Implementation of a network of nuclear reactions of moderate size aimed at simulating Type Ia supernova explosions

A key ingredient in any numerical study of supernova explosions is the nuclear network routine that is coupled with the hydrodynamic simulation code. When these studies are performed in more than one dimension, the size of the network is severely limited by computational issues. Nevertheless, the characteristic size of these networks has been increasing over the years, from around seven nuclei in pioneering multi-D calculations to roughly fifty at present times. The main goal of this work is to improve, optimize and test a nuclear network of 87 nuclei specially addressed to multidimensional studies of both types of supernova explosions, but with emphasis in thermonuclear Type Ia events. The nuclear network, Net87, is a natural extension of the old network with 14 species, Net14, which was routinely used by the UPC-SciCore collaboration to simulate supernova explosions with good results. Net87 includes reactions for neutrons, protons and alpha particles. One relevant, and original, feature is that electron captures on protons have been incorporated into the network, providing a better track of both, the neutronized species and the gas pressure. A second important feature is that the reactions are implicitly coupled with the temperature, which allows for a more stable approach to the nuclear statistical equilibrium regime and to the freeze-out of the reactions during the expansion. Here we analyze the performance of the Net87 routine in light of both: the computational overhead of the algorithm and the released nuclear energy and produced yields during the combustion in typical Type Ia Supernova (SN Ia) conditions

Approaching the exascale simulation of subsonic turbulence with smoothed particle hydrodynamics

The candidate will work in collaboration with the SPH-EXA and SKAO-Switzerland projects.Turbulence is key to many astrophysical and cosmological scenarios. Hence, a correct depiction of it in numerical simulations is of capital importance. Kolmogorov's theory states that in the subsonic regime the energy associated with the scale of the turbulent structures follows the power law � ∝ � −5∕3 , where � is the wave-number. Smoothed Particle Hydrodynamics simulations have traditionally shown difficulties building up a Kolmogorov-like turbulent cascade. The main reason for this can be traced back to the errors in gradient evaluation when standard SPH methods are used, jointly with over-viscous behavior from traditional artificial viscosity formulations. These problems can be tackled nowa- days with modern implementations of the gradient evaluation that are much more accurate, and also using adaptive switches and artificial viscosity cleaners that reduce dissipation where and when needed. With the goal of testing this new implementation, as well as the performance of the new state- of-the-art SPH-EXA code, a set of turbulence simulations have been carried out, that represent the most accurate and highest resolution SPH-based turbulence simulations to date. The combination of the high scalability of SPH-EXA with the use of upgraded hydrodynamics has shown a sizeable improvement in the results of the subsonic turbulence simulation