Samuel Langendorf

For more than 15 years, the magnetic recoil spectrometer (MRS) has been used to measure the DT fusion neutron spectrum in inertial confinement fusion (ICF) implosions at OMEGA and the National Ignition Facility (NIF). These measurements have provided essential information about implosion performance that has helped guide the mainline ICF programs to the recent demonstration of hydro-equivalent ignition (χ > 1) at OMEGA and to ignition and target gain (G > 1) at the NIF. Today, there are variants of the MRS being built across private industry, including spectrometers on the SPARC tokamak (expected Q > 1, 100 MW) and the Pacific Fusion Demonstration System (expected G ∼10, 100 MJ), both with planned electronic detection systems capable of measuring neutron spectra at high processing rates. In addition, an upgrade of the existing MRS on the NIF is being planned in which a collimator will be incorporated to extend the MRS measurement ceiling to ∼30 MJ. Meanwhile, electromagnet upgrades (MRSnext) have been designed to replace, or complement, the existing MRS systems on OMEGA and the NIF. These, plus other upgrades, will result in several notable improvements from a scientific and/or engineering perspective: significantly smaller focal planes, improved resolution, conversion foils positioned close to the magnet system, and enhanced signal-to-background. Here, we summarize the MRS motivation and history, concept, demonstrated performance, and many of the recent developments, highlighting the versatility of the technique for diagnosing fusion performance across approaches on the road to high energy gain and commercialization.

The MAgnetic Recoil Spectrometer (MARS) will be used to diagnose neutron spectra from deuterium–tritium fusion experiments at Pacific Fusion’s demonstration system, providing time-integrated measurements of yield (13–15 MeV), ion temperature, fuel and liner areal density, and alpha heating. Two design advances distinguish MARS from prior magnetic recoil spectrometers. First, redesigned ion optics reduce the focal-plane length to a size compatible with a silicon strip detector, making MARS the first inertial confinement fusion magnetic recoil neutron spectrometer with an electronic readout, enabling real-time data analysis and per-channel time-gating. Second, a dual-foil geometry (half CH2, half CD2) enables simultaneous spectral measurements of recoil protons and deuterons in a single shot, expanding neutron energy coverage to ∼6–20 MeV. The conceptual design of the instrument, synthetic modeling framework, and shielding strategy are described. Monte Carlo transport and ion optics simulations show signal-to-background ≫10 across the spectrum except for the alpha knock-on tail, with per-channel electronic time-gating providing additional background suppression. The open-source simulation framework additionally serves as a synthetic diagnostic for forward fits of parametric plasma models, showing good agreement with the true parameters.

High-yield inertial fusion offers a transformative path to affordable, clean, firm power and advanced defense capabilities. Recent milestones at large facilities, particularly the National Ignition Facility (NIF), have demonstrated the feasibility of ignition but highlight the need for approaches that can deliver large amounts of energy to fusion targets at much higher efficiency and lower cost. We propose that pulser-driven inertial fusion energy (IFE), which uses high-current pulsed-power technology to compress targets to thermonuclear conditions, can achieve this goal. In this paper, we detail the physics basis for pulser IFE, focusing on magnetized liner inertial fusion, where cylindrical metal liners compress DT fuel under strong magnetic fields and preheat. We discuss how the low implosion velocities, direct-drive efficiency, and scalable pulser architecture can achieve ignition-level conditions at low capital cost. Our multi-dimensional simulations, benchmarked against experiments at the Z facility, show that scaling from 20 to 50–60 MA of current enables net facility gain. We then introduce our Demonstration System (DS), a pulsed-power driver designed to deliver more than 60 MA and store approximately 80 MJ of energy. The DS is designed to achieve a 1000× increase in effective performance compared to the NIF, delivering approximately 100× greater facility-level energy gain—and importantly, achieving net facility gain, or Qf>1—at just 1/10 the capital cost. We also examine the engineering requirements for repetitive operation, target fabrication, and chamber maintenance, highlighting a practical roadmap to commercial power plants.

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Plasma-jet-driven magneto-inertial fusion is an alternative approach to controlled nuclear fusion, which aims to utilize a line-replaceable dense plasma liner as a repetitive spherical compression driver. In this experiment, first measurements of the formation of a spherical argon plasma liner formed from 36 discrete pulsed plasma jets are obtained on the Plasma Liner Experiment. Properties including liner uniformity and morphology, plasma density, temperature, and ram pressure are assessed as a function of time throughout the implosion process and indicate an apparent transition from initial kinetic inter-jet interpenetration to collisional regime near stagnation times, in accordance with theoretical expectation. A lack of primary shock structures between adjacent jets during flight implies that arbitrarily smooth liners may be formed by way of corresponding improvements in jet parameters and control. The measurements facilitate the benchmarking of computational models and understanding the scaling of plasma liners toward fusion-relevant energy density.

This paper introduces a novel approach for automated high-throughput estimation of plasma temperature and density using atomic emission spectroscopy, integrating Bayesian inference with sophisticated physical models. We provide an in-depth examination of Bayesian methods applied to the complexities of plasma diagnostics, supported by a robust framework of physical and measurement models. Our methodology is demonstrated using experimental observations in the field of magneto-inertial fusion, focusing on individual and sequential shot analyses of the Plasma Liner Experiment at LANL. The results demonstrate the effectiveness of our approach in enhancing the accuracy and reliability of plasma parameter estimation and in using the analysis to reveal the deep hidden structure in the data. This study not only offers a new perspective of plasma analysis but also paves the way for further research and applications in nuclear instrumentation and related domains.

This paper introduces a novel approach for automated estimation of plasma temperature and density using emission spectroscopy, integrating Bayesian inference with sophisticated physical models. We provide an in-depth examination of Bayesian methods applied to the complexities of plasma diagnostics, supported by a robust framework of physical and measurement models. Our methodology is validated through experimental observations, focusing on individual and sequential shot analyses. The results demonstrate the effectiveness of our approach in enhancing the accuracy and reliability of plasma parameter estimation, marking a significant advancement in the field of emission spectroscopy for plasma diagnostics. This study not only offers a new perspective in plasma analysis but also paves the way for further research and applications in nuclear instrumentation and related domains.

Magnetosonic waves are low-frequency, linearly polarized magnetohydrodynamic (MHD) waves commonly found in space, responsible for many well-known features, such as heating of the solar corona. In this work, we report observations of interesting wave signatures driven by injecting compact toroid (CT) plasmas into a static Helmholtz magnetic field at the Big Red Ball Facility at Wisconsin Plasma Physics Laboratory. By comparing the experimental results with the MHD theory, we identify that these waves are the fast magnetosonic modes propagating perpendicular to the background magnetic field. Additionally, we further investigate how the background field, preapplied poloidal magnetic flux in the CT injector, and the coarse grid placed in the chamber affect the characteristics of the waves. Since this experiment is part of an ongoing effort of creating a target plasma with tangled magnetic fields as a novel fusion fuel for magneto-inertial fusion (MIF), our current results could shed light on future possible paths of forming such a target for MIF.

At Plasma Liner Experiment, a set of 36 coaxial plasma guns are deployed quasi-uniformly over a 9 ft diameter spherical chamber and are used to form a high-Z spherically compressive plasma liner. Simulations indicate that for the concept to ultimately achieve optimal target density and temperature, a high degree of timing uniformity is required between all guns. To aid in quantifying and correcting gun-to-gun nonuniformities, a key diagnostic will consist of up to six fisheye-view CCD cameras positioned inside the main chamber such that each has all plasma guns within its view. The individual cameras can be triggered at different times to determine each plasma jet’s muzzle velocity and structure for different operating conditions. This camera array is currently under development, and the implementation needs and challenges for this camera array are discussed here. Additionally, we detail the analysis methodology for determining jet-to-jet uniformity deviations and how we can correct them, thereby improving overall liner uniformity.

This work studies the interaction between colliding plasma jets to understand regimes in which jet merging results in shock formation vs regimes in which the shock formation is mitigated due to the collisionless interpenetration of the jets. A kinetic model is required for this study because fluid models will always produce a shock upon the collision of plasma jets. The continuum-kinetic, Vlasov–Maxwell–Dougherty model with one velocity dimension is used to accurately capture shock heating, along with a novel coupling with a moment equation to evolve perpendicular temperature for computational efficiency. As a result, this relatively inexpensive simulation can be used for detailed scans of the parameter space toward predictions of shocked vs shock-mitigated regimes, which is of interest for several fusion concepts such as plasma-jet-driven magneto-inertial fusion, high-energy-density plasmas, astrophysical phenomena, and other laboratory plasmas. The initial results obtained using this approach are in agreement with the preliminary outcomes of the plasma liner experiment.