Proton Radiography of Bounded, Magnetized Plasma relevant to MagLIF*

A key physics issue for Magnetized Linear Fusion (MagLIF) is to pre-heat this plasma while maintaining a strong magnetic field in the fuel gas. Recent MagLIF results and shown the saturation of neutron yield and reduction of the magnetization of the fuel as the laser preheat energy increased [1].  Such trends were predicted by magneto - hydrodynamic simulations and are indicative of the influence of Nernst effect and blast wave which can lead to loss of magnetic flux in the fuel volume. Hence, the experimental study of this confinement stage of MagLIF is needed to benchmark exiting relevant MHD models to understand the magnetic field dynamics in liner and make further optimization of preheat phase.

 Here we report on a new experimental platform at OMEGA to study blast wave dynamics and subsequent physics of confinement of magnetic field and plasma energy in a laser-heated gas liner. The experimental parameters were scaled to study the preheating phase physics of MagLIF. The geometry consists of a laser-heated cylindrical gas cell with a thin wall (liner), applied magnetic field parallel to the liner axis, and laser heating parallel to the axis and magnetic field produced by MIFEDS. Proton radiography with 3 and 15 MeV monoenergetic protons produced from a DHe3 implosion was be used to measure the magnetic fields at several times [2], while the conditions of the plasma in liner were characterized by collecting X-ray emission using X-ray Framing Camera.  

We have observed the Nernst advection of magnetic field in liner at early expansion times and the interaction of the blast wave with the liner walls at later times, which led to fluctuation of magnetic flux. These results are compared with HYDRA and GORGON simulations. 

 

[1]  M. R. Gomez et al., Phys. Rev. Lett., 125, 155002 (2020)

[2] S. Malko, C. Johnson, W. Fox, D. Schaeffer et al. , Applied Optics 61(6) (2021).