Predictive Methodology for Tamped Direct Laser Impulse Parameter Optimization

OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): Advanced Materials The technology within this topic is restricted under the International Traffic in Arms Regulation (ITAR), 22 CFR Parts 120-130, which controls the export and import of defense-related material and services, including export of sensitive technical data, or the Export Administration Regulation (EAR), 15 CFR Parts 730-774, which controls dual use items. Offerors must disclose any proposed use of foreign nationals (FNs), their country(ies) of origin, the type of visa or work permit possessed, and the statement of work (SOW) tasks intended for accomplishment by the FN(s) in accordance with the Announcement. Offerors are advised foreign nationals proposed to perform on this topic may be restricted due to the technical data under US Export Control Laws. OBJECTIVE: Develop and demonstrate a fast-running approach, tool, or methodology for determining the necessary laser and tamper parameters to achieve a desired impulse on a material or 3D structure of interest. DESCRIPTION: Since the cessation of underground nuclear testing, the Department of Defense has utilized multiple types of simulators to impart relevant impulses to materials, structures, and systems. Recently, it has become possible to utilize lasers to impart relevant impulses directly on material coupon samples and 3D structures on the 1-1000 cm2 scale, with or without the use of transparent tampers. It is known that the resultant impulse imparted into a material, structure, or system will depend on the laser parameters (energy, pulse shape, wavelength), tamper parameters (material, thickness, adhesion layer), and substrate material thickness and geometry. While it is possible to model with varying degrees of uncertainty the relevant physics and materials interaction to predict the resulting impulse for a given set of parameters, there doesn't currently exist a predictive tool for experimental design that can work backwards from a desired impulse strength and profile to calculate the appropriate laser and tamper parameters. Multiple modeling uncertainties and experimental variabilities complicate predictive modeling of the resultant impulse. It is desired that any technical approach, method, or tool for predicting direct laser impulse be able to determine and propagate these uncertainties to inform and bound experimental design. Experimental variabilities include, but are not limited to, laser power, laser timing and pulse shape, laser spatial uniformity, tamper uniformity, tamper adhesion, substrate surface preparation, and diagnostic response. Of particular interest are laser parameters between 6J/cm2 and 30J/cm2 with square laser pulses between 5-20ns at 2 (0.53 m). Substrate materials of interest include, but are not limited to, aluminum, titanium, stainless steel, and tape wound carbon phenolics. Tamper materials of interest include, but are not limited to, PTFE tape, fused silica, sapphire, and LiF. PHASE I: The primary deliverable of Phase 1 is a technical approach, conceptual method, or tool concept for backward calculating laser and tamper parameters to deliver a specified impulse and predict diagnostic signals, such as PDI. A proof of concept with 1D code, flat samples, and limited materials is acceptable for Phase 1. PHASE II: Phase 2 should focus on the development and refinement of the technical approach, method, or tool from Phase 1, including the addition of multiple substrate and tamper materials. Phase II should include an approach to 3D structures and graded tampers as well as propagation of uncertainties. It is suggested that Phase 2 include verification and validation through a comparison to existing experimental data. PHASE III DUAL USE APPLICATIONS: Phase 3 may involve additional refinement of the technical approach, method, or tool developed in prior phases as well as integration of prior test data and diagnostic outputs. Further, Phase 3 may include automation, development of user interfaces, and additional substrates and tamper materials. Verification and validation with multiple experimental results would also be expected in Phase 3. REFERENCES: 1. National Ignition Facility User Guide, 2016. Lawrence Livermore National Laboratory (llnl.gov); 2. Tamper performance for confined laser drive applications, Sonny Ly, Janghyuk Lee, Alexander M. Rubenchik, Jonathan C. Crowhurst, Charles D. Boley, Vanessa N. Peters, And Wesley J. Keller, Optics Express, Vol. 31, No. 14 / 3 Jul 2023.; 3. J. F. Davis, K. Carpenter, B. Blue, S. Ly, D. Hinshelwood and A. Sibley, "Shock and Impulse of 2-D and 3-D Test Objects Using the LLNL NIF Direct Laser Impulse Facility," 2023 IEEE International Conference on Plasma Science (ICOPS), Santa Fe, NM, USA, 2023, pp. 1-1, doi: 10.1109/ICOPS45740.2023.10481417; KEYWORDS: NIF-DLI, Direct Laser Impulse, Tamper