5: Constraints on the age, ambient density, shock compression factor, and electron–ion temperature equilibration

Two Hubble Space Telescope narrow-band Hα images separated in time by 1.03 years are used for a proper motion measurement of the forward shock of the LMC supernova remnant 0509–67.5, the only spectroscopically confirmed LMC remnant of Ia origin. We measure a global shock speed of 6500 ± 200 km s{sup −1} and constrain the pre-shock neutral hydrogen density to be 0.084 ± 0.003 cm{sup −3}, for a typical mean number of Hα photons produced per neutral hydrogen atom entering the forward shock. Previously published broad Hα line widths from two locations on the rim and our corresponding shock speed measurements are consistent with Balmer shock models that do not include effects of cosmic-ray acceleration. For the northeastern rim location, we limit the post-shock electron temperature to 10% of the proton temperature by also using the broad-to-narrow flux ratio. Hydrodynamic simulations for different initial ejecta density profiles constrain the age and ambient medium density; for an exponential ejecta profile and initial explosion energy of 1.4 × 10{sup 51} erg, the remnant’s age is 310{sub −30}{sup +40} years. For all evolutionary models explored, the expansion parameter falls in the range of 0.41–0.73, indicating that the remnant is still firmly in the ejecta-dominated phase of its evolution. Our measured neutral hydrogen density of the ambient medium, combined with the shocked density obtained in Williams et al., disfavors forward shock compression factors greater than ∼7.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

In Operando XRD and TXM Study on the Metastable Structure Change of NaNi 1/3 Fe 1/3 Mn 1/3 O 2 under Electrochemical Sodium-Ion Intercalation

In operando XRD and TXM-XANES approaches demonstrate that structure evolution in NaNi 1/3 Fe 1/3 Mn 1/3 O 2 during cycling follows a continuous change, and the formation of a nonequilibrium solid solution phase in the existence of two phases. Here, an O3' and P3' monoclinic phase occur, and redox couples of Ni 3+ /Ni 4+ and Fe 3+ /Fe 4+ are mainly responsible in the charge voltage range from 4.0 to 4.3 V.

36 MATERIALS SCIENCE↗