Using Ross filter pairs to observe wall mix in MagLIF experiments at the NIF

In the MagLIF ICF scheme, a cylindrical gas volume is laser heated before the walls of the cylinder are driven radially inward to compress the heated gas. Exploring the effects of material from the walls and the laser entrance window mixing into the heated region are important considerations for MagLIF experiments^1,2,3,. The addition of these materials into the heated gas can potentially have detrimental effects, radiatively cooling the gas fill and degrading the yield. The NIF has been used to drive gas-pipe experiments where a tracer element (Ti) is placed on the LEH window or where strips of Ti and Sc are attached to the wall. Spatially and temporally resolved spectroscopic measurements of the Ti and Sc emission indicate the spatial location of these materials at various times during the interaction, assisting future predictions and mitigations of their propagation into the gas-pipe.

A single laser quad of 32 kJ energy and 13.6 ns pulse length initially enters the pipe to drive the target gas fill. Two additional quads on different vectors enter the target 55-70 ns later to reheat the tracer material so that the movement of that material into the interior of the gas pipe can be monitored. Gated X-ray detectors are used with Ross pair filters to give temporally and spatially resolved images of the gas-pipe emission. The analysis of these images and the extraction of spectral data will be presented as well as comparisons of the experimental data to simulations from codes such as HYDRA.

1. M. R. Gomez, S. A. Slutz, et al., PRL, October 2020, 125 155002.

2. A. J. Harvey-Thompson, M. R. Weis, et al., PoP, November 2018,  25 112705.

3. M. R. Weis, A. J. Harvey-Thompson and D. E. Ruiz, PoP January 2021,  28 012705.