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Nuclear Waffles | | A. S. Schneider
; D. K. Berry
; C. M. Briggs
; M. E. Caplan
; C. J. Horowitz
; | | Date: |
9 Sep 2014 | | Abstract: | The dense neutron-rich matter found in supernovae and neutron stars is
expected to form complex nonuniform phases referred to as nuclear pasta. The
pasta shapes depend on density, temperature and proton fraction and determine
many transport properties in supernovae and neutron star crusts. We use two
recently developed hybrid CPU/GPU codes to perform large scale molecular
dynamics (MD) simulations with $51200$ and $409600$ nucleons of nuclear pasta.
From the output of the MD simulations we characterize the topology and compute
two observables, the radial distribution function $g(r)$ and the structure
factor $S(q)$, for systems with proton fractions $Y_p=0.10, 0.20, 0.30$ and
$0.40$ at about one third of nuclear saturation density and temperatures near
$1.0$ MeV. We observe that the two lowest proton fraction systems simulated,
$Y_p=0.10$ and $0.20$, equilibrate quickly and form liquid-like structures.
Meanwhile, the two higher proton fraction systems, $Y_p=0.30$ and $0.40$, take
a longer time to equilibrate and organize themselves in solid-like periodic
structures. Furthermore, the $Y_p=0.40$ system is made up of slabs, lasagna
phase, interconnected by defects while the $Y_p=0.30$ systems consist of a
stack of perforated plates, the nuclear waffle phase. The periodic
configurations observed in our MD simulations for proton fractions $Y_pge0.30$
have important consequences for the structure factors $S(q)$ of protons and
neutrons, which relate to many transport properties of supernovae and neutron
star crust. A detailed study of the waffle phase and how its structure depends
on temperature, size of the simulation and the screening length showed that
finite-size effects appear to be under control and, also, that the plates in
the waffle phase merge at temperatures slightly above $1.0$ MeV and the holes
in the plates form an hexagonal lattice at temperatures slightly lower than
$1.0$ MeV. | | Source: | arXiv, 1409.2551 | | Services: | Forum | Review | PDF | Favorites | |
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