Proton deflectometry measurements of Biermann-battery fields in ring targets driven by a cone of the NIF

The production and advection of self-generated magnetic fields have been shown in MHD simulations to play an important role in heat and particle transport in indirect drive hohlraums. The Biermann-Battery mechanism () sources the B-fields which are then transported via frozen-in, Nernst, and Righi-Leduc advection and Ohmic dissipation.  Estimates show B-fields in the range of 0.1 to 2 MG and significant regions with Hall parameter , so that the electrons become magnetized.  Only very few experiments have attempted to characterize the amplitude and topology of B-fields in laser-driven cavities.  We have performed a series of measurements to characterize the B-fields present in a simple ring target representing a sub-section of a NIF hohlraum.  The 5.4 mm diameter, 2.5 mm tall rings are irradiated by 64 NIF lasers either from below or above the equatorial plane and in 8- or 16-fold symmetry patterns. Probing along the ring axes by 14.7 and 3.0 MeV protons shows distinct differences indicative of the E and B-field topology. We compare the measurements to Hydra simulations to understand the relative role of E and B fields in the laser-generated plasma.

 

This work was performed under the auspices of the U.S. Department of Energy by LLNL under Contract DE-AC52-07NA27344.