Session JP10: Poster Session IV: Science Education, High School, and Undergraduate Research. Inertial Confinement Fusion: Z-Pinch, X-Pinch, and Dense Plasma Focus, Magneto-inertial Fusion, X-ray and Neutron Diagnostics (2:00pm-5:00pm)

Alina’s Bowl: Demonstration of Macroscale Wigner Crystallization

The study of strongly-coupled and highly-correlated plasma is an important topic within the broader plasma physics community. When brought to extremes, strongly-coupled plasma can undergo solidification in a process known as Wigner crystallization. Example systems where crystallization has been observed include laser-cooled ion traps, electrons on the surface of liquid helium, and within the ultra-dense interior of planet-sized stars. Unfortunately, a hands-on demonstration of Wigner crystallization for instructing and inspiring the next generation of scientists is missing from our educational toolbox. Suitable for high school and university students, Alina's bowl will be presented which readily forms Wigner crystallization of macroscale objects using a gravity well. The strongly-coupled plasma within Alina's bowl exhibits long-range spatial order over a vast parameter space, which is ideal for students who wish to explore various topics such as plasma and condensed matter physics, classical and statistical mechanics, electrostatics, and tribology.   

Recent expansion of APS-DPP education and outreach activities

Since 1988 the APS-DPP has organized activities at the DPP conference with the aim of communicating with and exciting the local community about plasma physics and fusion. The two main activities have been the Teachers Day workshop, a teacher development program for local MS and HS teachers, and the plasma expo, a science fair-style event for the students. Additionally, every year undergraduate students present their research at a dedicated poster session; a panel of judges, members of APS-DPP, recognize the best posters with awards at a student reception. All of these activities are organized and coordinated by the Education and Outreach (E{\&}O) committee. In this poster, we present recent expansions of the activities as well as additional events organized by the E{\&}O committee, including a Graduate Fellowship Opportunities Panel for early and incoming graduate students, a Graduate School Fair in which graduate schools advertise their programs to prospective students, and an outreach event geared toward adult audiences.   

Expanding the Young Women's Conference (YWC) to other regions

Women remain underrepresented in the science and engineering workforce, with the greatest disparities occurring in engineering and computer sciences.$^{\mathrm{1}}$ For 17 years, the Princeton Plasma Physics Laboratory (PPPL) has been working to change those statistics by providing a day-long conference in STEM for young women in grades 7-10, where 750$+$ young women to spend the day with prominent female scientists, engineers, and technology professionals. The YWC's Attendance has tripled in size. Students travel from as far as Maryland to attend, and it is becoming evident that a single one-day event is insufficient to meet the demand. Using PPPL's model for the YWC, and partnering with General Atomics, University of California, San Diego, the American Physical Society's Conference for Undergraduate Women in Physics (CUWiP), among others we will pilot a new Young Women's Conference in STEM in San Diego, CA in 2020. This event will enable us to reach  as many students in a different region of the country, with the goal of inspiring more young women to pursue their future in a STEM field.   

New Initiatives to Develop the Plasma and Fusion Energy Workforce

As the US moves closer to a burning plasma device, the demand for a technical workforce in plasma physics and fusion energy is growing. In response, PPPL has created three engineering- and technician-focused training programs in 2019 that will develop and train future generations. These include a 10-week Engineering Undergraduate Internship, a 2-Year Engineering Rotational Program, and the 4-Year technical Apprenticeship. The Engineering Rotational Program consists of four six-months rotations to grow technical expertise in areas such as technology development, analysis and design, fabrication, installation, and experimental operation. The technical Apprenticeship is a federally certified program, in partnership with the State of New Jersey, consisting of 4 years of on-the-job training and nearly 600 hours of formal instruction. Upon completion, apprentices will be highly skilled and well-qualified fusion energy-relevant technicians. These new programs will develop pipelines of talent in the plasma and fusion energy workforce in areas critical to bringing the science of fusion to practical reality.   

A new popular science book: The Future of Fusion Energy

The gap between the state of fusion energy research and public understanding is vast. In an entertaining and engaging narrative, this popular science book gives readers the basic tools to understand how fusion works, its potential, and contemporary research problems. \\ Written by two young researchers in the field, ``The Future of Fusion Energy'' explains how physical laws and the Earth's energy resources motivate the current fusion program --- a program that is approaching a critical point. The world's largest science project and biggest ever fusion reactor, ITER, is nearing completion. Its success could trigger a worldwide race to build a power plant, but failure could delay fusion by decades. To these ends, this book details how ITER's results could be used to design an economically competitive power plant as well as some of the many alternative fusion concepts.   

Bringing Research Codes into the Classroom: A Case Study with Particle-In-Cell and Vlasov-Fokker-Planck Codes

The codes that serve plasma physics researchers could benefit a broad and diverse group of students and teachers, particularly when incorporated into narratives that include text, equations, interactive visualizations, and multimedia elements. Teachers and beginning students could potentially benefit from simulation output that illustrates fundamental concepts. Advanced students could benefit from simulations that reproduce classic research articles. Budding computational scientists could benefit from an illustration of the consequences of using different codes, different algorithms, or different parallelization strategies. Even researchers could benefit from clear and interactive educational material that enriches their current understanding which in turn rapidly leads to new research directions. Here we show how we are using Jupyter tools to create interactive educational narratives that utilize particle-in-cell and Vlasov-Fokker-Planck software for each group above.   

High speed camera studies of tokamak plasmas

High speed cameras have a wide range of uses on experimental tokamaks, including studying various plasma instabilities. The HBT-EP tokamak uses a Phantom v7.1 high-speed camera [1]. This camera picks up light in the visible spectrum, with a frame rate of 66 kfps. It is positioned with a tangential view of the tokamak. By analyzing magnetic and visual data, a correlation could be found between visual light fluctuations and magnetic fluctuations. We use the camera to investigate natural plasma instability behavior, as well as responses from applying nonaxisymmetric magnetic fields. We also study mode behavior when puffing a large amount of gas at the plasma edge while applying strong field perturbations. \\ {[1]} S. Angelini \emph{et al.}, Plasma Phys. Contr. Fusion, \textbf{57} 045008 (2015).   

Development of a database approach for analyzing a large dataset of simulated particle trajectories

A database method is developed for analyzing a very large dataset of simulated particle trajectories within a long aspect-ratio magnetic field structure called a Taylor state. Six hundred thousand protons are launched from a random distribution of velocities, directions, and positions within a static magnetic field computed from the differential equation curl B $=$ lambda B in a long-aspect ratio cylindrical boundary using the eigensolver code PSI-Tet. The behavior and transport of these particle can be studied by seeking patterns among initial conditions and their ultimate trajectories. The relational organization of the dataset allows access to a lot of information through an inexpensive query search, specifically using a SQL database.   

Axial velocity measurements of plasma plumes in the Bryn Mawr Magnetohydrodynamic Experiment (BMX)

Using a two-point correlation method, the axial velocity of turbulent plasma launched into a flux-conserving chamber by a magnetized coaxial plasma gun can be determined. Magnetic field measurements are made using an array of pickup coils inserted radially into the chamber and arrayed axially. The velocities for multiple shots were calculated using known separation distance between probes and a delay time computed from the position of the peak of the cross-correlation function of magnetic fluctuations of the adjacent probes. The distributions of velocities for multiple shots was determined for multiple shots and scanned for time periods within a shot and axially away from the source.   

The effects of azimuthal rotation of a cylindrical plasma are analyzed on the Large Plasma Device (LAPD) at UCLA

Rotating the plasma is employed as a method of further containment. Previous work has shown that outward transport is reduced, but that coherent modes can develop in the edge at large rotation rates. Before officially implementing this method into regular data collection and analysis, the effects of rotation on the plasma must be studied. The nature of this coherent mode is studied using a spatial cross-correlation method. This method compares ion saturation fluctuation data from two Langmuir probes separated in space. From these spatial correlations, a dispersion relation of the coherent modes is pursued. Understanding the properties of plasma at a high azimuthal rotation will be helpful in the future of cylindrical plasma data collection.   

Construction of a double Langmuir probe to measure fluctuating ion saturation current as a proxy for density fluctuations in the Bryn Mawr MHD Experiment

A double Langmuir probe is constructed for the evaluation of density in the turbulent plasmas generated by the coaxial magnetized plasma gun source of the Bryn Mawr Magnetohydrodynamic Experiment (BMX). The plasma within the BMX system is injected as magnetic helicity into a long, flux-conserving cylindrical chamber where a dense and extensive array of ports allow access to probe diagnostics such as magnetic pickup coils and this double Langmuir probe. The probe is comprised of tantalum rods set in 1/8th inch alumina. Steady bias voltage is supplied by six 1100mF capacitors in parallel. Density fluctuation spectra are discerned via measurements procured with a high-bandwidth current monitor of the double probe's ion saturation current. These spectra are compared to fluctuations in the magnetic field spectra.   

Taylor State Merging Experiments at SSX

We are studying magnetic reconnection that occurs with the high-velocity ($40~km/s$) merging of two Taylor state plasmas in SSX. We are using the merging configuration previously used by Gray, {\it et al}$^1$ ($L=0.86~m, R=0.17~m$). We record the ion temperature with ion Doppler spectroscopy, and electron density with a Helium-Neon interferometer. Magnetic field vectors {\bf B}(t) are measured with a 2D probe array at the midplane. We time the Taylor states so that both arrive at the center of the probe array within a microsecond. We have examined both co-helicity and counter-helicity merging of the Taylor states. Preliminary results show an increase in the magnetic field strength and electron density at the midplane, followed by an increase in ion temperature. We find the density to be ($\ge 0.5 \times 10^{16}~cm^{-3}$), proton temperature ($\ge 20~eV$), and magnetic field ($0.3~T$) of relaxed helical Taylor states. $^1$Gray \textit{et. al.}, Phys. Rev. Lett. 110, 085002 (2013).   

MHD simulation of Taylor state merging at SSX

We present results of a resistive MHD simulation of the evolution and merging of two Taylor state plasmas. The simulation models merging experiments at SSX, where we have characterized the magnetic structure, velocity ($40~km/s$), density ($0.5 \times 10^{16}~cm^{-3}$), proton temperature ($20~eV$), and magnetic field ($0.4~T$) of relaxed helical Taylor states (see K. Gelber, {\it et al}, this session). We simulated the merging of both co- and counter-helicity Talyor states. We are using the Dedalus framework, and run simulations on the Bridges Supercomputer. Dedalus solves differential equations using spectral methods, written with a Python wrapper in an open-source, MPI-parallelized environment (http://dedalus-project.org/). Simulations are run on a rectangular grid (NxMxP=28x24x180). Initially we have a 2x2x10 rectangular box with two spheromaks and dense plasma regions at each end and low density regions in the middle. Perturbation is added to the structure of the spheromaks to break axisymmetry. At the boundaries we have free slip and perfectly conducting walls. The code has been verified by solving the Hartmann problem (vertical magnetic field, uniform pressure gradient) on a rectangular grid of same size with no-slip and perfectly conducting boundary conditions.   

Proton Orbit Calculations in Relaxed Taylor States at SSX

We aim to analyze the dynamical properties of plasma particles within the cylindrical, helical “Taylor state” magnetic field structure. We also wish to study the potential confinement properties of the Taylor state to assess if it is a viable fusion energy configuration. We simulate the motions of particles in the Taylor state through of a total of $2 \pi \times 10^5$ orbits of particles with a set distribution of initial positions and velocities. The field structure itself is calculated by first solving the eigenvalue equation $\nabla \times {\bf B} = \lambda {\bf B}$ using the program PSI-Tet. Then, the Boris algorithm is implemented to solve the equations of motion for the particle orbits. The results of the simulation show that the majority of escaped particles escape either at the ends of the Taylor state or at points along the surface of the cylinder containing the state that have a weak field. In addition, we found that the particles that remain confined within the state for an extended period of time exhibit general trends for the distribution both radially and along the z-axis. The data also shows that particles initialized with greater initial velocities were generally more likely to escape the Taylor state, and approximately $55\%$ of particles stayed confined.   

Electron Density Measurement with Hairpin Resonator in Processing Plasma

Hairpin probes are used to measure electron density in plasmas. Previous hairpins have been described and are constructed as a quarter-wave resonant structure typically made from a folded piece of wire. The present work extends the hairpin measurement to approximately 10\textasciicircum 12/cm\textasciicircum 3, corresponding to a plasma frequency of about 9 GHz. We describe an easily reproducible implementation of the associated microwave electronics using commercial off the shelf components that are inexpensive compared to the network analyzer that is typically required. Correction coefficients are derived for both the plasma sheath effect and the wire coating. A third previously unreported correction in these probes accounts for the support of the resonant structure that masks direct contact with the plasma over a portion of the resonant wires. Measuring even higher densities requires increasing the resonant frequency, which we were unable to do below the scale of 4 mm. Toward this end we therefore report on operating a hairpin structure at its 3d harmonic (3/4 wavelength resonator). Measurements are taken in a plasma processing tool operating in Argon at pressures below 20 mTorr. Results are compared with Langmuir probe measurements and a microwave interferometer.   

Further Insight into the Nature of Atmospheric Water Plasmoids

There is a great deal of interest in pulsed atmospheric plasmas for applications in plasma chemistry, medicine and others. Here we study a plasma formed by a pulsed discharge (250 kW -- 1,350 kW) in water. In previous studies, a high-voltage capacitor bank was discharged between a cathode protruding from a container of weakly conducting electrolyte (Stelmashuk, Vitaliy {\&} Hoffer, P., IEEE, Trans. Plasma Sci, 2017) and a submerged ring anode. A plasmoid was produced and its light emission was photographed using a fast camera. This work extends these studies with the imposition of a magnetic field (100 G \textless B \textless 2 kG) parallel to the cathode. The long-lived plasmoid (t \textgreater 1 sec) was photographed with a fast framing camera (30,000 frames/sec). The highly collisional plasma was observed to rapidly rotate when the field was present. B-dot probes with onboard electronics and no connection to ground measured coherent low frequency fluctuations (f $=$ 50 Hz), which became chaotic at larger input powers. The photography revealed ``firefly'' streamers that drift away from the mushroom cloud above the spinning vortex. Aside from movies we present data from magnetic probe arrays, plasma density measurements and spectra.   

Hairpin Lock-in Circuit for Real-Time Plasma Density Measurements

We describe a circuit which allows a hairpin resonator probe to measure the plasma density in real time. Recent work has demonstrated that hairpin probes can be implemented cheaply and without too much difficulty using commercial o\textunderscore the shelf microwave electronics (see X. Fan, also at this conference). Using such a probe to diagnose the density has typically involved sweeping over a band of frequencies that includes the resonant peak, then identifying the resonance and deriving the corresponding density for that sweep. The present work adapts a lock-in type of circuit, which is commonly used to actively maintain resonance in high precision lasers, to find and lock onto the hairpin's resonance in real-time. An error signal is generated by introducing a small oscillation to the input of a voltage-controlled oscillator, and monitoring the output of the mixer that detects the transmitted signal from the probe. The response is then fed into a PID controller to maintain the control voltage at resonance. One goal of the current work is to shorten the time response of the lock-in circuit to 1 us or less. This would be sufficiently fast to allow the hairpin probe to be used as a diagnostic of the plasma density during an Alfven wave in the Large Plasma Device at UCLA.   

Modified Hairpin Resonator for Electron Density Measurements

This work explores hardware modifications to a previously developed hairpin probe, used to measure plasma density (see X. Fan, reported at this conference). The probe consists of a signal of adjustable frequency indirectly coupled to a U-shaped piece of wire that forms the resonator. Coupling is near the shorted end using a small loop formed at the end of a coax. A detected signal is received by a loop at the end of a second coax. The hardware describe here consists of a microwave oscillator, a coupler, an IQ-mixer and an amplifier, is an advanced version of the original circuit described by Fan. This new circuit is designed to a) use our own circuit board rather than the off-the-self components used by Fan, and b) replace the single output mixer with an IQ mixer. The new mixer circuit should enable automatic resonance tracking using a circuit described by S. Mackie, also at this conference. Detailed comparisons with other diagnostics for measuring plasma density will be presented, in particular an RF compensated Langmuir probe used in a process plasma, microwave interferometer line-integral data, and a normal Langmuir probe typically used in the Large Plasma Device at UCLA.   

Performance Measurements on the ECH/ECCD Top Launch System on the DIII-D Tokamak

On DIII-D, a new ECH installation is being tested which uses a flexible system in which a gyrotron operating at 117.5 GHz is installed in the top launch configuration. Experiments at TCV [1] showed that increased heating efficiency at the 3rd harmonic could be achieved with this vertical launch geometry, where the rf beam trajectory is approximately parallel to the resonance for a longer distance and the Doppler shift for the resonant electrons was higher than for low-field-side (LFS) injection [2]. Although important advantages are obtained by driving localized current in the plasma, a difficulty is that the current drive efficiency is relatively low, particularly when current drive is required at intermediate radii for advanced tokamak performance or for NTM suppression. Top launch current drive can be compared with LFS launch and is expected to increase the driven current. In addition to the 117.5 GHz frequency, a second frequency, 110 GHz, can also be used. A description of the installation, measurements of the top launch transmission line performance, and the status of the experiments will be reported.\newline[1] Alberti, S., et al., Nuclear Fusion, 45, 11, 1224-1231 (2005) \newline[2] Chen, X., et al., EPJ Web of Conferences, 203, 01004 (2019)   

Spatiotemporal Evolution of the Probability Distribution Function of Density Fluctuations near the L-H Transition on DIII-D

The Probability Distribution Function (PDF) of long-wavelength density fluctuations changes markedly in space and in time approaching the L-H mode confinement bifurcation. The dynamics of turbulence and flows approaching the L-H transition has been well documented, but requires complex and time- consuming diagnosis and analysis. Initial analysis of the PDF of these fluctuations demonstrates that it skews negatively and positively a couple centimeters inside and outside the separatrix, respectively, while approaching the L-H transition. This suggests a change in the near edge turbulence dynamics and transport properties approaching the transition. Studying the parametric dependencies of various statistical properties (e.g. skewness and kurtosis) of edge fluctuations could lead to new connections between theoretical and experimental descriptions of the L-H transition. Additionally, this analysis may provide a relatively straightforward method to determine if the L-mode edge turbulence dynamics are conducive to an L-H transition, or are far from such a transition, which may be of critical importance to anticipating and achieving H-mode in burning plasmas.   

Precision Machined Hohlraum Parameter Study for Inertial Confinement Fusion

In support of indirect drive Inertial Confinement Fusion (ICF) research at the National Ignition Facility (NIF), gold or uranium components, called hohlraums, are used to convert laser light into X-rays to drive the fuel-loaded capsule or other experimental packages.  These millimeter-scale components with micrometer-scale features are fabricated with a series of diamond turning operations.  Any deviation from specification or undesired feature can directly impact the symmetry and overall performance of the capsule implosion. The final quality of the machined parts is dependent on the material being machined, cutting tool material and configurations, as well as a variety of other machining and environmental parameters.  A systematic study of these parameters is presented to understand parameter windows and to optimize surface quality, feature dimensional accuracy, tool integrity and longevity, throughput, and burr reduction in hohlraum fabrication.   

Full-Wave Modelling and Integrated Transmission Line Testing for the ITER Low-Field Side Reflectometer

The low-field side reflectometer (LFSR) will provide important measurements of the electron density for ITER. The full-wave reflectometer code has been used to simulate microwave propagation of LFSR frequencies (30 -- 165 GHz) in an ITER plasma. The objective of the simulations was to study how plasma turbulence and errors in the magnetic field and electron temperature contribute to signal loss and to errors in the inferred density. In addition, a mockup transmission line provides a facility for system- and component-level testing of the diagnostic. The test facility was recently upgraded with an antenna array, vacuum window assembly, and waveguide periscope similar to the actual design. Test of these components focused on investigating their effect on the reflectometer signal in terms of mode conversion and insertion loss.   

Understanding of the Poloidal Structure of the Sawtooth Precursor

The linear MHD code MARS is used to explain phase folding in the poloidal direction observed by edge magnetic diagnostics during sawtooth instability events in the DIII-D tokamak. The sawtooth relaxation is an MHD instability that occurs when an m = n = 1 flux surface exists in the plasma. The instability occurs cyclically as the safety factor q on axis oscillates from $q(0)>1$, creating good core confinement, to $q(0)<1$, allowing the instability to grow and the confinement to weaken. Weak confinement allows the q(0) value to grow and restart the cycle. Mirnov coils are used to measure external magnetic field variation during the sawtooth cycle. Fourier analysis of the data shows that the structure of the instability closes on itself after one toroidal turn but the structure of the instability in the poloidal direction, as seen at the wall, has a non-monotonic ''zigzag'' pattern. Ideal MHD MARS simulations are compared to experimental data. In these simulations, poloidal mode number superposition and wall effects are examined to reproduce experimental data and understand the sawtooth poloidal structure.   

Performance of Coaxial RF Transmission Line Components at 476 MHz

A system for helicon current drive at 476 MHz is under construction at DIII-D, with initial operation planned for early 2020. Most of the transmission line components being used to convey the rf power from the klystron to the comb-line antenna on DIII-D were originally part of a 60-120 MHz ICRF system. To evaluate the applicability of these components at the significantly higher frequency, electromagnetic simulations are performed with the RF package in the COMSOL Multiphysics software suite and compared with low-power measurements using a vector network analyzer. One large and expensive component of particular interest is the dual channel 2 $\times$ 2 MW dummy load obtained from Spinner, which was designed for use at frequencies in the 30-120 MHz range. Substantial cost savings may be achieved if the Spinner dummy load can be used at 476 MHz. Details of the simulations and measurements are presented.   

Influences of 3D Features on 2D Equilibrium Reconstructions

In this work, a new method for mapping kinetic profile measurements to magnetic flux surfaces is used to assess discrepancies in the electron and ion densities near the last closed flux surface of DIII-D plasmas. The apparent misalignment between these densities is hypothesized to be the combined result of a misshapen poloidal field coil, toroidal separation between the Thomson scattering and charge exchange recombination spectroscopy (CER) diagnostics, and the assumption of toroidal symmetry in the equilibrium generated by the EFIT reconstruction code. In this work, equilibria are made using two different sets of toroidally displaced magnetic probes in EFIT, one closer to the Thomson location and one closer to the CER toroidal location. The relative alignment of Thomson and CER in these two equilibria is compared to a historical method for aligning the profiles, which shifts the Thomson data based on the results of fitting a modified hyperbolic tangent function to the electron temperature. This comparison is done for limited, single null, and double null plasma shapes, which are affected by the misshapen coil by different amounts.   

Study of internal magnetic island bifurcations produced by resistive MHD plasma simulations

Numerical studies are performed to understand how RMP-driven magnetic islands in tokamak plasmas can exhibit internal bifurcations that involve the creation of new X and O fixed-points. These bifurcations result in a splitting of magnetic island centers, or O-points, into two separate centers. Each of these new centers has its own separatrix and the two new separatrices are connected at one point, known as the X-point, which can also be found between separate magnetic islands. An efficient method of finding O- and X-points is needed to study how these new fixed points are created. A B\textunderscore perp minimizer is created that will find O- and X-points using the TRIP3DGPU magnetic field line integration code together with input fields from the resistive M3D-C1 magnetohydrodynamic plasma response code. Knowing how these fixed points move prior to and during the bifurcation will allow us to test a model of the process and provide further understanding of magnetic island behavior, which is a key aspect of tokamak plasma stability. Results from modeling of the fixed-point movement with increasing 3D magnetic field amplitude produced by non-axisymmetric perturbation coils will be discussed.   

New Parameterization of Tokamak Flux-Surface Equilibria

Equilibrium force-balance in a tokamak gives rise to toroidally-symmetric magnetic flux surfaces throughout the plasma volume. The calculation of this equilibrium is routinely carried out using codes such as the EFIT code. The solution from EFIT is given in the form of a flux field on a two-dimensional (R,Z) mesh. This toroidal equilibrium solution is required as an input to kinetic turbulence and transport codes. However, for use in these codes, a parameterized form of the flux-surface geometry is required. One popular model parameterization is the D-shaped formula, which characterizes the flux surface in terms of the elongation, triangularity, squareness, etc. In this work, we develop a new, more systematic approach for this parameterization. The method more accurately represents the flux surface geometry in the plasma edge, near the X-point, where the shaping is strongly non-circular and close to singular. The parameterization also forms the basis of a new inverse Grad-Shafranov solver to compute the equilibrium given the shape of a boundary magnetic surface.   

Atomic modeling of stability and thermal characteristics of metastable tungsten as a plasma-facing fusion material

Plasma-facing materials must be able to sustain large heat and particle fluxes in future fusion reactors. Recent experiments have suggested the existence of a metastable W-B phase at room temperature [1] which may be a suitable plasma-facing material. Exploring the influence of implanted species on lattice stability and thermal properties therefore provides additional insight. First, the stability of W phases BCC and FCC is analyzed by solving the phonon dispersion relation at various temperatures (0-4000K) and pressures (100-105 atm). The phonon spectra are deduced from the eigenvalues of the dynamical matrix obtained from molecular dynamics simulations (LAMMPS) [2], and compared to existing calculations for pure W [3] to assess the validity of the phonon calculation and interatomic potential. The effects of impurities on the stability of W phases are examined from the phonon spectra when H, He, and B impurities are introduced into a W lattice. [1] Y. Raitses, 60th APS-DPP conference 2018 [2] Zhang, H. Y (2018). Computational Materials Science, 144, 32-35 [3] Kong, L. T. (2011). Computer Physics Communications, 182(10)   

Implementation and Calibration of the Wide Emission Spectral (WiSE) Diagnostic on DIII-D

The Wide Spectral Emission (WiSE) diagnostic is a set of moderate spectral and temporal resolution spectrometers co-viewing vertically through the plasma, now being installed on the DIII-D fusion device for study of neutral, ion, and molecular emissions. Together, these instruments provide a spectral `footprint' of the tokamak plasma from 185 nm, the deep ultraviolet, up through 5000 nm, the medium wavelength infrared (MWIR). Spectrometers and optics utilized for the WiSE diagnostic have been calibrated for wavelength and absolute intensity using NIST-calibrated light sources. A standalone LabView-based interface employing independent triggering of each device has been implemented and tested. Each spectrometer is paired with a dedicated compact PC for operation and data acquisition. Details of setup and operation of the WiSE diagnostic will be presented, as well as initial analysis of spectra for fuel and impurity species in the plasma.   

Ion Particle Transport in DIII-D H-Mode Plasmas

This paper will look at ion particle transport in the presence of a perturbative gas puff modulation in DIII-D H-mode plasmas. The deuterium ion response to the modulation is analyzed using the charge exchange recombination (CER) diagnostic system. With this data, we can extract perturbative transport coefficients for the ions and compare them to prior results looking at the electron transport in various turbulence regimes (S. Mordijck et al 2015 Nucl. Fusion 55 113025). Theoretical models suggest ion and electron transport are not identical; the ion turbulent transport is significantly larger than the electron turbulent transport in the ion temperature gradient (ITG) regime, while the opposite is true in the trapped electron mode (TEM) regime (C. Bourdelle et al 2018 Nucl. Fusion 58 076028). Large ion particle transport coefficients imply that the ion density profiles are uncorrelated to the corresponding ion source, thus providing confidence that experimentally measured peaked ion profiles are the result of an inward pinch, not a core source of particles. By analyzing the changes in the modulation of the ion channel, we can assess the validity of such theoretical models in various turbulence regimes in H-mode plasmas.   

Start-Up Phenomena in a Surface Dielectric Barrier Discharge Device

Surface dielectric barrier discharge (DBD) arrays have applications as plasma actuators for airflow control and as sources of reactive species for sterilization, wound healing, and surface treatment. In some cases, e.g. in biological applications, it is desirable to operate such devices at low duty cycles - at or below 30\% - in order to reduce gas heating and to increase device longevity. Under these conditions, devices can exhibit start-up phenomena which take place over timescales of seconds. We experiment with a flexible surface DBD device with a ground electrode patterned with millimeter-scale square cavities and separated from the flat high-voltage electrode by a layer of polyimide tape. This device is driven by AC voltage and operates in ambient air. During start-up, this device transitions spontaneously from dark to glow modes, with the timing of these transitions showing a dependence on the temperature of the device and air flows over its surface. These results demonstrate the influence that the surrounding environment can have on the operation of such DBD devices and help to establish suitable operating conditions for applications.   

A machine learning algorithm for the nonlinear Fokker-Planck-Landau collision operator in XGC

XGC1 is a~gyrokinetic particle in cell code that uses the~Lagrangian~equation of motion for time advancing marker particles to solve the gyrokinetic Boltzmann equation. It includes a two-dimensional solver of the~nonlinear~Fokker-Planck-Landau collision operator, which simulates small-angle collisions in velocity space. The run time for the current implementation of the operator is O($n^{\mathrm{2}})$, where $n$ is the number of plasma species. As the XGC1 code begins to attack problems including more impurity species, the collision operator will become expensive computationally. An alternative to the Picard iteration algorithm used currently for the collision operator is presented in the form of a deep neural network.~Various types of neural networks, primarily convolutional,~are considered in the attempt to~predict~the nonlinear transformation of the collision operator.~While initial training was begun on JET simulation data, a wide enough range of~collisionality~has been considered to ensure the full domain of collision physics is captured. Special attention has also been paid to ensuring the machine learning algorithm does not violate conservation properties of the collision operator.   

Floating Potentials of End Plates in the PFRC-2 Divertor Regions

Floating probes were used to measure key plasma parameters in the PFRC-2. Previous experiments in RMF-sustained discharges have shown heating of a minority electron population to T \textgreater 300 eV in the center cell (CC). To infer the density and energy of the fast electrons escaping the CC, we have measured the floating potentials and current to ground of a Ta disk in the Far End Cell (FEC), and a steel plate in the Source End Cell (SEC) located at the opposite axial end of the PFRC-2. At an RMF power of 70 kW, a floating potential of -1,300V was measured on the Ta disk, which implies electrons with temperature near 400 eV and a density greater than 5{\%} of the bulk plasma in the FEC. The floating potentials were also used to characterize time-dependent behavior of the FEC electron density. When compared to data from the CC interferometer, there was strong agreement on fluctuations seen during electron decay. For RMF pulses near 10 ms and low initial filling pressures, \textit{ca.} 0.4 mTorr, a staircase-like density decay was measured by the interferometer concurrent with potential steps seen on the Ta disk.   

Preliminary Experimental Study of Coronal Plasma Jets due to Spheromak Tilt Instability

Activity in the solar corona such as flares, coronal mass ejections, and coronal jets are driven by the release of energy through magnetic reconnection events. Understanding the mechanism(s) behind coronal jets has been long sought-after in solar and space physics. We propose coronal jets could be modeled by embedding a hemispherical spheromak-like closed field structure inside a large scale open field. In the boundary between these structures, current filaments form then undergo a reconnection event linking them to the open field lines, thereby allowing the filaments to become a plasma jet(1). It is postulated that this reconnection event may be related to the global reconnection which occurs during the spheromak tilt instability. This poster explores the results from a preliminary experiment done on the Magnetic Reconnection Experiment (MRX) in which a spheromak is formed inside of an equilibrium field. Using a magnetic probe array and correlating fast camera data of the CII and CIII lines, the interaction between the closed spheromak structure and the equilibrium field is observed and analyzed. Ref. P.F. Wyper et al., Nature 544, 452, 2017   

Investigation of ash removal from fusion reactors via palladium and PdN-layered membranes

While the D-3He fuel proposed for some fusion reactors is aneutronic, deuterium (D) ions in the plasma can fuse with each other to produce either tritium (T) or 3He. The T fusion ash must be extracted to avoid energetic neutron production in the plasma. One way of separating the 100-keV T from the 100-eV D is by introducing a high H permeability, usually high-Z, material to prevent energetic fusion ash from re-entering the core plasma. Palladium (Pd) is a strong candidate. Pd has a high H sorption rate and permeability through conversion to a metallic hydride when heated to high temperatures, increasing H diffusion. Under these conditions, surface impurities may dissolve and allow H isotopes to be released equally from the front and back surfaces. Pure Pd would not separate the D from the T. However, introducing a thin (\textasciitilde 0.1 $\mu $m) diffusion barrier beneath the surface would suppress the back-streaming of deeply implanted T. We will report data on H permeability in Pd and PdN foils at a temperature range of 300-800 K, focusing on the effects of pressure and temperature to destroy permeation barriers that could separate low energy and higher energy fusion ash, (T).   

Diagnostics for Turbulence in Plasma

Turbulence is a complex phenomenon which characterizes certain fluid flows. Developing tools to extract statistics from turbulence is an integral part of understanding this phenomenon. To model turbulence, two- and three-dimensional fluid and kinetic simulations are performed using the Gkeyll code.This project focuses on creatinggeneral tools to understand the impact of various parameters on turbulence spectra, detecting and characterizing intermittent structures such as blobs and current sheets, and minimizingresolution requirements to extract a given structure and scale in a plasma.   

A New Method For The Optimization Of Finite Build Stellarator Coils

To date, all major stellarator coil optimization codes, such as FOCUS, ONSET, REGCOIL, COILOPT$++$, and NESCOIL ultimately produce current-carrying single filament coils. In reality, stellarator coils have finite depth and thickness, which can make the single filament model a poor approximation, particularly when coils are placed close to the plasma. The finite build of a coil, termed the "winding pack", can be approximated by a multi-filament model. In this model, each coil is comprised of a set of closely packed single filaments. The torsion of the winding pack, determined by the multi-filaments, is not determined a priori and is a parameter that should be optimized over. Here we present a new method to construct stellarator coils with a finite build given a set of single filament coils; we also provide a mechanism to optimize for the winding pack torsion using the multi-filament model. The method is applied to compare the difference in fidelity, to producing a desired magnetic boundary, between the single filaments, unoptimized multi-filaments, and optimized multi-filament coils.   

Evolution of Evaporative Coatings of Lithium from LTX-$\beta $ with Temperature and Their Analysis with XPS and LEIS

Plasma-material interactions (PMI) strongly influence lifetimes of plasma facing components (PFCs) and plasma performance. The choice of low-Z PFCs such as lithium (Li) offer attractive features such as lower radiative power loss and the possibility to operate in a flat temperature profile regime, as demonstrated by evaporative coatings on LTX-$\beta $. We present X-ray photoelectron spectroscopy (XPS) and low energy ion scattering spectroscopy (LEIS) analysis of witness samples using the Sample Exposure Probe (SEP), a portable ultrahigh vacuum (UHV) chamber, which introduces samples to LTX-$\beta $. These witness samples can then be transported to a surface analysis station. Li coatings on witness samples are then analyzed using XPS and LEIS to make observations on the effects of the LTX-$\beta $ environment on the first wall. The combined XPS and LEIS illustrate the oxidation of the Li coatings, forming Li$_{\mathrm{2}}$O and LiOH on top of evaporatively coated Li. The evolution of these oxides has a strong temperature dependence. We present XPS and LEIS analysis of these witness samples and how they evolve with temperature.   

Investigation of deuterium retention and uptake in lithium plasma-facing components in fusion reactors

The reaction of incident energetic deuterium (D) and hydrogen (H) ions and atoms with surfaces plays a critical role in plasma-surface interactions in nuclear fusion experiments. Liquid metals, such as Lithium, offer solutions to significant problems of the plasma-facing components (PFC) in fusion energy systems. Lithium is a widely accepted candidate for PFCs because of its ability to retain both D and H over a wide range of temperatures. In this study, temperature programmed desorption and Auger electron spectroscopy will be used to obtain quantitative measurements on D uptake and retention to elucidate the surface chemistry of Li coatings on metal PFCs in high power fusion energy devices. We will report data on the sputtering yields and time dependent retention of D ions on Li and Li2O films under ultra-high vacuum conditions.   

A study of RMF-plasma coupling on varying seed plasma parameters

We describe the effects of seed-plasma parameters on the repeatability of rotating magnetic field (RMF) plasma formation in the PFRC-2. The initial plasma is a steady-state, tenuous (1x109 - 1x1011 electrons/cm3) hydrogen plasma, formed by an RF capacitively-coupled external antenna in the source chamber of the device. Previous measurements have shown this relatively low power (2-500 W) plasma may contain a small population of energetic electrons (up to 35 keV), in addition to bulk electrons with temperatures near 5 eV. This `seed plasma' flows along the main axial magnetic field into the region between the RMF antennas in the main chamber. A high power (up to 50 kW), pulsed (up to 300 ms duration), odd-parity RMF at frequencies between 2 and 14 MHz is then applied to the seed plasma. A higher density (up to 5x1012 electrons/cm3) plasma is formed as a result. Our experiments have studied the effects of varying the seed plasma's parameters on the formation of the RMF plasma. The RMF plasma's breakdown time and the efficiency of power coupling are measured as functions of the initial hydrogen pressure, the main axial magnetic field strength, the RMF antenna power, and the seed plasma RF power. Plasma formation mechanisms are considered.   

Laboratory Experiments for Exploring Solar Flux Rope Stability

Magnetic flux ropes (MFR) on the solar surface are thought to be the precursors of coronal mass ejections (CMEs), and these ejection events may correlate with magnetohydrodynamic instabilities such as the torus instability and kink instability. However, in some cases where an MFR is torus-unstable, magnetic self-organization events may reduce the energy and prevent an eruption. These self-organization events conserve helicity over their timescales, and for toroidal plasmas Taylor showed that the profile of $\mu\equiv\frac{\bf{J.B}}{B^2}$ is constant for the minimum-energy state.$^1$ The Magnetic Reconnection Experiment (MRX) was outfitted with electrodes in order to create MFR. An array of over 300 in-situ magnetic probes was used to capture a 2D cross-section of the magnetic field along with limited out-of-plane measurements. Earlier work by Myers, et. al created classifications for the experimental MFR behavior as either eruptive, failed-eruptive, or stable.$^2$ In this poster, the dynamics of $\mu\equiv\frac{\bf{J.B}}{B^2}$ are more closely examined for correlations with the behavior of the MFR and for signals of Taylor relaxation.\newline 1. Taylor, \textit{Rev. Mod. Phys.} \textbf{58}, 741-763 (1986) \newline 2. Myers, et. al. \textit{Nature} \textbf{528}, 526-529 (2015)   

Piezo-thermal effect in gas and plasma

When compressed, a gas immersed in a potential field has been predicted to develop a temperature differential [1]. This phenomena, called the piezo-thermal effect, results in hot and cold regions corresponding to the locations of the maximum and minimum potential energy respectively. Previous numerical simulations confirmed this temperature differential for centrifugal and gravitational potentials. In this study, generalizations of the effect will be discussed. Although plasma features a number of complications, similar effects might also be imagined in compressing plasma. ~\\ ~\\ {[1]} V.I. Geyko and N.J. Fisch, Phys. Rev. E \textbf{94} 042113 (2016).   

Design of PPPL's tabletop permanent magnet stellarator

One of the leading magnetic plasma confinement configurations is the stellarator. With its unique non-symmetric shape, it provides a confining magnetic field without requiring plasma current. This reduces instabilities (vs. tokamaks) and can confine fusion relevant plasmas. Current stellarators are built using irregularly shaped coils, which represent a challenge in design and manufacturing. PPPL, in collaboration with the Simons Foundation, is working on a new concept involving the use of permanent magnets for a fusion relevant stellarator experiment. In this poster we present the design of a PPPL tabletop stellarator, which tests the permanent magnet technology at a small scale. The purpose of this device is to showcase the innovative permanent magnet stellarator in a simplified and transportable fashion while keeping the cost and construction time low. We envision this device to be portable enough to serve as an outreach platform to highlight the magnetic confinement configuration, while versatile enough to be used to study flux surfaces with different magnetic field geometries and strengths.   

Applying Deep Learning to GPI data to analyze edge turbulence in the SOL

Understanding the edge dynamics of magnetically confined plasmas is an important aspect of increasing confinement and, eventually, putting fusion power on the grid, especially for large fusion machines such as ITER. The aim of this project is to use deep learning (DL) methods to analyze diagnostic data of the edge and scrape-off-layer (SOL) of NSTX, both to search for unidentified patterns and lay the groundwork for future DL projects. Success of this project could encourage plasma physics to use DL more in its data analysis, to match DL's growing prevalence in other fields of physics and science. Authors will explore data from the Gas Puff Imaging (GPI) diagnostic on NSTX using various types and architectures of DL, such as convolutional neural network (CNN), hybrid recurrent neural network and CNN, and unsupervised networks with autoencoders.   

Analysis of Separation Efficiency of an Advanced Annular Couette Centrifuge

Experiments on modified Taylor-Couette devices have shown that the fluids rotating in them have sufficiently low turbulence to allow for efficient centrifugal separation. The Advanced Annular Couette Centrifuge (AACC) has differentially rotating lids, a pump connected to several configurable inlets and outlets, and an inner and outer cylinder spinning in the same direction. The inner cylinder spins faster by no more than the squared ratio of the cylinder radius ratio to achieve high shear without inviting hydrodynamic instabilities. The differentially rotating lids are critical for controlling the turbulence at high Reynolds number. AACC holds 15 gallons of water and uses sub-micron titanium dioxide powder as the separation test particles. Various methods of measuring the powder concentration will be discussed, including laser refractometry and absorption spectroscopy, and results from the experiment will be compared with those of traditional centrifuges to look for improved separation, which could have important applications to a broad range of existing applications and open-up new application areas.   

Integrated test cases for the kinetic neutrals code Eunomia

B2.5-Eunomia is a code that couples kinetic neutral and multifluid plasma models. Eunomia [1] was developed as a replacement for Eirene with a focus on linear geometries. This makes it suitable for modeling experiments such as those involving linear plasma generators like Magnum-PSI; e.g. Eunomia can simulate passing a Magnum-PSI plasma beam through a chamber filled with neutral lithium gas as an experiment towards the development of the lithium vapor box divertor. Prior to this work, Eunomia did not possess a suite of integrated tests. We developed regression test cases to verify properties such as the velocity invariance of the collision operation. In order to test this, a new boundary condition for flowing gas was added. This boundary condition can be used to validate the code against analytic solutions as well as to model the neutral particles that flow adjacent to a plasma beam. In addition to the development of test cases, parts of the code have been modified to improve readability and vectorization. ~\\ ~\\ {[1]} Wieggers, Rob. ``B2.5-Eunomia simulations of Pilot-PSI.'' PhD Thesis, Dutch Institute for Fundamental Energy Research, 2012.   

Improved Experimental Setup for the Read Out of Superheated Emulsion Bubble Detectors

An improved experimental setup with 3D localization of bubbles has been designed and is under construction for the quick and accurate read out of superheated emulsion bubble detectors. Since 1979, bubble detectors have found use in dosimetry, radiation alarms, and potentially nuclear warhead verification. Droplets suspended in a gel matrix undergo a phase transition when struck by high-energy neutrons in the detectors and are easily counted using optical methods. However, at high fluence the accuracy of counts is reduced due to occultation. Currently, our group uses images of a rotating detector to localize and count bubbles far past the occultation limit. To improve the precision of localization and to reduce the time needed to read detector output, upgrades have been made to the control algorithm and setup of the bubble counter. Instead of capturing single-frame images, high-resolution videos of the rotating detectors are taken using a DSLR camera controlled by a Raspberry Pi. This new experimental setup has a more precise placement of its components, lighting, and rotation allowing for better reproducibility of experimental results. Additionally, the new setup provides a more user-friendly control interface and is contained in a compact enclosure.   

Neutral gas inventory in the PFRC-2 during RMF plasma heating

The inventory of hydrogen neutral gas within the PFRC-2 contributes to the ionization rate, axial and radial losses, momentum loss, current-drive efficiency, and plasma duration. We measure the neutral gas using MKS capacitive manometers, Baratron. Two Baratrons, one fast (10 ms) and one slow (1 s), were connected to each of the PFRC-2's three chambers: the source end cell (SEC), center cell (CC), and far end cell (FEC). The CC Baratrons showed a decrease in pressure following each RMF pulse, interpreted as ionization in the CC followed by axial transport of hydrogen out of the CC. The susceptibility of the Baratrons to pickup created by the PFRC-2's RMF current drive and heating system has caused us to use an alternative method to derive the pressure during the pulse. By measuring the pressure after the RMF for pulses of 0.5 to 20 ms we extract the pressure drop during the plasma discharge. Pressure rise seen at pulse initiation is attributed to the creation of Franck-Condon neutrals. Combined with theoretical calculations of electron dissociation rates, gas conductance, and relative pressures of atomic and molecular hydrogen, this experimental data allows us to construct a partial model for the movement of neutral gas within the PFRC during each RMF pulse.   

Simulation of Nonresonant Stellarator Divertor with Islands

Recently a new and efficient simulation method for nonresonant stellarator divertor is developed by Boozer and Punjabi [A. H. Boozer and A. Punjabi, Phys. Plasmas \textbf{25}, 092505 (2018)]. In this method, magnetic field lines are given an artificial radial velocity and the strike points of the lines on wall are calculated. The trajectories of field lines with radial velocity are calculated from the Hamiltonian for the field lines using area-preserving maps. The poloidal magnetic flux is the Hamiltonian for the field lines. In nonresonant stellarator divertor, the shape parameters in the Hamiltonian control the shape of the magnetic surfaces. There are three shape parameters which control the elongation, triangularity, and sharp edges on the outermost confining surfaces. It is found that by appropriate choice of shape parameters, it is possible to design a nonresonant stellarator divertor with islands. A wall that covers the islands for all toroidal angles can be designed. The wall is hexagonal in shape. The results on the foot-points on this wall calculated from the simulation method will be presented.   

Analysis of the development of Hydrodynamic Instability waves

Hydrodynamic instabilities occur in high energy density situations which contain pressure, density and velocity gradients such as those which are found in astrophysical and inertial confinement fusion experiments. Our experiment produces a shockwave that collides with a wedge shaped target that produces Kelvin-Helmholtz and Richmyer-Meshkov instabilities. We use the CRASH code, a radiation hydrodynamic code developed at the University of Michigan to simulate the experiment. IDL software was then used to analyze these simulation results and determine the height of the waves (manifestations of the hydrodynamic instabilities) produced and give a better illustration of the development of the instabilities as the shock progresses along the targets diagonal interface.   

Fluctuations and Transport in Two-Dimensional (Axial/Azimuthal) Hybrid Hall Thruster Simulations.

Simulations of Hall thrusters that aim to resolve the global discharge plasma generally use either fluid, or hybrid (fluid/PIC) models in the axial and radial coordinates. Those descriptions, which do not resolve azimuthal flows, employ ad-hoc electron transport parameters in order to reproduce experimental measurements. On the other hand, experiments, theory, as well as kinetic simulations indicate that azimuthal fluctuations likely play an important role in regulating such cross field ``anomalous'' electron transport.$^{\mathrm{1}}$ In this work we report on results from an axial/azimuthal hybrid model which does resolve the azimuthal dynamics. Our findings indicate that while azimuthal fluctuations naturally emerge in the simulations, their phase is not optimal for transport, and as a result the overall simulated discharge current is well below that found in experiments. Work is underway to implement an electron transport model in the simulations in order to better reproduce experimental current levels. [1] Lafleur, T., Baalrud, S. D., Chabert, P., Theory for the Anomalous Electron Transport in Hall Effect thrusters. II. Kinetic Model, Phys. Plasmas, Vol. 23, 2016, pp. 053503-053513.   

Probing Dusty Plasma Simulation Structure Parameter Space

A complex (dusty) plasma consists of ions, electrons, and micron-sized solid particles, commonly referred to as dust. The complex plasma research space includes research in astrophysics, planetary science, atmospheric physics, fusion research, materials physics, and advanced manufacturing. Traditional simulation design patterns are unable to cope with this large problem space. Switching between physical systems or numerical models normally requires significant program modifications. Here we present DRIAD (DRIAD Runs Ions And Dust), a highly generic physics simulation generation framework implemented as a domain specific embedded language written in C$++$. DRIAD allows for rapid simulation development and extensive code reuse between disparate physical environments and numerical algorithms. Examples include simulations modeling aggregate dust grain charging in protoplanetary disks, effects of microsecond DC discharge inhomogeneities on millisecond time-scale dust dynamics, electrostatically-confined equilibrium dust structures in lab experiments, and dust self-organization in the PK-4 experiment on-board the international space station.   

Measuring Multiphoton Ionization Yields with Mid-IR Laser Avalanche Breakdown

Mid-infrared lasers have opened up a new regime in strong field physics, impacting research on high harmonics, interactions with near-critical plasma, laser wakefield acceleration, and more. Recently, we demonstrated that avalanche ionization driven by a 50 picosecond 4 micron laser is a sensitive way to measure low electron densities. We have used this method to measure extremely low yields in multiphoton ionization at low laser intensities for several pump wavelengths. This poster will discuss the experiment's data extraction and analysis, as well as~the design and testing of a lead sulfide autocorrelator to measure mid-infrared pulse lengths.   

Improving diagnostics capabilities for dynamic loading experiments using high pulsed powers drivers

The CEA operates several High-Pulsed Power (HPP) drivers dedicated to dynamic loading experiments. The aim of these experiments is to provide quantitative information about the dynamic behavior of various materials of interest including metallic and nonmetallic samples. Diagnosing such experiments has mainly relied on surface velocity measurements through laser-Doppler interferometry and current pulse measurements based on electromagnetic field sensors. Efforts were recently undertaken to significantly improve and extend the performance of diagnostics fielded on all of our HPP platforms. In addition to developing a robust pre-heating device suitable for all types of solids, we have implemented a novel photonic Doppler system for line and 2D discrete surface velocity measurements and are currently studying the feasibility of incorporating fiber optic-based ruby pressure gauges to the set of diagnostics. All of these developments are presented within the context of technical constraints associated with experiments in severe electromagnetic environments.   

Using an XPinch source on gas gun to detect phase transition.

Understanding the phase transition material under dynamic loading is of great interest in materials science. However the comprehension of the mechanisms governing such phenomena remains a great issue. Past studies have shown that macroscopic measurements on shocked materials do not provide enough information to fully understand the various processes involved. X-ray diffraction is a complementary technique that brings a new insight for studying materials at the atomic scale on shocked single crystals or polycrystalline materials. Tin is a material of great interest, it possesses a low pressure beta solid- gamma solid phase transition at 9 GPa. We are developing a novel experimental setup based on a compact High Pulsed Power generator capable of producing intense X radiation by generating a plasma through an X-pinch. This source is specifically designed for time-resolved X-ray diffraction in reflexion geometry on gas gun experiments at laboratory scale. We propose to describe this source and the promising preliminary data obtained under static and shock conditions.   

Developing a Time-of-Flight Spectrometer for Rutherford Backscattering Studies with Low Energy Ions

A Time-of-Flight Spectrometer is being developed at the Low Energy Ion Facility at the State University of New York at Geneseo to perform surface analysis with low energy (25-50 keV) ions via Rutherford backscattering. The Time-of-Flight Spectrometer has been designed to measure the energy spectrum of elastically scattered helium ions or deuterons produced by a Peabody Scientific PS-100 Duoplasmatron ion source. Scattered ions pass through a biased 5 $\mu$g/cm$^{2}$ carbon foil, causing the foil to emit electrons, which are detected by a Channeltron electron multiplier (CEM), producing a “start” signal. The ions then propagate a certain distance, or flight path, before striking another CEM, producing a “stop” signal. The time between the start and stop signals is the time-of-flight for the ion. The modular design of the spectrometer allows one to modify the length of the ion flight path. The kinetic energy of 50 keV and 25 keV incident alpha particles has been measured for various targets, resulting in reasonable agreement with predicted values. Preliminary studies indicate that the count rate of the CEM detectors decreases as their temperatures increase; current work focuses on alleviating this problem to enable reproducible quantitative analysis of thin films and surfaces.   

Intensity Distribution along a Partially Obstructed Axicon Focal Line

Bessel beams, typically produced using axicons, are used in the generation of plasma waveguides and for laser machining, but these applications can involve obstructions, such as gas nozzles, that block part of the beam. This distorts the beam and reduces the peak intensity along the focal line (along z). We investigated, with experiment and propagation simulation, the intensity distribution of an obstructed Bessel beam. In the experiments, a 2.5cm diameter laser beam was focused by a transmissive axicon and blocked by obstructions of varying cross sectional profiles and lengths. The propagation path-dependent intensity profile was constructed by imaging it all along z. The images were then compared to a 3-D beam propagation simulation of the same system. Plasma waveguides up to 10 cm in length were then generated in the same geometry and the z-dependent peak electron density was compared to the z-dependent intensity profile.   

Thermionic Emission Enhanced by Ion Trapping Beyond the Space-Charge Current Limitation

Recent one-dimensional simulations of planar plasma sheaths revealed how surface electron emission and collisions cause transitions between classical, space-charge limited and inverse sheath regimes [1]. However, multidimensional effects of strongly emitting surfaces on plasmas with collisions remained unexplored by simulations. We developed a novel 2D-2V continuum kinetic code to study the sheath physics, current flow and potential distributions in various configurations including floating and biased emissive probes, filament discharges, and nonuniformly emitting surfaces. The simulations provide an improved understanding of the I-V traces of emissive probes and indicate that strongly emitting probes float above the plasma potential. We found that even small negatively biased cathodes such as filaments can restructure the plasma to an inverse mode where ions are globally confined. Also, we report a previously unrecognized process by which trapped ions in the virtual cathode around a small hot cathode can raise the current flow well beyond the maximum predicted by collisionless space-charge limited sheath models. [1] Johnson and Campanell, Plasma Phys. Rep. 45, 69 (2019)   

PIC Simulations of Multipole Plasma Trap Diagnostics and Loading Methods

The multipole plasma trap program at the UAA Plasma Lab investigates confining quasineutral plasma using RF multipole fields. The ability to load the trap with the desired distribution of particles is an important area of study, and methods for doing so are investigated here via 2D and 3D PIC simulation. These can include electron beam ionization of neutral gas puffed into the trap, thermionic emission of electrons or ions from filaments near the trap boundary, or channeling of plasma into the trap using a 2D linear RF multipole. Diagnosing the trapped plasma is also a key part of the program, and further PIC simulations of insertion of mechanical probes during trap operation will be presented, as will means of collecting particles at the trap boundary at the termination of trapping.   

Electrical and Mechanical Design of Electrodes and RF System for a Multipole Plasma Trap

A mechanical design of copper electrodes and in-vacuum structure for a 32-pole spherical multipole plasma trap of radius 25-cm is presented. The trap will be installed in a cylindrical stainless steel ultrahigh vacuum chamber at the UAA Plasma Lab, and it can be located along the cylindrical axis for optimization with respect to ports and diagnostic sight lines, as well as plasma and beam sources outside the trap that will load it with particles. The electrical connections, RF power feedthroughs, and external RF hardware needed to drive the trap at frequencies from 10-250 MHz, and RF voltages from 100-1250 V will be illustrated as well. Computer modeling of the RF electrical environment is conducted, and performance of the trap over the desired frequency and voltage range is predicted and discussed.   

Electrostatic Potential Map for ALPHA's Penning-Malmberg Traps

Composed of a positron and an antiproton bound together, antihydrogen is the antimatter counterpart of hydrogen. According to the charge, parity, and time reversal (CPT) symmetry theorem, hydrogen and antihydrogen must have the same energy levels, mass, and net charge. Finding CPT violation would be problematic for our current understanding of physics described by the Standard Model, but it would help explain the mysterious matter-antimatter asymmetry in the universe. Because of antihydrogen's neutrality and correspondence with the hydrogen atom, it is a useful system for investigation of possible CPT violation. In the ALPHA experiment, antihydrogen is produced by first confining antiproton and positron plasmas at cryogenic temperatures and then mixing them. The plasmas sit in the potential wells produced by stacks of hollow cylindrical electrodes also known as Penning-Malmberg traps. By changing the voltages applied to each electrode, we can move and tailor the plasmas. Precise modeling of the potential produced by the electrodes is crucial for manipulating such plasmas. This is achieved by numerically solving the Laplace equation for each of our trap geometries and displaying it in LabVIEW.   

SECAR: The Separator for Capture Reactions in Nuclear Astrophysics

Knowledge of the reaction rates of proton and alpha capture reactions that take place in the high temperature and density plasma of stellar explosions (e.g., X-Ray Bursts, Novae, etc.) is crucial to understanding the mechanisms behind those explosions and the nucleosynthesis at those sites. The SEparator for CApture Reactions (SECAR) is a recoil separator that will be dedicated to measure the reaction rates of astrophysically relevant capture reactions on unstable isotopes of mass 15 to 65. SECAR is currently under construction at the National Superconducting Laboratory (NSCL) and the Facility for Rare Isotope Beams (FRIB). It consists of 8 dipoles, 15 quadrupoles, 3 hexapoles,1 octopole and 2 Wien filters with stringent performance conditions. This presentation will focus on the tools used to optimize beam transport. The magnet acceptance procedure including testing for magnetic field reproducibility, will also be presented.   

Helium Targets for Low-Energy Deuteron Bombardment

The $^{\mathrm{3}}$He(d,p)$\alpha $ reaction can produce protons with energies in excess of 20 MeV at deuteron bombarding energies of 3 MeV. This makes it a useful accelerator-based reaction for calibrating CR-39 plastic detectors with high energy protons. Helium targets are most frequently made via ion implantation. This approach confines the Helium in the inner atomic structure of a thin Palladium getter. The getter is produced by evaporating Pd at 2963 $^{\circ}$C on a glass slide treated in a releasing agent and carbon substrate. The 4 $\mu$m thickness film is then placed in a pure Helium environment and heated to 300 $^{\circ}$C for 4 hours. The targets were bombarded with 3 MeV protons generated by SUNY Geneseo's 1.7 MV Pelletron Accelerator. Analysis of the elastically scattered Helium ion was used to determine the concentration of Helium as a function of the beam heating and vacuum chamber evaporation.   

Radioactive Decay Measurements of 41Ar for SLIC

The short lived isotope-counting system (SLIC) being built for the OMEGA laser facility at LLE requires gaseous radioisotopes for calibration purposes. Using a Plutonium-Beryllium (Pu-Be) source at SUNY Geneseo, 41Ar was made by capturing thermal neutrons via the 40Ar(n,gamma) reaction. Once activated, 41Ar beta decays to produce an electron with an endpoint energy of 1.198 MeV. The daughter product is found to be in the second excited state of 41K 99.1% of the time. This promptly decays to the ground state and emits a 1.293 MeV gamma ray. To accurately measure the beta activity of 41Ar for SLIC calibrations, the Gamma-X counting system at Geneseo has been repurposed as a high precision counting station. Gamma-X is composed of 3 orthogonal pairs of Thallium doped NaI detectors surrounding a central cubic counting region with sides of 8 cm. Each of the six detectors is shielded in 11.5 cm of lead and clad in aluminum to reduce background radiation. The calibration was performed by integrating the counts in the 1.293 MeV gamma peak. Measuring the decay curve of the peak counts confirms the origin of the peak. The radioactive 41Ar gas will then be used as an electron calibration source for the SLIC system used in ICF and HEDP nuclear reaction studies.   

Radial Basis Functions as Generators of the Inviscid Burger's Equation

A perennial struggle in the world of interpolation is accurately capturing steep gradients and discontinuities without nonphysical oscillations such as the Gibbs phenomenon. Radial basis functions are a relatively new tool for solving partial differential equations that show great promise due to their ability to work mesh-free and capability to be generalized to multiple dimensions [Sara, Applied Numerical Mathematics 2005]. In this study, we utilize radial basis functions (RBFs) to construct nodal radial basis functions (NRBFs), functions that are one at one center and zero at all other centers. We then use these NRBFs as a basis to solve the inviscid 1D Burger's equation which is known for developing shocks. The goal of this study is to improve shock capturing capabilities in implicit magnetohydrodynamics code.   

Detection of \textgreater 100 keV electron and ion emission from 10 kJ Dense Plasma Focus

A dense plasma focus (DPF) is an intense source of neutrons and x-rays [1]. Ion and electron beams generated by the device along its central axis during the collapse phase of the plasma are of interest since the accelerated ions are believed to contribute to the neutron production in these devices. Furthermore, 100 keV ions are of particular interest since they exceed the energy threshold required for fusion reactions. We report on the detection of 100 keV electrons and ions from the particle beams emitted by a recently-constructed 10 kJ Mather-type DPF. For the ion beam diagnostic, an avalanche photodiode (APD) is positioned opposite the anode. For the electron beam diagnostic, a similar diagnostic setup, with a different APD model, is used with the polarity of the DPF reversed.~~~ \newline [1] M. Krishnan, IEEE Transactions on Plasma Science \textbf{40} , 3189-3221 (2012).   

Charging of aggregates in a plasma with ion flow

In dusty plasmas spherical dust grains with radii on the order of $\mu$ms stick together to form aggregates. The aggregates collect ions and electrons from the surrounding plasma, and reach a stable equilibrium charge when the net current to the surface is zero. A previous numerical model, OML\_LOS, calculated the charge distribution on the aggregate by dividing the surface into patches and calculating the electron and ion currents incident on each patch using Orbital Motion-Limited (OML) theory. The currents are adjusted by only allowing electrons or ions to hit the patch along open Lines-of-Sight (LOS). It is assumed in this model that the electrons and ions are isotropically distributed and that the trajectories are approximately straight line paths. Here we present a new numerical model for calculating aggregate charge in a flowing plasma. The electron current is calculated using the same method as before, but the dynamics of the ions are calculated explicitly, and the ion current is calculated from ion collisions on the dust surface. Results of this simulation are compared to those from OML\_LOS. While the overall charge is found to be in good agreement, the charge distribution differs with changing ion flow velocities, affecting the resultant dynamics of the dust grains.   

Cooling Electrons through Resonant Mode-Mode Coupling

Low temperature plasma physics is of importance to antimatter research, where cyclotron cooling of positrons brings energetic antimatter to antiatom-creation temperatures. Resonant cavity cooling, or cooling of a nonneutral plasma by coupling the radiation field with the electromagnetic modes inside a trap cavity, is a useful technique to cool plasmas to wall temperatures (\textasciitilde 10K) but may be difficult to perform due to plasma location or trap geometry. Thus, understanding the effectiveness of mode-mode coupling in plasmas is essential---by coupling an easily cooled plasma to a mode, and the mode to another mode or plasma, a previously warm plasma may be cooled. We intend to determine if this methodology is possible using the Berkeley electron trap's high-resonance cavities. Based off the results, using cavities or resonating circuits across electrodes may be used in conjunction with or in lieu of collisional cooling to obtain very cold plasmas. This may help to increase the production rate of testable antihydrogen in collaborations such as ALPHA at CERN, and lead to extreme precision on fundamental symmetry tests.   

Non-Linear Plasma Wave Decay to Longer Wavelengths

We measure the decay of plasma waves to longer wavelengths for low phase velocity Electron Acoustic Waves (EAWs). These EAWs are kinetic waves which exist in the low frequency branch of electrostatic plasma waves in neutralized, pure electron and pure ion plasmas. At small amplitudes, EAWs have a phase velocity $v_{ph} \simeq 1.4\bar{v}$ and are strongly Landau damped. At larger amplitudes, EAWs nonlinearly trap particles near $v_{ph}$, hence flattening the distribution function, turning off the effects of Landau damping. We conduct experiments with pure electron plasmas in a Penning-Malmberg trap. To excite EAWs we use a long burst ($\sim$100 cycles) that gently modifies the velocity distribution function of the particles until the desired flat spot is achieved. We measure the decay of the standing plasma wave with $k_z=m_z\pi/L_p$, where $L_p$ is the length of the plasma, for $m_z=2 \rightarrow m_z=1$. There exists an amplitude threshold for the $m_z=2$ wave above which we observe phase locked exponential growth of the $m_z=1$ wave at frequency $f_1=f_2/2$.   

The Role of Ionization versus Transport in Setting Plasma Density Profiles in LAPD

In this paper we study the effects of neutral density variations and turbulence upon the electron density profile on LAPD. Both magnetically confined plasmas for fusion applications as well as astro-physical plasmas have regions that are a mixture of plasma and neutral interactions. LAPD allows us to do experiments to address how the plasma dynamics vary with various neutral pressures and power. In short linear devices, 1D theory gives a good approximation for the plasma density and temperature. Conforming to this model, we do see the general trends predicted such as temperature being set by ionization and therefore generally decreasing with increasing neutral pressure and that density is set by increasing discharge power. In this paper, we will compare the results against the 1D theory and investigate the changes in turbulence and particle flux using probe measurements. Finally, we will expand the 1D theory to include the measured radial transport effects and investigate whether they improve the matches to experimental profile measurements.   

Full Wave Simulations of Alfven Waves in the Large Plasma Device

A full wave solver is used to simulate the propagation of shear Alfven waves in the Large Plasma Device (LAPD). The Petra-M code is used to directly solve Maxwell’s equations with realistic antenna and experimental geometry, that is, spatially varying density and magnetic field under the cold plasma approximation. Petra-M is a finite element analysis software developed using the MFEM partial differential equation solver library. Simulations of the LAPD were done to investigate antenna coupling, propagation of shear waves into axial gradients of the Alfven speed, and generation and propagation of shear waves in multi-ion species plasmas.   

Monitoring oxygen levels in the~OMEGA~nTOF scintillators using cosmic ray muons

HEDP and ICF facilities measure neutron energies using a time of flight method, where the laser pulse is used as the start signal and a xylene scintillator is used as the stop signal. To improve timing performance, the scintillator liquid is oxygenated. This reduces the light production of the scintillator and subsequently decreases the scintillation decay time. The timing characteristics of the detector degrade over time as oxygen diffuses from the scintillator ultimately reducing the energy resolution of the detector. A real-time in-situ monitoring system using cosmic ray muons to determine oxygen concentration is being developed at SUNY Geneseo. The method uses a vertical stack of two EJ200 plastic scintillators with an oxygenated xylene detector placed between them.~ As cosmic ray muons pass through the stack of three collinear detectors, a triple coincidence is formed in the electronics. The coincidence confirms that the pulse was created by a muon.~The xylene muon signals are recorded, fit with a modified Gaussian and the fit parameters are analyzed. This analysis is a good indicator of the oxygen concentration.~The process is continuous allowing for a record of the oxygen concentration as a function of time and helps to determine when to re-oxygenate the xylene detector.   

Inertial Confinement Fusion as a Tool to Study Fundamental Nuclear Science

Inertial confinement fusion may be used to make fundamental nuclear science measurements of low-energy light-ion cross sections also of interest in astrophysics and fusion research. The feasibility of collecting and counting the beta decay of the reaction products (half-life 20 ms to 20 s) in the expanding neutral gas after the ICF shot is being studied using a special vacuum system that allows gas to be released, trapped, and counted in-situ using different techniques. Initial experiments use a turbopump to trap the gas in the foreline, where it can be counted by a 4$\pi $ phoswich beta detector. The construction of this detector and tests using $^{\mathrm{41}}$Ar gas produced via the $^{\mathrm{40}}$Ar(d,p)$^{\mathrm{41}}$Ar reaction will be described, as well as an OMEGA laser ride-along experiment to measure background rates from milliseconds to seconds after the laser shot. Funded in part by a grant from the DOE through the Laboratory for Laser Energetics, and by SUNY Geneseo and Houghton College.   

Categorization of Surface Damage by Laser Ablation to Material Targets as a Proxy for Plasma Exposure Erosion Using Digital Holography

In situ measurements of the accumulating erosion or damage on Plasma Facing Components (PFCs)- essential to the development of a viable magnetic fusion device-are not possible with conventional techniques. Using Laser Induced Breakdown Spectroscopy (LIBS) laser and Digital Holography (DH) under development at Oak Ridge National Lab, it is possible to use LIBs to simulate plasma-eroded samples, and to measure the damage with DH. The LIBS system has been used for sample preparation to create craters of various sizes in material targets by varying the energy of each laser pulse and the number of pulses. Target measurements were obtained by both confocal microscopy and DH. A categorization of the ablation damage derived from the tests will be shown. This categorization will provide guidance for future experiments with the eventual goal of making in situ DH measurements of PFC surface erosion.   

Radiation Hydrodynamics Simulations of Radiative Shear Experiments at the National Ignition Facility

The Shock/Shear platform was developed at LANL to study turbulent mixing in high-energy-density systems. By using a radiative shock, we seek to develop a similar experiment, which explores effects of a radiation on the developing structure of the experiment. The shock tube containing a solid plastic ablator and various types of foam is irradiated by halfraum that will drive either a radiative shock or adiabatic shock into the foam material. The radiation hydrodynamic code, Hyades, was used to scope the experiment. We show the results of a parameter study to determine an optimal experiment design by varying the foam material (CRF and SiO2), the foam density, and ablator thickness. Our simulations provide plasma parameters under which a successful experiment is possible.   

Measurements of Global Dynamics and Shock Structures in Centimeter-Scale Plasma Jets and Bubbles*

Recent experiments on PBEX (Plasma Bubble Expansion eXperiment), conducted at the University of New Mexico's HelCat (Helicon-Cathode) linear plasma device, have focused on studying the global dynamics, as well as fluid instabilities in plasma jets and bubbles. These plasmas, which exist on centimeter spatial scales and microsecond timescales, can be launched into steady-state background magnetic fields and magnetized plasmas, which cause stabilization of the kink instabilities in the jets, and the formation of Magneto-Rayleigh Taylor instabilities as well as double shock structures and the leading edge of the plasma bubble. Additionally, two-dimensional magnetized shock structures are being studied at the intersection of supersonic plasma jets with solid magnetized objects. Experiment setup and measurements using fast framing cameras and magnetic probes to study the dynamics of the bubbles and jets will be presented.   

Optimization of laser-driven ion acceleration from micro-structured targets by PIC simulations including ionization processes

The development of laser technology has enabled the use of high laser intensities (\textgreater 10$^{\mathrm{21}}$ W/cm$^{\mathrm{2}})$ to enhance ion acceleration. With the addition of micro-structure targets (tube, pillar) at the target film front-side, accelerated ion energy increases with the laser self-focusing as a result of structure guiding. However, this acceleration is limited by the structure-preserving time since the irradiated laser field is shattered after the plasma expansion of the front structures. To find the optimized parameter for the ion acceleration, we calculated the laser interaction with the micro-structured target by using the Particle-In-Cell (PIC) code EPIC, which includes field and impact ionization processes. This modeling showed the detailed acceleration mechanism and parameter dependence of the accelerated ion energy on the structure size ($\mu $m) and laser pulse width (fs).   

Focal Fluctuations in the Hundred Terawatt Thomson Laser Plasma Accelerator at BELLA

Fast pointing jitter fluctuations in the focal point of high power laser systems can be detrimental for precision experiments and applications especially where more than one beam is involved.\^{A}  Thomson scattering experiments on narrow energy spread MeV photon beams, with applications including nuclear nonproliferation, utilize two high power lasers with 2.7 and 0.6 J respectively (on target) at 5 Hz and \^{a}\textasciiperthousand \textyen 40 fs. Focal fluctuations are seen at $+$/- 10 \^{A}\textmu m (peak to valley) and 4 \^{A}\textmu m RMS on a spot size of 20 \^{A}\textmu m. We have used a kHz co-propagating laser to look at the fluctuation frequencies of both the electron drive laser and the scatter laser. Fluctuations caused by building and optic vibrations are observed in the 10 - 200 Hz range. This supports\^{A}  identification of pointing jitter sources in the system, the correlation of both, and to inform future plans to actively stabilize the lasers.   

Femtosecond Pulse Length Diagnostics for the BELLA Hundred-Terawatt Thomson Laser

This year, the Hundred-Terawatt Thomson (HTT) group at the BELLA Center has commissioned a 100TW, 3.8J laser system delivering 38fs pulses. This laser system is used to drive a laser-plasma accelerator (LPA), which is designed to interact with a separate scatter laser pulse to create quasimonoenergetic MeV gamma beams with energies adjustable from 1 to 9 MeV. This poster presents motivations, efforts, and the results of creating real-time laser pulse diagnostics by an internally-constructed single-shot autocorrelator, as well as some of the systematic and methodological approaches to the resolution of fluctuating pulse duration issues.   

Radiation hydrodynamics simulations of shock imaging with a betatron x-ray source at BELLA

The feasibility of high-resolution imaging of the evolution of high-energy-density hydrodynamic experiments using new laser-plasma accelerator radiation sources at the BELLA Laser is studied using CRASH, a radiation hydrodynamic simulation code. The BELLA facility features a Joule-class, femtosecond laser, which can produce a brilliant high-flux betatron x-ray source with 2--3 $\mu $m spot, well-suited to probe hydrodynamic instability experiments. CRASH simulations show that the dynamics produced by the 1 J laser with a 200 ps pulse length in a \textasciitilde 40 $\mu $m spot size (irradiance of 4e14 W cm$^{\mathrm{-2}})$ can launch a shock in a water stream. Changes in the phase of the x-ray beam in the material are to be recorded, allowing for greater sensitivity to small density variations compared to measurements of amplitude. Synthetic radiographs from a 3D simulation are used to illustrate the nature of the shock front development. Simulations were conducted across a range of accessible backlight energies, of which the 4-keV result is the most useful. The results from these simulations demonstrate the applicability of the BELLA laser to diagnose shock waves in high-energy-density systems.   

Ablation of Be$^{\mathrm{+}}$ to load a Penning trap for Antihydrogen formation

Antihydrogen, the antimatter counterpart of hydrogen, is an exciting system for testing fundamental symmetries such a CPT (Charge, Parity and Time) and the weak equivalence principle. The ALPHA collaboration has in recent years made the first precision measurements of both the ground state hyperfine splitting and the ground (1S) to first excited stated (2S) two photon transition in antihydrogen. In addition, ALPHA has recently expanded its discovery potential by adding an apparatus allowing for direct tests of the gravitational acceleration of antihydrogen, thus testing the weak equivalence principle. These initial measurements have benefitted from increased trapping rates of antihydrogen achieved principally by using colder positrons. We plan to improve the trapping rates by using laser-cooled Be$^{\mathrm{+}}$ to sympathetically cool the positrons. However, a significant challenge has been how to load Be$^{\mathrm{+}}$ into the Penning trap used for Antihydrogen formation without jeopardizing the antihydrogen formation and trapping. Due to the stringent geometrical constraints we have developed an ablation source that directly produce the Be$^{\mathrm{+}}$ ions. We present thresholds for production of Be$^{\mathrm{+}}$ and Be$^{\mathrm{++}}$, as well as the energy distribution of the ablated ions and discuss the implications for loading a trap.   

Hairpin Lock-in Circuit for Real-Time Plasma Density Measurements

We describe a circuit which allows a hairpin resonator probe to measure the plasma density in real time. Recent work has demonstrated that hairpin probes can be implemented cheaply and without too much difficulty using commercial off the shelf microwave electronics (see X. Fan, also at this conference). Using such a probe to diagnose the density has typically involved sweeping over a band of frequencies that includes the resonant peak, then identifying the resonance and deriving the corresponding density for that sweep. The present work adapts a lock-in type of circuit, which is commonly used to actively maintain resonance in high precision lasers, to find and lock onto the hairpin’s resonance in real-time. An error signal is generated by introducing a small oscillation to the input of a voltage-controlled oscillator, and monitoring the output of the mixer that detects the transmitted signal from the probe. The response is then fed into a PID controller to maintain the control voltage at resonance. One goal of the current work is to shorten the time response of the lock-in circuit to 1 us or less. This would be sufficiently fast to allow the hairpin probe to be used as a diagnostic of the plasma density during an Alfven wave in the Large Plasma Device at UCLA.   

Simulations of Nozzle Gas Flow and Gas-Puff Z-Pinch Implosions with Magnetic Fields in the Weizmann Z-Pinch

Till recently, measurements of the magnetic field in gas-puff z-pinch implosions were limited to low density and temperatures typically found at very early times and outside the pinch radius ( $r$ $\ge $9 mm and $t$ $\le -$90 ns). However, recent, more accurate measurements at higher densities and temperatures at various R and Z-locations on the generator at the Weizmann Institute of Science (WIS) have yielded information close to stagnation and beyond. These measurements seem to be inconsistent with earlier 2D radiation-magneto-hydrodynamics simulations using MACH2-TCRE as well as simple snowplow models when using the inductive current notch, pinch length the pinch radius. It is shown that some of these inconsistencies can be resolved by simulating the entire gap of 18mm. Simulations of magnetic field evolution using the 2D radiation-magneto-hydrodynamic code, MACH2-TCRE are presented. Comparisons are made with the measured data of magnetic field and radius. It is shown that simulating the nozzle geometry and outflow significantly improves the comparison between the measurements and the pinch simulations.   

Simulation of Magnetically Driven HEDP/ICF Experiments with a Lagrangian/ALE Code

Magnetic drive has recently received a great deal of attention in the context of high energy density physics (HDEP) as well as inertial confinement fusion (ICF). Here, stored electrical energy in converted into mega-Gauss level magnetic fields that accelerate a conductor that, in turn, drives materials to HEDP regimes or compresses fusion fuel. Most prevalent are cylindrical Z-pinch configurations where a pulsed, axial current generates an azimuthal field via Lorentz forces. The system may or may not be complemented by a static axial field to aid in confinement. Another configuration utilizes a planar geometry for either shocked or quasi-isentropic loading. In order to study the performance of these emerging designs, sophisticated computational tools are required. At the very least, a single-fluid, resistive, magneto-hydrodynamics (MHD) model must be implemented. Shown here are recent developments and applications of the Lagrangian/ALE FLAG code to such problems. Through verification test problems, an explicit, ideal MHD algorithm is shown to be second order on smooth test problems and first-order on problems involving shock discontinuities. The operator-split, implicit, resistive diffusion algorithm is shown to be second-order on arbitrary polyhedral/polygonal meshes. Finally, results of simulation of relevant Z-pinch and planer configurations for HEDP and ICF applications are shown.   

Magnetohydrodynamic Calculations of Resistively Exploding Aluminum Rods

The magnetic field diffusion into a conductor driven by intense pulsed power is of interest for current-driven instabilities such as the electrothermal instability (ETI). ETI is thought to develop on the surface of a conductor due to uneven ohmic heating and variation in resistivity that follows the spatial distribution of the current density as impacted by surface roughness and inclusions. The magnetic field also diffuses radially inward to the center of a cylindrical rod in a nonlinear magnetic diffusion wave (NDW)—diffusing more rapidly into the conductor interior because of resistivity increases driven by rising temperatures. The NDW interplays with the inward shock wave caused by the magnetic force and ejection of low-density material from the conductor surface. The ASC Magnetohydrodynamic (MHD) code FLAG developed by Los Alamos National Lab was used to numerically calculate the radial magnetic field diffusion within an exploding rod, in the skinned current regime, including hydrodynamic effects.   

Hybrid Particle-in-Cell Modeling of Dense Plasma Foci

A dense plasma focus (DPF) device drives current through a set of coaxial electrodes to assemble plasma inside the device and then implode that plasma on axis to form a Z-pinch. This implosion drives instabilities that generate strong electric fields, which produces a short intense pulse of x-rays, high-energy (\textgreater 100 keV) electrons and ions, if using fusion-reactant ions (e.g. D, T), will generate neutrons. As well as being dependent on a the generation of high-energy ion ``beam'', neutron production relies on the formation of a long, high-density, magnetized ``plasma target'' that the ions will pass through. Generally, such simulations have been performed either a) using single-fluid magnetohydrodynamic codes, which do not intrinsically capture the formation of ion beams, or b) using fully-kinetic simulations that capture the beam acceleration, but can be computationally prohibitive. Here we will present a middle ground between these two extremes, by using a hybrid model within the framework of the PIC code Chicago [Thoma \textit{et al}. PoP \textbf{24}, 062707 (2017)]. This method follows the motion of (fluid or kinetic) ions and models electrons using a magnetized Ohm's law. Prepared by LLNL under Contract DE-AC52-07NA27344.   

\textbf{Simulating the Filamentation Instability in Dense Plasma Focus}

A dense plasma focus (DPF) is an open-ended coaxial plasma gun designed to accelerate a plasma discharge down the length of the coax terminating in a Z-pinch configuration on axis. The plasma on axis goes rapidly unstable and can produce a short, intense pulse of neutrons and x-rays when deuterium is used as the working gas. The neutron yield scales strongly with the pinch current. A poor breakdown/lift-off of the plasma along the insulator can lead to current restrikes, diverting current away from the pinch and decreasing the yield. One possible cause of a poor sweep-up of the gas along the insulator is the electro-thermal instability, which can cause the plasma to breakup into individual filaments during the breakdown/lift-off stage. Plasma filamentation has recently been observed in experiments a small-scale (100J) DPF at LLNL. In this work, the filamentation instability during the lift-off stage of a DPF is studied using an extended-magnetohydrodynamic (MHD) model. The filamentation instability wavevector is along the magnetic field. 2D simulations in the R- plane are presented. The results are compared with data from the aforementioned experiments.   

Experimental Results from the LLNL Megajoule class Dense Plasma Focus MJOLNIR

A dense plasma focus (DPF) is a relatively compact coaxial plasma gun which completes its discharge as a Z-pinch. These devices have been designed to operate at a variety of scales in order to produce short ($<$100 ns) pulses of ions, X-rays, or neutrons. LLNL has recently constructed and brought into operation a new device, the MJOLNIR (MegaJOuLe Neutron Imaging Radiography) DPF which is designed for radiography and high yield operations. This device has been commissioned over the last year and has achieved neutron yields up to 3E11 neutrons/pulse at 2.2 MA pinch current while operating at up to 1 MJ of stored energy. MJOLNIR is equipped with a wide range of diagnostics, including activation foils, neutron time of flight detectors, a fast framing camera, optical light gates, and a time-gated neutron and x-ray imager. In this presentation, we will describe the device operation and recent results. Preliminary x-ray and neutron images will be presented as well.   

Simulations of the MJOLNIR Dense Plasma Focus

Dense plasma focus (DPF) Z-pinches are compact pulse power driven devices with coaxial electrodes.~ The discharge of a DPF consists of three distinct phases: generation of a plasma sheath, a plasma rail gun phase where the sheath is accelerated down the electrodes, and finally an implosion phase where the plasma stagnates into a z-pinch geometry.~ During the z-pinch phase, DPFs can produce MeV ion beams, x-rays and neutrons.~ The MegaJOuLe Neutron Imaging Radiography (MJOLNIR) DPF was brought online at the end of 2018 and currently delivers greater than 2 MA to the load.~ Kinetic simulations using the code Chicago (C. Thoma, Phys. Plasmas 24, 062707 (2017)) and results from a reduced physics model will be presented for shots from the commissioning campaign. LLNL-ABS-780277   

Electron Beam Studies and X-ray Spectroscopy of Dense Plasma Focus Experiments.

The study of electron beam generation in a dense plasma focus (DPF) can yield insight into the physical mechanisms that lead to the formation of electron beams in pinched plasmas. A detailed understanding of these mechanisms may enable the production of a high-intensity x-ray source for various applications. We plan to use plasma polarization spectroscopy (PPS) to measure the degree of polarization of several x-ray spectral lines emitted by a DPF driven by NRL's Hawk pulsed-power generator. Initial experiments will focus on diagnosing the plasma electron temperature in DPF experiments doped with Ar gas. This data will be used to validate a finite volume MHD code that calculated the plasma temperature and density of a Hawk shot doped with Ar gas. To measure the degree of polarization experimentally, two spectrometers will be configured with identical crystals that yield a Bragg angle as close to 45$^{\circ }$ as possible. The measured polarization will be compared with atomic and radiation calculations in order to determine the beam energy and infer the strength of the accelerating fields in the DPF. The development of a magnetic sublevel kinetics code, which will complement future spectropolarimetry studies, is also discussed.   

Spectroscopic Investigation of a Dense Plasma Focus with Local Plasma and Gas Injection

Charged particle acceleration is being investigated in a dense plasma focus (DPF) driven by the Hawk pulsed-power generator at the Naval Research Laboratory and initialized using local injection of neutral gas and plasma into a vacuum chamber, rather than a conventional neutral gas fill. A neutron yield of 5E10 at a peak current of 670 kA has been measured using rhodium foil activation counters, significantly above the yield expected based on scaling with current from conventional DPFs. A suite of spectroscopic diagnostics, including a high resolution, fiber-coupled, imaging spectrograph, is used to characterize the plasma, both prior to and during the DPF current pulse.   

Gamma Reaction History on Sandia's Z Machine

A Gamma Reaction History (GRH) diagnostic has been fielded successfully at the OMEGA laser facility and the NIF for several years to measure fusion reaction history in ICF experiments. Recently, the OMEGA GRH was removed and is currently being modified to field on Sandia's Z machine to demonstrate the ability to measure gamma ray reaction history. The introduction of tritium into the z-pinch experiments provides the necessary gammas for analysis of the reaction history. We will outline the proposed experiments which include mixtures of deuterium (99{\%}) and tritium (1{\%}) as well as deuterium (50{\%}) and helium 3 (50{\%}) with the ultimate goal of diagnosing the evolution of the fusion plasma on Z. D3He also has a steep dependence on ion temperature, making the reactivity ratio between DT and D3He a sensitive ion temperature indicator. D3He is also highly sensitive to non-thermal beam reactions and can provide an indication of the degree of thermalization of the fusion plasmas. X-ray backgrounds are currently being assessed with Aerogel Cherenkov Detectors (ACD) to determine the feasibility of measuring DT and D3He gammas above the background.   

Z-pinch experiments on the UCSD LTD generator.

Linear Transformer Drivers (LTDs) are based on the state of the art pulsed power generator technology, featuring small footprint, high energy coupling to high energy density loads, low inductance, multi-stage modularity, and potentially high repetition rate [1]. A LTD generator capable of producing up to 1 MA in 150 ns has recently been assembled at UCSD based on a prototype from Sandia National Laboratories [2]. We present the first results from Z-pinch experiments conducted on this machine in both wire arrays and gas puff configurations. The experimental data include machine performance diagnostics, such as monitors for all the spark gap switches and load current probes, and plasma diagnostics such as XUV time-gated and time-integrated images, filtered X-ray photodetectors, time-gated and time-integrated spectroscopy, and laser probing. \begin{enumerate} \item R. D. McBride et al., IEEE Trans. Plasma Sci. 46, 3928 (2018) \item J. R. Woodworth et al., Phys. Rev. ST Accel. Beams 14, 040401 (2011) \end{enumerate}   

Status Update on the BLUE Linear Transformer Driver (LTD) System at the University of Michigan

BLUE is a 4-cavity linear transformer driver (LTD) system currently being constructed in the University of Michigan’s Plasma, Pulsed Power, and Microwave Lab. The four 10-brick cavities were previously part of the Ursa Minor experiment at Sandia National Laboratories. When fully assembled, the BLUE system should be capable of delivering 8 kJ to a proper load in an 800-kV, 100-ns pulse. Dual 100-kV, 12-kW Spellman power supplies allow a theoretical rep-rate of >1 Hz for high-power microwave experiments. The first prototype cavity has been assembled and single-cavity testing has begun. Of special interest is the selection of a proper charging impedance to permit rep-rated operation while maintaining brick-to-brick isolation during pre-fires. A polycarbonate lid allows operation of the first BLUE cavity as an impedance-matched Marx generator (IMG). The construction status of the BLUE system will be presented in addition to experiments relevant to the advancement of the LTD concept.   

Extending Experimental and Diagnostics Capabilities on the 1-MA, 100-ns MAIZE Pulsed Power Facility

The Z-machine is instrumental in plasma physics research across a range of applications. University-scale z-pinch experiments, such as gas-puff z-pinches, can inform the high-value experiments conducted at Sandia. A gas puff z-pinch requires gas to be puffed into the region between two electrodes, which is then pulsed with a high voltage. The gas is ionized, accelerated, and compressed as the current flows across the electrodes, allowing for study of pinch phenomena including fusion reactions. Fusion is largely the result of micro-pinch instabilities, which are regions of extreme pressures and temperatures within the plasma and are poorly understood. We report on the progress made in developing this system for MAIZE. Additionally, we have revamped switch diagnostics on MAIZE, which consists of a set of 40 capacitor-switch-capacitor “bricks”. Discharging these capacitors is carried out by the breakdown of the switch, resulting in emission of light. Monitoring this light provides information on switch performance. A circuit can be set up that reduces a PMT to a binary digit and six PMTs can then uniquely identify a single pre-firing switch out of 40. Lastly, we report on the development of an LT Spice model for the charging and discharging of the entire MAIZE facility.   

Inductively driven transmission lines: fringe-field-driven devices for powering diagnostic X-ray sources on the Z Pulsed Power Facility

Pulsed-power-driven diagnostic X-ray sources such as X-pinches have long been fielded in series with the load on 1-MA pulsed power facilities. However, the substantially larger load currents and more stringent inductance constraints at the Z Pulsed Power Facility have thus far prevented the fielding of diagnostic X-pinches on Z experiments. Here we introduce the inductively driven transmission line (IDTL) concept, whereby a secondary transmission line is inductively coupled to fringe magnetic fields that are generated in the final power feed on Z. Short-circuit IDTL experiments on Z have demonstrated that 10--200$+$ kA of current can be driven in an IDTL without perturbing the primary load. Given these results, a surrogate IDTL platform has been developed on the 1-MA Mykonos facility to enable rapid X-pinch source development. In this paper, short-circuit IDTL results are presented from both high-current IDTLs that will ultimately be used to power X-pinches as well as low-current IDTLs that serve as self-common-mode-rejecting load current monitors.   

Proof-of-principle of the ion deflectometry for B-field measurements in Z-pinch plasmas.

We have successfully tested the feasibility of the ion deflectometry in deuterium gas-puff MA Z-pinch experiments on GIT-12. In a unique configuration, we employ ion beams, accelerated during a Z-pinch current disruption, for ion imaging technique as a diagnostic tool for B-field measurements in Z-pinch plasma. Pinhole-camera detectors obtain experimental images of the deflected ion beams. Simulations of ion trajectories deflected in B-fields are used to analyze experimental data and show capabilities of this diagnostic method. For the first time, we can study magnetic fields on-axis of the Z-pinch and to estimate a Z-pinch current.   

Current channel evolution in ideal Z pinch for general velocity profiles

Recent observations in gas-puff Z pinches, enabled by novel methods of diagnosing the magnetic field evolution, suggest an unexpected, radially-outward motion of the current channel, while the plasma moves radially-inward [C. Stollberg, Ph.D thesis, Weizmann Institute, 2019]. In this paper, a mechanism that could explain this current evolution is described. We examine the impact of advection on the distribution of current in a cylindrically symmetric plasma. In the case of metric compression, $|v_r| \propto r$, the current enclosed between each plasma fluid element and the axis is conserved, and so the current profile maintains its shape. We show that for more general velocity profiles, this simple behavior quickly breaks down, allowing for non-conservation of current in a compressing conductor, rapid redistribution of the current density, and even for the formation of reverse currents. In particular, a specific inward radial velocity profile is shown to result in radially-outward motion of the current channel, recovering the surprising current evolution discovered at the Weizmann Institute.   

Electrostatic gyrokinetic simulations of m=0 mode in sheared flow Z-pinch plasmas

Stability properties of axisymmetric sheared flow Z-pinch plasmas are studied by making use of the gyrokinetic approximation in the long-wavelength limit. Numerical simulations are performed by the high-order finite-volume electrostatic code COGENT for the parameters characteristic of the FuZE experiment. Linear growth rate of the axisymmetric m=0 sausage mode is found as a function of wave number $k_z$ for different values of shear flow velocity. The reduction of the growth rate and stabilization of high-$k$ modes by the sheared flow are observed. The results are elucidated by making use of a local dispersion relation analysis, and the importance of finite Larmor radius effects is shown. In addition, the results are compared to ones provided by ideal MHD models and fully kinetic PIC simulations. A good agreement with PIC results is demonstrated, in particular, for high-$k$ part of the spectra where ideal MHD models are unable to produce adequate mode description.   

Computational exploration of the spatiotemporal effects of laser interaction with x-pinches.

We seek to explore the spatial and temporal effects of laser interaction with x-pinches. It has been established that hot spot formation occurs following a neck-cascading process. The eventual hot spot is formed in the region of highest compression (minimum neck diameter). Due to the uncertainty in the cascading phenomena, the exact hot spot location and timing is difficult to predict. Simulations will explore the laser/pinch interaction by varying the timing and power deposition of the laser. This study is motivated by trying to understand x-pinch physics on much shorter time scales, with a precision only made possible by XFEL such as LCLS. The simulations will show how the MEC lasers can control the location and timing of the x-ray burst. The XMHD simulation (PERSEUS) statistically explores the generation of a hot spot by a laser triggered instability using the current profile of a 250kA LTD system (LASSIE).   

Hybrid X-Pinch Optimization

We are planning detailed spectroscopic studies of the X-ray bursts produced by hybrid X-pinches using 20 ps time resolution X-ray streak cameras. The purpose is to investigate whether radiative collapse occurs in the micropinches that produce the X-ray bursts. In order to do that, we want 1 strong X-ray burst from the hybrid X-pinch at a time that is reproducible within $+$/- 1 ns. As a first step, we have optimized Hybrid X-Pinches made of Al, Ag, Mo, and Ti by varying the gap distance between the two conical electrodes, keeping the mass per unit length constant across all the different materials. For all materials, 0.5-1.5 mm gap appears to be satisfactory to assure a single micropinch from a 250-300 kA, 50 ns rise time current pulse on the XP pulsed power generator. We also optimized the timing of the X-ray burst for Ti wire loads, so that more than 50 percent of the shots produced X-rays at a consistent time. Time consistency was achieved by varying the gap distance and changing the wire diameter. It was found that smaller diameter wires with larger electrode gap distances, were more consistent. We are also in the process of expanding this study to include more data points, as well as other load wire materials.   

Millimeter-wave to near-infrared radiometry and collective Thomson scattering for studies of power balance in COBRA gas puff pinch plasmas

Radiometer diagnostics from millimeter-wave to near-infrared bands and collective Thomson scattering diagnostics are being developed in order to characterize radiated power and turbulent density fluctuations in gas puff plasmas in the COBRA accelerator at Cornell University. The purpose of these measurements will be to study the overall power balance in COBRA plasmas under various conditions. An initial millimeter-wave radiometer channel will operate in the 94 GHz range, and three near-infrared channels will operate at 1100, 1310, and 1550 nm. The multiple channels in IR along with an envisioned expansion of the millimeter-wave radiometer to a number of channels covering the 10-300 GHz range will allow for a detailed characterization of emission vs frequency across both the IR and microwave band. The coherent Thomson scattering system will operate at 1064-1550 nm in the Bragg scattering limit, with detection at several scattering angles in order to characterize the evolution of the density fluctuation spectrum in terms of amplitude and wavenumber. Diagnostic system design, data, and results will be presented.   

High-Voltage Solid-State Trigger for HEDP Applications

Eagle Harbor Technologies (EHT), Inc. is developing a solid-state thyratron replacement that can be used to trigger higher voltage spark-gap switches at Sandia and other laboratories. The current trigger generators used at Sandia are marginally reliable and have a long manufacturing and delivery time, and there is concern about the long-term availability of these thyratrons. When measured over short timescales, thyratrons typically have a jitter of a few nanoseconds; but over longer timescales, they can have a much larger drift. Additionally, thyratrons need stable, high-current, low-voltage power sources, have long warm-up times, and require conditioning shots to achieve a stable operating point. In the Phase I program, EHT will develop a first-generation prototype solid-state thyratron replacement, which will be able to produce 20 kV into 50 $\Omega $ with a sub-10 ns rise time and 100 ns e-folding fall time. EHT will present the Phase I program plan and initial results.   

Low inductance high voltage multi-gap gas switch for high repetition rate pulsed power applications

The ability to perform high repetition rate pulsed power experiments depends crucially on several factors including fast switching and fast power supply charging times. We present the design~and characteristics of a switch intended for use in a 10Hz fast dense plasma focus experiment to be conducted at the Air Force Research Laboratory at the Wright-Patterson Air Force Base. More importantly, due to the relatively simple design with low cost for parts, modifications such as changes to the internal gas pressure or the number of electrodes can be easily made to increase the versatility of the switch. Furthermore, we intend to demonstrate how the use of annular electrodes can be a better alternative to the conventional solid disk electrodes by the reduction of inductance from the formation of a cylindrical plasma current carrying sheath and overall switch weight.   

Plasma jets generated by a 1-kJ pulsed-power system

Plasma jets will be generated by using a 1-kJ pulsed-power system to study space sciences, particularly in simulating solar winds. Plasma jets are generated by using conical-wire arrays driven by the pulsed-power system using a parallel-plate capacitor bank. The system consists of twenty 1-uF capacitors. Two capacitors are first connected in series forming a brick. Five bricks are connected in parallel forming a wing. Finally, two wings are connected in parallel and connected to the high-voltage feedthrough at the bottom of the vacuum chamber via parallel-plate transmission lines. Therefore, the total capacitance of the system is 2.5 uF storing 1 kJ of energy when it is charged to 20 kV. One rail-gap switch is used in each wing. Each switch is triggered by a trigger pulse with peak voltage less than -50 kV with a falling speed of -8+-1 kV/ns generated from a 3-stage Marx generator. Discharge of a single wing provides a peak current of 59.2+-0.7 kA with a rise time of 1280+-10 ns with a jitter of 11 ns. We are expecting a total current of ~120 kA with a similar rise time, i.e., a power of ~800 MW, when the system is built in Summer, 2019. Finally, the current output of the pulsed-power system and time-integrated images of plasma jets generated by conical-wire arrays will be shown.   

Improvement of Diagnostics for Measurement of Multi-MeV Ions Produced in Deuterium Gas-Puff Z-Pinch

The investigation of the deuterium gas-puff z-pinch as a source of high energetic ions (\textgreater 40 MeV) is still in progress on the GIT-12 generator (600 kV output voltage, 3 MA current level). The previously used ion diagnostics (3-pinhole system, linear multi-pinhole with five pinholes, beam detectors) were improved for a better description of the ion source, and a better understanding of the ion acceleration mechanism. During the recent campaign in 2019, (i) the obstacles between the ion source and diagnostic were placed, (ii) the array of collimators was used together with beam detectors, and (iii) new type of ring beam detector was installed. The ion diagnostics contained stacks with various absorbers, CR-39 track detectors, and several types of radio-chromic films (HD-V2, EBT-3, FWT-60, XR-QA2). The conclusions based on measured results were supported by numerical simulation of the ion trajectories in z-pinch plasma.   

Formation of Transient Plasmas with Beta and Hall Parameters Simultaneously Greater than Unity

We report results from the head-on merging of two coaxial-gun-formed pre-magnetized plasma jets. This is an exploratory first step toward forming thermal-pressure-dominated plasmas with tangled magnetic fields [1], which may be of interest as a plasma target for magneto-inertial fusion [2] or as a novel platform for laboratory astrophysics studies. In these experiments, we vary the gun current and magnetic flux linking the electrodes to study those parameters' effects on the resulting plasma collision. A Langmuir probe, magnetic probe array, and visible fast-framing camera are used to diagnose the plasma conditions at the plasma-merging region to experimentally infer both the $\beta$ and Hall parameters (assuming $T_e=T_i$). A second experimental campaign is planned to include measurement of $T_i$. The objective is to achieve a transient plasma state where $\beta$ and the Hall parameter $\omega \tau$ (for both electrons and ions) are simultaneously greater than unity. Using the FLASH code, we study the jet-merging process and the compression of the transient plasma state (at higher densities) by a plasma liner. [1] D. D. Ryutov, Fus. Sci. Tech. 56, 1489 (2009). [2] S. C. Hsu and S. J. Langendorf, J. Fusion Energy 38, 182 (2019). LA-UR-19-26020.   

FuZE Compact Fusion Device - Scaling the sheared-flow stabilized pinch to reactor conditions

The University of Washington, Lawrence Livermore National Laboratory, and now Zap Energy Inc, have partnered under ARPA-E to advance the sheared-flow stabilized (SFS) Z-pinch concept and assess its potential for scaling to fusion conditions. The Fusion Z-pinch Experiment (FuZE) expands on UW's ZaP and ZaP-HD SFS devices by employing higher power-handling electrodes, flexible gas injection, and independently-switched capacitor bank modules to provide flexible tailoring of the discharge current and distribution of gas to establish the required plasma flow and pinch current. An extensive set of diagnostics provide key measurements. Experimental campaigns are underway to increase the pinch current, duration of pinch stability, and DD fusion neutron production guided by both fully-kinetic and continuum-based computer simulations. These efforts aim to understand the underlying science of scaling this concept to the pinch current, plasma density, and plasma temperature required for a compact, low-cost fusion reactor.   

Experimental investigation on neutron production in a sheared-flow stabilized Z-pinch (FuZE)

Sustained neutron production has been demonstrated on the Fusion Z-pinch Experiment (FuZE), a sheared-flow-stabilized Z-pinch device.[1] Fusion-relevant plasma parameters, 200 kA plasma current, 1-2 keV ion temperatures and \textgreater 10$^{\mathrm{17}}$ cm$^{\mathrm{-3}}$ densities, have been achieved. Absolute neutron yields of up to 10$^{\mathrm{5}}$ neutrons per discharge are measured. Measurements indicate that neutron production is primarily the result of thermonuclear processes. No obvious beam-target mechanism is observed. To further investigate the origin of detected neutron production, multiple calibrated plastic scintillator detectors, operating in pulse-counting mode, are used to characterize azimuthal directional property of neutron productions at various z-axial positions with respect to the Z-pinch plasma. Temporally- and spatially-resolved neutron production measurements are also conducted to characterize the neutron emission along z-axis. Moreover, multiple detectors are placed at various radial distance to the plasma to further investigate the neutron production properties. Experimental setup will be presented. Physics discussion on the results will be provided in detail. [1] Zhang et al. Phys. Rev. Lett. 122 135001 (2019).   

Axial Silicon Emission and External Magnetic Field Investigation on the Fusion Z-Pinch Experiment (FuZE)

Previous studies on the Fusion Z-Pinch Experiment at the University of Washington (FuZE) have indicated emission lines of silicon associated with neutron production. Here the relationships between silicon emissions and external magnetic fields with both neutron production and plasma pinch current are investigated for the purposes of identifying potential instabilities and characterizing the plasma's neutron production period. Silicon emissions are studied axially along FuZE's compression region to construct a temporally and spatially resolved profile; these emissions imply plasma protrudes from the slotted outer conductor on FuZE and ionizes the silica windows of the vacuum vessel. Magnetic fields are studied adjacent the windows at peak silicon emission locations to consider whether this leakage plasma is current carrying; their magnitudes are compared against simulated 2D magnetic field profiles for FuZE's geometry with no leakage plasma. Silicon emissions appear around the peak pinch current time and increase exponentially until a peak intensity roughly 9 $\mu $s later. Magnetic field estimates at 18 cm off-axis for on-axis 300 kA pinch currents and uniform return currents agree with the measured magnitude of 10-3 T at this location, and furthermore the vector profile suggests significant contributions from unexpected radial currents in addition to the expected plasma column's axial current. Possible theories are developed to explain the presence of silicon emissions with plasma instability and plasma expansion and their relationship with neutron production.   

Control of sheared flow stabilized Z-pinch plasma properties with electrode geometry

The FuZE device produces a 0.3 cm radius by 50 cm long Z-pinch between the end of the inner electrode of a coaxial plasma gun (cathode) and an end wall (anode) 50 cm away. The plasma column is stabilized for thousands of instability growth time by an embedded radially-sheared axial plasma flow. The mechanisms that affect sheared flow are investigated. MACH2 MHD simulations show that abrupt transitions from the coaxial accelerator to the Z-pinch create less favorable flow profiles while gradual transitions promote adiabatic compression and favorable shear. Different coaxial accelerator nose cone geometries are tested and their effects on flow and pinch properties are analyzed. End wall geometries are also tested. The transparency is increased by changing the center hole design to a spoked design. It is found that the end wall influence on the upstream Z-pinch is minimal. The plasma is frozen in the magnetic field, preventing the increased transparency from allowing plasma to escape the assembly region, which acts as a flux conserver. However, plasma can be transiently allowed to exhaust with increased ram pressure. The ram pressure can be increased by changing the input energy, controlled by the bank voltage, and changing the injected density, controlled by the gas valves.   

Interferometric plasma density measurements on the Fusion Z-pinch Experiment FuZE

The Fusion Z-Pinch Experiment (FuZE) is a sheared flow stabilized (SFS) Z-pinch experiment investigating the scaling of SFS Z-pinch plasmas towards fusion conditions. Sustained neutron production has been measured from cylindrical plasmas[1]. As the fusion yield increases, efforts are underway to understand the pinch dynamics. This will require measurements of the plasma density. Density measurements are possible with 2 unique interferometers: A digital holographic interferometer (DHI) and a He-Ne interferometer. The DHI uses a Nd:YAG laser with a digital camera to produce holograms from the plasma assembly region. Digital holograms are numerically reconstructed to obtain the chord-integrated electron density of the compressed plasma. Radial density profiles are reconstructed from these chord-integrated electron density data. The He-Ne Interferometer is a multi-chord (8), heterodyne, quadrature, Mach-Zehnder interferometer. Each chord produces a line-integrated electron density measurement through the plasma. Chord-integrated density and radial density plasma data are presented from FuZE. [1] Y. Zhang et al., PRL 122, 135001 (2019).   

Diagnostic Development for Spatio-Temporal Resolution of a Sheared Flow Stabilized Z-Pinch

The ZaP-HD Flow Z-Pinch Experiment investigates using a tri-axial electrode configuration to increase the current in a sheared flow stabilized Z-pinch. The ZaP machine produces a 50 cm-long flowing hydrogen pinch with a radially sheared axial velocity profile that is stable for up to 60 \textmu s. Conditions within the pinch exceed densities of 2e17 cm$^{\mathrm{-3}}$ and temperatures of 800 eV. A suite of diagnostics is used to measure plasma properties including magnetic field probes, digital holographic interferometry (DHI), and ion-Doppler spectroscopy (IDS). Both the DHI and IDS systems have been expanded to more fully characterize the pinch properties. Initially, the IDS system collected one radially resolved temperature measurement at a single axial location for each plasma pulse. The spectrometer has been coupled to an ultra-fast framing camera to record up to 100 spectra per pulse. This provides the complete evolution of plasma ion temperature over the pinch lifetime. In addition, DHI was limited to a single two-dimensional electron density profile per plasma pulse. The system is being expanded to include a second, perpendicular view of the pinch at the same axial location. These data will be used to reconstruct the three-dimensional electron density along 1.5 cm of the pinch axis.   

Evidence for thermonuclear neutron production on a sheared-flow stabilized (SFS) Z-pinch*.

The Fusion Z-pinch Experiment (FuZE) produces quasi-steady-state neutron emission with yields ranging from 1e4--1e7 for durations ranging from 2--8 us. Spatially-resolved neutron energy spectra are largely isotropic, consistent with thermonuclear fusion. FuZE is a sheared-flow stabilized (SFS) Z-pinch device that establishes a radially-sheared, axial plasma flow to limit growth of MHD instabilities, allowing the pinch to persist for thousands of radial Alfven transit times. In this work we present detailed yield and energy spectra results. Multiple detectors are used to determine the axial extent (34 cm) of the neutron producing region. Neutron energy spectra are determined by reconstructing the energy spectra of recoil protons in fast plastic scintillators. Initial analysis indicates emission is spatially isotropic with an upper limit of 50keV for any axial beam-target reactions. These results are encouraging for scaling of SFS Z-pinches toward reactor conditions. *For USDOE ARPA-E by UW and LLNL under Contract DE-AC52-07NA27344.   

Overview of the FuZE Fusion Z-Pinch Experiment

Closely coupled with computational studies, the FuZE project is investigating the sheared flow stabilized (SFS) Z-pinch as a novel approach to thermonuclear fusion in a compact device. The SFS Z-pinch is immune to the instabilities that plague the conventional Z-pinch yet maintains the same favorable radial scaling. Diagnostic measurements of the plasma equilibrium and stability indicate that in the presence of a sufficiently large flow-shear, gross Z-pinch instabilities are mitigated, and radial force balance is achieved. Fluid and kinetic simulations support the experimental observations. The FuZE device generates stable, 50-cm-long plasma columns that are compressed to small radii (3 mm), producing increases in magnetic field (10 T), density (1e17 /cc), and electron temperature (1 keV) as predicted by adiabatic scaling relations. When operated with deuterium, the plasma reaches fusion conditions as indicated by a sustained neutron production that is consistent with a thermonuclear process. Experimental observations generally agree with theoretical and computational predictions, indicating that sheared flows can indeed stabilize and sustain a Z-pinch equilibrium.   

Scaling of the Sheared-flow Stabilized Z-Pinch toward Reactor Conditions

Zap Energy Inc. (ZEI) is scaling the sheared-flow stabilized (SFS) Z-pinch toward fusion reactor conditions. The UW and LLNL collaborated on the Fusion Z-Pinch Experiment (FuZE), sited at the UW. FuZE has demonstrated long-duration D-D fusion production periods of 8 $\mu$s [Zhang {\em et al}., PRL 2019], thousands of times longer than the 1 ns MHD m=0 (sausage) and m=1 (kink) instability growth times. FuZE has reached 300 kA pinch currents, 1-2 keV ion temperatures, $1-2\times10^{23}$ m$^{-3}$ densities, and neutron yields of $>10^5$ neutrons / pulse (for 20\% D$_2$ / 80\% H$_2$ admixtures). The UW and LLNL are presently upgrading the FuZE capacitor bank power supplies to push to 400 kA pinch currents. ZEI and the UW are teaming to measure electron temperatures on these 400 kA pinches. A new device will be built at ZEI with the goal of reaching equivalent scientific breakeven (scaling D-D operating conditions to “equivalent” Q if it were operated instead with D-T) at approximately 600 kA pinch currents. Status, plans, and reactor embodiment designs will be presented.   

Thermonuclear fusion by counter-propagating laser beams in magnetized overdense plasmas

Efficient energy transfer from electromagnetic waves to ions has been demanded to understand the nature of space plasmas and to control laboratory plasmas for various applications. However, there exists a serious unsolved problem that most of the wave energy is converted easily to electrons, but not to ions. We investigate an energy conversion process to ions in overdense plasmas associated with whistler waves. We find that ions in the standing whistler waves acquire a large amount of energy directly from the waves in a short timescale comparable to the wave oscillation period. Thermalized ion temperature increases in proportion to the square of the wave amplitude and becomes much higher than the electron temperature in a wide range of wave-plasma conditions. This efficient ion-heating mechanism is applicable to various plasma phenomena in space physics and fusion energy sciences. For the purpose of ICF, ions should be heated up to high temperature exceeding keV in imploded dense plasma. The standing whistler wave heating might give an advanced technique for an alternative ignition scheme of ICF by a completely different use of magnetic fields from the previous ideas. The keV ion plasma generated by this method could also be an efficient thermal neutron source.   

Toward Advanced Modeling of Transport in Magnetized Inertial Confinement Fusion Targets

The effects of externally applied magnetic fields on the performance of fusion targets has been an open topic of research since the inception of inertial confinement fusion (ICF) and is still a topic in which our understanding can be greatly improved. Previous work has suggested that for high-gain 1-D targets, improved burn characteristics from magnetization are offset by the impediment of burn-wave propagation for little net improvement. Similar studies have shown that the application of axially aligned fields to cylindrical targets may lower the required areal density for ignition, but detailed analysis of burn-wave propagation in magnetized cylindrical targets has not been performed, aside from a cursory look using fluid models relying on Braginskii transport coefficients. Over the course of the past summer, using the results of a paper by Velikovich [1] et al. as a foundation, work has been done to explore simulation of magnetized cylindrical ICF systems with 1-D magnetohydrodynamics, and using the results of a study by Basko [2] et al. with 2-D particle-in-cell methods. Following this, initial work had been done on the development of a magnetized smoothed particle hydrodynamics model of similar systems. [1] A. L. Velikovich, J. L. Giuliani, and S. T. Zalesak, AIP Conf. Proc. 1639, 59 (2014). [2] M. M. Basko, A. J. Kemp, and J. Meyer-ter-Vehn, Nucl. Fusion 40, 59 (2000).   

\textbf{Introduction to TriForce: A Multiphysics Code for Hybrid Fluid-Kinetic Simulations}

We report on development progress of an open-source 3-D particle-based hybrid fluid-kinetic framework named TriForce, which is being benchmarked to data from HEDP facilities. The current status of the project and its applications will be surveyed. The hybrid model is constructed by combining meshless particle-based fluid algorithms with an electromagnetic and kinetic particle code. Current and planned modular packages, not all of which are mutually compatible, include: (a) gravity; (b) explicit and implicit EM fields and kinetic particles; (c) rectangular and triangular AMR; (d) extended MHD; (e) adaptive particle management; (f) user-supplied material models; (g) material strength and surface tension; (h) multigroup thermal diffusion and nonlocal transport; (i) low-noise laser ray tracing; (j) diffusion and particle-based radiation transport; (k) generalized collisional radiative model for atomic physics; (l) nuclear fusion with charged-particle and neutron transport; (m) molecular dynamics; (n) a circuit model; and (o) CPU and GPU parallelism.   

Subsystem Validation for the HJ1 Plasma Accelerator

The HJ1 plasma coaxial gun under development by HyperJet Fusion Corporation and HyperV Technologies Corp. for the PLX-$\alpha$ project at LANL requires integration of a number of critical subsystems each of which has to perform reliably over many shots. In addition to the coaxial electrode assembly and capacitor bank, there are a high speed high mass gas valve, six high current switches per gun, and a pre-ionizer system, Each must perform within tight specifications in order to achieve optimal performance of the gun. We present the results from independent testing of the switches and gas valve, each on a dedicated instrumented test stand which allows for precise measurement of performance. We also present results from testing of the preionization system which is done on the fully assembled gun with a dedicated set of diagnostics. The gas valve test stand allows us to carefully quantify repeatability from shot to shot and valve to valve, which are the primary considerations for this subsystem. Of primary concern for the switches is reliable operation, jitter, and lifetime, all of which are addressed using the test stand developed for that purpose.   

HJ1 Coaxial Plasma Gun Development for PJMIF

We describe the engineering and technical improvements, as well as provide a detailed overview of the design choices, of HyperJet Fusion's latest coaxial plasma gun, called HJ1, designed for the 4$\pi$ scaling study of spherically imploding plasma liners as a standoff driver for plasma-jet-driven magneto-inertial fusion. Each gun incorporates a compact 7.5kJ capacitor module with integral transmission line and sparkgap switching, an ultra-fast precision gas dispensing valve and a gas pre-ionization system utilizing a self-switching glow discharge. The evolution of the latest HJ1 coaxial plasma gun is presented with emphasis on its upgraded performance and improved packaging. Capacitor module changes include a new geometry with reduced overall footprint and improved access to components requiring maintenance, reduced transmission line gaps and rotating flanges for mounting. Additional improvements have been made to the gas valve design such that drive coil coupling efficiency has been improved by $\sim$70\%. These changes result in a more robust gun, with improved workability for installation, use, and maintenance. [1] Hsu et al., IEEE Trans. Plasma Sci. 40 (2012). [2] Y.C.F. Thio et al., Fus. Sci. Tech., accepted (2019).   

Backlighter development for EXAFS experiments at the OMEGA Laser Facility

Extended X-ray Absorption Fine Structure (EXAFS) allows the study of chemical bonding and local structure in solid, liquid and amorphous matter. It requires a bright and continuous x-ray source and high spectral resolution in the detection system to capture the modulations of the absorption coefficient above the material absorption edge. As an effort to improve resolution, the use of large area backlighter has been put aside in favor of slit-apertured backlighter, resulting in a reduction of the photon fluence. It is then critical to choose the brightest backlighter at our disposal. A series of experiment have been conducted at the OMEGA laser facility to characterize titanium (Z $=$ 22), iron (Z $=$ 26), germanium (Z $=$ 32), molybdenum (Z $=$ 42), silver (Z $=$ 47) and gold (Z $=$ 79) foil backlighter illuminated by 6 to 20 beams. The spectra have been recorded using the Dual Crystal Spectrometer (DCS), a two-channel spectrometer that covers 11 keV to 45 keV and 19 keV to 90 keV energy bands. DCS has been calibrated so that the spectral intensities could be compared between different campaigns. We present the results of this multi-campaign backlighter development study. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. LLNL-ABS-780051   

High-resolution imaging of warm x-ray sources with a Wolter optic on the Z Machine

We have developed a Wolter optic$^{\mathrm{\thinspace }}$to image warm (\textgreater 15 keV) x-ray sources on the Z Machine, the first-ever instrument of its kind specifically designed and fabricated for HED applications. Adapted from observational astronomy for Z, the optic uses curved x-ray mirrors to form an energy band-limited 2D image of a source with 5-mm FOV and better than measured 100-$\mu $m resolution on-axis. The first images obtained by the instrument of Mo wire array z-pinches on the Z Machine demonstrate unprecedented spatial resolution and signal-to-noise compared to pinhole imaging, revealing small-scale structures not previously observed in these sources.   

\textbf{Investigation of charged-particle response of CR-39 nuclear track detector relevant for spectrometer design }

High Energy Density (HED) plasmas are generated by taking millimeter-sized capsules filled with fusion fuel (such as deuterium and tritium) and imploding them using high energy lasers. Our experiments use CR-39, a plastic nuclear track detector used at HED laser facilities. Charged particles leave trails of damaged chemical bonds in the plastic which can be revealed through chemical etching and recorded with an automated microscope system. This detection through mechanical means is preferred to electromagnetic detectors because of its insensitivity to large electromagnetic fields (x-rays) associated with fusion reactions. Here we present data collected at MIT's Linear Electrostatic Ion Accelerator (LEIA) to measure CR-39 detection efficiency of D-D protons at incident angles up to 50 degrees. Understanding the CR-39 response to charged particles at an angle is essential to designing a D-D neutron spectrometer at the Z facility, which uses CR-39 to detect protons incident at an angle. In addition, we measure detection of D-He3 protons on Wedge Range Filter (WRF) Spectrometers at incident angles relevant for experiments at the National Ignition Facility (NIF). This work was supported in part by the U.S. DoE, SNL, LLE and LLNL.   

\textbf{The MIT HEDP Accelerator Facility for Diagnostic Development for OMEGA, Z, and the NIF }

The MIT HEDP Accelerator Facility utilizes a 135-keV, linear electrostatic ion accelerator; DT and DD neutron sources; and two x-ray sources for development and characterization of nuclear diagnostics for OMEGA, Z, and the NIF. The accelerator generates DD and D$^{\mathrm{3}}$He fusion products through the acceleration of D$^{\mathrm{+}}$ ions onto a $^{\mathrm{3}}$He-doped Erbium-Deuteride target. Accurately characterized fusion product rates up to 10$^{\mathrm{6}}$ s$^{-}^{\mathrm{1}}$ are routinely achieved. The DT and DD neutron sources generate up to 6\texttimes 10$^{\mathrm{8}}$ and 1\texttimes 10$^{\mathrm{7}}$ neutrons/s, respectively. One x-ray generator is a thick-target W source with a peak energy of 225 keV; the other uses Cu, Mo, or Ti elemental tubes to generate x-rays with a maximum energy of 40 keV. Diagnostics developed and calibrated at this facility include CR-39-based mono-energetic particle radiography, charged-particle spectrometers, neutron detectors, and the particle Time-Of-Flight (pTOF) CVD-diamond-based bang time detector. The accelerator is also a valuable hands-on tool for student education at MIT. This work was supported in part by the U.S. DoE, SNL, LLE and LLNL.   

Improved X-ray conversion efficiency using cavity backlighter sources from 7.2keV to 11.6keV

X-ray sources consisting of small (1mm diameter) cylindrical cavities have been developed for use as backlighters on the NIF. These sources use 8 NIF beams to irradiate the inner surface of the cavity and demonstrate significantly improved laser-to-X-ray conversion efficiency over traditional flat foil sources. Data suggests this improved efficiency is due to the formation of a stagnation feature on the axis of the cavity. Since the direction of the plasma flow in these sources is predominantly perpendicular to the axis of the cavity, these sources do not exhibit a Doppler shift when viewed along the cavity axis. When used as a backlighter for the narrow-bandwidth Crystal Backlighter Imager (CBI), a spherically-bent crystal imaging system on the NIF, the lack of Doppler effects can further improve the performance of the imager. Spectral and spatial measurements determining conversion efficiency, source size and dynamics will be presented for cavity sources made of Cobalt (7.2keV), Germanium (10.2keV) and Selenium (11.6keV). Additional results will be presented from experiments in which cavity backlighter sources were coupled to CBI, demonstrating both significantly improved signal and no measurable Doppler shift. Prepared by LLNL~under~Contract~DE-AC52-07NA27344.   

Developing implosion shape characterization experiments for the metal graded Pushered Single Shell implosions using the Advanced Radiographic Capability

The pushered single shell concept uses a spherical capsule with a metallic layer to compress a fusion fuel mixture to achieve ignition. While the high-Z pusher, located at the gas-shell interface traps core radiation losses, lowering ignition threshold, the pusher-fuel mix can cool the core and compromise ignition. This concept is being studied at the National Ignition Facility using a hohlraum driven with 192 laser beams [Dewald, et al. 2019]. The laser drive will be tuned to symmetrize the PSS implosion based on a series of in-flight radiography measurements with a high enough photon energy to probe the opaque shell. The backlighter scheme utilizes the Advanced Radiographic Capability (ARC) [J. M. Di Nicola, et al. 2015] to produce two x-ray point sources at different times using Au wires. The initial radiography test compares two possible configurations: one with a bare wire and one with the wire enclosed by a two-dimensional plastic parabolic structure designed to redirect and focus the low intensity wings of the ARC beamlets onto the wire [R Tommasini et. al., to be submitted].   

Quantifying x-ray diagnostics’ accuracy when imaging ICF capsule implosions using Monte Carlo simulations

Cutting edge research on Inertial Confinement Fusion (ICF) is undertaken at the National Ignition Facility (NIF) to achieve fusion ignition. Accurately measuring the temporal and spatial evolution of ICF capsules during implosion is crucial to analyze each experiment. Multiple x-ray diagnostics have thus been developed at the NIF to monitor the implosions. Each instrument uses different technologies to record the experiment, and they therefore each have their own advantages and weaknesses. We compare the performance and limitations of different diagnostics used at NIF, such as micro-channel plate (MCP) detectors or drift-tube-based detectors. This is achieved by performing Monte Carlo simulations of the different diagnostics and comparing how the latter record different images of the same source. This task involves a very large amount of data to be processed in parallel. Therefore, the simulations are performed using both the CPU and the GPU through the use of the Open Computing Language (OpenCL), which allows for much faster and more accurate simulations. These simulations are then used to quantify the detectors’ accuracy to measure asymmetries in the shape of implosions, and therefore assign a confidence level to the measurement provided by each diagnostic.   

Signatures in Emitted Light from Compressed Media

Layered materials with discontinuities in refractive index modify the transport of emitted radiation. We investigate how this changes when the bulk material undergoes rapid compression. Through examining the behavior of the emitted radiation’s intensity and frequency we will discuss possible signal characteristics which can be inverted to investigate the compression. Patterns in the signals' frequency chirp and spread could help elucidate the initial and dynamical behavior of the internal structure of the volume.   

\textbf{Understanding the Impact of Neutron Scattering on Neutron Yield Isotropy Measurements at the NIF}

Recently, the neutron yield diagnostics at the NIF have been upgraded to include 48 detectors placed around the NIF target chamber to assess the DT neutron yield isotropy for inertial confinement fusion experiments. The real-time neutron-activation detectors (RT-NAD's) are used to understand yield asymmetries due to variations in the fuel and ablator areal densities, Doppler shifts in the neutron energy due to hotspot velocities, and other physics effects. In order to isolate target physics effects, we must understand the contribution due to neutron scattering associated with the different hardware configurations used for each experiment. Our goal is to achieve 1{\%} or better precision in determining the yield isotropy. We present Monte Carlo simulations and experimental measurements to quantify this impact. This work was performed under the auspices of the US Department of Energy by Lawrence Livermore National Laboratory under Contact No. DE-AC52-07NA27344.   

One-Dimensional Imager of Neutrons (ODIN) Simulation and Experimentation for Neutron Response at Sandia Z Facility

The one-dimensional imager of neutrons (ODIN) at the Sandia Z facility was designed to determine the size, shape, and location of the neutron producing region in Sandia's baseline ICF concept, namely magnetized liner inertial fusion (MagLIF). MCNP modeling efforts continue to advance the neutron imager and have built on the previous simplified-geometry point spread model. The MCNP point spread study of the entire diagnostic configuration will be shown with potential redesigns of ODIN 1.5 to reduce scattering environment and explore imaging the source in other dimension. Finally, the MCNP response functions were used with a weighted x-ray source image to forward calculate a composite neutron image and compared to an experimental neutron image. SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525.