Target Fabrication and Pre-implosion Diagnostics for Laser Inertial Confinement Fusion Research Using Two-Photon Polymerization and Cryogenic Coherent Anti-Stokes Raman Scattering Microscopy

The University of Nebraska-Lincoln (UNL), in collaboration with Lawrence Livermore National Laboratory (LLNL) and Laboratory for Laser Enegetics (LLE), will investigate on target fabrication and pre-implosion diagnostics for laser inertial confinement fusion research using two-photon polymerization (TPP) and cryogenic coherent anti-Stokes Raman scattering (cryo-CARS) microscopy.The goal of this research is to improve laser fusion ignitions by advancing target fabrication and pre-implosion diagnostics essential for the DOE Fusion Energy Science (FES) Program using TPP and cryo-CARS. Through TTP, we will produce hydrocarbon (CH) and high-density-carbon (HDC) foam targets with high sphericity, extreme surface smoothness, and sufficient size to contain the deuterium-tritium (DT) fuel for nuclear ignition. Cryo-CARS will enable us to achieve precise in-situ diagnostics of the targets with DT isotopes condensed inside. This combined approach promises a new era in target fabrication and pre-implosion analyses. The research goal will be achieved through conducting two research tasks.

The UNL team will advance foam target fabrication via TPP 3D printing. Successful fusion requires a uniformly symmetrical implosion of targets using lasers. Small perturbations, such as nanoscale pits/voids on targets and contaminations, are amplified due to the instability growth, leading to ignition failure. To advance targets, the research team will 1) develop fuel targets meeting the shape accuracy using digital and photochemical approaches, 2) fabricate large-scale foam targets over 1 mm in size by stitching, 3) achieve ultrasmooth target surfaces by precise compensation of terrace errors, and 4) develop precise high-density-carbon (HDC) targets.

The team will conduct pre-implosion diagnostics via narrowband cryo-CARS. The cryo-CARS will provide the capability of 3D topographical, compositional, and isotopic mapping with spatial resolutions below 600 nm. The team will address an important question about how isotopes distribute under different condensation conditions that could not be diagnosed until now with the aim to integrate the cryo-CARS system from a lab demonstration to a laser fusion facility. The team will 1) develop narrowband cryo-CARS for target diagnostics, 2) determine the distribution and ratios of fuel mixtures within targets, and 3) extend the imaging capability to capture the wetting process in foam targets.

UNL, through its pioneering work in target development and pre-implosion diagnosis, has established unique scientific insight and engineering capabilities. The proposed UNL-LLNL-LLE partnership aims to strengthen Nebraska’s capacity, as an EPSCoR jurisdiction, in training graduate students and early career researchers. This collaborative effort will contribute to supporting fusion science in the U.S. by leveraging diverse talents, including individuals from rural areas.