Magnetohydrodynamic instabilities in ablation fronts and coronal plasmas

We consider the effect of self-generated magnetic field (B) on ablation front and coronal instabilities in inertial confinement fusion (ICF) with semi-analytic methods. Experimental evidence of the spontaneous generation of B fields in coronal plasmas has been reported in the last decade.^, Among the different sources leading to spontaneous B-field generation, the so-called Biermann-battery effect, which is due to misalignment between gradients of temperature and density, plays a dominant role in the conduction layer separating the ablation front from the coronal plasma. These fields can play an important role in ICF implosions because they modify heat transfer to the target. However, their effect on the ablation front and coronal dynamics that are subject to hydrodynamic instabilities remains less clear. We propose a self-consistent fluid model of the conduction layer to assess the B-field effect during the linear stage of three main instabilities: ablation-front–driven Rayleigh–Taylor (RT), Darrieus–Landau (DL), and magnetothermal (MT). We find that the B-field effect on the RT instability depends exclusively on the Froude number (Fr). In the weak-acceleration, large-Fr regime, the B field plays a stabilizing role by shortening the range of unstable wavelengths. The DL instability, characteristic of flow configurations with energy deposition, remains unaffected by the B field. The MT instability is exclusively driven by the self-generated B field and only occurs in a region adjacent to the critical surface. The MT instability has always been characterized as convective. We prove for the first time its absolute character and we derive criteria for this instability to occur for short perturbation wavelengths. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0003856.