LANL-AFRL MRT Instability Analysis

Technical Problem Analysis: MRT Instability in MTF Concepts This analysis assesses the research conducted by Los Alamos National Laboratory (LANL) and the Air Force Research Laboratory (AFRL) to understand and mitigate the Magneto-Rayleigh-Taylor (MRT) instability within their joint Magnetized Target Fusion (MTF) program, culminating in the Field-Reversed Configuration Heating Experiment (FRCHX). The MRT instability, a magnetohydrodynamic instability that occurs when a magnetic field is used to accelerate a conducting fluid or plasma, represents a critical potential failure mode for any concept relying on the implosion of a solid metal liner to compress a plasma target. 1 The central finding of this report is that circa 2013, the joint LANL/AFRL program was fundamentally constrained by a critical precursor challenge: achieving a sufficiently long-lived and stable Field-Reversed Configuration (FRC) plasma target. This prerequisite issue consumed the vast majority of the program's documented scientific and engineering efforts. As a result, dedicated research into the subsequent and equally critical problem of MRT instability mitigation during liner compression was not a programmatic priority and remained at a very low level of maturity. 1. Analysis of LANL Research: Capability vs. Application Analysis of LANL's documented activities reveals a significant dichotomy between the laboratory's world-class institutional capabilities in instability modeling and diagnostics and the actual research focus of the specific groups executing the FRCHX experiment. While LANL possessed the necessary tools and expertise to address the MRT problem, these resources were not directed toward the MTF program, which was preoccupied with a more immediate technical obstacle. Simulation & Modeling A review of LANL's broader research portfolio establishes the laboratory as a global leader in the simulation of hydrodynamic and magnetohydrodynamic instabilities. Its theoretical divisions (T-Division) and applied physics groups have a long history of developing and utilizing advanced, multi-physics computational codes such as FLASH and HYDRA to model complex high-energy-density physics (HEDP) phenomena. 3 This expertise is routinely applied to understanding instability growth in major national security programs, including Inertial Confinement Fusion (ICF) at the National Ignition Facility (NIF) and Magnetized Liner Inertial Fusion (Mag LIF) at Sandia National Laboratories. 1 These efforts demonstrate a deep institutional capability to simulate MRT evolution in both planar and cylindrical geometries under relevant conditions. In stark contrast, the documented modeling efforts of the LANL P-24 Plasma Physics group, the lead entity for the FRCHX collaboration, were centered almost exclusively on the physics of the FRC plasma target. Their simulations, often employing codes like MACH2, focused on the initial stages of the MTF sequence: FRC formation via theta-pinch, translation out of the formation region, and capture within the liner prior to implosion. 9 The key finding from this analysis is the conspicuous absence of published simulation work from either the P-24 group or LANL's theoretical divisions that specifically models MRT growth for the unique FRCHX configuration: a solid, relatively thick aluminum liner imploding onto a high-beta FRC plasma target. This absence is not an intelligence gap but rather a positive indicator of the program's scientific priorities. A logical research program would not dedicate significant computational resources to modeling a secondary failure mode (liner instability during compression) when the primary, antecedent failure mode (the plasma target dissipating before compression could be effective) had not yet been solved. The FRCHX program was demonstrably struggling to achieve the required FRC plasma lifetime of ~20 μs needed to match the liner implosion timescale. 9 The program's focus was therefore necessarily fixed on this more immediate and fundamental FRC lifetime problem, revealing a clear and logical prioritization of R&D challenges. Diagnostic Development LANL's institutional capability in diagnostic development mirrors its strength in simulation. The laboratory is a world leader in conceiving, building, and fielding advanced diagnostics for HEDLP experiments at premier facilities like Omega and NIF. 5 This includes a portfolio of sophisticated, high-resolution x-ray radiography techniques, such as the Crystal Backlighter Imager (CBI), which are specifically designed to image the fine-scale features of hydrodynamic and magnetohydrodynamic instabilities as they evolve. 1 This establishes that LANL possessed the core competency to create and deploy the tools necessary to experimentally observe MRT growth on an imploding liner. However, the actual diagnostic suite planned and employed for the FRCHX experiment was overwhelmingly focused on characterizing the FRC plasma target, not the liner's integrity. The documented diagnostic set included multi-chord laser interferometers to measure plasma density, various forms of spectroscopy to assess temperature and purity, and arrays of external magnetic probes to determine the plasma's shape, position, and trapped magnetic flux. 10 While diagnostics such as soft x-ray imaging and neutron detectors were planned for the final implosion shots, their primary purpose was to measure the state of the compressed plasma (i.e., temperature and fusion yield), not to provide high-resolution, time-resolved imaging of the liner's surface during its inward flight. 10 No specialized diagnostic techniques were developed or fielded on FRCHX with the specific mission of detecting the onset or quantifying the growth of MRT instabilities on the solid aluminum liner. The choice of diagnostics for a complex experiment is a direct reflection of its scientific priorities. The FRCHX diagnostic suite was a perfect mirror of the FRC lifetime problem; the team needed to measure plasma density, temperature, and magnetic flux to understand why the FRC was decaying too quickly. High-resolution liner radiography was not pursued because the liner's stability was a secondary concern. If the plasma target was not viable, the liner's performance during compression was a moot point. This confirms, from an experimental hardware perspective, that MRT was not the primary research question being addressed by the program circa 2013. 2. Analysis of AFRL Collaboration: The "Hammer" and its Limitations The Air Force Research Laboratory's role in the collaboration was to provide the "hammer"—the powerful liner implosion capability—to compress the FRC plasma target developed by LANL. This capability was the application of a mature, pre-existing defense technology. It was not a new research and development effort focused on creating novel MRT mitigation techniques specifically for the fusion energy mission. Experimental Mitigation The FRCHX experiment consistently utilized solid aluminum liners, typically of the 6061-T6 alloy, with dimensions of approximately 1 mm in thickness, 10 cm in diameter, and 30 cm in length. 9 The primary experimental objective documented in the final years of the program was the extension of the FRC plasma lifetime to match the ~20 μs timescale of the liner implosion. 9 The most current research from this period is captured in a July 2013 abstract by G.A. Wurden et al., which details a significant breakthrough. By physically lengthening the magnetic trap within the liner, the team successfully increased the FRC's trapped flux lifetime from a range of 8-11 μs to a much more promising 14-16 μs, bringing it close to the programmatic requirement. 9 This work on the plasma target itself represented the cutting edge of the program's publicly documented research. There is no evidence in the available research of any systematic experimental campaigns conducted on FRCHX to test or develop MRT mitigation strategies. The research record shows a complete absence of studies on: ● Alternative Liner Materials: Unlike the parallel Mag LIF program at Sandia, which investigated the use of beryllium liners, there is no indication that FRCHX explored materials other than aluminum. 9 ● Magnetic Field Shaping: There is no mention of experiments employing advanced stabilization techniques such as magnetic shear, dynamic screw pinches, or tailored current pulse shapes from the Shiva Star driver. 19 ● Other Mitigation Techniques: There is no evidence of the use of dielectric coatings or other methods that were being actively investigated in the broader HEDP community to suppress instability seeds. 25 The experimental goal for the liner was to achieve a symmetric, uniform implosion using the existing, well-characterized hardware configuration developed for prior defense programs. 16 AFRL's contribution was its mature liner implosion capability, a technology honed over many years for other national security applications. 9 FRCHX was an application of this capability to a new type of plasma target. It was not a program designed to advance the state of the art in liner stability physics. The broader research landscape clearly shows that MRT mitigation was an active, complex, and distinct field of study at the time. 21 The FRCHX program did not engage in this parallel research track because its mission was different: to determine if a pre-existing "hammer" (AFRL's liner implosion) could successfully compress a novel "nail" (LANL's FRC plasma). The failure to solve the "nail" problem—i.e., achieving a robust, long-lived FRC—meant the program never graduated to the subsequent stage of optimizing the "hammer." Key Personnel The AFRL contribution to the MTF collaboration was led by a core team of experts from the Directed Energy Directorate at Kirtland Air Force Base. Analysis of consistent co-authorship across numerous FRCHX-related publications and conference proceedings identifies the principal AFRL investigators. Key AFRL Personnel Primary Affiliation Assessed Role & Expertise in MTF Collaboration Key Supporting Evidence (Publication Topics) Dr. John H. Degnan AFRL Directed Energy Directorate, Pulsed Power Branch Lead, Liner Implosion Physics. Senior expert on the design and execution of magnetically-driven solid liner implosions using the Shiva Star facility. Solid/spherical liner implosions (pre-FRCHX); Integrated FRCHX compression results 18 Dr. Edward L. Ruden AFRL Directed Energy Directorate Principal Investigator, HEDP Diagnostics & Analysis. Expertise in plasma diagnostics and continuum dynamics for integrated experiments. Integrated FRCHX experiments; HEDP diagnostics; FRC lifetime studies 2 Dr. Chris Grabowski AFRL Directed Energy Directorate Principal Investigator, Pulsed Power & FRC Integration. Expertise in pulsed power engineering (crowbar switches) and FRC Integrated FRCHX experiments; Pulsed power hardware; FRC lifetime studies 14 formation/lifetime studies. Dr. Matthew T. Domonkos AFRL Directed Energy Directorate Core Researcher, Integrated Experiments. Key member of the experimental team for integrated liner-on-plasma tests. Integrated FRCHX experiments; FRC lifetime studies 9 This team, particularly Dr. Degnan, brought a deep, pre-existing knowledge base in solid liner implosion physics to the collaboration. 18 This expertise was foundational to the program, providing the high-power compression capability that LANL lacked. However, the publication record of this team during the FRCHX era is dominated by papers on integrated experiments and the persistent FRC lifetime issue, with no specific publications detailing dedicated research into MRT mitigation for the MTF application. 29 3. Final Assessment The synthesis of the preceding analysis provides a definitive, confidence-scored conclusion regarding the maturity of MRT mitigation strategies within the LANL-AFRL MTF program as of 2013. The evidence converges on a single, coherent picture: the LANL/AFRL collaboration's primary programmatic focus was solving the FRC target lifetime problem, which was a necessary precondition for any meaningful compression heating experiment. LANL's world-class MRT simulation and diagnostic capabilities were not applied to the FRCHX program because resources were directed at the more immediate FRC stability issue. Similarly, AFRL's role was to provide a mature liner implosion capability, not to conduct new R&D into MRT mitigation techniques within the scope of the FRCHX project. Maturity Assessment (Circa 2013): The maturity of MRT mitigation strategies specifically developed for and tested on the FRCHX platform is assessed as Technology Readiness Level (TRL) 1-2 (Basic principles observed/Technology concept formulated). This low TRL reflects the fact that while the MRT instability was recognized as a critical future challenge for the MTF concept, it had not yet become the subject of dedicated, systematic experimental or computational investigation within the program itself. Confidence Score: HIGH. This assessment is based on strong, convergent evidence from the program's own publications, which overwhelmingly emphasize the FRC lifetime problem, and the conspicuous absence of publications on FRCHX-specific MRT mitigation. This absence is particularly telling given the vibrant research landscape on the topic in adjacent HEDP programs like Mag LIF, indicating a deliberate and logical prioritization of effort within the FRCHX program. Determination of Prototype Readiness: The research circa 2013 did not indicate that MRT mitigation strategies were sufficiently advanced to enable a successful, stable implosion in an operational MTF prototype. The program had not yet reliably demonstrated a stable, long-lived plasma target that could survive until the point of maximum liner compression. Without a viable target, the question of the liner's stability during the subsequent compression phase, while critically important, remained a future research challenge. The MTF concept, as pursued in FRCHX, was still in the basic science phase of validating its core components and had not yet earned the technical right to address the complex, integrated physics of liner stability in a fusion context. Works cited 1. Measurements of Magneto-Rayleigh-Taylor Instability Growth during the Implosion of Initially Solid Al Tubes Driven by the 20-MA, 100-ns Z Facility | Phys. Rev. Lett. - Physical Review Link Manager, accessed August 24, 2025, https://link.aps.org/doi/10.1103/Phys Rev Lett.105.185001 2. 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