Foam Fills for Laser-Plasma Instability Suppression

Project Overview

Current use of low gas-fill hohlraum designs (~0.3 mg/cc) on the NIF is motivated in part by the need to keep stimulated Raman scattering (SRS) on the (long pathlength) inner laser beams low, since SRS has plagued high gas-fill designs (>1 mg/cc) in the past. However, the low gas-fill design develops an outer-beam gold "bubble" at late time. The gold bubble eventually blocks passage of the inner beams, inhibiting symmetry control for longer pulses, and ultimately limiting the design space for inertial confinement fusion (ICF). This is especially problematic considering future NIF power and energy upgrades that will deliver longer pulses and/or greater laser intensities. For this reason, this research investigated whether using an ultra-low density 1 mg/cc silicon aerogel foam to partially fill the hohlraum can mitigate laser plasma instability (LPI) risk and limit the bubble excursion for enhanced symmetry control compared to a pure gas fill design.

In collaboration with Oxford University, Rutherford-Appleton Laboratory and Commissariat Energie Atomique a two-shot experimental campaign (with and without aerogel foam filling of the hohlraum) on the Laser MegaJoule (LMJ) facility in France was successfully performed in early 2023 under the auspices of this project. The data show a large reduction in SRS compared with pre-shot predictions, particularly for the case of low-density aerogel foam (~20x). These results support a strategy of using higher gas fill densities in tandem with (open celled) aerogel foams to access longer laser drives without undue risk of SRS backscatter and hot electron generation. Moreover, burying dopants in the foam via atomic layer deposition could further tailor the backscatter environment at cryogenic temperatures (~19 °K), in contrast to gas-filled hohlraums.

Mission Impact

This project contributes to the NNSA goal of understanding the condition of the nuclear stockpile and supports the Lawrence Livermore National Laboratory's high-energy-density science core competency. The impact of this research may open up new regions of hohlraum parameter space to allow lower-adiabat capsule designs that require a longer duration laser pulse. For a given driver scale such as the NIF, lowering the fuel adiabat is a robust means of increasing the target gain and accessing high thermonuclear yields for inertial fusion energy studies and applications to strategic deterrence. The ability to limit backscatter - in particular SRS - allows higher gas-fill designs to extend hohlraum symmetry control to longer times by slowing the hohlraum wall motion and delaying problematic plasma filling. This inaugural Lawrence Livermore National Laboratory-LMJ set of shots was successful in demonstrating a new platform for backscatter remediation and promises to provide the basis for further multi-laboratory collaboration in FY24.

Publications, Presentations, and Patents

M. A. Belyaev, P. Amendt, R. Bingham, T. Caillaud, S. Depierreux, G. Gregori, S. Iaquinta, O. Jones, J. Kroll, L. LeDeroff, J. Milovich, A. M. Murphy, "LPI Comparison of Foam and Gas-Filled Hohlraum Experiments on LMJ" (Oral Presention, 51st Anomalous Absorption Conference, Mammoth Lakes, CA, 2023).

J. L. Milovich, N. Izumi, O. Landen, D. Hinkel, T. Doeppner, O. Jones, M. Belyaev, C. Schroeder, S. Sepke, S. Depierreaux, T. Cailaud, S. Debesset, A. Casner, L. LeDeroff, G. Gregory, S. Iaquinta, B. Bingham, A. Murphy, C. Heinbockel, J. Kroll, M.S tadermann and R Wallace, "Design of a long pulse in a low gas-fill hohlraum to drive a low adiabat CH-ablator target" (Oral Presentation, Commissariat à l'énergie atomique et aux énergies alternatives. Paris, France, March 21, 2023).

J. L. Milovich, N. Izumi, O. Landen, D. Hinkel, T. Doeppner, O. Jones, M. Belyaev, C. Schroeder and S. Sepke, S. Depierreaux, T. Cailaud, S. Debesset, A. Casner, L. LeDeroff, G. Gregory, S. Iaquinta, B. Bingham, A. Murphy, C. Heinbockel, J. Kroll, M.Stadermann and R Wallace, "Pre-shot simulations of the LMJ Foam-filled hohlraum experiments" (Oral Presentation, Commissariat à l'énergie atomique et aux énergies alternatives, LMJ Facility. Bordeaux, France, March 27, 2023).

M. A. Belyaev, J. L. Milovich, P. Amendt, O. Jones, S. Langer, S. Depierreux, G. Gregori, S. Iaquinta, and R. Bingham, "Mitigating LPI and gold bubble expansion using ultra low density foams" (Presentation, 50th Anomalous Absorption Conference. Skytop, PA, 2022).

M. A. Belyaev, J. L. Milovich, P. Amendt, O. Jones, S. Langer, S. Depierreux, G. Gregori, S. Iaquinta, and R. Bingham,"Mitigating LPI and gold bubble expansion using ultra low density foams" (Presentation, APS DPP 64, Spokane, WA, 2022).

J. L. Milovich, M. A. Belyaev, P. Amendt, O. Jones, S. Langer, S. Depierreux, G. Gregori, S. Iaquinta, and R. Bingham, "Using Aerogel Foams to Improve Performance in Low Density Gas-Filled Hohlraum Designs" (Presentation, 50th Anomalous Absorption Conference, Skytop, PA, June 5-10, 2022).

Jose Milovich, P. Amendt, M A. Belyaev, B. Bingham, T. Caillaud, S. Depierreux, G. Gregori, S. Iaquinta, O. Jones, J. Kroll, L. LeDeroff, and A. M. Murphy, "Analysis of the recent LLNL-LMJ COMPAS campaign on foam-filled hohlraums and future directions" (Presentation, CEA - Commissariat à l'énergie atomique et aux énergies alternatives, Paris France, June 5, 2023).

Jose Milovich, P. Amendt, M A. Belyaev, B. Bingham, T. Caillaud, S. Depierreux, G. Gregori, S. Iaquinta, O. Jones, J. Kroll, L. LeDeroff, and A. M. Murphy, "Analysis of the recent LLNL-LMJ COMPAS campaign on foam-filled hohlraums and future directions" (Presentation, LMJ Users Meeting, Bordeaux, France, June 8, 2023).

Jose Milovich, P. Amendt, M A. Belyaev, B. Bingham, T. Caillaud, S. Depierreux, G. Gregori, S. Iaquinta, O. Jones, J. Kroll, L. LeDeroff, and A. M. Murphy, "Results of a LLNL-LMJ experimental campaign on partial foam-filled hohlraums" (Presentation, 12th International Conference on Inertial Fusion Science and Applications, Denver, CO, September 25-29, 2023).