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Title: Appearance of metastable B2 phase during solidification of Ni 50 Zr 50 alloy: electrostatic levitation and molecular dynamics simulation studies
Award ID(s):
1308099
NSF-PAR ID:
10045416
Author(s) / Creator(s):
; ; ; ; ;
Date Published:
Journal Name:
Journal of Physics: Condensed Matter
Volume:
27
Issue:
8
ISSN:
0953-8984
Page Range / eLocation ID:
085004
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
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  1. Abstract

    We investigate a secondary proton beam instability coexisting with the ambient solar wind turbulence at 50R. Three-dimensional hybrid numerical simulations (particle ions and a quasi-neutralizing electron fluid) are carried out with the plasma parameters in the observed range. In the turbulent background, the particle distribution function, in particular the slope of the “bump-on-tail” responsible for the instability, is time-dependent and inhomogeneous. The presence of the turbulence substantially reduces the growth rate and saturation level of the instability. We derive magnetic power spectra from the observational data and perform a statistical analysis to evaluate the average turbulence intensity at 50R. This information is used to link the observed frequency spectrum to the wavenumber spectrum in the simulations. We verify that Taylor’s frozen-in hypothesis is valid for this purpose to a sufficient extent. To reproduce the typical magnetic power spectrum of the instability observed concurrently with the background turbulence, an artificial spacecraft probe is run through the simulation box. The thermal-ion instabilities are often seen as power elevations in the kinetic range of scales above an extrapolation of the turbulence spectrum from larger scales. We show that the elevated power in the simulations is much higher than the background level. Therefore, the turbulence at the average intensity does not obscure the secondary proton beam instability, as opposed to the solar wind at 1 au, in which the ambient turbulence typically obscures thermal-ion instabilities.

     
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