Samuel Langendorf

The Plasma Liner eXperiment (PLX) recently demonstrated formation of an imploding plasma liner via the merging of 36 discrete jets. Magnetized targets have been routinely formed by head-on collision of two deuterium jets magnetized by the interaction with fields from external solenoids. These jets are formed by coaxial pulsed plasma accelerators. Our three-dimensional simulation tool SPFMax has been validated against these experimental data, providing confidence to perform integrated simulations including plasma liner formation, magnetized target formation, and target compression. SPFMax is used to model the effects of plasma jet initial conditions on fusion yield in a reactor relevant parameter space. The fusion parameter space is defined by the Lindl-Widner diagram. Critical parameters such as hot spot temperature, hot spot areal density and magnetic field are used to determine potential pathways to achieve self-ignition for reactor scale fusion energies.

The Plasma Liner Experiment (PLX) at Los Alamos National Laboratory is studying plasma-jet driven magneto-inertial fusion (PJMIF), an innovative fusion approach in which a magnetized target plasma is compressed and heated by a spherically imploding plasma liner. We report on experimental efforts towards target formation experiments using colliding magnetized plasma jets, formed by coaxial plasma guns with applied field. In the collision of high-beta magnetized jets, we observe aspects of collisional and collisionless plasma dynamics during the jet collision and stagnation, informed by Doppler ion spectroscopy measurements of ion bulk flow and thermalization. Implications for future integrated liner-on-target compression experiments are presented. We also describe a range of kinetic and fluid modeling efforts studying both the near-term experimental scale as well as scaling of the broader PJMIF concept.

Alfven waves are low-frequency, transverse magnetic tension waves that travel along magnetic field lines and can be excited in any electrically conducting fluid permeated by a magnetic field. They are commonly found in space, responsible for many well-known features, such as heating of the Sun's outer atmosphere, acceleration of solar wind, and aurora formed in high-latitude regions of the Earth. In this work, we present observations of standing Alfven waves excited by injecting compact toroid (CT) plasmas into a static Helmholtz magnetic field at the Big Red Ball (BRB) Facility at Wisconsin Plasma Physics Laboratory (WIPPL). The CT plasmas are injected in parallel with the magnetic field. The topology of the magnetic field in the standing Alfven waves is characterized using a 3-axis Bdot probe array.

The Plasma Liner Experiment (PLX) group at LANL is studying the formation and properties of spherically imploding plasma liners at supersonic speeds, used in the novel plasma-jet-driven magneto-inertial fusion (PJMIF) concept. At PLX, a set of 36 coaxial plasma guns over the spherical chamber each deliver a plasma jet towards the center, merging into a liner to compress a low-Z plasma target. Recent upgrades have enabled a reduction in jet-to-jet speed variability and therefore improved liner uniformity towards that required for adequate heating and confinement of the target. We present preliminary results of the present campaign on PLX which aims to study the temporal and spatial evolution of characteristics of the plasma liner and its formation, without target injection. Liner electron temperature will be studied using a multi-chord visible light spectroscopy system, line-integrated electron density using a multi-chord interferometer, and a wide-view multi-camera array (WMCA) for determining velocities of all individual jets, as well as visually assessing liner merging characteristics.

Spherically imploding plasma liners 1 are a proposed low-cost, reactor-relevant magneto-inertial-fusion (MIF) driver for compressing magnetized plasma targets to fusion conditions. The Plasma Liner Experiment-ALPHA (PLX-α aims to demonstrate the formation of subscale plasma liners via dozens of merging supersonic plasma jets (with initial ion density ~ 10 16 cm -3 , velocity ≈50 km/s, mass ~ 1 mg, and using various gas species). In the ongoing, first set of PLX-α experiments, we plan to merge six and seven plasma jets to form a conical section of a spherically imploding plasma liner in order to assess the shock heating (and associated Mach-number degradation) and uniformity of the liner upon jet merging and during further convergence, before proceeding to fully spherical liner-formation experiments (if warranted by the conical-liner results). In this talk, we will summarize experimental findings to date on characterizing plasma jets formed by the newly designed PLX-α guns and conical-plasma-liner formation with up to seven guns. Gated fast-framing-camera images from initial shakedown experiments suggest that shock formation between adjacent merging jets is consistent with oblique-shock formation as observed in earlier two- and three-jet merging experiments. 2,3

Spherically imploding plasma liners 1 are a potential reactorrelevant approach to compressing magnetized plasma targets to fusion conditions, for example as in magneto-inertialfusion (MIF). We use the USim code, a multi-dimensional hydrodynamic code with treatments for MHD and fusion effects, to estimate the gain for various liner conditions. We performed 1D and 2D simulations, with and without density perturbations, and with different models for alpha particle energy deposition. Specifically, we show that gain greater than one is possible for liners of argon gas with density 85 kg/m 3 and velocity 60 km/s, even with 10% density perturbation. We also show gain \sim 20 for ideal conditions. We also compare these results with recent semi-analytic work 2 .

The Plasma Liner Experiment-ALPHA (PLX-α) is investigating the merging of supersonic plasma jets into a spherically imploding plasma liner as a driver for use in magneto-inertial fusion (MIF) architectures. 1 The present work is focused on characterizing the merging of six and/or seven plasma jets, converging in a cone of solid angle 0.4 \pi over a distance of 1.3 meters. Results from high-speed imaging, photodiode arrays, self-emission visible survey spectroscopy, and self-emission visible high-resolution spectroscopy will be presented, yielding measurements of plasma velocity, number density, electron/ ion temperatures, and mean ionization state pre- and post-merge. Anticipated plasma parameter regimes are \mathrm {n}\sim 10 ^{15}-10 ^{17} cm^{-3}, \mathrm {T}\sim 1-10 eV, and \mathrm {v}\sim 50 km/s, with gas species varied among argon, nitrogen, neon, krypton, and xenon. Images and spectra will be compared with synthetic data generated from 3D fronttracking and smooth-particle-hydrodynamic simulations coupled with atomic physics / opacity analysis codes. Results will inform questions of liner-Mach-number and lineruniformity evolution throughout the jet-merging and subsequent liner-convergence process.

The Plasma Liner Experimnent-ALPHA (PLX-α project is developing spherically imploding plasma liners as a standoff driver for a plasma-jet-driven magneto-inertial-fusion (PJMIF) concept, in which merging supersonic plasma jets form a plasma liner that compresses a magnetized plasma target to fusion conditions. One main aim of the simulation component of the PLX-α project is to perform highly resolved simulations of supersonic plasma jets at experimental conditions, their propagation and merger, and formation and implosion of liners. Detailed numerical studies of hydrodynamic processes in plasma jets and liners have been performed using the FronTier and SPH codes enhanced with radiation, physical diffusion, and plasma-EOS models. In this talk, we discuss predicted properties of plasma liners, in particular 4π-averaged liner density, ram pressure, and Mach number, the degree of nonuniformity, strength of primary and secondary shock waves, and the scaling of these quantities with the number of plasma jets, initial jet parameters, and other input data. In addition to direct analysis of liner states, simulations also provide synthetic data for direct comparison to experimental data from a multi-chord interferometer, survey and high-resolution spectrometers, and high-speed cameras. A detailed comparison of simulations with the first series of PLX-α experiments operating with 6 and 7 jets will be presented. Verified against experimental data, both codes will be used for predictive simulations of spherical plasma liners for upcoming PLX-α experiments and potential scaled-up future experiments.

Spherically imploding plasma liners 1 are a proposed reactorfriendly magneto-inertial-fusion (MIF) driver for compressing magnetized plasma targets to fusion conditions. The Plasma Liner Experiment-ALPHA (PLX-α) is aiming to demonstrate the formation of such liners via dozens of merging supersonic plasma jets (with ion density \sim 10 ^{16} cm^{-3}, velocity \approx 50 km/s, mass \sim 1 mg, and various species). In the ongoing, first set of PLX-α experiments, we are merging 6 and 7 plasma jets to form a conical section of a spherically imploding plasma liner in order to assess the shock heating (and associated Mach-number degradation) and uniformity of the liner upon jet merging and during further convergence. Diagnostics include single- and multi-frame fast-gated ICCD cameras, visible survey spectrometer, high-resolution spectrometer, 12-chord visible interferometer, and visible photodiodes. Presented here will be the first results of the density and electron temperature uniformity of 6- and 7-jet merging using several gas species (argon, nitrogen, neon, krypton, xenon). Several 12-chord laser interferometry configurations are fielded with both end-on and crosssectional laser chord paths to determine density distribution and evolution. Results presented here will be compared to synthetic data from 3D simulations run using both smoothedparticle-hydrodynamics and the FronTier codes.

Summary form only given. We present comparison of simulations of plasma-jet-driven magneto-inertial fusion (PJMIF) with analytic results and with results from established codes 1 . The liners are spherically symmetric xenon plasma with implosion velocities of 60-120 km/s (assumed to be formed by merging plasma jets). At the center of the liner is a DT target that is compressed by the liner and the resulting high density and temperature creates neutron yield. We investigate, in particular, the effect of equation of state, radiation, thermal conduction and alpha particle production on the neutron yield. The goal of this work is to guide design of high gain configurations of PJMIF for a fusion power reactor 2 . A prototype of such a device is the PLX-Alpha project, currently operating at Los Alamos National Laboratory 3 .