Numerical study of core collapse supernovae

Context : Numerical study of core collapse supernovae. A core collapse supernova begins with the collapse of the core. Once the density goes beyond nuclear matter density, it becomes extremely hard. The collapsing matter bounces on it and creates a shock. The shock propagates and then stalls. The situation is the following : the shock is stationary. Neutrino coming from deep in the core heat the matter close to the shock and tend to push the shock forward, onto stellar explosion. On the other hand, the rest of the star is still collapsing, and this pushes the shock inwards, which in turn tends to black hole formation. The knowledge of which progenitor (which massive star) explodes and which creates a black hole is an active research topic : there is no clear and reliable way, without doing a detailed numerical simulation, to know whether a given progenitor explodes or whether it forms a black hole.

Objectives : Acquire a good knowledge of the supernovae physics, stellar physics, and also the neutron star physics and the black hole physics. Acquire a good knowledge on the development of a numerical physics code. Acquire a good knowledge on the link between numerical physics and laser physics.

Process : The student will acquire knowledge on radiative hydrodynamics with neutrinos, in a relativistic context. The student will also acquire knowledge on general relativity. The possibility of reproducing some aspects of the supernova explosion in laboratory with laser experiments will be studied. The possible link between the progenitor (the massive star about to collapse) and the explosion (whether it explodes or it forms a black hole) will be studied in details numerically. The student will produce simplified progenitors. In these, the student will be able to vary some well chosen parameters. Finally, many possibilities exist to improve this study : implementation of other numerical methods, 3d, implementation of nucleosynthesis, etc. The student can also suggest its own way.

Stability of ablation flows in inertial confinement fusion: transient growth

Inertial confinement fusion (ICF) aims at producing energy from thermonuclear fusion reactions between low atomic-number elements. A possible approach for reaching the high densities and temperatures needed for triggering these reactions, consists in imploding a spherical capsule, filled with a mixture of fusible elements, by means of a high energy density irradiation. This irradiation induces a violent vaporization – ablation – of the capsule outer shell that drives the implosion. The finite duration of these implosions emphasize the need for investigating possible perturbation transient growth that may dominate the flow over short-time horizons. For this project, we wish to investigate such transient growth in strongly accelerated self-similar ablation flows, with planar of spherical symmetry, which are relevant to the main stage of an implosion. This work will be carried out using a direct-adjoint method of non-modal stability theory, previously devised for weakly accelerated self-similar ablation flows in planar symmetry, that will have to be adapted to handle strongly accelerated configurations. Results could be used to setup, in a more realistic setting, `multi-physics' simulations of capsule implosions.