Bulletin of the American Physical Society
63rd Annual Meeting of the APS Division of Plasma Physics
Volume 66, Number 13
Monday–Friday, November 8–12, 2021; Pittsburgh, PA
Session NP11: Poster Session V:
Poster
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Room: Hall A |
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NP11.00001: TURBULENCE & TRANSPORT
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Not Participating |
NP11.00002: Turbulence in L-H transitions on MAST and MAST-U Lena Howlett, Istvan Cziegler, Simon Freethy, Hendrik Meyer, Daniel Dunai As several studies have shown, there exists a critical power threshold PLH beyond which tokamak plasmas transition to a state of reduced turbulence and improved confinement, known as the H mode. There does not yet exist a quantitative model for PLH and attempts at finding an empirical scaling law have not yet produced one which captures all the parameter dependencies. A scoping study on MAST data (expanded from [L. Howlett et al. EPS Plasma Phys. conf. proc. P3.1073 (2021)]) will be presented which reveals MAST H mode behaviour with density, with different types of transitions and boundary behaviours present in different locations of the parameter space. Studies on C-Mod [Y. Ma et al. Plasma Phys. Control. Fusion 54 (2012)] have shown a dependence of PLH on divertor geometry parameters. The nature of this dependence will be explored through experiments comparing L-H transitions with conventional and Super-X divertor configurations on MAST-U. Initial results of these experiments will be presented, including a study of edge turbulence dynamics using data from the beam emission spectroscopy (BES) diagnostic. |
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NP11.00003: Automated analysis of turbulent electron temperature fluctuation measurements at ASDEX Upgrade Christian Yoo, Rachel Bielajew, Garrard D Conway, Calvin Cummings, Pedro A Molina Cabrera, Pablo Rodriguez-Fernandez, Anne E White Turbulent transport is generally found to determine energy and particle confinement times in tokamaks. The correlation electron cyclotron emission (CECE) diagnostic installed on the ASDEX Upgrade tokamak measures broadband, long-wavelength (kθρs < 0.3) electron temperature fluctuations, yielding insight into turbulence-driven transport. Analysis of CECE data is well-suited to automation during the steady-state conditions often used for experimental studies. Such an automated analysis must account for the presence of artifacts, stemming from sources including electronics noise and low-frequency MHD modes, that can obscure the actual temperature fluctuations and impact the validity of the measurements. Here results of an automated, noise-filtering computational method for the analysis of CECE data are presented. The automated analysis is used to create a large experimental database of CECE analysis results. The database provides a unique opportunity to search for trends in turbulent electron temperature fluctuation levels over a large range of parameter space and allows for direct comparisons with cutting-edge numerical models. |
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NP11.00004: Cause of transport-channel decoupling in TJ-II, examined from its sensitivity to the relative phase between density and temperature fluctuations Mark E Koepke, I. Nedzelskiy, E. de la Cal, A. V Melnikov, I. Voldiner, L. G Eliseev, A. Chmyga, M. Drabinskiy, T. Estrada, C. Hidalgo, P. O Khabanov, A. S Kozachek, L. I Krupnik, G. Martin, U. Losada, J. L de Pablos, C. Silva Uncoupling transport channels is a key goal for reactor-scenario optimization. We seek insight from a new retarding-field energy analyzer method, measuring the plasma ion temperature T fluctuations [1], combined with a new Langmuir probe method [2]. In TJ-II, T evolves during the transition from the electron-root to the ion-root in the Scrape-Off-Layer (SOL) region. As line-averaged density n increases above a threshold, the edge radial-electric-field Er reverses from + to -- values, as predicted by the neoclassical electron-to-ion root transition. Results in the SOL show a decrease in T, concomitant with reduced edge-SOL turbulence spreading, controlled by edge Er. A helium-line-ratio technique in TJ-II [3] measures n of turbulent coherent structures in the plasma edge using fast (15 usec), few-mm-resolution, 2-dim imaging of n -- an upgrade uses a triple-bundle technique which 2-dim-maps n,T fluctuations and relative phase. Spatially overlapped heavy-ion-beam probe (HIBP) [4] profiles (from core to edge) and Langmuir probe profiles (at plasma edge), which agree very well, allow novel baffle-probe configurations to be tested, and provide plasma-boundary conditions for HIBP calibration. [1] RSI 82 (2011) 043505; [2] Contr. Plasma Phys. 44 (2004) 689; [3] NF 56 (2016) 106031; [4] NF 51 (2011) 083043. |
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NP11.00005: Development of a novel ion energy analyzer for electric potential diagnosis of fusion plasmas Peter J Fimognari, Thomas P Crowley, Diane R Demers Direct measurement of potential in magnetically confined plasmas can help validate theoretical models and advance understanding of electric fields and shear on transport. A beam probe can obtain spatially localized measurements of equilibrium electric potential and ion-scale fluctuations of potential in the interior of hot plasmas. It precisely measures the difference between the energies of injected beam particles and detected secondaries originating from small regions of the plasma. Factors often limiting deployment of beam probe diagnostics are their size and cost. To permit diagnostic deployment at a wider range of facilities, we are developing a smaller analyzer that is more economical, yet also maintains necessary energy measurement precision. To achieve this, we are merging a cylindrical ion energy analyzer with a beam angle detector. This will enable precise inference of particle energy (and thus plasma potential) by combining particle entrance angle data with measurements of particle deflection through the cylindrical analyzer and onto detectors. Simulations guiding the design and predicting the performance of this analyzer will be presented. Once fabricated, we will calibrate the analyzer on a beamline test stand then deploy it on the Madison Symmetric Torus at WIPPL. |
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NP11.00006: Magnetic island width change by turbulence spreading in electrostatic gyrokinetic simulation Wonjun Tae, Min Sup Hur, Jae-Min Kwon, Eisung Yoon Magnetic island is attributed to flattening of temperature profile inside the island and steepening outside. Considering profile gradient as a driving source, it is anticipated that turbulence is quite strong outside the island and barely grows inside. In that regard, magnetic island can be an ideal setup for studying physics of turbulence spreading. |
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NP11.00007: Assessing Physics of ITG Turbulence via Hierarchical Reduced-Model Representations Paul W Terry, Ping-Yu Li We probe the saturation physics of ion temperature gradient (ITG) turbulence by studying how amplitudes and scalings with key parameters vary across a hierarchy of reduced models. The models derive from nonlinear fluid equations for toroidal ITG turbulence under approximations to the mode coupling interactions in wavenumber space and the representation of turbulent decorrelation. Mode coupling approximations include local-in-wavenumber treatments like the spectral density of flux in quasilinear theory, a truncation to three nonlinearly interacting waves, and the interactions in a cascade to high radial wavenumber kx mediated by a single zonal flow. Turbulent decorrelation treatments are based on the triplet correlation time with and without eddy damping. Model fidelity is assessed by the scalings and magnitudes of the squared amplitudes of unstable mode, stable mode, and zonal flow with respect to the flow-damping rate and temperature gradient. We show that all models reproduce fundamental scalings provided they incorporate the coupling of unstable mode, stable mode and zonal flow. Accurate amplitude prediction requires eddy damping in the triplet correlation time and proper representation of the zonal-flow drive from cascade interactions. |
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NP11.00008: Turbulence Suppression in Negative Triangularity and Negative Central Shear Toroids Jessica L Li, Michael Cole, Allan Reiman, Michael C Zarnstorff Plasma transport in tokamaks and optimized stellarators is dominated by turbulence. It has been shown both experimentally and numerically that negative triangularity shaping and negative central shear in toroidal plasmas produces a stabilizing effect, likely due to the suppression ion-scale modes, which leads to lower levels of turbulent transport and thus improved confinement. We present the results of global gyrokinetic simulations directly comparing turbulent instability growth rates of equivalent low-beta positive- and negative-triangularity geometries, with both positive and negative central shear. The effects of various temperature, density, and safety factor profiles are explored. We also examine the effectiveness and viability of this turbulence suppression mechanism when moving to reactor-relevant parameters such as high beta. |
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NP11.00009: Effect of Triangularity on Ion-Temperature-Gradient-Driven Turbulence Joey M Duff, Benjamin Faber, Chris C Hegna, MJ Pueschel, Paul W Terry Transport driven by ion temperature gradient (ITG) turbulence is an important loss channel in tokamaks. We model how changing triangularity δ, both negative and positive, affects ITG linear growth rates and turbulent saturation. Linear and nonlinear properties of an ITG scenario with adiabatic electrons are analyzed using the gyrokinetic code GENE. Peak linear growth rates decrease with negative δ but increase in finite radial wavenumber kx with positive δ. The growth-rate spectrum broadens in kx with negative δ and significantly narrows with positive δ. The effect of δ on linear instability properties can be explained through its impact on field line bending and curvature. Nonlinear heat flux is weakly dependent on triangularity for |δ| ≤ 0.5, decreasing significantly with extreme δ, regardless of sign. Zonal modes play an important role in nonlinear saturation in the configurations studied, and artificially suppressing zonal modes increased nonlinear heat flux by a factor of about four for negative δ, increasing with positive δ to almost a factor of 20. Proxies for zonal-flow damping and drive suggest that zonal flows are enhanced with increasing positive δ. |
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NP11.00010: Verification of collision modules for neoclassical simulations in Tokamak Dongkyu Kim, Janghoon Seo, Gahyung Jo, Jae-Min Kwon, Eisung Yoon Collision physics is important to predict transport which influences confinement in Tokamak fusion plasma. In numerical simulations, collision operator should be properly treated to estimate transport quantities reasonably and correctly. In this research, we conducted verification of two grid-based collision modules for Dougherty operator [1, 5] and test particle part of linearized collision operator [2] against neoclassical physics in Tokamak. The collision modules are incorporated into a new gyro-kinetic continuum code, gKPSP2, based on discontinuous Galerkin method [3]. For these verification exercises, in particular, parameter scans of heat flux and poloidal flow over ν* are conducted by adjusting density profile. The neoclassical quantities obtained from the simulations are compared against theoretical predictions by Chang-Hinton formula and Sauter formula, respectively [4]. Also, results of cross verification with a gyro-kinetic PIC code will be presented. |
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NP11.00011: Electrostatic gyrokinetic simulation of ultra-high-beta(β~1) equilibria Rahul Gaur, William D Dorland, I. G Abel We present a microstability analysis of ultra-high-beta(β~1) equilibria for tokamaks. These equilibria have previously been studied in the context of MHD stability (Hsu, Artun and Cowley PoP 3,266 (1996)), however no microstability calculations have been performed. We use linear gyrokinetic stability calculations performed with the GS2 (bitbucket.org/gyrokinetics/gs2) code to examine how susceptible these equilibria are to turbulence caused by microinstabilities. We examine the stability of these equilibria to two major sources of electrostatic turbulence: Ion-Temperature Gradient modes and (Collisionless) Trapped-Electron modes. To understand the trend with a changing beta, we compare these ultra-high-beta equilibria with an intermediate beta(β~0.1) and a low-beta(β~0.01) equilibrium at two different radial locations: the inner core(Normalized radius ρ = 0.5) and the outer core(ρ = 0.8) for two different triangularities: δ = 0.4 and δ = -0.4. We find that the ultra-high beta equilibria are stable to both the ITG and TEM mode over a wide range of gradient scale lengths(R/L_T and R/L_n). To justify our findings and build intuition, we compare various figures of merit such as the local shear, field-line curvature, precession drift and relate their values to the behaviour of the electrostatic modes. |
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NP11.00012: Gyrokinetic Simulations of Zonal Flow Generation by Intermediate-Scale Electron Temperature Gradient Turbulence in Tokamak Plasmas Stefan Tirkas, Haotian Chen, Gabriele Merlo, Scott E Parker The mechanism of anomalous electron heat transport in tokamaks is currently not well-understood. In fluid models, the zonal flow generation by electron-temperature-gradient (ETG) turbulence has shown to be much weaker than that of similar ion (ITG) turbulence, leading to the expectation of a saturated state characterized by radially elongated streamers at electron-gyroradius scales. However, gyrokinetic electron simulations have shown that zonal flow (ZF) modes can contribute to long-time-scale behavior by breaking up these streamers into isotropic eddies. A recent toroidal, gyrokinetic-electron theory [1] has shown that as the ETG spectrum cascades downward a stronger Navier-Stokes type nonlinearity couples the intermediate-scale ETG and ZF modes, thus allowing for relevant ZF generation. We provide gyrokinetic-ion ETG simulation results from GENE, a 5-d gyrokinetic continuum code, with both single-mode ETG and full ETG spectra results compared to the aforementioned theory. We will specifically look at the strength of ZF generation via ETG modes at intermediate and short-wavelength scales, as well as the role of magnetic shear and collisionality in affecting the strength of the ZF generation. |
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NP11.00013: The Dynamics of Strongly-Driven Electron Temperature Gradient Turbulence in a Slab William D Dorland, Ian G Abel, Rahul Gaur Electron Temperature Gradient (ETG) turbulence, enabled by curvature |
Not Participating |
NP11.00014: Recent Progress in EM-GTS code Edward A Startsev, Weixing X Wang Spherical tokamaks like NSTX-U are high beta machines where electrons anomalous transport is in a large part due to global electromagnetic drift modes such as KBM and MTM. Here we report on the recent progress in the development of the electromagnetic capabilities in the gyrokinetic code EM-GTS which is now capable of linear and non-linear simulations of finite-beta ITG, KBM and MTM modes in NTSX-U geometry. Linear and non-linear EM-GTS simulations of the low-n MHD modes such (2,1) tearing mode which are responsible for the thermal quench will also be presented. |
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NP11.00015: Reduced models for ETG transport in the pedestal David R Hatch, Ben Chapman, Craig Michoski, Max Curie, Michael R Halfmoon, Ehab Hassan, Michael T Kotschenreuther, Swadesh M Mahajan, Gabriele Merlo, MJ Pueschel, Justin Walker Electron temperature gradient (ETG) driven turbulence is likely a major contributor to electron heat transport in the pedestal. Nonlinear gyrokinetic simulations have demonstrated realistic transport levels for several discharges. There exist, however, few (if any) reduced models for pedestal ETG transport, which is the topic of this presentation. In the pedestal, ETG turbulence does not rely on streamers to enhance transport beyond the standard mixing length arguments—low transport is, after all, the defining characteristic of a transport barrier. Rather, significant heat fluxes follow simply from the enormous pedestal gradients compensating for low diffusivities. Pedestal ETG modes are rather exotic in nature, having, for example, multiple branches (toroidal and slab) in different wavenumber ranges. Moreover, many ETG modes can be unstable simultaneously at a single wavenumber and growth rates can peak at finite ballooning angle. These characteristics make reduced modeling of slab ETG challenging. We will present a reduced model of ETG pedestal transport that effectively reproduces the nonlinear transport levels across a database of several dozen nonlinear simulations. This reduced model is a generalization of the standard quasilinear approach. |
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NP11.00016: Global theory of microtearing modes in the tokamak pedestal Joseph Larakers, Max Curie, David R Hatch, Swadesh M Mahajan, Richard D Hazeltine During the inter-ELM period, tokamak pedestals commonly display bands of magnetic fluctuations with discrete mode numbers. These ion scale fluctuations correlate with the evolution of the electron temperature profile and rotate in the electron direction. Though the observed spectrum is consistent with the microtearing mode (MTM), the conventional MTM theory does not explain the discrete nature of the fluctuations. In fact, due to the many rational surfaces present in the steep gradient region, conventional theory predicts a broadband of magnetic fluctuations. Here we extend the conventional local theory of the MTM to include the global variation of the temperature and density profiles. The offset between the rational surface and the location of the pressure gradient maximum emerges as a crucial parameter for MTM stability. Our extended theory predicts that an interaction of pressure and magnetic shear profiles is what leads to the n (the toroidal mode) number discrimination. Our predictions match observations on the Joint European Torus. Armed with these new insights from linear theory, we extend our investigation by constructing a weak turbulence model for the coupling, nonlinear evolution, and saturation of this unstable set of pedestal microtearing modes. |
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NP11.00017: Gyrokinetic study of impurity transport in the H-mode pedestal Neeraj Kumar, Stefan Tirkas, Gabriele Merlo, Shaun R Haskey, Brian A Grierson, Scott E Parker We investigate ion-scale turbulent transport in the edge pedestal of DIII-D H-mode plasmas and the impact of impurities. In the H-mode pedestal, we find that for the ITG modes the carbon impurity has a negligible effect on the instability, but for the TEM-like modes it can have a significant impact with growth rates decreasing by ~40% compared to a pure deuterium plasma. At low kyρi ( 0.1≤ kyρi ≤1.5) the most unstable eigenmode is an ion mode with positive frequency (ITG-like), with electron mode (TEM-like) with negative frequency at higher kyρi ( 1.6≤ kyρi ≤2.0). Here, linear gyrokinetic calculations are first carried out for inter-ELM DIII-D H-mode discharges during the buildup of the pedestal to investigate turbulent transport at three radial locations ρtor= 0.80, 0.85 and 0.90 using the gyrokinetic code GENE in the local limit. Following this, the quasilinear (QL) fluxes will be calculated and compared to nonlinear fluxes to test the validity of quasilinear approximation. Finally, QL fluxes will be compared with GENE neoclassical fluxes to quantify the importance of anomalous transport levels. |
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NP11.00018: Analysis of gyrokinetic microinstabilities driving anomalous losses in DIII-D pedestal region Michael R Halfmoon, David R Hatch, Michael T Kotschenreuther, Swadesh M Mahajan, Andrew O Nelson, Egemen Kolemen, Florian M. Laggner, Ahmed Diallo, Ehab Hassan, Max Curie, Richard J Groebner There remain multiple candidate mechanisms to account for transport across the H-mode pedestal[1], including microtearing modes (MTM), ion temperature gradient/trapped electron modes(ITG/TEM), electron temperature gradient (ETG) modes, and kinetic ballooning modes (KBM). In this study, gyrokinetic simulations are performed for DIII-D discharge 174082 using the GENE code with inputs from equilibrium profiles reconstructed from experimental data[2]. Local nonlinear simulations have shown that electron heat flux has contributions from ETG-driven transport, but not at levels required to fully satisfy power balance, even with variations to the background profiles. MTMs are identified in both linear gyrokinetic simulations and magnetic fluctuation data, providing an additional mechanism to account for electron heat transport. Neoclassical transport is investigated to account for the remaining observed energy losses in the ion channel. The MTM instabilities found in these simulations are consistent with observed magnetic fluctuations, having frequencies in the electron diamagnetic direction. Modifying the equilibrium profiles can result in MHD-like modes becoming the most unstable linear global mode, with "fingerprints" that are distinct from MTM's. We investigate magnetic field and density fluctuations for both MHD-like modes and MTMs in an effort to establish a useful "fingerprint" for distinguishing these two modes in both simulations and experiments. We investigate the structure and underlying physics of this MHD-like instability. Quasilinear models for MTM transport are also investigated across scans in collisionality, beta, and electron temperature gradient[3]. |
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NP11.00019: Micro-Tearing Modes in the DIII-D plasma edge Alexei Pankin, Tariq Rafiq, Santanu Banerjee, Jie Chen, Kshitish Kumar Barada, Richard J Groebner, Orso-Maria O Meneghini, Francesca M Poli, Terry L Rhodes, Tim Slendebroek, Sterling P Smith, Zheng Yan The Micro Tearing Model (MTM) [T Rafiq et al. Phys. Plasmas 23 (2016) 062507] in the Multi-Mode Model 8.2 [T Rafiq et al. Phys. Plasmas 20 (2013) 032506] is used in OMFIT to examine the dependence of the MTM linear growth rate on plasma parameters in DIII-D. In DIII-D, these modes might contribute to the development of the H-mode pedestal structure and play a role in the electron thermal transport at the H-mode pedestal top. In this study, analysis of recent DIII-D discharges shows that MTMs can be unstable near the H-mode pedestal top even in the discharges with small or moderate β. Electromagnetic in nature, these modes are driven by the electron temperature gradients. However, MTMs also have electrostatic components that become important in the discharges with relatively small β. For these discharges, large electron density gradients become a primary mechanism of MTM triggering. The role of different plasma parameters in driving the MTM modes in the DIII-D discharges with different β is investigated in this research. The ranges of temperature and density scale lengths as well as plasma collisionality that are favorable for triggering of MTMs in the DIII-D plasma edge are found in a set of scans. |
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NP11.00020: Electromagnetic reduction of transport and heat-flux width in gyrokinetic simulations of a helical scrape-off layer model Noah R Mandell, Gregory W Hammett, Ammar Hakim, Manaure Francisquez We demonstrate that cross-field transport in the scrape-off layer (SOL) can be reduced by electromagnetic effects in high-beta regimes, resulting in steeper pressure gradients and a narrower heat-flux width. This conclusion is taken from full-f electromagnetic gyrokinetic simulations of a helical SOL model that roughly models the SOL of the National Spherical Torus Experiment (NSTX). In a high-beta case, the electron pressure gradient steepens by 60%, the heat-flux width λq is 10% smaller, and the power-spreading factor S is reduced by 50% when electromagnetic effects are included. We show that stabilizing effects related to magnetic-field-line bending are key to the reduction in perpendicular transport. Field-line bending is produced by the combination of interchange dynamics near the midplane and line tying of field lines on the endplates due to conducting-plate sheath boundary conditions. This results in line-tied ballooning modes with parallel wavelengths of order the connection length. The simulations have been performed with the Gkeyll code, which has recently demonstrated the first capability to simulate electromagnetic gyrokinetic turbulence on open magnetic field lines. |
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NP11.00021: Theory, modeling, and validation for a range of innovative fusion concepts using high-fidelity moment-kinetic models Ammar Hakim, Bhuvana Srinivasan, Colin S Adams, Stefano Brizzolara As part of the ARPA-E BETHE program Virginia Tech and Princeton Plasma Physic Laboratory are designing novel theoretical and experimental tools to understand the physics of innovative fusion concepts funded by that program. In this talk we give an overview of our effort, in particular, the development of high-fidelity moment and moment-kinetic solvers to understand two mirror concepts (at University of Wisconsin and University of Maryland) as well as plasma-material interaction in Z-pinches and other pulsed machines. Many pulsed fusion machines plan to use liquid metal walls to handle high current and heat loads efficiently. Hence, we are building a test-stand to study the interaction of pulsed plasma currents with liquid metals in an effort to understand how high current pulses disturb the liquid surface and the amount of high-Z material that can potentially enter the main plasma. The liquid metal experiments are backed with multi-phase resistive MHD simulations to provide a validated tool to understand plasma-liquid-metal interaction in different fusion concepts. |
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NP11.00022: gkylzero: the Lightweight Library Underpinning the Gkeyll Simulation Framework James L Juno, Ammar Hakim, Manaure Francisquez, Noah R Mandell, Tess Bernard, Petr Cagas, Kolter Bradshaw, Liang Wang, Rupak Mukherjee, Jason M TenBarge, Gregory W Hammett The Gkeyll simulation framework and the variety of plasma physics-relevant solvers contained in the framework, from multi-fluid multi-moment to full-f electromagnetic gyrokinetic, have been used to tackle problems in a wide variety of plasma systems, from global modeling of planetary magnetospheres to turbulence in the scrape-off layer of tokamaks. We present here an overview of the lowest level of the Gkeyll simulation framework, gkylzero, which constitutes a lightweight library underpinning the whole framework and which can be compiled and linked to independent of the rest of the simulation framework. This software design not only permits significant runtime flexibility in everything from choice of solver to choice of architecture, but also provides a means of utilizing Gkeyll's core solvers outside of the rest of Gkeyll's infrastructure should one desire. We focus on a number of improvements to the overall code structure this design permits, including the practical consequences for the diverse array of applications Gkeyll is used for, as well as how one can utilize gkylzero as a library, thus allowing other codes access to the high quality solvers for multi-fluid multi-moments, Vlasov-Maxwell, and gyrokinetics for applications such as code coupling. |
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NP11.00023: A twist-shift boundary condition algorithm for discontinuous Galerkin discretizations Manaure Francisquez, Noah R Mandell, Ammar Hakim, Gregory W Hammett Modern local gyrokinetic simulations account for the turbulent anisotropy ($k_\parallel\sim 1/qR$, $k_\perp\rho\sim 1$) to construct computational grids aligned with the equilibrium magnetic field ($B$). Such technique efficiently distributes degrees of freedom and results in more affordable calculations. These flux-tube simulations have a limited extent along $B$ and impose twist and shift boundary conditions (BCs) [1]. These BCs exploit the small turbulent correlation lengths and the axisymmetry of the device to enforce periodicity in the parallel direction at a fixed poloidal angle. Historically this BC has been employed in pseudo-spectral codes, yet the Gkeyll code [2] uses a discontinuous Galerkin (DG) representation to which the spectral algorithms do not transfer. We thus formulated a DG implementation of twist-shift BCs based on the concept of weak or Galerkin equality and a DG representation of the magnetic safety factor ($q$). Carrying out the necessary integrals in a conservative manner leads us to split up the problem into a series of sub-cell integrals depending on the computational grid and $q$. We present basic tests of the implementation in Gkeyll and a time-dependent local flux-tube simulation. |
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NP11.00024: Toward exascale whole-device modeling of fusion devices: Porting the GENE gyrokinetic microturbulence code to GPU Kai Germaschewski, Bryce Allen, Tilman Dannert, Markus Hrywniak, John Donaghy, Gabriele Merlo, Stephane Ethier, Ed D'Azevedo, Frank Jenko, Amitava Bhattacharjee The GENE code solves the five-dimensional gyrokinetic equations to simulate the development and evolution of plasma microturbulence in magnetic fusion devices. In order to use the emerging computational capabilities to gain new physics insights through whole device modeling, several new numerical and computational developments are required. Here, we focus on the fact that it is crucial to efficiently utilize GPUs that provide the vast majority of the computational power on such systems. We introduce a novel library called gtensor that was developed along the way to support the GENE GPU port in a performance portable and maintainable fashion. Performance results are presented for the ported code, which on a single node of the Summit supercomputer achieves a speed-up of almost 15x compared to running on CPU only. Typical GPU kernels used in GENE are memory-bound, achieving about 90% of peak. Our analysis shows that there may still be room for improvement if we can refactor/fuse kernels to achieve higher arithmetic intensity. We also performed a weak parallel scalability study, which shows that the code runs well on a massively parallel system, but communication costs start becoming a significant bottleneck when using 1000s of GPUs. |
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NP11.00025: Optimization of GEM using OpenMP GPU Offloading Qiheng Cai, Junyi Cheng, Yang Chen, Oryspayev Dossay, Paul Lin, D'azevedo Ed, Scott E Parker GEM is a particle-in-cell gyrokinetic code for investigation of low-frequency phenomena such as micro-turbulence and energetic particle driven Alfven waves in tokamak plasma. In the GEM code, the particle arrays should be moved from CPU memory to GPU memory with all particle loops performed in GPUs. Moreover, the particle shift consists of two steps: the initialization step and actual data movement, in which the first step should be modified to enable more loops to run on GPU while the actual transferred particles in the second one should be updated between CPU and GPU. In order to minimize the data transfer and offload the calculation processes from CPU to GPU, the porting of GEM code from OpenACC to OpenMP GPU offload is implemented. The details of conversion from OpenACC to OpenMP GPU offloading are illustrated. Furthermore, we make the comparison of acceleration performance between CPU and GPU as well as OpenACC and OpenMP. Additionally, the results about comparison of profiling data between weak scaling (fixed grid size and increased particle number) and strong scaling (increased both grid and particle number in proportion) for different machines (e.g., Summit and Cori) are presented and discussed. |
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NP11.00026: A Learned Fluid Closure for Phase Mixing Applied to a Turbulent Gradient-Driven Gyrokinetic System in Simple Geometry Akash Shukla, David R Hatch, Craig Michoski, William D Dorland We present a new method for formulating closures that learn from kinetic simulation data. We apply this method to phase mixing in a simple gyrokinetic turbulent system - temperature gradient driven turbulence in an unsheared slab. The closure is motivated by the observation that in a turbulent system the nonlinearity continually perturbs the system away from the linear solution, thus demanding versatility in the closure scheme. The closure, called the learned multi-mode (LMM) closure, is constructed by, first, extracting an optimal basis from a nonlinear kinetic simulation using singular value decomposition (SVD). Subsequent nonlinear fluid simulations are projected onto this basis and the results are used to formulate the closure. We compare the closure with several other closures schemes over a broad range of the relevant 2D parameter space (collisionality and gradient drive). We find that the turbulent kinetic system produces phase mixing rates much lower than the linear expectations. In contrast with the other closures, the LMM closure is able to capture this reduction. In comparisons of heat fluxes, the LMM closure exhibits errors substantially lower than the other closures. |
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NP11.00027: Effects of an artificial source in global gyrokinetic simulations Yang Chen, Junyi Cheng, Scott E Parker Global gyrokinetic simulations without a source do not reach a steady state due to profile relaxation. Since the physical velocity-dependent source is usually not known with sufficient accuracy, artificial sources are used that prevent profile relaxation and ensure a steady state. To compare the turbulent fluxes from simulation with experiment, the simulation result must be insensitive to the artificial source. This problem is of fundamental importance for the validation of the gyrokinetic model. Several of the common forms of energy/particle source have been implemented in the GEM ????-PIC code. Nonlinear simulations with kinetic electrons are carried out varying the source form and the source rate. It is found that the ion heat flux increases linearly with the source rate when the source rate is small and becomes less sensitive for larger source rates. When the source rate is near 10% of the maximum linear growth rate, the dependence of the flux on the source rate becomes significant with variations depending on the form of the source. We also investigate the closely related problem of marker distribution in PIC simulations. We show that, in partially-linearized PIC simulations, the marker density necessarily evolves away from the initially loaded marker distribution. Such evolution invalidates the typically used weight evolution equation in the ????-method. Techniques to mitigate this problem are presented. |
Not Participating |
NP11.00028: Exploring Novel Electromagnetic Algorithms for Efficient Particle-in-Cell Simulations Andrew T Sexton, John G Shaw, Ayden Kish, Michael Lavell, Sreepathi Pai, Adam B Sefkow In particle-based fluid-kinetic plasma simulations1, an electromagnetic-field solver is coupled to the particles via a mesh. Explicit finite-difference time-domain (FDTD) methods solve Maxwell’s equations and require very small time steps when high-resolution meshes are used. Long-time-scale simulations might require 105 to 107 time steps in order to reach the hydrodynamic time of interest. A critical area of research is to accelerate these computations using GPU hardware. The use of implicit methods generally requires additional operations to solve banded matrices and has a more-complex algorithm design, but benefits from being unconditionally stable and unrestricted by the need to resolve the speed of light on the mesh. This enables larger time steps and shorter computation times. The fundamental locally one-dimensional complying divergence (FLOD-CD) FDTD method2 is an unconditionally stable semi-implicit non-iterative method. We report on our efforts to test this and similar algorithms for accuracy, efficiency, memory use, and how well they can be accelerated and parallelized. Our goal is to stably and accurately achieve very long simulation times for inertial confinement fusion, high-energy-density physics, and magnetic fusion energy applications. |
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NP11.00029: A New Gauge-Compatible Finite Element PIC Algorithm on an Unstructured Mesh Alexander S Glasser, Hong Qin We develop and study various aspects of a new structure-preserving particle-in-cell algorithm. Applying the formalism of finite element exterior calculus, our study extends a previously developed gauge-compatible canonical Hamiltonian PIC method [J. Plasma Phys. 86, 835860303 (2020)] to an unstructured mesh. We derive the momentum map of this new algorithm and its corresponding exact charge conservation law. We further describe its scaling to whole-device tokamak simulation. Our study is oriented toward PIC development suitable for the new generation of exascale supercomputers. |
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NP11.00030: Comparison of Coulomb Collision Models in Simulations of Odd-Parity Field Reversed Configuration Michael J Lavell, John G Shaw, Ayden J Kish, Andrew T Sexton, Aditya R Srinivasan, Scott Sikorski, Adam B Sefkow Accurately computing Coulomb interactions in collisional plasmas is a key component of the kinetic description achieved in particle-in-cell (PIC) simulations. Two common approaches for solving the Landau–Fokker–Planck collision operator are the binary method that performs energy and momentum conserving pairwise collisions, and the grid-based Langevin equations method that computes the drag and diffusion on particles in response to the local field. These Monte Carlo techniques are computationally expensive because of the large number of simulation particles required to sufficiently resolve velocity space and the scattering process. In this talk, we investigate a low-noise PIC method that uses Gauss–Hermite quadrature to initialize particles and compute collisions. This reduces the number of particles needed to resolve velocity space and, similar to the quiet direct simulation technique, eliminates the strong dependence on dense random number sampling for accuracy. We report on validation efforts of the new model through electrical conductivity and stopping-power measurements. We will also discuss a comparison of the methods in simulations of an odd-parity field reversed configuration that demonstrates electron heating by rotating magnetic fields. |
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NP11.00031: Progress on implementing general parallel moment equations in NIMROD Hankyu Lee, J. Andrew Spencer, Eric D Held, Jeong-Young Ji General parallel moment equations are implemented in NIMROD to obtain parallel closure relations for time-dependent fluid simulations. The parallel moment equations are obtained by taking velocity moments of the first order drift kinetic equation. By truncating the moment equations at a certain order of moment, a system of moment equations can be solved. The parallel closure relations are obtained from the moment solution. For less collisional plasmas, the convergence of parallel closures is shown by increasing the number of moments of the system. As a benchmark test, ion parallel flows and bootstrap currents are compared to continuum kinetic calculations in NIMROD. |
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NP11.00032: Differential RF Heating as a Control Tool the Cross-phase: A Mechanism for Controlling I-modes and Other Enhanced Confinement Regimes? David E Newman, Dempsey Rogers, Soma R Panta, Paul W Terry, Raul Sanchez The I-mode and similar new transport regimes offer good confinement properties with reduced density limit issues and potentially better control. While a number of different mechanisms have been identified for the formation and maintenance of enhanced confinement regimes few if any allow enhanced confinement in one channel but not another which is seen in the I-mode. We propose differential cross-phase modification as a possible mechanism for different transport in different channels and investigate control tools. Simple dynamical models have been able to capture a remarkable amount of the dynamics of the core and edge transport barriers found in many devices. By including in this rich though simple dynamic transport model a simple model for cross phase effects, due to multiple instabilities, between the transported fields such as density and temperature, we can investigate whether the dynamics of more continuous transitions such as the I-mode can be captured and understood. If this mechanism is valid, what can the model tell us about control knobs for these promising regimes? Here we investigate the use differential electron and ion heating to control the I-mode regime. Using both location modification and modulation amplitude and duration as the control knobs we demonstrate the ability to stay in the I-mode without slipping into the H-mode regime. |
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NP11.00033: The Nonlinear State of Strong Interchange-Type Turbulence Kenneth W Gentle, Mark E Koepke, Samuel H Nogami The Helimak is an approximation to the infinite cylindrical slab with a size large compared with turbulence transverse scale lengths, but with open field lines of finite length. A pressure gradient in unfavorable magnetic curvature is unstable to interchange-type modes, leading to large amplitude nonlinear fluctuations similar to those in a tokamak SOL, except there are no field-line connections to favorable curvature. A novel magnetically-baffled probe cluster permits full characterization of the turbulence, including density, temperature, and plasma potential fluctuations as well as particle and thermal radial transport rates across the full plasma profile. Turbulence varies in a complex way with plasma parameters, but it can be most strongly modified by the application of bias to alter the transverse (poloidal, orthogonal to B and R) flow patterns. Linear theory offers little guidance. The local density, temperature, and potential fluctuations show modest time correlations at best, flow shear has little predictive value, and the local interchange growth rate is poorly associated with turbulent amplitudes, with strong turbulence persisting in regions of linear stability. Transport is stochastic, being only loosely time-correlated with its electrostatic driving terms. |
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NP11.00034: Dynamics of Edge Shear Layer Collapse and the Density Limit Mikhail A Malkov, Patrick H Diamond Density limit phenomenology has been associated with the collapse of edge shear layers at high density. Theoretical work has suggested that the onset of such collapse can occur when adiabaticity α drops below α ≈ 1. Here, we explored shear flow dynamics in a spatially varying density profile in a channel flow configuration. The gradient in adiabaticity triggers the formation of a barrier shear layer, which separates the region of isotropic turbulence from a zonal flow. The barrier is pinned to the location of α_crit and does not propagate. We observe that this spontaneously generated shear layer forms for α = α_cr, and disappears when α < α_cr, throughout the domain. This behavior is suggestive of that observed at the density limit, when high edge density forces a drop in the edge layer value of α. The intensity, flux, and zonal profiles are calculated. Inhomogeneous mixing of density is observed, suggesting the development of an E × B staircase in the edge layer. Emphasis will be on neutral drag effects, but we will also explore neutral entrainment and its impact on transport. |
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NP11.00035: Shearless Transport Barriers Ibere L Caldas, Ricardo L Viana, Jose D Szezech Jr, Antonio M Batista, Philip J Morrison We discuss properties of shearless transport barriers associated with extrema of non-monotonic plasma profiles. Initially, we introduce shearless transport barriers in nontwist maps, systems with nonmonotonic rotation number profiles. We show how this barrriers existence depends on the map control parameters. Next, we introduce a symplectic nontwist map to describe the magnetic field lines in tokamaks. For this map, we present the scenarios of the onset and break up of shearless transport barriers as the control parameters, namely, the plasma current and the amplitude of the perturbing resonant field, are varied. |
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NP11.00036: ICF
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NP11.00037: Targets and plasma diagnostics experimental systems at the Laser MegaJoule (LMJ) Tony CAILLAUD, Michel Ferri, Serge Debesset, Véronique Prevot, Romain Diaz, Laurent Le Deroff, Remi Du Jeu, Michel Martin, Cyril Lesaffre, Damien Antigny, Louis De Laval, Benjamin Fourton |
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NP11.00038: A Travelling Optical Thomson Scattering Diagnostic in Support of ARPA-E's Fusion-Energy Program Clement S Goyon, Jacob T Banasek, Simon C Bott-Suzuki, George F Swadling, Phillip S Datte, Drew P Higginson, James S Ross, Harry S McLean ARPA‐E supports the exploration and development of potentially transformative fusion‐energy concepts. Multi‐point, spatially and temporally resolved measurements of plasma parameters and their spatial profiles would greatly benefit these fusion experiments by establishing the level of performance that has been achieved. We have developed an optical Thomson scattering system to investigate plasma parameters including electron density, electron temperature, ion temperature, and flow velocity. Scattering of a 532nm, 1.6ns, 8 J Nd-YAG probe laser is collected from 8 points within the plasma column and delivered by a fiber bundle to 2 spectrometers with gated CMOS cameras. One spectrometer is dedicated to the electron plasma wave, while the other records the ion acoustic wave. In addition, a fraction of the laser is used to perform shadowgraphy simultaneously with the Thomson scattering measurement, providing the location probed by the laser with respect to the plasma. We will present our initial deployment on the shear flow Z-pinch machine FuZE at ZAP Energy inc. to measure the electron temperature and density along with initial data. |
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NP11.00039: Extending the use of RTNADs capabilities at the NIF Kelly D Hahn, Richard M Bionta, Eugene A Henry, Dean R Rusby, Alastair S Moore, David Barker, Edwin Casco, Tony Golod, Gary Grim, Edward P Hartouni, Shaun M Kerr The real-time neutron activation detector (RTNAD) array, with 48 elements, measures the un-scattered primary DT-neutron-yield isotropy for inertial confinement implosions at the NIF. The array also characterizes fuel and ablator areal density distributions for DT experiments. We are investigating the ability to use present or modified versions of the RTNADs to measure additional physics parameters including the DD-neutron isotropy for DD-fuel experiments, hot-spot motion for both DT- and DD-fuel experiments, and high-energy photon yield and energy distributions for the Advanced Radiography Campaign. We also consider extending the RTNAD capability to assess DT-neutron isotropies at much higher yields (i.e., > 1e17) than presently achieved. |
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NP11.00040: Time resolved measurement of electron density and temperature in NIF compressed capsules with the dHIRES x-ray spectrometer Kenneth W Hill, M Bitter, Lan Gao, B Kraus, P.C. Efthimion, N. Pablant, M.B. Schneider, D.B. Thorn, H. Chen, R.L. Kauffman, D.A. Liedahl, M.J. MacDonald, A.G. MacPhee, S. Stoupin, R. Doron, E. Stambulchik, Y. Maron, B. Lahmann The dHIRES x-ray spectrometer has been used to measure time resolved electron temperature (Te) and density (ne) in the hot spot of four NIF compressed capsules at stagnation from high resolution Kr helium-β x-ray spectra. The inferred, time averaged ne values mainly agree with ne values from neutron diagnostics within uncertainties, but neutron time of flight values of Tion are consistently higher than dHIRES Te values by 200 – 700 eV. The dHIRES measurements and measurement technique, uncertainty analysis, and discussion of comparisons with measurements with neutron diagnostics will be presented. |
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NP11.00041: Developing a Forward Model of Single-hit Array Detector for Reaction-In-Flight Neutrons Measurement Yongho Kim, Hermann Geppert-Kleinrath, Carlton S Young, Thomas J Murphy, Kevin Meaney, Anna Hayes, Michael Springstead, David Schwellenbach, Jessica Clayton In deuterium-tritium (DT) nuclear fusion, primary reactions produce 14.1 MeV mono-energetic neutrons. A small fraction of DT fuel ions undergo a knock-on process by the 14.1 MeV neutrons, which results in the production of high energy neutrons with energy up to 30 MeV (i.e., reaction-in-flight (RIF) or tertiary neutrons). It is beneficial to observe and analyze RIF neutrons as they include useful information such as fuel areal density and mix, however, measuring the shape of RIF neutron energy spectrum is challenging due to its small production yield compared to primary DT yield (10-4 – 10-8). In the past, single-hit neutron arrays have demonstrated the ability to measure a small quantity of DT neutron spectral information during deuterium-deuterium fusion. A similar forward model has been developed to determine if the single-hit array approach can be applicable in measuring the energy distribution of the RIF neutrons in inertial-confinement-fusion. |
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NP11.00042: The MIT HEDP Accelerator Facility for Diagnostic Development for OMEGA, Z, and the NIF Brandon J Lahmann, Maria Gatu Johnson, Andrew Birkel, Cody Chang, Skylar Dannhoff, Tucker Evans, Tim M Johnson, Neel Kabadi, Justin H Kunimune, Jacob A Pearcy, Patrick J Adrian, Benjamin Reichelt, Graeme Sutcliffe, Ernie Doeg, Robert Frankel, Johan A Frenje, Chikang Li, Fredrick H Seguin, Richard Petrasso The student-run MIT HEDP Accelerator Facility uses a 125-keV ion accelerator, DT and DD neutron sources, and two x-ray sources for development and characterization of diagnostics for OMEGA, Z, and the NIF. The accelerator generates DD and D3He fusion products through the acceleration of D+ ions onto a 3He-doped Erbium-Deuteride target, with fusion product rates up to 106 s−1 routinely achieved. The DT and DD neutron sources generate up to 6´108 and 1´107 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 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. This poster includes discussion about recent x-ray filter calibration experiments for use in new OMEGA temporally and spatially resolving x-ray diagnostics PXTD and XRIS, as well as development of precision Step-Range-Filter particle spectrometers for NIF and OMEGA, and analysis techniques for a new Z neutron spectrometer. This work was supported in part by the U.S. DOE, the MIT/NNSA CoE, LLE, SNL and LLNL. |
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NP11.00043: One-dimensional, axially resolved and time-integrated neutron images from MagLIF experiments at Sandia’s Z Pulsed Power Facility Michael A Mangan, David N Fittinghoff, Adam J Harvey-Thompson, Gary Cooper, Fredrick H Seguin, Johan A Frenje, Gary Whitlow, Patrick Lake Inertial confinement fusion (ICF) experiments conducted on the Z-Facility at Sandia present an extreme environment for neutron diagnostics with large amounts of radiation due to electromagnetic pulses and Bremsstrahlung radiation in addition to X-rays emitted from fusion processes in the experiments. The one-dimensional imager of neutrons (ODIN) has been used in ICF experiments to collect time-integrated axially resolved neutron images of the imploding targets. CR-39 track-etch detectors have used in ODIN due to their proven ability to detect neutrons in environments with harsh x-ray backgrounds. Recently, in collaboration with MIT, the ability to etch and scan CR-39 has been established at Sandia’s Z-facility. Data from ODIN collected from a subset of MagLIF experiments will be shown that illustrate this capability. |
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NP11.00044: Data processing to improving the signal of one-dimensional neutron images at Sandia's Z Pulsed Power Facility Michael A Mangan, Sidney Ricketts A one-dimensional imager of neutrons (ODIN) is being used to image neutrons emitted from a line source created in Magnetized Liner Inertial Fusion (MagLIF) experiments on the Z facility. MagLIF experiments produce DD total neutron yields that range from ~1 x 1012 to ~1 x 1013. The neutrons which pass through a 100-mm thick tungsten rolled-edge slit are imaged on multiple CR39 pieces used as detectors and held in alignment with pins though each piece. Each CR39 piece is etched and scanned with a microscope and the images recorded. The observed tracks are then re-binned to ODIN resolution (~500 µm). The binned data are then integrated to produce an axial profile of neutron data. New data analysis techniques have been developed to integrate multiple CR39 scans to increase signal to noise ratio. A key part of this process is correcting rotated or shifted data points that may be present from misalignments during the scanning process. Accurate accumulation of CR39 scans provide an increase in statistical accuracy of the axial profile, especially for lower yield experiments. |
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NP11.00045: Schlieren Refraction Measurements of Implosion Density Profiles Daniel J Haberberger, Alexander Shvydky, Steven T Ivancic, Valeri N Goncharov, Christian Stoeckl, Dustin H Froula In inertial confinement fusion implosions, the plasma density profile on the inner side of the driven shell is important to the performance of the design. If the profile is of higher density or longer scale length than that predicted by hydrodynamic simulations, the mass increase in the hot spot can decrease its compressibility and reduce performance compared to what is expected from the simulations. The density profile inside the imploding shell is largely shadowed in radiography caused by the large integrated absorption through the dense shell twice. We propose measuring the refraction of an x-ray probe through schlieren imaging. Because of the dependence of the signal on the gradient of density as opposed to density itself, this measurement has the capability of uncovering more information about the density profile inside the shell. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0003856. |
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NP11.00046: Calculated gamma-ray images from simple models of imploded ICF capsules for inference of structure at stagnation Nelson M Hoffman, Petr L Volegov, Verena Geppert-Kleinrath, Carl H Wilde, Kevin Meaney, Yongho Kim, Hermann Geppert-Kleinrath New gamma-ray images of fusion capsules* at ICF facilities raise the question of how to interpret such data. Comparisons of observed images and calculated images from detailed 2D and 3D rad-hydro capsule simulations will be useful, but it may be expensive to carry out such analyses, and to interpret discrepancies. So, to complement such detailed analyses, we investigate the use of simple static models of the imploded capsule, allowing a rapid scan of model parameter space followed by the inference of best-fit parameters, to describe what the image tells us about the imploded capsule. A typical model might consist of a two-region shell-and-core geometry, parameterized by inner and outer radii of the shell and the regions’ carbon densities. We use the MCNP6® code to calculate the image resulting from 4.4-MeV C(n,n')γ gamma rays, together with the DT fusion gamma rays. We discuss the additional constraints on the models from gamma-ray reaction-history measurements, and the importance of data such as the DT branching ratio and the scintillator response, in computing these images. |
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NP11.00047: A two-temperature thermonuclear burn condition for inertial confinement fusion targets with high-Z pushers Sean M Finnegan Two-temperature threshold conditions for the onset of thermonuclear (TN) self-heating and robust volume-burn in optically-thin plasma surrounded by a high-Z (opaque) pusher are presented. Volume-ignition ICF target designs employing high-Z metal pushers aim to minimize radiative plasma cooling by “trapping” bremsstrahlung radiation inside the fusion fuel cavity, lowering the required fuel energy for the onset of TN burn and ignition.[1] Traditional treatments have assumed that the onset of TN burn occurs while the plasma and radiation are in thermal equilibrium. However, simulations consistently suggest that this is not guaranteed. Here, a multi-fluid plasma model is used to derive threshold conditions for the onset of TN burn, where thermal equilibrium between the plasma and radiation at the initiation of TN self-heating is not assumed, and coupling between photons and electrons is retained. Additionally, the role of the thermodynamic evolution of the pusher, specifically the time-evolution of the pusher-wall temperature, in regulating the power-balance in the plasma and the time-dependent evolution of the self-heating threshold is discussed. |
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NP11.00048: Compression and Robust Burn in the Presence of Low-Mode Asymmetries for Double Shells David S Montgomery, Joshua P Sauppe We previously reported a metric for robust burn in double shell implosions, where the specific power deposited by alpha heating must exceed the specific power due to expansion cooling losses of the hot spot [1]. This criterion results in a minimum hot spot temperature at stagnation in the absence of burn. Margin is obtained for designs by the degree that they exceed this minimum no-burn temperature. In this present work, we extend this model to include simple low-mode asymmetry using a quasi-adiabatic approximation, and compare predictions of this simple model to 2D xRAGE simulations of double shell capsules. We further examine the role that radiation losses, due to increased surface area of the fuel-pusher interface, play in failing to meet ignition conditions, and how one might place experimental bounds on that loss. |
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NP11.00049: Kinetic Mix at Gas-Shell Interface in Inverted Corona Fusion Experiments William Riedel, Nathan Meezan, Drew P Higginson, Matthias Hohenberger, Mark A Cappelli, Siegfried Glenzer Gas-filled, laser-driven "inverted corona" fusion targets have attracted interest as a low-convergence neutron source and platform for studying kinetic physics. At the fill pressures under investigation, ejected particles from the shell can penetrate deeply into the gas before colliding, leading to significant mixing across the gas-shell interface. Here we use kinetic-ion, fluid-electron hybrid particle-in-cell (PIC) simulations to explore the nature of that mix. Simulations of the system demonstrate characteristics of a weakly collisional electrostatic shock, whereby a strong electric field accelerates shell ions into the rarefied gas and reflects upstream gas ions back against themselves. This interpenetration is mediated by collisional processes: at higher initial gas pressure, fewer shell particles pass into the mix region and reach the hotspot. This effect is detectable through neutron yield scaling vs. gas pressure. Predictions of neutron yield scaling show excellent agreement with experimental data recorded at the OMEGA laser facility, suggesting that 1D kinetic mechanisms are sufficient to capture the mix process. |
Not Participating |
NP11.00050: Using planar analogue experiments to aid design of double shell capsules Steven H Batha, Evan Dodd, Elizabeth C Merritt, Thomas J Murphy, Sasi Palaniyappan, Willow Wan, David S Montgomery, Eric N Loomis, Tana Morrow, Derek Schmidt Qualitative observations provide guidance for double shell capsule design choices. Consideration of material density and opacity properties led to a series of planar analog experiments using the Omega laser facility. These experiments showed aluminum to be the best material for the ablator (outer shell). The joint between the two outer shell hemispheres, required for fabrication, can introduce large distortions of the capsule symmetry during implosion. Of the three different joint shapes tested, the grooved joint showed less distortion. Shock timing measurements showed that an Eulerian radiation-hydrodynamics simulation code was adequate to use for detailed design. |
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NP11.00051: Improvements to the Modeling of the Opacity-on-NIF hohlraum for Anchor 2 Evan Dodd, Natalia Krasheninnikova, Ian L Tregillis, Kathy Opachich, Heather M Johns, Robert F Heeter, Thomas Day, Todd Urbatsch, Melissa R Douglas, Ted S Perry The Opacity-on-NIF experiments have begun taking data for LTE opacity measurements of iron at conditions referred to as Anchor 2: 180 eV and 3´1022 cm-3 [1]. Iron opacities are important for understanding the structure of the sun, yet there is an ongoing disagreement between opacity theory and data that makes corroboration highly important. We use Lasnex calculations to predict hohlraum temperature and to aid in understanding spectrometer background. The modeled hohlraum temperature comes from both the conversion of laser power to X-ray radiation and the coupling of radiation within the complex features of the Apollo hohlraum [2]. These processes are dependent on LTE tables of opacity and EOS and on inline calculations of non-LTE opacity. By using variations of these tables, we will show that the Apollo hohlraum geometry leads to separate LTE and non-LTE regions. We will also show results from recent updates to the non-LTE opacity model, and a comparison of calculated temperature to measurement. |
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NP11.00052: Gold L-shell Spectroscopy of Laser-Heated Hohlraums Duane A Liedahl, Hui Chen, Nobuhiko Izumi, Christine M Krauland, Otto L Landen, Edward V Marley, John D Moody, Marilyn B Schneider, Tod Woods Ablation of wall material in laser-heated hohlraums produces a high-temperature non-LTE plasma consisting of a high-Z material, usually gold, that expands against a low-Z gas fill. At electron temperatures of a few keV, gold becomes ionized into the M shell, as evidenced by soft X-ray line emission arising from ion-electron collisional processes. In the photon energy range 8-14 keV, gold L-shell spectra comprise three dominant features, each of which is an unresolved blend of inner-shell n=3 to n=2 emission lines simultaneously representing several charge states. Variations in electron temperature are accompanied by variations in the charge state distribution and the energy centroids of the emission-line blends. To first order, the energy centroids track the electron temperature, thereby providing a temperature diagnostic signature that is based on a “natural” hohlraum constituent. We present results of spectroscopic measurements and analyses of gold L-shell spectra acquired at the National Ignition Facility, including an evaluation of the level of consistency with K-shell tracers, sensitivity to electron density and radiation temperature, spectral model comparisons, and potential implications for radiation hydrodynamics simulations of hohlraums associated with ICF research. |
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NP11.00053: Analytic Modeling of Hohlraum Drive for High Performing HDC capsules. Mordecai D Rosen We present here a fully analytic derivation for the temperature, T(t), drive history of a typical hohlraum (with DU walls) containing a high performing High-Density-Carbon (HDC) capsule at the National Ignition Facility (NIF). A method to model the laser's complex temporal pulse shape is presented, which uses power laws, in time, for T(t) that differ in two temporal regimes, the foot of the pulse and the main power pulse. For each power law we use our published theory [Hammer & Rosen PoP 10, 1829 (2003)]. We match both the temperature T, as well as the absorbed diffusive ("Marshak wave") flux into the walls at the transition point between those two temporal regimes. Other complications, that are dealt with, are the dynamic motion of both the capsule and of the Laser Entrance Hole (LEH), and the time dependence of the conversion efficiency of turning laser power into x-ray drive. Good agreement with complex simulations [e.g. Callahan et al PoP 27, 072704 (2020)] and with data ensues. |
Not Participating |
NP11.00054: Measurements of Improved Ablation Front Stabilization using a Multi-ablator Material Inertial Confinement Fusion Capsule Joseph E Ralph, Vladimir Smalyuk, Daniel S Clark, Abbas Nikroo Experiments using a 430 TW, 970 kJ laser pulse have been conducted on the NIF (National Ignition Facility) to investigate the effect of a CH overcoat on the ablation front stability. Using the 3-rise inertial confinement fusion design, similar to recent burning plasma designs (see A. Zylstra), simulations show that the addition of a 10 μm layer significantly reduces ablation front instability growth from surface perturbations over all modes. Experimental measurements using pre-imposed surface ripples were conducted at two modes on an uncoated and CH-overcoated capsule. Results indicate a 5× reduction in growth at mode-150 and a 20× reduction in growth at mode-90 compared uncoated HDC capsules. The results are shown to be in-line with simulation predictions. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. |
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NP11.00055: Mitigating the Joint Feature in Double Shell Implosion Simulations David Stark, Joshua P Sauppe, Brian M Haines, Sasikumar Palaniyappan, Ryan F Sacks, Irina Sagert, Paul A Keiter, Theresa Quintana, Lindsey Kuettner, David S Montgomery, Tana Morrow, Brian Patterson, Lynne A Goodwin, Steven H Batha, Eric N Loomis Double shell capsules provide an attractive alternative in inertial confinement fusion experiments due to their potential for achieving a low-convergence, robust burn. However, symmetry degradation and accompanying reduced fuel confinement harm capsule performance due to the joint between the two hemispheres of the outer shell. The gap widens during irradiation and this perturbation grows and imprints onto the inner shell during the collision. xRAGE Eulerian radiation-hydrodynamic simulations predict significant reductions in deuterium–tritium fusion yields compared to joint-less simulations when the depth of the outer joint is increased. We explore how the technique of plating the insides of the outer gap with gold can mitigate the impact of this feature. Gold-plating in quantities comparable to or exceeding the “missing” outer shell mass shows promise toward restoring both implosion symmetry and yield closer to the joint-less levels. We show that x-ray synthetic radiographs can capture the shape and symmetry retention in the outer and inner shells. Finally, the performance of alternative coating materials is discussed. |
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NP11.00056: Studying shape transfer of low-mode deformations in Double Shell capsule implosions Irina Sagert, Joshua P Sauppe, Eric N Loomis, Brian M Haines, Paul A Keiter, David S Montgomery, Ryan F Sacks, Sasi Palaniyappan, Tana Morrow, John L Kline, Sean M Finnegan, Peter A Amendt We present numerical studies of Double Shell capsule implosions to understand the transfer of low-mode perturbations from the ablator to the inner shell. Double Shells are composed of a low-Z ablator (or outer shell) and a high-Z inner shell which encloses the fuel. During the implosion, the outer shell collides with the inner shell, setting it in motion. The latter then compresses the fuel to densities and pressures that are sufficiently high for volumetric ignition. However, asymmetry sources from the hohlraum radiation and capsule fabrication can result in low-mode deformations of the ablator. During shell collision, these can imprint on the inner shell affecting implosion symmetry and capsule performance. |
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NP11.00057: Simulations of thin-foil liner implosions driven by a dynamic screw pinch Shailaja Humane, Jeff M Woolstrum, Ryan D McBride Magnetically driven liner implosion experiments are conducted to generate and study fusion for energy, basic science, and stockpile stewardship applications. One of the challenges associated with the liner implosion method is that instabilities, such as the magneto-Rayleigh-Taylor instability (MRTI), develop during the implosions. These instabilities degrade the implosion symmetry and reduce fusion performance. Dynamic screw pinch (DSP) configurations on thin foil liner implosions have shown reduced MRTI amplitudes compared to standard z-pinch (SZP) configurations [P. C. Campbell et al., PRL 125, 035001 (2020)]. MRTI from SZP and DSP cases are analyzed using PERSEUS, an extended magnetohydrodynamics (MHD) code. These simulations are compared to SZP and DSP experiments conducted on the 1-MA COBRA pulsed-power driver to better understand the relative stabilization obtained with the DSP configuration. |
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NP11.00058: Instabilities and radiation flow at a hot plasma interface Matthew P Hill, Kevin P Driver, Peter Graham, Steven H Langer, Christine Cuppoletti, Clay Henning, Michael S Rubery, Alex Do, Steve Johnson, Stefano Schiaffino, Elvin R Monzon, Warren J Garbett, Shon T Prisbrey Mixing and radiation flow have a complex relationship in laser-driven hohlraums, an environment in which the formation and evolution of hydrodynamic instabilities may not be well suited to analysis using mix models calibrated for low temperature materials. The Hohlraum Wall Heating campaign at the National Ignition Facility aims to quantify the influence of radiation on mix (and vice-versa) at a high-Z/low-Z interface through simultaneous radiation burn-through measurements and high-resolution x-ray radiography. We discuss the qualification of the platform and data from our initial shots compared to 3D radiation hydrodynamic simulations and present options for future development. |
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NP11.00059: Viscosity Control in High Energy Density Regimes Relevant to Inertial Confinement Fusion Ioana D Dumitru, William A Angermeier, Joshua P Sauppe, Brett Scheiner Simulations of inertial-confinement-fusion (ICF) implosions play an important role in the design and analysis of different ICF targets. Hydrodynamic instabilities that occur during the implosion result in a non-uniform fuel compression and can mix colder ablator material into the fuel, both of which reduce the yield. However, viscosity is known to act as a saturation mechanism for hydrodynamic instabilities. This work utilizes simulations to investigate regimes where plasma viscosity is most influential for the behavior of ICF implosions. We analyzed this by characterizing different parameters such as coupling strength, Debye length, viscosity, and shock propagation while changing the materials and laser pulse shape in radiation-hydrodynamics simulations of these implosions. We identify parameter regimes where viscosity is expected to play a role in stabilizing hydrodynamic instabilities. |
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NP11.00060: A new atomic mix model library available in HYDRA* Michael M Marinak, Brandon E Morgan, Chris R Schroeder A new library of Reynolds Averaged Navier Stokes (RANS) mix models is now available in HYDRA. The RANSBox library, developed at LLNL, currently implements 17 RANS atomic mix models. These include KL-type models, K-epsilon, BHR-2 and BHR-3.1. These augment the existing set of atomic mix models available in HYDRA. These models are intended as an option for modelling instability growth at specific interfaces where stabilization due to ablation is absent. RANS models have been applied to a variety of experiments where turbulent mix may occur. For an embedded interface in a cryogenic ICF capsule, in which a variety of stabilization mechanisms reduce instability growth, direct simulation of multimode hydrodynamic instabilities is considered to be the most predictive. For these targets a RANS model may serve as a reduced model for high mode mix phenomena incorporated in a low-resolution simulation. These models are available for 1, 2 and 3 dimensional problems for all mesh types. We will examine how the extent of mixing obtained with particular RANS models compares with high resolution direct simulations for specific capsule designs. |
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NP11.00061: A Deep Learning Approach to Design Inertial Confinement Fusion Implosions Rahman Ejaz, Varchas Gopalaswamy, Riccardo S Betti The physics of inertial confinement fusion is rich and complex. Simulation codes that are used to design experiments are computationally expensive and lack the predictive capability required for extensive parameter exploration in search of a high-performing design for laser direct drive. In this work we use deep learning to build a fast emulator of experiments. The deep learning model is trained on a vast array of simulation data and is subsequently calibrated to expensive and limited experimental data using a technique known as “transfer learning.”1 The resulting deep-learning model can reproduce key experimental observables with high accuracy and inference times on the resulting model are unprecedented relative to those achieved with simulation codes. We use the model to search for a design that maximizes the experimental ignition threshold factor by iterating through input parameter space. Once a high-performing design is identified, high-fidelity simulations are used to understand the key physics of the design. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0003856. 1 K. D. Humbird et al., IEEE Trans. Plasma Sci. 48, 61 (2020). |
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NP11.00062: Energy-Conserving Particle-Pushing Algorithms for Hybrid Fluid-Kinetic Simulations Ayden J Kish, John G Shaw, Michael Lavell, Andrew T Sexton, Adam B Sefkow TriForce is a computational environment using a hybrid fluid-kinetic model to execute higher-fidelity simulations in shorter time frames. At its core are a particle-in-cell model and a meshless hydrodynamic model that can be coupled to perform modeling across multiple spatiotemporal scales and approximation regimes. The key to performing these calculations over large numbers of time steps is the management of accumulating numerical error. Energy-conserving algorithms for the integration of the particle equation of motion, also called "particle pushers," are needed to maintain accuracy while simultaneously loosening the spatial and temporal resolution requirements of the simulation. However, no one algorithm is suited for every task. As such, the TriForce Fundamental Algorithm Testing Environment is being developed as a stand-alone platform in Python to provide the opportunity to quickly implement, characterize, and compare algorithms for further use in TriForce's Library for Integrated Numerical Kinetics, which is the kinetic half of TriForce. Presented here are initial, side-by-side analyses of particle-pushing algorithms for TFLink, comparing their performance across multiple computational and physical situations. |
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NP11.00063: Influence of speckles on laser intensity profile near turning points Nicolas A Lopez, Eugene Kur, Thomas D Chapman, David J Strozzi, Pierre A Michel Ray-tracing codes have difficulty simulating beams near caustics (eg. turning or focal points) due to the wavelength-scale features that develop in the laser-spot intensity profile. Compounding the issue is the propensity for caustic-driven intensity amplification to trigger deleterious parametric instabilities such as cross-beam energy transfer between incident and reflected components of the wavefield (sometimes called `self-CBET'). Such instabilities can limit fusion yields in laser-driven fusion schemes by reducing the drive symmetry or increasing energy losses, so their accurate prediction is paramount. At the National Ignition Facility (NIF), phase plates are used to condition the laser spot at best focus, giving it a well-characterized profile. A byproduct of this process is the introduction of fine-scale intensity modulations called speckles, which further complicate the modeling of caustics. Here, we present a new analytical model for the behavior of a speckled laser beam near a turning point that illustrates how speckles modify the typically assumed Airy function profile. We discuss the limits in which the model reduces to Airy behavior in terms of practical constraints on system parameters, such as the f-number of the laser aperture. Finally, we present numerical simulations to verify the new analytical model. The findings from this study will be used to inform future reduced modeling efforts of speckled laser beams. |
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NP11.00064: Overview of TriForce: Projects, Progress, and Plans Adam B Sefkow, John G Shaw, Ayden J Kish, Michael J Lavell, Andrew T Sexton, Steinar Borve, Alex Bowman, Matthew Burns, Jonathan Carroll-Nellenback, Samuel A Cohen, Sandhya Dwarkadas, Marc Haddad, Keagan Hemsley, Abdallah Kokash, Yousef Lawrence, Robert L McCrory, Abdul Nahar, Sreepathi Pai, Aayush Poudel, Tamoy Seabourne, William Scullin, Scott Sikorski, Aditya R Srinivasan, Hristijan Stojkovich, Alex Velberg, Kagan Yanik, Shuang Zhai We report on development progress of our particle-based hybrid fluid-kinetic simulation framework named TriForce. The code recovers results from both radiation-magnetohydrodynamic and fully kinetic codes, and is being designed to operate in between, where both descriptions may coexist and interact. The hybrid method enables capabilities beyond either of the individual modeling methods alone, and is being used to investigate a range of topics in fields such as inertial confinement fusion, magneto-inertial fusion, magnetic confinement fusion, and high-energy-density physics. The goal of the TriForce Center for Multiphysics Modeling is to provide better predictive capability and access to modern, accelerated, and parallelized models for the benefit of the academic community. The current status of the project and its applications will be surveyed. |
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NP11.00065: The Effect of Transport on Multi-Ion shocks Liam Welch, Bhuvana Srinivasan, James L Juno Shock-driven multi-ion implosions are of importance both in astrophysical scenarios and in inertial confinement fusion (ICF) efforts. The transport processes that occur in these implosions are presently being studied numerically and experimentally and the effect of transport in plasmas with multiple ion species remains an open research area. In this work, we use the multi-fluid capabilities of Gkeyll to simulate shocks with transport effects for two-fluid (single ion and electron species) and three-fluid (two ion and electron species) plasmas. Results of shocks will be presented and compared with experimental data in weakly-coupled and moderately-coupled regimes. |
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NP11.00066: Examining the effects of variation of plasma conditions on the performance of high-energy long-pulse Brillouin amplifiers using one- and two-dimensional simulations Elias R Hansen, Vamshi Balanaga, Thomas D Chapman, Matthew R Edwards, Eugene Kur, Pierre A Michel, Jonathan S Wurtele The plasma Brillouin amplifier uses an ion acoustic wave (IAW) to transfer energy from a "pump" laser to a "seed" laser, and can generate short, high-intensity pulses without being subject to the damage limits of conventional optical systems. The concept is the subject of a feasibility study at the National Ignition Facility (NIF), and we have developed a two-dimensional time-dependent simulation code for studying Brillouin amplification in such high-energy long-pulse systems. We apply our code to the NIF parameters and test the robustness of the amplification process to the variation of plasma and laser conditions expected around the nominal experimental parameters, with particular attention paid to the non-trivial spatial variation of plasma density and temperature. We compare our 2D simulations with the results of a standard three-wave 1D model, showing that for non-zero crossing angle between pump and seed beams the 2D overlap geometry produces strong transverse variation resulting from asymmetric amplification not seen in 1D. We report detailed simulations that can be used to inform the planned experiments at NIF. |
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NP11.00067: Novel Mechanism to Generate Suprathermal Electrons by Anti-Stokes Langmuir Decay Instability Cascade Qingsong Feng, Ramy Aboushelbaya, Marko W Mayr, Ben T Spiers, Robert W Paddock, Iustin Ouatu, Robin Timmis, Lihua Cao, Zhanjun Liu, Chunyang Zheng, Xiantu He, Peter A Norreys Here, a new mechanism for electron acceleration by anti-Stokes Langmuir decay instability cascade of forward stimulated Raman scattering is proposed. The problem is divided into three regions. When the electron temperature is Te = 2.5 keV, the first region is between densities of ne < 0.108nc (Region I). Here, the backward stimulated Raman scattering of forward stimulated Raman scattering and corresponding Langmuir decay instability accelerate the electrons to high energy. The second region is when the densities are between 0.108nc < ne < 0.138nc (Region II). Here, anomalous hot electrons with kinetic energies above 100 keV are also generated. This process cannot be explained by traditional acceleration mechanisms. Evidence is presented to show that these hot electrons arise from anti-Stokes process of Langmuir decay instability cascade of forward stimulated Raman scattering. Finally, the third region is ne > 0.138nc (Region III), where the electrons trapped by backward stimulated Raman scattering induced Langmuir wave are accelerated by the forward stimulated Raman scattering induced Langmuir wave directly. This new mechanism not only explains anomalous energetic electron generation in indirectly driven inertial confinement fusion experiments and the significant energy losses on the inner cones of beams for the first time (compensated by cross-beam energy transfer at the laser entrance holes of the holhraum targets), but also provides a new way of accelerating the electrons to higher energy in the laser-driven wakefield accelerator research. |
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NP11.00068: Higher Dimensional Effects in Laser Plasma Interactionns Relevant to Inertial Fusion Frank S Tsung, Benjamin J Winjum, Roman Lee, Warren B Mori In inertial confinement fusion, laser plasma interactions, where the incident laser decays into a backward going light wave and a collective mode of the plasma can reduce laser coupling by reflecting the incident laser and also cause pre-heat which can can degrade compression. In SRS, the instability itself is primarily one dimensional, meaning that the scattered light and the plasma waves both travel in the same direction as the laser. However, higher dimensional effects, which can be caused by laser speckles used by laser smoothing schemes, or higher dimensional effects in laser plasma interactions near the quarter critical surface such as side-scatter or the two plasmon decay, requires two- or even three-dimensional simulations. In this work, we will present two dimensional and three dimensional, and quasi-3D simulations of laser plasma interactions relevant to current and future ICF experiments to illustrate these effects. |
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NP11.00069: Bow shock formation in a plasma flowing across randomized laser beams Wojciech Rozmus, Joshua Ludwig, Stefan Hueller, Harvey A Rose, William A Farmer, George F Swadling, Bradley B Pollock, Colin J Bruulsema, Pierre A Michel High energy lasers interacting with flowing plasmas can produce a plasma response that leads to beam bending and, by momentum conservation, to slowing down of the plasma flow velocity [1]. For the incoming plasma flow, with a velocity slightly greater than sound speed, the plasma response to a ponderomotive force exerted by speckled laser beams is the strongest, such that slowing down of the flow leads to the formation of a shock. We present hydrodynamic simulations of plasma flow about speckled laser beams that demonstrate shock formation. Linearized theory of the plasma penetration length across a laser beam that is necessary to achieve subsonic flow velocity is confirmed in simulations. A cumulative effect of many speckles produces shock propagating first across the laser beam that emerges next from the speckled laser beam and freely propagates upstream with the velocity and jumps of the flow velocity and density that satisfy Rankine-Hugoniot relations. Perturbations of plasma parameters associated with the shocks are on the order of tens of the percent of their background values. We have repeated the simulations and the analysis for the randomized beams with the temporal incoherence using RPP and SSD corresponding to NIF parameters. For SSD we have also examined the influence of the inherent speckle motion on the ponderomotive force and the shock formation. We have established scaling laws accounting for the SSD parameters. Results of the simulations and theoretical analysis are also discussed in the context of the planned NIF experiments. |
Not Participating |
NP11.00070: Study of stimulated Raman scattering of laser speckles in the inertial confinement fusion regime using 2D2V Vlasov simulations* Thomas D Chapman, Richard L Berger, Jeffrey W Banks, William Arrighi We present simulations of stimulated Raman scattering occurring in laser speckles with laser parameters and plasma conditions typical of inertial confinement fusion experiments. Our simulations leverage recent advances in numerical methods for solving the Vlasov equation using high-order-accurate numerical schemes, permitting previously unreachable scales to be simulated in a 2D2V phase space. Our simulations include relativistic and collisional effects. The employed continuum representation of the particle distribution functions can be noiseless to machine precision. Such a property is useful for the precise study of instabilities, particularly those that are resonant in the far tail of the distribution. However, many applications benefit from the presence of noise that approximates physical thermal fluctuations, such as the study of simultaneous and competing instabilities (as is the case here). We describe a particle-based method to model fluctuations within continuum codes from which instabilities may subsequently grow. |
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NP11.00071: The importance of laser wavelength for driving inertial fusion targets. Andrew J Schmitt, Stephen P Obenschain It is well known that the wavelength of the laser determines many of the fundamental parameters of the laser coupling that drive an inertial fusion target. Deposition density, mass ablation rate, absorption fraction, hydrodynamic efficiency, and laser-plasma instability thresholds are all influenced by laser wavelength, with shorter laser wavelength being uniformly favorable. What may be less appreciated is the synergistic effects of decreasing the laser wavelength, and its implications for ICF. We show that ostensibly minor decreases in laser wavelength --- e.g., changing the drive wavelength from the common 351 nm ( frequency-tripled glass laser) to 248 nm (KrF laser) or 193 nm (ArF laser) --- can have much larger effects on the resulting target performance. The increase in usable bandwidth for the shorter wavelength lasers also has a profound impact, decreasing laser imprint and further increasing parametric instability thresholds, and can increase the design space for icf targets even further. We will show simulation results that reinforce these points. |
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NP11.00072: Acceleration of ions in the corona of laser fusion pellets for fast ignition Robert Bingham, Elisabetta Boella, Robert Alan Cairns, Raoul M Trines, Marija Vranic, Nitin Shukla, Luis O Silva Experiments on the interaction of high power lasers with laser fusion targets have shown evidence of shock-like structures with very high electric fields existing over very short distances. These fields are responsible for ion acceleration and species separation in the laser fusion targets. It has also been demonstrated using particle in cell simulations, (E. Boella et al., Phil. Trans. R. Soc. A 379, 20200039, 2021) that an intense laser pulse, distinct from the drive laser, interacting with the long scale-length corona plasma is able to launch a collisionless shock around the critical density. The shock structure travels rapidly up the density gradient reflecting and accelerating ions to MeV energies leading to the possibility of fast ignition using these shock accelerated ions. The accelerated ions generate plasma turbulence that can influence the spectrum of accelerated ions. We will present results of the role plasma turbulence plays in the propagation of the shock wave and ion acceleration as well as considering the effect of magnetic fields on the shock dynamics. This latter part makes connection with magnetised target fusion (MTF) experiments. |
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NP11.00073: On the possibility of achieving ignition with ions accelerated via laser-driven electrostatic shocks in the corona of an inertial confinement fusion pellet Elisabetta Boella, Robert Bingham, Robert Alan Cairns, Peter A Norreys, Raoul M Trines, Robbie H Scott, Marija Vranic, Nitin Shukla, Luis O Silva Ion-driven fast ignition is a promising approach to inertial confinement fusion. In the traditional scheme, ions are accelerated via Target Normal Sheath Acceleration from a target placed outside the hohlraum [1]. |
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NP11.00074: Shock-Augmented Ignition Using Indirect Drive William T Trickey, Nigel C Woolsey, Robbie H Scott Shock ignition[1] is an ignition concept that uses a late-time power spike to drive a strong shock that collides with a rebounding primary shock driven by the capsule compression process to ignition. This has been thought unfeasible with indirect drive because the thermal capacity of the hohlraum makes it difficult to produce sufficiently fast rises in hohlraum temperature. The “shock-augmented” pulse shape, a concept proposed by Scott et al.,[2] enables the generation of a strong shock strength at drive power and intensity much below those needed for shock ignition. This is possible by decreasing the drive immediately before the ignition spike. This talk shows that the shock-augmented approach relaxes the rate at which hohlraum temperature is required to change, making indirect-drive shock-augmented ignition possible. One-dimensional radiation-hydrodynamics simulations illustrate the drive requirements to achieve ignition and that ignition is robust with respect to the timing and strength of the igniting shock. [1] R. Betti et al., Phys. Rev. Lett. 98, 155001 (2007). [2] R. Scott et al., Bull. Am. Phys. Soc. 65, GO09.00010 (2020). |
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NP11.00075: Studying scaling physics of the MagLIF platform on the Z accelerator facility Daniel E Ruiz, David A Yager-Elorriaga, Matthew R Gomez, Paul F Schmit, Matthew R Weis, Adam J Harvey-Thompson, Christopher A Jennings, Eric Harding, William E Lewis, Gabriel A Shipley, David J Ampleford, Kristian Beckwith Magneto-inertial fusion (MIF) concepts, such as the Magnetized Liner Inertial Fusion (MagLIF) platform [Phys. Rev. Lett. 113, 155003 (2014)], constitute a promising avenue for achieving ignition and significant fusion yields in the laboratory. A theoretical framework [Phys. Plasmas 27, 062707 (2020)] was recently developed to self-similarly scale MagLIF targets to larger, more powerful pulsed-power drivers while not significantly deviating from the physical regimes studied on the present-day Z accelerator facility. This framework is based on identifying the key dimensionless quantities describing a MagLIF system and scaling the MagLIF experimental parameters to preserve such quantities to the furthest extent possible. The theory determines the scaling rules for the MagLIF experimental parameters and performance metrics as functions of peak current Imax. Based on this approach, in the upcoming years, we shall study MagLIF scaling physics on the Z facility within the 12-20 MA peak-current range. In this talk, we review the proposed multi-year experimental plan, and we compare pre-shot HYDRA simulations to predictions of the theoretical model. HYDRA simulations demonstrate scaling that is consistent with the theoretical results for a variety of performance metrics. |
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NP11.00076: Dense cryogenic fuel layers for high performance magnetized liner inertial fusion Stephen A Slutz, Thomas J Awe, Jerry A Crabtree Magnetized Liner Inertial Fusion (MagLIF) implosions driven by the Z machine produce greater than 1013 DD fusion reactions [M.R. Gomez et al. Phys. Rev. Lett. 113, 155003 (2014)]. Simulations indicate that much higher yields should be possible with increased drive current, fuel density, preheat energy, and dense cryogenic fuel layers [S.A. Slutz et al. Phys. Plasmas 23, 022702 (2016)]. Dense cryogenic fuel layers (deuterium or deuterium/tritium) on the inner surface of liners should also reduce mix enhanced radiation losses by separating the fuel from typical liner materials such as beryllium. However, at temperatures low enough to form hydrogen ice the vapor density is only 0.3 mg/cc, which is not high enough for MagLIF operation. We present two solutions to this problem. First, a fuel wetted low density plastic foam can be used to form a layer on the inside of the liner. The desired vapor density can be obtained by controlling the temperature. This does however introduce carbon into the layer, which will enhance radiation losses. Second, we show that low temperature gaseous fuel can be introduced into the liner just before the implosion without melting a significant amount of a pure frozen fuel layer. This approach is the most promising for high yield and gain with MagLIF. |
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NP11.00077: Diagnostics and first results for the PLX PJMIF target plasma jets Andrew Case, Edward Cruz, Marco Luna, Robert Becker, Adam Cook, Franklin D Witherspoon The PLX BETHE team will perform a liner on target experiment for Plasma Jet Magneto-Inertial Fusion (PJMIF) at LANL. The target is made by stagnating multiple magnetized plasma jets. The goal nominal jet parameters are density of 3x1014 cm-3, temperature above 5 eV, velocity of 100 km/s, and magnetic field of 1 kG. To verify these parameters we measure velocity, Te, density, and magnetic field. The diagnostics are interferometry, movable B-dot probe array, movable triple probe, spatially resolved photodiodes, high speed imaging, and time resolved spectroscopy. A second chord has been added to the interferometer with provision for a third, and SNR has been improved by a factor of ten. Automating data collection (using LabView) and analysis speeds up the evaluation of parameters (accelerator voltage, dispensed gas mass, gas valve timing, magnet current, etc.) which produce the best target plasma. The supersonic magnetized plasma poses diagnostic challenges due to shock formation around probes which are discussed along with the means used to address them. |
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NP11.00078: Measurements of Shock-Front Separation in Multi-Ion-Species Plasma Shocks Feng Chu, Samuel J Langendorf, Andrew L LaJoie, Brett Keenan Collisional plasma shocks generated from supersonic flows are an important feature in astrophysical systems and high-energy-density (HED) experiments. Compared to single-ion species plasma shocks, plasma shock fronts with multiple ion species contain more features, one of which is interspecies ion separation. This phenomenon has been previously investigated both in theory and simulation, however, few experimental studies of the structure inside a shock front have been performed. This work presents direct measurements of shock-front separation in multi-ion-species collisional plasma shocks, produced by head-on merging of two plasma jets composed of inert gas mixtures of varied concentration. Jet collisions are performed both in a free vacuum and a confining shock tube, resulting in different expansion dynamics out of the plane of the shock. A 1D ion-kinetic simulation is also performed, and the simulation results are compared with experimental results. |
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NP11.00079: Overview of Present and Planned Diagnostics of the Plasma Liner Experiment (PLX) Andrew L LaJoie, Feng Chu, Lucas G Webster, Samual J Langendorf, Mark A Gilmore The Plasma Liner Experiment (PLX) is studying an innovative fusion approach, plasma-jet-driven magnetoinertial fusion (PJMIF). We provide an overview of the diagnostic approaches planned to assess critical characteristics of the implosion, and ultimately the device's potential as a controlled fusion apparatus. Liner uniformity, which can influence the ultimate target compression ratio and instability growth rate, may be examined using a set of high-speed cameras at various vantage points, making use of spectral techniques to enhance contrast and tomographic reconstruction of 3D spatial profiles. Relative emission strengths will used to determine electron temperature and impurity presence in the liner via UV-VIS-NIR imaging spectrographs. Bolometers will be implemented to gauge the radiated power from the liner, which is indicative of the liner stagnation parameters via comparisons with integrated modeling. Other diagnostics include a set of fish-eye CCD cameras which will be used to determine individual jet speeds and balance, the existing multi-chord interferometer system to determine line-integrated electron density, and lastly both traveling and fixed Thomson scattering systems in the design stage, which will be used for characterization of the eventual magnetized target. |
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NP11.00080: Three Dimensional Modeling of High \ Beta Magnetized Targets for Plasma-jet-driven Magneto-inertial-fusion (PJMIF) Aalap Vyas, Jason Cassibry, Samual J Langendorf, Douglas Witherspoon Numerical simulations of compact toroid formation from supersonic plasma jets have been performed using Smooth Particle Fluid with MAXwell equation solver (SPFMax), a smooth particle hydrodynamics (SPH) code supporting the PLX-BETHE project. The physics includes radiation, Braginskii thermal conductivity and ion viscosity, separate ion and electron temperatures, tabular EOS (LTE and non-LTE), nonlocal fusion product deposition, and a novel electromagnetic field solver based on a combination of transmission line theory and Biot Savart's law. Initial plasma jet conditions are derived from the experimental output of Hyperjet-designed plasma guns. Variation in initial velocity, density, temperature, ion species, interpenetration physics, and initial velocity gradients will be included to study the effects on synthetic interferometry, temperature, and pressure within the imploded jets. Primarily this will be a study limited to 36 jets to facilitate comparisons with experimental data available via the PLX-BETHE experiments. |
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NP11.00081: Design of Thomson Scattering System on the Plasma Liner Experiment Lucas G Webster, Andrew L LaJoie, Samuel J Langendorf, Mark A Gilmore The Plasma Liner Experiment (PLX) is a proof-of-concept experiment for Plasma-Jet driven Magneto-Inertial Fusion (PJMIF) application. It uses supersonic imploding plasma liner for compressing magnetized plasma fuel to fusion temperatures and pressures. Its main goal is to explore the physics of the formation of a spherical plasma liner and it is being jointly developed by HyperJet Fusion and Los Alamos National Laboratories (LANL). |
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NP11.00082: Measurement of the magnetic field and wall motion of hohlraum materials for the MagNIF platform Bernard Kozioziemski, John D Moody, Evan Carroll, Jay Javedani, Anthony Johnson, Sergei O Kucheyev, Christopher Provencher, Vincent Tang, Dexter K Yanagisawa The MagNIF experimental platform at the National Ignition Facility (NIF) is developing the technology necessary to apply a magnetic field to a deuterium-tritium fuel layer in an indirect-drive inertial confinement fusion (ICF) target. Simulations suggest that application of a seed magnetic field exceeding 25 T will increase the implosion ion temperature and neutron yield. The hohlraum material needs to allow the magnetic field to penetrate with minimal loss of energy into the hohlraum itself to prevent motion and heating of the hohlraum wall. We will present measurement of the magnetic field and wall motion of both gold and a tantalum-gold alloy hohlraums. We will demonstrate that the tantalum-gold alloy is suitable for use in a MagNIF experimental platform. |
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NP11.00083: Exploring extreme magnetization phenomena in directly-driven imploding cylindrical targets Chris Walsh, Ricardo Florido, Mathieu Bailly-Grandvaux, Francisco Suzuki-Vidal, Jeremy P Chittenden, Aidan C Crilly, Marco A Gigosos, Roberto C Mancini, Gabriel Perez Callejo, Christos Vlachos, Christopher McGuffey, Farhat N Beg, Joao J Santos This poster shows extended-magnetohydrodynamics (MHD) simulations exploring an extreme magnetized plasma regime realisable by cylindrical implosions on the OMEGA laser facility. This regime is characterized by highly compressed magnetic fields (greater than 10~kT across the fuel), which contain a significant proportion of the implosion energy and induce large electrical currents in the plasma. Parameters governing the different magnetization processes such as Ohmic dissipation and suppression of instabilities by magnetic tension are presented, allowing for optimization of experiments to study specific phenomena. For instance, a dopant added to the target gas-fill can enhance magnetic flux compression while enabling spectroscopic diagnosis of the imploding core. In particular, the use of Ar K-shell spectroscopy is investigated by performing detailed non-LTE atomic kinetics and radiative transfer calculations on the MHD data. Direct measurement of the core electron density and temperature would be possible, allowing for both the impact of magnetization on the final temperature and thermal pressure to be obtained. By assuming the magnetic field is frozen into the plasma motion, which is shown to be a good approximation for highly magnetized implosions, spectroscopic diagnosis could be used to estimate which magnetization processes are ruling the implosion dynamics; for example, a relation is given for inferring whether thermally-driven or current-driven transport is dominating. |
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NP11.00084: Field-Reversed Configuration lifetime scaling under compression Thomas E Weber, John C Boguski, Ian A Bean Matching the confinement timescales of the target plasma to the compression timescale is a central challenge of Magnetized Target Fusion (MTF). Field-Reversed Configuration (FRC) plasmoids are commonly considered as a candidate target plasma for MTF due to their relatively high average beta. However, the maximum achievable lifetime appears too short for slow compression schemes, such as liquid liner compression (e.g., LINUS, General Fusion), and has proven difficult even for fast compression schemes, such as pulsed-power-driven solid liners (e.g., LANL/AFRL MTF collaboration). We examine FRC lifetime scaling under liner and flux compression scenarios to determine required starting conditions needed for fusion gain and discuss driver characteristics needed to achieve the necessary target plasma parameters and/or compression timescales. |
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NP11.00085: Updates to the Laser Gate Experiment for Increasing Preheat Energy Coupling in Magnetized Liner Inertial Fusion (MagLIF) Stephanie M Miller, Stephen A Slutz, Akash Shah, Brendan J Sporer, Carolyn C Kuranz, Matthew R Gomez, Nicholas M Jordan, Ryan D McBride Magnetized Liner Inertial Fusion (MagLIF) is an inertial confinement fusion concept being tested at Sandia National Laboratories (SNL). MagLIF targets feature a laser entrance hole covered by a thin (few-micron-thick) window to hold the pressurized fusion fuel in place. There are energy losses as a preheating laser beam ablates through this plastic window. Laser-window interactions reduce heating efficiency and mix window and target materials into the fuel. To reduce these losses and improve fusion yield, we are implementing a system to remove this plastic window before the laser beam passes through the window opening. This window removal method is referred to as "Laser Gate". We have demonstrated a Laser Gate proof of concept at the University of Michigan (UM) [S.M. Miller et al., RSI 91, 063507 (2020)]. More recently, we have added an interferometer to measure the density of the gas/fuel as it escapes from the target. This UM test stand will allow us to further study window opening dynamics, assess system jitter, and determine design specifications for upcoming preheat experiments at SNL. We will report on the results of our intermediate experiments at UM as well as our designs for integrating this version of Laser Gate into the already established preheat platform at SNL. |
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NP11.00086: Diagnosing current losses in the MJOLNIR DPF Paul C Campbell, Clement S Goyon, Steven Chapman, Alexander P Povilus, Rick Anaya, Michael G Anderson, Don Max, Anthony J Link, Christopher M Cooper, Andrea E Schmidt A dense plasma focus (DPF) is a compact coaxial plasma gun which completes its discharge as a z-pinch. At LLNL the MJOLNIR (MegaJOuLe Neutron Imaging Radiography) DPF is designed for radiography and high yield operations. This device 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. The experiments run on MJONILR are complemented by unique particle-in-cell simulations of the DPF discharges. These detailed simulations show a mismatch between the simulated and measured currents, suggesting that current loses are occurring somewhere in the DPF head. In order to determine if, and where, current is being lost a set of B-dot probes and Rogowski coils have been developed. Both the probe designs and preliminary results from this set of new diagnostics will be presented. |
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NP11.00087: Neutron diagnostics and timing on the MJOLNIR dense plasma focus Christopher M Cooper, Clement S Goyon, Andrea E Schmidt, Rick Anaya, Michael G Anderson, Paul C Campbell, Steven Chapman, Owen B Drury, Luis Frausto, Drew P Higginson, Anthony J Link, Don Max, Alexander P Povilus, Sophia Rocco, William Waggoner, Kurt Walters The MJOLNIR dense plasma focus (DPF) prototypes configurations to optimize flash neutron radiography. In order to properly time the neutron camera to the unscattered neutrons, the “prompt” neutron pulse is measured using a series of shadowbarred detectors at the location of the neutron camera scintillator. The pulse is transformed back into the DPF pinch location and time within a few ns and is correlated with other diagnostics. |
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NP11.00088: Dense Plasma Focus Simulations at LLNL Anthony J Link, Rick Anaya, Michael G Anderson, Justin R Angus, Gustavo Bartolo, Paul C Campbell, Steven Chapman, Christopher M Cooper, Owen B Drury, Clement S Goyon, Drew P Higginson, Luis Frausto, Don Max, Matt McMahon, Yuri A Podpaly, Alexander P Povilus, Sophia Rocco, William Waggoner, Kurt Walters, Amanda Youmans, Andrea E Schmidt Dense plasma focus (DPF) Z-pinches are compact pulsed 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 was recently upgraded to 2 MJ of stored energy. 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 of the full bank. |
Not Participating |
NP11.00089: Optimizing Dense Plasma Focus Neutron Yields via Kinetic Simulations Matthew M McMahon, Justin R Angus, Drew P Higginson, Anthony J Link, Andrea E Schmidt We report on a study using the particle-in-cell code Chicago(C. Thoma, Phys. Plasmas 24, 062707 (2017)) to perform fully kinetic simulations of dense plasma focus (DPF) with a variety of anode and target configurations. The evolution of a DPF is broken into several phases. The first phase involves a plasma sheath being formed from the electrical breakdown of fill gas along the insulator. JxB forces then accelerate this plasma along the anode and then inwards towards the axis. The final phase occurs when the plasma implodes on axis and pinches to high density and temperature. During this final phase DPFs can accelerate MeV ion beams and the interaction of these beams and the target formed can produce neutrons. In order to optimize the neutron yield during this final phase simulations are performed modeling the The MegaJOuLe Neutron Imaging Radiography (MJOLNIR) DPF with a variety of anode configurations. Variations on the anode length, shape, and the inclusion of a high density on axis gas jet are explored in order to find the configuration that provides the optimal target density and temperature for neutron production during the high-density pinch phase. |
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NP11.00090: Modelling high energy density systems with strong radiative loss using static mesh refinement Nikita Chaturvedi, Jeremy P Chittenden, Nicolas Niasse Radiative collapse occurs in dense plasmas where radiative loss drops the thermal pressure below the compressional magnetic pressure, leading to a runaway collapse to very small scale lengths. This is typically studied in Z-pinch plasmas when the current applied exceeds the Pease-Braginskii current (where the pinch is in pressure equilibrium). Studies have also been extended to X-pinch loads, where the crossing point between two wires forms a micro Z-pinch with even stronger j×B compression. The collapse can be terminated by various processes; development of instabilities, reaching the photon self-absorption (optically thick) limit, or in extreme cases the electron degeneracy limit. |
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NP11.00091: Development of an energy-dispersive X-ray absorption fine structure spectroscopy diagnostic driven by a portable X-pinch backlighter Jergus Strucka, Jack W Halliday, Tatiana Shelkovenko, Sergei Pikuz, Simon N Bland We present progress in the campaign to develop energy-dispersive X-ray absorption fine structure (EDXAFS) diagnostic driven by a small portable X-pinch. |
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NP11.00092: Double Gas Puff Z-pinch Experiments on the CESZAR LTD Fabio Conti, Apsara M Williams, Jeff Narkis, Nicholas Aybar, Vladimir Fadeev, Farhat N Beg Gas puff Z-pinches1 are intense sources of X-rays and/or neutrons and are of interest to study the physics of high energy density matter. Experiments were conducted on the CESZAR linear transformer driver2 (LTD) with 500 kA, 160 ns current pulses, using a double nozzle producing an annular shell and a central jet. The effect of changing gas species was studied using metrics like instability amplitude and energy coupling. We show that a low-impedance LTD can implode a variety of gas puff loads with energy coupling efficiency of order ~10% from the primary storage. The addition of the central jet improves pinch stability, reproducibility, and energy coupling compared to a hollow shell gas puff. Magneto-hydrodynamic simulations are used to compare plasma kinetic energy and instability amplitude, and to infer values of internal energy. Trends of stability versus gas atomic number are discussed and related to the X-ray emission characteristics. |
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NP11.00093: Magnetized gas puff Z-pinch experiments on the CESZAR LTD Apsara M Williams, Fabio Conti, Vladimir Fadeev, Nicholas Aybar, Jeff Narkis, Farhat N Beg Z-pinches are powerful sources of X-rays and neutrons but are prone to developing disruptive magneto-Rayleigh Taylor (MRT)instabilities. One proven [1] mitigation technique is embedding an axial magnetic field into the plasma column prior to implosion. Recent experiments [2] on gas puffs imploded on an 300kA, 1.6ns driver showed that the axial magnetic field stabilized the pinch but also increased implosion time and decreased pinch compression. Here, we present results of gas puff Z-pinches with a pre-embedded axial magnetic field conducted on the CESZAR linear transformer driver (LTD) at UCSD with 500kA current and 150ns rise time. The pinch stability and implosion times were measured for values of initial axial magnetic field, Bz0 = 0-1T using a combination of diagnostics including filtered photodiodes, time-gated XUV pinhole imaging, laser schlieren imaging and interferometry. These results provide insight on the effects of axial magnetic fields on fast (≤ 200 ns) implosions driven by low-impedance current generators. |
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NP11.00094: Effects of Pre-Ionization on Current Distribution in a Gas-Puff Z-Pinch Akash Shah, Brendan J Sporer, George V Dowhan, Kristi W Elliott, Krishnan Mahadevan, Nicholas M Jordan, Ryan D McBride The Z-machine at Sandia National Laboratories is instrumental in plasma physics research across a range of applications. University-scale gas-puff z-pinch experiments at lower currents (~1-MA), can inform the higher-current (~20-MA) experiments conducted on the Z-machine. A gas-puff z-pinch puffs gas into the anode-cathode gap, 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. The initial ionization or pre-ionization condition of the gas-puff prior to compression is poorly understood1. The effects of pre-ionization on the current distribution through the gas-puff as the implosion progresses is also an open question. Quantifying how the pre-ionization and current distribution affect x-ray and fusion production, which are largely the result of micro-pinch instabilities, is crucial to understanding z-pinch physics. We report on the development of, and initial results from, the gas-puff experiment for the 1-MA, 100-ns MAIZE Linear Transformer Driver. 1. J. Giuliani, “A Review of the Gas-Puff Z-Pinch as an X-Ray and Neutron Source”, IEEE Trans. Plasma Sci. 43, 2385 (2015). |
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NP11.00095: Recent Simulations of Nozzle Gas Flow and Gas-Puff Z-Pinch Implosions With Magnetic Fields in the Weizmann Z-Pinch Varun Tangri, John L Giuliani, Arati Dasgupta, Tal Queller, Eyal Kroupp, Yitzhak Maron Recent measurements1 of densities and temperatures at various R and Z-locations near stagnation seem to be inconsistent with earlier 2D simulations using MACH2-TCRE as well as simple snowplow models.
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NP11.00096: Wire-Array Z-pinch within a Dynamic Magnetic Mirror Chiatai Chen, Eric S Lavine, William M Potter, Bruce Kusse A dynamic axial magnetic mirror could reduce end losses of cylindrical magneto-inertial fusion targets and could be implemented in MAGLIF experiments using auto-magnetizing liners to increase fuel density. To study the plasma confinement by a pulsed-power driven dynamic mirror, COBRA, a 1MA, 100-ns rise time pulsed-power machine, was used to implode arrays of wires threaded through twisted tubes that form helical current paths on the two ends to produce the mirror field. The wire arrays are composed of 8 Al wires with a wire diameter of 17 μm, an initial array diameter of 11 mm and an array length of 10 mm. Two mirror designs with a mirror ratio of 2 and peak mid-point axial magnetic fields of 0.77 T and 1.5 T respectively are tested along with the standard Z-pinch control case without any axial/mirror field. The pinch dynamics are monitored by a 12-frame optical high-speed camera, and XUV pinhole cameras while time-resolved X-ray power measurements were collected by a set of diamond PCDs and Si diodes. The high field case (1.5 T) showed an improved repeatability over the control case in the integrated PCD signal that corresponds to the total X-ray yield. Shot experiments with the dynamic magnetic mirror were also done with wire arrays twisted in the opposite direction to produce an opposing axial magnetic field. |
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NP11.00097: Measurements of the imploding plasma sheath in triple-nozzle gas-puff z pinches on 1-MA COBRA Eric S Lavine, Sophia Rocco, Jacob T Banasek, William M Potter, Jay S Angel, Euan Freeman, David A Hammer, Bruce Kusse The conditions of imploding gas-puff z-pinch liners are measured on the 1-MA, 220-ns COBRA generator at Cornell University for various gas species and initial densities midway through the run-in phase of the implosion. The gas-puff loads are initialized by a 7 cm diameter triple-nozzle gas valve assembly with concentric outer and inner annular nozzles and a central gas jet. A 526.5-nm, 10-J Thomson scattering diagnostic laser provides spatially resolved flow and temperature profiles at a radius of 1-1.5 cm with a resolution up to 250 μm. Laser shearing interferometry provides measurements of the local electron density while extreme ultraviolet pinhole cameras record the time evolution of the collapsing plasma column. Additional diagnostics include filtered photoconducting diodes to measure x-ray emission near stagnation. The results reveal distinct differences in velocity and temperature profiles between the various gas species at similar mass densities, as well as between identical gas species at different initial densities. In some cases, the scattered laser spectra suggest additional non-thermal broadening that is inconsistent with local velocity gradients and may be indicative of small-scale hydrodynamic motion. |
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NP11.00098: Observation of XUV emission from Al Z-pinch plasmas in the 40-700Å range Haritha K Hariharan, Kyle J Swanson, Roberto C Mancini, Vladimir V Ivanov, Bernhard Bach, Alexey L Astanoviskyi, Ryan P Schoenfeld, Enac Gallardo-Diaz The radiation emission from Al wire-array Z-pinch plasmas was recorded in the XUV range from 40 to 700Å. Cylindrical, 6mm in diameter, 20mm tall arrays with eight 15m Al wires were imploded using the 1MA Zebra pulsed power generator at the University of Nevada Reno. At the collapse of the implosion, the Z-pinch plasma radiates up to terawatts of broadband x-ray power. This high x-ray output makes them attractive as x-ray sources for radiation-driven experiments. Characterization of the x-ray emission is important for understanding the spectral distribution of the x-ray flux impinging on a sample as well as for informing models of the Z-pinch implosion. We present measurements of the time-integrated x-ray emission spectrum from the Z-pinch recorded in the range from 40 to 700Å using a grazing incidence Acton spectrometer equipped with a spherically bent 1.5m-radius diffraction grating. The data was collected in a series of nominally identical experiments. The observed spectrum is rich in line emission from transitions in several charge states. We discuss the experimental results and an initial interpretation of the line spectrum. |
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NP11.00099: Operation and Performance of a 750 kJ Dense Plasma Focus at Verus Research Jonathon Heinrich, Michael Butcher, Manual Alan, Carl Willis, Robert Dwyer, Shelby Huber, Phillip Martinez, Brian Gorgas Verus Research designed, built, and operates a high-power dense plasma focus (DPF) in Albuquerque, NM, with the objective of creating a next-generation, high-fluence, fusion neutron source. Verus Research recently completed a 4-year research and development campaign to significantly mature the DPF design. We present the experimental performance of the Verus Research DPF, including repeatability, neutron yield, lessons learned, and the effect of various plasma facing materials and geometries. |
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NP11.00100: Optimal conditions for high neutron yields in deuterium gas-puff z-pinches Daniel Klir, Alexander V Shishlov, Stuart L Jackson, Rustam K Cherdizov, Jakub Cikhardt, Fedor I Fursov, Volody A Kokshenev, Jozef Kravarik, Pavel Kubes, Nikolai E Kurmaev, Jakub Malir, Vojtech Munzar, Jan Novotny, Nikolai A Ratakhin, Karel Rezac Deuterium gas-puff z-pinches are researched primarily as efficient sources of DD fusion neutrons. The first experiment with a deuterium gas jet was carried out in 1978 [1]. Since then, several D2 gas-puff experiments were performed on various pulsed-power generators. The highest DD neutron yields of about 4×1013 were observed on the Z-machine 15 years ago [2]. More recently, we have carried out z-pinch experiments on the HAWK (NRL, Washington, DC) and GIT-12 (IHCE, Tomsk) generators at 0.7 MA and 3 MA currents, respectively. On GIT-12, we observed average neutron yields of 2×1012 neutrons and neutrons up to 60 MeV [3]. To confirm the efficient neutron production and high neutron energies independently on another device, we performed several experimental campaigns on the HAWK generator [4]. Comparing the GIT-12 and HAWK experiments helped us understand which parameters are essential for optimized neutron production and how ion acceleration scales with the current. |
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NP11.00101: HED
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NP11.00102: Magnetized bow shocks in radiatively cooled collisional plasma flows Rishabh Datta, Jack D Hare, Clayton E Myers, David J Ampleford, Jeremy P Chittenden, Aidan C Crilly, William R Fox, Jack W Halliday, Christopher A Jennings, Hantao Ji, Carolyn C Kuranz, Sergey V Lebedev, Raul F Melean, Dmitri A Uzdensky We investigate magnetized bow shock formation in strongly radiatively cooled collisional plasma flows using the 3D resistive MHD code GORGON. We simulate bow shocks from the interaction of supersonic, super-Alfvénic plasma, generated during the ablation phase of an inverse z-pinch array, with dielectric blunt obstacles. Mass ablation from the wire array produces radially diverging, highly collisional (λii<<a), β∼0.1 upstream flows with frozen-in magnetic flux (Rem>>1). Obstacles mimic B-dot probes and are aligned to measure the advected azimuthal magnetic field. Bow shock shape is modified by flux pile-up at the probe; so opening angle and stand-off distance vary with the angle between the shock and the magnetic field – thus, these shocks exhibit a 3D structure. We investigate the effect of probe size and strong radiative cooling on shock structure and the post-shock magnetic field measured by the probe. |
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NP11.00103: Simulations of strong radiatively cooled magnetic reconnection for the MARZ campaign on Z Jack D Hare, Clayton E Myers, Jeremy P Chittenden, Aidan C Crilly, Rishabh Datta, William R Fox, Jack W Halliday, Christopher A Jennings, Hantao Ji, Carolyn C Kuranz, Sergey V Lebedev, Raul F Melean, Dmitri A Uzdensky Strong radiative cooling can significantly modify the structure of a reconnection layer, leading to instabilities and rapid radiative collapse. The MARZ (Magnetically Ablated Reconnection on Z) campaign on the Z machine (Sandia National Laboratories) scales up an existing pulsed-power driven reconnection platform from 1 MA to over 20 MA, in order to access this regime of strong radiative cooling. This platform uses two exploding wire arrays driven in parallel, which create streams of magnetized, β∽1 plasma which collide at the mid-plane, generating a current sheet. |
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NP11.00104: Development of the MARZ platform (Magnetically Ablated Reconnection on Z) to study astrophysically relevant radiative magnetic reconnection in the laboratory Clayton E Myers, Jack D Hare, David J Ampleford, Carlos Aragon, Jeremy P Chittenden, Anthony P Colombo, Aidan C Crilly, Rishabh Datta, Aaron Edens, William R Fox, Matthew R Gomez, Jack W Halliday, Stephanie B Hansen, Eric Harding, Roger L Harmon, Michael C Jones, Christopher A Jennings, Hantao Ji, Carolyn C Kuranz, Sergey V Lebedev, Quinn Looker, Raul F Melean, Sonal Patel, Dmitri A Uzdensky, Timothy J Webb MARZ (Magnetically Ablated Reconnection on Z) is a new fundamental science platform being developed at the Z Pulsed Power Facility (Sandia National Laboratories) to study astrophysically relevant radiative magnetic reconnection in the laboratory. MARZ is a 20 MA scale-up of a side-by-side exploding wire array reconnection platform developed at 1 MA on the MAGPIE facility [Hare et al. Phys. Plasmas 25, 055703 (2018)]. This scale-up substantially increases the magnetic field strength, plasma density, and physical size of the reconnection layer. The result is a reconnecting plasma that is predicted to experience a radiative collapse that homogenizes the layer and stalls the reconnection process. Here we describe the experimental development of the MARZ platform, both in terms of the design of the pulsed power configuration for the side-by-side exploding wire arrays and the suite of diagnostics that will be used to observe the ablated plasma inflows and the reconnection layer. This diagnostic suite includes gated x-ray imagers, linear x-ray imaging diode arrays, Al K-shell spectrometers, inductive probe arrays, streaked visible spectrometers, and load current velocimetry among other instruments. The first MARZ experiment is scheduled for the end of 2021. |
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NP11.00105: 2D Magnetohydrodynamic Simulations of the Electrothermal Instability in Metallic Liners Matthew J Carrier, Bhuvana Srinivasan, William A Farmer, Robert L Masti The Lawrence Livermore National Laboratory (LLNL) code Ares is used to study the electrothermal instability (ETI) - a resistive magnetohydrodynamic (MHD) instability that occurs due to a material’s resistivity being temperature- and density-dependent. The ETI often seeds other MHD instabilities like the magneto-Rayleigh-Taylor instability and commonly occurs in pulsed power applications. Using one-dimensional (1D) and two-dimensional (2D) axisymmetric resistive MHD simulations, the Virginia Tech team is modeling University of Nevada Reno and University of New Mexico experiments that pulse 0.8MA currents through 0.8mm diameter metallic rods in 100ns time-scales using the MYKONOS-V driver at Sandia National Laboratory. Lagrangian 1D simulations show liner melt times and velocity profiles of the outer surface of the liner that are similar to experimental values measured by collaborators. 2D simulations seeded with an initial surface perturbation show that mode growth occurs when a dielectric coating is present, but outward expansion slows as dielectric thickness increases. |
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NP11.00106: Deceleration stage Rayleigh-Taylor instability studied in planar and cylindrical geometries Camille Samulski, Bhuvana Srinivasan, Mario J Manuel, Kumar S Raman The Rayleigh-Taylor (RT) instability has been identified as one of the largest inhibitors to successful inertial confinement fusion experiments. Thus, understanding the RT instability growth during deceleration and the potential damping effect externally applied magnetic fields can have on instability growth is crucial. A study in planar and cylindrical geometry demonstrates the potential for measurable damping of the RT instability growth during deceleration in the presence of a magnetic field. Planar and cylindrical parameters are derived from experimental designs for NIF. The configurations are simulated utilizing FLASH's MHD capabilities, as well as Ares MHD capabilities. |
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NP11.00107: Development of the BLUE LTD System at the University of Michigan Roman Shapovalov, Brendan J Sporer, Nicholas M Jordan, Ryan D McBride In this paper, we present recent experimental data from the BLUE LTD system presently being developing in the University of Michigan’s Plasma, Pulsed Power, and Microwave Laboratory. BLUE is a Linear Transformer Driver (LTD) system comprised of up to 4 LTD cavities stacked in series. The 1st LTD cavity was successfully assembled and tested in 2020,[i] and the 2nd cavity is currently under construction. When completed, the 4-cavity system will be able to store up to 8 kJ of energy, which can be released as an 800-kV (open circuit), 100-ns pulse, with a peak current of up to 240 kA into a matched load. This pulse can be coupled with high-energy-density physics (HEDP) loads (e.g., x pinches, z pinches, and dense plasma focuses) and high-power microwave (HPM) loads (e.g., magnetrons). Of particular interest is the HPM load called the magnetically insulated line oscillator (MILO).[ii] We will provide updates on the BLUE system construction and present recent experimental data from a MILO driven on BLUE, where 1.2-GHz microwave oscillations have been successfully generated. [i] B. Sporer et al., “Testing of the First BLUE Linear Transformer Driver (LTD) Cavity at the University of Michigan,” presented at the 62nd Annual Meeting of the APS Division of Plasma Physics, Virtual, Nov. 2020. [ii] D. A. Packard et al., “HFSS and CST Simulations of a GW-Class MILO,” IEEE Transactions on Plasma Science, vol. 48, no. 6, pp. 1894–1901, Jun. 2020. |
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NP11.00108: Staged Z-pinch modeling of high and low atomic number liners compressing deuterium targets using parameters of the Z pulsed power facility Emil Ruskov, Paul Ney, Hafiz U Rahman The staged Z-pinch is a potentially transformative magneto-inertial fusion energy concept where a high atomic number liner implodes on a deuterium or deuterium-tritium target using multi-MA pulsed current. Over the past several years this concept was studied experimentally on 1 MA facilities with Ar or Kr gas puffs compressing a magnetized deuterium target. Consistent thermonuclear neutron yield of 1010 per shot was measured with Kr liners. Here we investigate the fusion performance of D-targets of varying density undergoing compression with low (Be) and high atomic number liners (Ag, Ta) using parameters of the Z pulsed power facility, and the MACH2 code. Ag and Ta liners create strong shocks which preheat the target plasma above 100 eV, and pile-up liner material at the liner-target interface. The increased mass density at the interface creates strong ram pressure just before the pinch stagnation time. 1-D simulations show that the high atomic number liners produce neutron yield orders of magnitude higher than the yield from the low atomic number liner: 1.5x1011 for Be, 5x1015 for Ag, and 2x1017 for Ta. 2-D simulations predict up to an order of magnitude lower yield, depending on the wavelength of the Magneto Rayleigh-Taylor instability. |
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NP11.00109: An Analysis of RT Instability in Stagnated Magnetized Plasmas Stefano Merlini, Jack D Hare, Guy C Burdiak, Jack W Halliday, Lee G Suttle, Danny R Russell, Vicente Valenzuela-Villaseca, Jeremy P Chittenden, Andrea Ciardi, Thomas Varnish, Katherine Marrow, Mark E Koepke, Sergey V Lebedev The structure of stagnation regions formed in the interaction of supersonic plasmas with an obstacle can be strongly affected by the presence of the advected magnetic field in the flow. Here, we present studies of stagnation layer formed in collision of super magneto-sonic plasmas (B ∼ 5T, MA ∼ 2, MS ∼ 6) with planar conducting obstacles. The plasma flow (ne ∼ 1018 cm-3, V ∼ 70 km s-1) is formed by the ablation of metallic wires (Al, Cu, W) using an inverse wire array configuration at the MAGPIE generator (1.4MA, 240ns). |
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NP11.00110: Zeeman Spectroscopic Determination of Magnetic Field on Gas Puff Z-Pinches Jay S Angel, Euan Freeman, William Potter, Dave Hammer Zeeman Polarization Spectroscopy on 1 MA gas-puff z-pinches in Argon and CO2 is being used to determine the magnetic field distribution in the plasma during implosion. Light is collected parallel to the azimuthal magnetic field tangential to the gas puff implosion sheath. The light is split into left and right hand circularly polarized components and then focused into two linear fiber bundles and delivered to a 750 mm spectrometer. The Zeeman components can resolve the peaks of the two polarizations despite Stark Broadening. This method was developed for z-pinch experiments on a 500 kA, 500 ns rise time generator by G. Rosenzweig et al.1 |
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NP11.00111: Zeeman Polarization Spectroscopy on gas-puffs at 1-MA on COBRA Euan Freeman, Eric S Lavine, Jay S Angel, David A Hammer, William M Potter This poster will present results on magnetic field measurements in the imploding sheath of a magnetically imploded gas-puff Z-pinch at 1-MA on COBRA at Cornell. These results are obtained via a polarization splitting method, which separates the sigma components of a magnetically split transition observed perpendicularly due to the Zeeman effect via polarization optics and determines the magnetic field magnitude due to the energy difference of the magnetic levels. These measurements are combined with Thomson scattering, Faraday rotation, and interferometry measurements of the ion temperature, gross magnetic field, and density to determine the magnetic field distribution at measured densities and temperatures in an imploding gas-puff Z-pinch. |
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NP11.00112: A Dispersion Interferometer Diagnostic used for Low Electron Density Measurements in Magnetically Insulated Transmission Lines on Sandia's Z-Machine Nathan Hines, Robert H Dwyer, Mark A Gilmore, Sonal Patel, Daniel J Scoglietti, Darrell Armstrong, George Laity, Michael E Cuneo A needed expansion in the understanding of current loss mechanisms in presently operating pulsed power machines, such as Sandia's Z-machine, will improve reliable delivery of current to magnetically driven loads. This is an important issue for the design of next generation large-scale pulsed power drivers currently being developed. Electron sheath formation on magnetically insulated transmission lines (MITLs) is a fundamental characteristic of power delivery in such pulsed power systems, as increased electron flow reduces coupling efficiency and electron flow can generate electrode plasmas. A fiber-based dispersion interferometer (DI) will enable the first direct measurements of electron sheath flow on Z and will reduce the current lower limit for electrode plasma density measurements available. This DI design will operate at 1550 nm CW, with frequency-doubling to 775 nm. Prior to deployment on Z, the interferometer will be characterized on two smaller devices. First, the HelCat (Helicon-Cathode) basic plasma device at the University of New Mexico while being compared against well-known density profiles measured by a 40GHz microwave interferometer and scanning double Langmuir probe. Next, it will be fielded in a moderate pulsed power environment on the 1 MA Mykonos driver at Sandia National Labs. Finally, it will be deployed to directly measure the electron densities in magnetically insulated flows on the Z-Machine, as well as to characterize plasmas that form on the electrodes. |
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NP11.00113: A Solid-State High Voltage Trigger for HEDP Application James R Prager, Kenneth E Miller, Chris Bowman, Kyle McEleney Thyratron-based generators are used to trigger higher voltage switches at the Z Machine at Sandia National Laboratory. The trigger generator long-term availability, reliability, and lead times are a concern for future projects. Thyratrons need stable, high-current, low-voltage power sources, have long warm-up times, and require conditioning shots to achieve a stable operating point. 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. |
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NP11.00114: Constraining magnitudes of nonzero temperature and density gradients using absorption spectra of radiatively heated target-foil plasma Gregory A Riggs, Mark E Koepke, Theodore S Lane, Pawel M Kozlowski We report the deduction of best-fit gradient-aligned profiles of temperature T and density n across tamped NaFMgO target-foil plasmas, heated and backlit by z-pinch radiation. Reliant on the minimization of a chi-squared statistic, our approach compares the spectroscopic output of a collisional-radiative model (PrismSPECT) with soft-xray absorption spectra collected on Sandia's Z Machine. Pattern of minimum-chi-squared in highly-dimensional parameter space is obtained with Monte Carlo sampling, and is seen to agree with a more efficient, two-parameter model. Results show that a nonzero gradient is likely to exist in both n and T, by virtue of the pinch-facing side of the foil absorbing the bulk of the incident energy. Predicted sensitivity of line spectra to the gradient-aligned profile of △T or △n is documented for each spectral feature, so that Stark broadening experienced by individual lines (for density) or line-area ratio between pairs of features (for temperature) may be assessed as proxies for the existence and quantification of such gradients. |
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NP11.00115: Development of broadband hard x-ray radiography for pulsed power-driven warm dense plasmas Hiroshi Sawada, Lei Chen A solid material driven by Mega Ampere current from a pulsed power system is predicted to be in warm dense matter/plasma regimes. Such a high density, low temperature plasma can be created with a university-scale pulsed power generator by cylindrically compressing a thick metal wire. However, diagnosing the interior condition of the plasma in the enclosed geometry requires an external hard x-ray probe. To develop a short-pulse laser-based hard x-ray radiographic capability for pulsed power-driven high-density plasma, we carried out an experiment using a 50TW Leopard laser at the University of Nevada Reno's Zebra pulsed power laboratory. The intensity, spectrum and source size of broadband x rays produced by the laser interacting with silver targets (10, 20 and 100 μm thick foils and 25 μm diam. wire) were studied by measuring bremsstrahlung and radiographic images of solid Al wires. The measurements show that a high x-ray intensity was observed with the 10 μm thick foil, while a high contrast x-ray image was obtained with the wire. The results of the laser-only experiment, an optimized x-ray source target designed with a 3D hybrid particle-in-cell code, LSP, and the design of a laser-pulsed power coupled experiment will be presented. |
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NP11.00116: Overview of the General Atomics LAboratory for Developing Rep-rated Instrumentation and Experiments with Lasers (GALADRIEL) Gilbert W Collins, Mario J Manuel, Christopher McGuffey, Alicia Dautt-Silva, Brian Sammuli, Devin Vollmer The backbone of the GALADRIEL facility at General Atomics is a commercial ~1 TW (<20 fs, 25mJ, 800nm) Ti:Sapph laser system capable of up to 10Hz operation. GALADRIEL will serve as a platform for advancing technologies capable of diagnosing the rep-rated (~0.1-10Hz) High-Energy-Density (HED) environments created in existing and next-generation HED science facilities. Rep-rated diagnostic concepts for measuring optical and x-ray photons as well as particles (e-, p, etc.) are presently under development. Design and implementation of automated control systems also necessitate development in mass data analysis, machine learning, and feedback systems to leverage the rep-rated operation of these diagnostics. In the future, the GALADRIEL facility will develop systems and alignment protocols to accurately deliver complex targets (i.e. not tape drives) to target chamber center for use at large-scale, rep-rated HED facilities. However, the first experiments on GALADRIEL, planned for early 2022, will generate laser wakefields by driving a laser into a gas jet to produce relativistic electron beams. Current diagnostic development efforts are focused on implementing a rep-ratable electron spectrometer and a wavefront diagnostic to characterize the plasma density at 10Hz. |
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NP11.00117: Laser-accelerated protons for the study of fission in exotic nuclei Jeffrey Burggraf, Pascal Boller, Alex B Zylstra, Thomas Küehl, Dieter H G Schneider Our understanding of nuclear fission is largely based on studies of Californium- 252 and the long-lived isotopes of uranium, plutonium, and thorium. A lack of data on the fission of exotic nuclei precludes the development of a nuclear "standard model". Recent progress in the production of laser accelerated high flux proton beams opens up new possibilities for the study of fission on short-lived isomers. To this end, we are currently pursuing two fronts: the swift gas transport, collection, and identification of fission products, and the creation of high energy density plasmas capable of accessing low-lying excited nuclear states. The former has been recently demonstrated using target normal sheath accelerated protons at the PHELIX laser facility, and feasibility tests of the latter at the OMEGA laser facility are planned. The identification of fission products is achieved using gamma spectroscopy, which has been demonstrated for short-lived fission products with lifetimes down to 40 seconds. Discrepancies between measured and established fission yields were observed, likely due to the measurement apparatus. Aspects of the detector system including fragment stopping, gas flow in the fission chamber, and efficiency of the fragment collection are studied at the Idaho Accelerator Center using their 21 MeV linear electron accelerator. Work performed under the auspices of the U. S. Department of Energy by LLNL under contract DE-AC52-07NA27344. |
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NP11.00118: Fresnel Zone Plate Imaging of Laser-Driven Hydrodynamic Instabilities Benjamin J Tobias, Sam Myren, Alexandria Strickland, Justin Jorgenson, Thomas Archuleta, John J Ruby, Alexandre Do, Steven T Ivancic, Frederic J Marshall, Alexander Rasmus, Elizabeth C Merritt, Kirk A Flippo Fresnel Zone Plate Imaging addresses the need for μm-scale resolution in laser-driven hydrodynamic campaigns as a diffractive optic collecting a larger solid angle than a pinhole imager yet producing a sharp, well-defined focus. The design of the camera (including the diffractive optic), optimization of the radiographic conjugates, and subsequent analysis of image data are aided by forward modeling of the multiple diffractive orders while accounting for the spectral content of the backlighter source. Here, we describe designs generated for common platforms fielded at the University of Rochester’s Laboratory for Laser Energetics and show the results of experiments where emphasis has been placed on compatibility with standard manipulators and X-Ray Framing Cameras typically used for pinhole imaging. In particular, a design for the standard 25x nosecone assembly where the diffractive optic is placed a little more than 2 cm from target chamber center and Fresnel Zone Plate Imaging is compared side-by-side with 15 μm pinhole imaging. |
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NP11.00119: Pulsed power produced cylindrically convergent shockwaves in water at the Mega-Ampere Level Simon N Bland, Jergus Strucka, Savva P Theocharous, David Yanuka, Jeremy P Chittenden, Luis Sebastian Caballero Bendixsen, Joshua Read, Cristian Dobranszki, Hugo W Doyle, Yakov Krasik, Daniel Maler, Alexander Rososhek We report on the first experiments using Mega ampere currents to explode wire arrays in water, driving cylindrically convergent shockwaves towards the array’s axis and creating extreme pressures in the vicinity of implosion. Our research was performed on the Cepage generator at First Light Fusion with array diameters of 13mm consisting of 80 x 160µm copper wires. Currents of 1.2MA were measured through the array – more than twice that of any previous experiments - and the energy deposited into the exploding wires reached ~25kJ. The shockwaves generated in the water were imaged by laser backlit multiple frame photography, whilst a high-speed streak camera imaged across the array diameter. In spite of non-perfect current contacts and initial asymmetries in wire expansion, the shockwaves ‘self-healed’ becoming ever more symmetric during implosion, and reached significantly higher velocities - 5kms-1 at 1mm radius, which is ~1.7 higher than in experiments driven by 550kA currents. Inside a radius of 1mm, the shockwaves appeared to accelerate to at least 12kms-1 likely due to convergence, creating pressures >5Mbar in the vicinity of implosion axis. With the high level of current available on Cepage we were able to field cylindrical foil liners instead of wire arrays for the first time – these also showed a highly symmetric, high velocity implosions resulting from explosion of the copper foil. |
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NP11.00120: Investigation of Geometric and Radiative Effects in a Shock-Driven Shear Flow Sonya Dick, Griffin S Cearley, Matthew Trantham, Carolyn C Kuranz, Eric Johnsen Although the hydrodynamics of interfacial instabilities have received significant attention in high-energy-density physics studies, far less is known about the role of radiation on perturbation growth [1]. We present a theoretical and computational platform to study the role of radiation in HED shock-driven shear flows by modifying the design of the shock-shear experiments in [2]. To isolate the hydrodynamics from radiative effects, the perturbation growth is theoretically investigated in a simplified geometry, in which two counter-propagating flows are separated by a perturbed finite-thickness layer representing the tracer. The effect of the tracer thickness on the perturbation growth rate is investigated. Using CRASH, a block-adaptive Eulerian radiation-hydrodynamics code with flux-limited multigroup diffusion, we conduct two-dimensional simulations to investigate more complex and experimentally relevant geometry. The perturbation growth rates due to the shear flow are presented with and without radiation. |
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NP11.00121: Using data science methods to efficiently and effectively plan HED experiments and analyze data Codie Y Fiedler Kawaguchi, Eric Johnsen, Xun Huan, Michael J Wadas, Kirk A Flippo, Elizabeth C Merritt, Benjamin J Tobias, Alexander Rasmus, Joseph M Levesque, Alexander Cram, Sam Myren, Anthony Palmer, Noah Dunkley High Energy Density (HED) science is the study of the behavior of material under extreme conditions of temperature and pressure (above 1 Mbar). Understanding the growth and properties of hydrodynamic instabilities and the transition into turbulence in high energy density regimes is important in many HED processes and will also yield insights into other areas of science where hydrodynamic instabilities occur. |
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NP11.00122: Anode Shape and Hollow Effects on Neutron Yield in a 4.4 kJ Dense Plasma Focus Device Veronica Eudave, Eric Hahn, Swarvanu Gosh, Jeff Narkis, Fabio Conti, Farhat Beg Dense Plasma Focus (DPF) is a Z-pinch configuration that consists of coaxial electrodes that guide a dynamic plasma sheath along the anode, resulting in a hot dense pinch near the anode tip. A DPF can produce X-rays, energetic ions, and high intensity fast neutron pulses depending on the fill gas. We report on experiments using a 4.4 kJ Mather-type DPF exploring the role of anode geometry with a focus on curved and flat anodes with and without a hollow center, such as highlighted in recent studies1,2. The dynamics of the collapsing plasma are described in terms of the contribution of anode geometry and deuterium pressure. The resulting pinch structure is quantified optically and neutron yields, as measured by a Be-activation detector, will be described. |
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NP11.00123: Hydrodynamic Density Functional Theory of Dense, Heterogeneous Plasmas Chris M Gerlach, Michael S Murillo, Liam G Stanton Strongly-coupled plasmas, such as ultracold neutral plasmas, dusty plasmas and warm dense matter, can be difficult model, as a complete understanding of the physics relies on both the dynamics and the underlying particle correlations. Density functional theory (DFT) is a natural formalism for describing such correlations but is limited to equilibrium systems. For non-equilibrium systems, hydrodynamic DFT (HDFT) provides a dynamic generalization of DFT that has recently been applied to plasmas [1, 2]. One of the primary advantages of HDFT is that it establishes a direct connection to atomic-scale correlations self-consistently and without the need for an ad hoc equation of state. Here, we explore the numerical implementation of the HDFT model and address some of the theoretical challenges that arise from heterogeneous and strongly-coupled systems. Furthermore, we explore the role that correlations play in plasma waves. |
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NP11.00124: Study of neutron production from a 4.4 kJ dense plasma focus May Ghosh, Eric Hahn, Veronica Eudave, Fabio Conti, Jeffrey Narkis, Farhat Beg The Dense Plasma Focus (DPF) is a pulsed power Z-pinch configuration capable of producing neutrons and energetic electron/ion beams from a high density and high temperature deuterium plasma pinch. The length of insulator sleeve plays an important role in the dynamics of plasma sheath which affects the pinch quality and the neutron yield. Experiments are carried out using a 4.4 kJ (250 kA, 21 kV) Mather-type DPF equipped with a Be-activation detector and laser probing diagnostics at fill pressures ranging from 2 to 8 torr D2, where varying insulator sleeve length (1/8-2/5 the anode length) is investigated. Neutron production with an intermediate insulator sleeve length equal to 1/3 the anode length demonstrated the lowest shot-to-shot variation and greatest neutron production on average. An optimal fill pressure for neutron production is identified between 4-5 torr, resulting in >108 neutrons/pulse. Deuterium fill pressures above 6 torr result in plasma filamentation that degrades the performance of the DPF. |
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NP11.00125: Implementation and Verification of Braginskii Viscosity in the FLASH Code Abigail Armstrong, Adam Reyes, Marissa B Adams, Periklis Farmakis, Edward C Hansen, Yingchao Lu, David Michta, Kasper Moczulski, Don Q Lamb, Petros Tzeferacos The inclusion of ion viscosity when solving a radiative magnetohydrodynamic ansatz to simulate high-energy-density physics (HEDP) laser-driven plasma experiments is key to correctly capturing momentum diffusion and the flow’s fluid Reynolds number (Re). When the diffusion time scale becomes comparable to the advection timescale, ion viscosity will impact flow dynamics and transport properties. Here we present the numerical implementation of Braginskii ion viscosity[1] in the FLASH code. We detail the numerical implementation that couples with the flux-based viscosity module in the code and show results from an array of verification benchmarks. The inclusion of a realistic ion viscosity significantly broadens the range of plasma regimes where FLASH can be applied and enhances the fidelity of HEDP simulations where Re . |
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NP11.00126: Implementation and Verification of LC Circuit for Z-pinch FLASH Simulations Kasper Moczulski, Adam Reyes, Marissa B Adams, Abigail Armstrong, Pericles S Farmakis, Edward C Hansen, Yingchao Lu, David Michta, Don Q Lamb, Petros Tzeferacos High-fidelity simulations of pulsed-power–driven high-energy-density physics experiments frequently necessitate the modeling of the electrical interplay of current between the vacuum-insulator stack and the load (i.e., the plasma generated across the anode–cathode gap). Recent additions to the FLASH code, the high-performance computing, radiation magnetohydrodynamics code developed by the Flash Center for Computational Science, have enabled it to model Z-pinch experiments. Here we discuss the implementation in FLASH of the circuit model presented by McBride et al., who proposed a simple LC model to be used as a drive circuit in refurbished Z accelerator simulations. We outline the numerical implementation and show results from select verification benchmarks. |
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NP11.00127: Simulating Dynamic Triggering Events in Field Distortion Spark Gap Switches Imani Z West-Abdallah, James Young, Matthew Evans, Hannah R Hasson, Marissa B Adams, Pierre-Alexandre Gourdain Low inductance closing switches are a critical component of linear transformer drivers (LTD) and other pulsed power systems. While these devices are vital to controlling the timescale of triggering events, present designs have shown limitations due to their lack of specification toward LTDs. These limitations include high inductance and excessive erosion of the switch electrodes. To reduce the overall inductance and minimize maintenance on the High Amperage Driver for Extreme States (HADES), we have designed a single channel field distortion ball switch that addresses these disadvantages. COMSOL studies (2-D) of dynamic DC and pulsed triggering events at +/- 100 kV are used to investigate potential current paths and rise times inside of the switch cavity. Our COMSOL studies will inform changes to our design before testing our switches in a multi-brick system. |
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NP11.00128: Design of Radiation Transport through Heterogeneous, Stochastic Media Tom Byvank, Chris Fryer, Chris J Fontes, Shane X Coffing, Corey Skinner, Andy S Liao, Suzannah R Wood, Pawel M Kozlowski, Heather M Johns, Harry F Robey, David D Meyerhofer, Todd Urbatsch Radiation flow through media containing optically thick particulates dispersed in an optically thin background can challenge high energy density physics models. Typically available transport models depend on a single material equation of state and opacity per spatial cell, such that the solutions may have to average over heterogeneous regions using atomic mix schemes. Direct numerical simulation (DNS) at sufficient resolution can model a particular small-scale stochastic-medium configuration, but many DNS calculations are required to obtain an average solution where stochastic media are defined only probabilistically. Levermore-Pomraning models and extensions are somewhat mature for linear, uncoupled transport, but less so for thermal radiation transport with hydrodynamics. The X-ray Flow Over Lumps (XFOL) experiment at the OMEGA facility seeks to use the COAX spectral diagnostic to measure, in more detail than ever before, radiation flow through stochastic media. In this work, we present design considerations for these experiments using Cassio simulations of radiation flow through optically thin Sc-Si-aerogel foams containing optically thick V-oxide particulates. We compare averaged homogeneous calculations with DNS calculations of the heterogeneous stochastic media. |
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NP11.00129: GPU-accelerated particle-in-cell (PIC) simulations of laser-ablated HED plasmas with the PSC code John Donaghy, Kai Germaschewski, William R Fox, Derek B Schaeffer The PSC code is a modern C++14 based PIC code that has been optimized for running large-scale 2-D and 3-D simulations of HED plasmas on GPU-based machines like ORNL's Summit. These end-to-end simulations, which self-consistently generate the magnetic fields through the Biermann-battery effect and follow their evolution until they reconnect as the plasma plumes collide are challenging to run efficiently due to their large and evolving load imbalance. We describe enhancements to the PSC code, including the integration with the gtensor library for performance portability, using pooled GPU memory allocation using the RMM library, and a defragmentation algorithm. As an application we present a large 3-d simulation of plumes that collide and their intrinsic anti-parallel magnetic fields reconnect. We have also added the option to add a separate seed population of high-energy electrons to investigate Fermi acceleration. |
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NP11.00130: Expanding the Tabulated Equation-of-State Implementations in the FLASH Code for the SESAME Database Pericles S Farmakis, Mary McMullan, Adam Reyes, Jordan T Laune, Marissa B Adams, Abigail Armstrong, Edward C Hansen, Yingchao Lu, David Michta, Kasper Moczulski, Don Q Lamb, Petros Tzeferacos We present the enhancement of the tabulated equation-of-state (EOS) capabilities of FLASH, a high-performance computing, finite-volume radiation magnetohydrodynamics code developed by the Flash Center for Computational Science. FLASH has extended physics capabilities that enable the code to treat a broad range of physical processes in astrophysics, laboratory plasma physics, and high-energy-density physics (HEDP). Here we extend the tabulated EOS implementation of the FLASH code to make use of the SESAME EOS database (LAUR-92-3407), generated and curated by the Los Alamos National Laboratory. This improvement provides FLASH with high-fidelity data for the materials used in laser-driven and pulsed-power-driven experiments. We verify the new capability with benchmark HEDP problems and show how they favorably compare against FLASH's previous tabulated EOS implementations. |
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NP11.00131: VISRAD, 3-D Target Design and Radiation Simulation Code Igor E Golovkin, Joseph MacFarlane The 3-D view factor code VISRAD is widely used in designing HEDP experiments at major laser and pulsed-power facilities, including NIF, OMEGA, OMEGA-EP, SLAC, ORION, LMJ, Z, and PLX. It simulates target designs by generating a 3-D grid of surface elements, utilizing a variety of 3-D primitives and surface removal algorithms, and can be used to compute the radiation flux throughout the surface element grid by computing element-to-element view factors and solving power balance equations. Target set-up and beam pointing are facilitated by allowing users to specify positions and angular orientations using a variety of coordinates systems (e.g., that of any laser beam, target component, or diagnostic port). Analytic modeling for laser beam spatial profiles for OMEGA DPPs and NIF CPPs is used to compute laser intensity profiles throughout the grid of surface elements. We will discuss recent improvements to the software package and plans for future developments. |
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NP11.00132: Automated Iterative Forward Analysis for Pressure Determination in Dynamic Compression Experiments Connor Krill, Raymond F Smith, Suzanne J Ali, Jim A Gaffney, June K Wicks High-powered laser compression experiments can provide insights into material behavior at solar and planetary cores - some of the most extreme environments in the Universe. To fully understand material response at such extreme conditions, the pressure within the sample must be accurately determined. However, pressure cannot be measured directly. Experiments combine the velocity measured within a sample with the material's equation of state to extract a pressure history. As new driver developments increase laser shot rate, going from once a day at the National Ignition Facility to the upcoming sub-Hertz pace at the European X-ray Field Electron Laser, there is a growing need for an automated process to convert experimentally measured velocities into pressure histories. The work reported here implements an automated iterative forward analysis using the HYADES hydrocode that can scale with the growth of modern laser facilities to accurately retrieve pressure histories from a broad range of experimental conditions. We discuss this work in the context of ramp compression of various materials on the OMEGA laser facility. |
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NP11.00133: Kinetic model for a collisionless ionization wave launched by a high energy-density plasma Haotian Mao, Kathleen Weichman, Todd Ditmire, Hernan J Quevedo, Alexey Arefiev A high energy-density plasma embedded in a neutral gas can launch an outward-propagating nonlinear collisionless ionization wave driven by a strong sheath field [Phys. Rev. Lett. 112, 045002 (2014), Phys. Rev. E 103, 023209 (2021)]. The key feature is the trapping field structure that enables the wave to carry energetic electrons at high density. These electrons maintain a strong sheath field, ensuring long-lasting wave propagation with relativistic velocity over distances that greatly exceed the initial size of the plasma. We present an analytical solution of the kinetic equation that self-consistently describes the structure of the wave. The solution predicts a threshold for the ratio of the ambient gas density and the density of the hot trapped electrons. We also present 1D kinetic simulations supporting the analytical solution. |
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NP11.00134: Development of spin polarization-dependent quantum radiation reaction in Osiris QED module Qian Qian, Daniel Seipt, Marija Vranic, Thomas Grismayer, Alexander G Thomas The next generation of high-intensity laser facilities around the world will reach the multi-Petawatt power level. These high-intensity lasers will allow the exploration of the strong field quantum electrodynamics (QED) regime. Particle-in-cell (PIC) codes are a common way to simulate high-intensity laser-matter interactions. In PIC codes, such as the OSIRIS framework, QED effects were implemented through Monte-Carlo interaction processes to simulate strong-field QED-plasma experiments in the near future. Existing PIC+QED modules can capture plasma kinetic effects and calculate the quantum emission spectrum. However, they do not take into account the spin polarization, as the QED processes are implemented using unpolarized rates. Including the dependence of spin polarization to the existing QED module is important because it will not only change the QED emission rates, but also allow tracking how the electron or positron spin polarization evolves in the strong field QED experiment. Here, we present progress in developing the Osiris QED module to include the spin polarization dependence, including consideration of the spin-basis and Monte-Carlo emission processes. |
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NP11.00135: Constructing frequency dependent spectra sources for use in high energy density physics and inertial confinement fusion simulations Ryan F Sacks, Paul A Bradley, Robert E Tipton Many experiments in inertial confinement fusion/high energy density physics utilize indirect drive, where lasers shine into a hohlraum and the light is converted to x-rays. Laser packages in simulations provide the most complete physics for comparison to experiments, but are complex and time consuming to run, especially when the target (and not the hohlraum or laser pulse) is being changed in a design process. Simplified time dependent temperature profiles on a target are faster to simulate, but miss important physics associated with higher photon energies from the hohlraum. A middle ground is to run a frequency dependent spectral (FDS) source, but these are nearly always derived from previous simulations that include the laser package, which may not be practical to run. In this talk, we present a method for constructing an FDS source from a time dependent temperature history and ways to include non-Planckian terms such as hohlraum M-band and L-band emission from the high-Z wall. The constructed sources are used in simulations and compared to both extracted FDS sources and temperature histories. Release number LA-UR-21-26577. This work conducted under the auspices of the U.S. DOE by LANL under contract 89233218CNA000001. |
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NP11.00136: Synthetic phase-contrast imagining using CRASH simulation results Matthew Trantham, Mario Balcazar, Julian Kinney, Rachel Young, Carolyn C Kuranz Recent laboratory experiments explored radiation hydrodynamics of a laser driving a shock into |
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NP11.00137: Short Characteristics Radiation Transport in SPECT3D Timothy Walton, Joseph MacFarlane, Igor E Golovkin Short Characteristics (SC) is a method of calculating radiation transport in non-LTE plasmas wherin the transport equation is solved along rays through a given number of nearest-neighboring cells. At the cost of accuracy, SC can save immensely on computation time compared to Long Characteristics (LC), where transport is calculated all the way to the plasma edges for each plasma zone. This is especially important for large grids where LC becomes prohibitively expensive. SPECT3D is a collisional-radiative spectral analysis package which can utilize SC and LC for radiation transport in 1D, 2D and 3D geometries. Here we present improvements to SC modeling in SPECT3D, including a new angle grid model for focusing the grid of transport rays in order to resolve known radiation hotspots. |
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NP11.00138: A self-consistent study of the electron cyclotron maser instability as a source of coherent radiation Pablo J Bilbao, Charles D Arrowsmith, Robert Bingham, Gianluca Gregori, Luis O Silva The electron cyclotron maser instability (ECMI) is a plasma process capable of generating intense and coherent electromagnetic emissions. Recent studies have examined different initial momentum distributions as drivers for the instability. Resorting to the particle-in-cell code OSIRIS, we investigate the ECMI closer to realistic conditions and we address effects that had so far been neglected, i.e. finite spatial width, different magnetic field geometries, and multidimensional effects. These simulations explore parameters that can be realised in proposed laboratory experiments.. Our theoretical results, alongside proposed experimental setups, are relevant to understanding the plasma processes that underpin the coherent emission in solar and more exotic astrophysical plasmas. |
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NP11.00139: Plasma formation from micron-scale defects on ultra-pure aluminum rods* Maren W Hatch, Thomas J Awe, Edmund P Yu, Trevor M Hutchinson, Kevin Yates, William Tatum, Kurt Tomlinson, Bruno S Bauer, Mark A Gilmore The electrothermal instability (ETI) is a Joule heating-driven instability that can initiate in the solid state in magnetically driven fusion targets, specifically in current-carrying, fuel-filled metallic liners. ETI generates azimuthally correlated (striated) temperature and density perturbations, which may seed the magneto Rayleigh-Taylor (MRT) instability, limiting implosion uniformity and stagnation pressure. Previous experiments conducted on the ~ 1 MA Mykonos driver at Sandia National Laboratories have observed ETI growth from extremely smooth (Ra values <15nm), 99.999% pure aluminum rods in a z-pinch configuration by using ICCDs and a 12-frame imager to monitor overheating around characterized micron-scale "engineered" defects (ED) machined into the rod surface. New data comparing different ED size and orientation will be presented, revealing the surface structure of local overheating. "Cat eye" emission patterns, with bright emission spots above and below the ED, have been observed, as well as premature plasma filamentation sourced from ED. Experimental data has been compared with 3D-MHD simulations, denoting agreement in overheating surface structures including plasma filaments, peak intensities between ED pairs, and heating similarity for geometrically scaled defects. |
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NP11.00140: Enhanced collisionless energy absorption in plasma with strong background magnetization Lili Manzo, Yuan Shi, Matthew R Edwards Strongly magnetized collisionless laser-plasma interaction (LPI) is a largely unexplored subject. Previous research on weakly magnetized LPI, where gyrofrequency ωc is much lower than plasma frequency ωp, has shown that magnetization increases the amount of energy absorbed by the plasma by raising the threshold for kinetic inflation and decreasing laser energy backscatter. We studied collisionless LPI with background magnetic fields (B0) on the kilotesla scale (where ωc >> ωp) to investigate how strong magnetization impacts laser-to-plasma energy transduction. We used a particle-in-cell code to simulate strongly magnetized LPI and found that at resonant B0 values the laser excites magnetized plasma waves on a picosecond timescale. Collisionless damping of these waves increases the number of hot electrons in the plasma by multiple orders of magnitude in comparison to non-resonant cases, signified by a broadening in the velocity distribution functions and a decrease in transmitted energy. Higher efficiency laser-to-plasma energy transfer is important in a wide variety of applications, from compact x-ray sources for medical devices to inertial confinement fusion. Additionally, the physics behind these interactions may provide insight to phenomena such as the solar coronal heating problem. |
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NP11.00141: The impact of anomalous resistivity in vacuum contaminant plasmas on the electrothermal instability Robert L Masti, Bhuvana Srinivasan, William A Farmer This manuscript presents an assessment of the electrothermal instability (ETI) in the presence of anomalous resistivity (AR) in vacuum contaminant plasmas (VCP) when applied to a magnetized liner inertial fusion (MagLIF)-like load. Pulsed-power driven dielectrically coated metallic liners, like in MagLIF, experience the current-driven electrothermal instability which occurs when a material's resistivity changes with temperature and is subject to ohmic heating. Large scale pulsed-power facilities that use magnetically insulated transmission lines (MITL) have been shown to generate low-density plasma which enters the target chamber and coalesces around the load. The low-density high-temperature vacuum contaminant plasmas (VCP) can parasitically divert current from the load through causing a short in the anode-cathode gap inside the target chamber. Resistive magnetohydrodynamic (MHD) simulations of these VCP experience unphysical runaway ohmic heating due to under predicting the resistivity by using a purely collisional resistivity model. AR provides a physics-based way to address this runaway heating through increasing the resistivity in a proportional way with the drift speed. The effect that AR in VCP has on the magnetic diffusion rate is assessed through 1D simulations, and 2D simulations show how this effect manifests in the nonlinear striation form of the ETI for a MagLIF-like load. Beryllium and aluminum dielectrically coated liners are used for the 1D and 2D simulations to explore the impact of AR in VCP has on striation ETI. |
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NP11.00142: Neutrino-electron magnetohydrodynamics in an expanding Universe Lorenzo Maria Perrone, Gianluca Gregori, Brian Reville, Luis O Silva, Robert Bingham We derive a new model for neutrino-plasma interactions in an expanding universe that incorporates the collective effects of the neutrinos on the plasma constituents. We start from the kinetic description of a multi-species plasma in the flat Friedmann-Robertson-Walker metric, where the particles are coupled to neutrinos through the charged- and neutral-current forms of the weak interaction. We then derive the fluid equations and specialize our model to (a) the lepton epoch, where we consider a pair electron-positron plasma interacting with electron (anti-)neutrinos, and (b) after the electron-positron annihilation, where we model an electron-proton plasma and take the limit of slow ions and inertia-less electrons to obtain a set of neutrino-electron magnetohydrodynamics (NEMHD) equations. In both models, the dynamics of the plasma is affected by the neutrino motion through a ponderomotive force and, as a result, new terms appear in the induction equation that can act as a source for magnetic field generation in the early universe. A brief discussion on the possible applications of our model is proposed. |
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NP11.00143: Systematic measurements of quasi-static B-fields from laser-driven coil targets in intensity regime relevant for magneto-inertial fusion experiments CHRISTOS VLACHOS, Valeria Ospina-Bohorquez, Gabriel Perez Callejo, Michael Ehret, Mathieu Bailly-Grandvaux, Sophia Malko, Channprit Kaur, Morgane Lendrin, Pierre Guillon, Matthew Gjevre, Eitan Soussan, Michel Koenig, Xavier Vaisseau, Laurent Gremillet, Bruno Albertazzi, Robert Fedosejevs, Joao J Santos Strong quasi-static magnetic fields to be applied in high-energy density plasma experiments can be driven from laser interactions with coil-targets (CT), which geometry provides easy access for several diagnostics and do not produce a significant quantity of debris. |
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NP11.00144: X-ray spectroscopic studies of Hybrid X-pinches Ahmed T Elshafiey, Sergei Pikuz, Tatiana Shelkovenko, David A Hammer We are planning detailed spectroscopic studies of the X-ray bursts produced by hybrid X-pinches using a ~20 ps time resolution X-ray streak camera and <700 ps resolution filtered silicon diodes. The purpose is to investigate whether the X-ray spectroscopic features associated with radiative collapse can be seen in the X-ray bursts produced by the Hybrid X-pinches. A nickel wire has been used as the load and time integrated L and K-shell spectra were recorded on imaging plates. In addition, silicon diodes were focused on specific emission lines from the X-ray spectrometer crystals to track their intensity evolution. Time-resolved temperature and density measurements can be estimated throughout the implosion and expansion phases from these diagnostics. Time-resolved source size measurements are also being carried out using the ~20 ps time resolved streak camera to determine the change of the spot size on a picosecond timescale. Sufficiently high magnification studies are being carried to determine the source size in the 1-10 μm range. |
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NP11.00145: PrismSpect and Spect3D with Flexible Atomic Code Data Ming F Gu, Igor E Golovkin, Timothy Walton, James L Sebald, Joseph MacFarlane PrismSpect and Spect3D belong to a suite of codes developed at the Prism Computational Sciences Inc. They employ detailed collisional radiative kinetics models and multi-dimensional radiative transfer to compute emission and absorption spectra of plasmas under a wide variety of physical conditions. Flexible Atomic Code (FAC) is a widely used computational atomic physics software package capable of generating complete data sets of energy levels, radiative transition rates, and collisional cross sections of arbitrary atomic ions. Here we present the integration of FAC atomic data with the Prism Atomic Model Builder Application to generate customized atomic model files, which can then be used in PrismSpect and Spect3D for both LTE and nonLTE spectral modeling. Detailed Comparisons of resulting spectra with those generated from Prism's standard ATBASE atomic data will be discussed, as well as those generated from FAC's built-in collisional radiative model. |
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NP11.00146: Limitations on Plasma Optics due to Non-Linear Ion Wave Physics Robert K Kirkwood, Patrick Poole, Daniel H Kalantar, Thomas D Chapman, Scott Wilks, Matthew R Edwards, Pierre A Michel, Laurent Divol, Nathaniel J Fisch, Peter A Norreys, Wojciech Rozmus, Jeff Bude, Brent E Blue, Kevin B Fournier, Bruno Van Wonterghem The success of plasma optics in producing a high energy beam with a 1ns duration with stimulated Brillouin scatter (SBS) [1,2,3,4] motivates their development for new applications. We have described a second stage pulse compressor for such a beam that could use SBS to produce a <~ 0.1 ns output pulse [5] with 10’s to 100’s of kJ of energy if non-linear plasma wave effects remain benign. Suppression of the secondary instabilities of filamentation and backscatter dictates that the 15 cm plasma in such a compressor be <~ 0.1% crit., [5] where particle trapping in the desired ion waves may limit the optics performance, if it is not mitigated by Coulomb collisions. We describe existing experimental evidence of such non-linearities and compare it with theoretical metrics of trapping and its modification by collisions, to guide the design of new optics as well as motivate modeling of trapping and near term experiments to validate it. |
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NP11.00147: Effect of small normalized magnetic fields on rescatter of SRS in the kinetic regime Roman Lee, Benjamin J Winjum, SJ Spencer, Frank S Tsung, Warren B Mori, Simon Bolanos We have previously shown [1] how small magnetic fields can significantly modify the evolution of backward stimulated Raman scattering (SRS) in the kinetic regime ($k\lambda_{De} \approx 0.20 - 0.35$ for backscattered plasma wave) due to the enhanced dissipation of nonlinear electron plasma waves propagating perpendicular to magnetic fields. We present results of OSIRIS simulations of SRS in the kinetic regime for unmagnetized and magnetized plasmas at densities low enough ($n_e/n_c \lessapprox 11\%$) such that rescatter (where the daughter wave backscatters) is possible. We show that when rescatter occurs, the magnetic field can increase the overall reflectivity by mitigating the initial backscatter event and hence the subsequent rescatter. We present 1D and 2D simulations for a variety of parameters to illustrate this effect. |
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NP11.00148: Water droplet characterization and broadband microwave emission from laser plasmas generated in water droplets Anna M Janicek, Jennifer Elle, Erin A Thornton, Adrian P Lucero, Ralph Apodaca, Chris Urbina, Andreas Schmitt-Sody A high-power ultrashort laser pulse focused in air generates a plasma that radiates broadband electromagnetic waves. The transient current source responsible for the radiation remains an open area of study. The aim of this investigation is to understand the influence of water droplets on plasma formation and its effects on radio frequency (RF) radiation. More RF emission is seen as water droplet density increases, likely due to increased absorption of laser energy. Beyond a threshold droplet concentration, laser energy is depleted and RF signal decreases. An antenna is used to measure the radial pattern of RF from 2 to 13.6 GHz produced by the laser plasma. Our research demonstrates a method to control water droplet density, allowing study of the relationship between droplet concentration and the laser plasma radiation mechanism. |
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NP11.00149: PIC simulations characterizing the THz radiation response of a copper target excited by an ultra-short laser pulse Alexander C Klepinger, Pedro Spingola, Nashad Rahman, Douglass W Schumacher The interaction of an intense, ultrashort-pulse laser with a solid target leads to dramatic modification of its surface and subsequent emission of electromagnetic (EM) radiation. This radiation may be an interesting probe of the laser-target interaction or useful in its own right. We have used 2D LSP [1] particle-in-cell (PIC) simulations to characterize the THz range radiation response of copper targets illuminated by single high intensity ultra-short laser pulses with intensities up to 1018 W/cm2. Our simulations treat the material permittivity and reflectivity using a realistic collision model [2] based on the binary collision algorithm. This permits a realistic treatment of the target’s dynamically changing electromagnetic response and thermal evolution beginning from a room temperature state, which then establishes the initial conditions for the subsequent current evolution and EM emission. Accordingly, we describe efforts to model the evolution over several picoseconds using staged simulations covering first the laser-target interaction and then the subsequent evolution of the target. We measure the resulting EM emission in the target near-field looking at both the spectrum and angular distribution. |
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NP11.00150: EMP Characteristics in HERCULES and Lambda Cubed Laser Facilities Joshua L Latham, Marko W Mayr, Yong Ma, Patrick Skrodzki, Jon Murphy, Milos Burger, Anatoly M Maksimchuk, John Nees, Alexander G Thomas, Peter A Norreys, Karl M Krushelnick Measurements of Radio Frequency (RF) emission may be a useful diagnostic for electron dynamics in laser-plasma interactions. Such radiation can also be detrimental as a significant source of noise for other diagnostics. EMP measurements were made during interactions of high-power short-pulse lasers with gaseous density targets using the HERCULES and Lambda Cubed laser facilities at the University of Michigan. In a nitrogen-doped helium target experiment with two collinear, time-separated laser beams, EMP was maximized at a particular timing between the two beams. The increase in RF was correlated with the X-ray signal. However, there was also a population of shots where simultaneous increases in the X-ray and electron signal were observed, but the RF was not significantly increased. Potential explanations for this phenomenon will be discussed. Strategies for control and mitigation of RF are also presented. |
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NP11.00151: Charge and energy confinement of strongly coupled plasma within a phase-coexisting supercritical fluid Seungtaek Lee, Juho Lee, Dong-Eon Kim, Gunsu S Yun Strongly coupled plasmas (SCPs) are believed to exist in various places in the universe. Neutron stars, white dwarf stars, and the cores of Jovian planets are some examples. Several theoretical models and numerical simulations have been developed in recent decades to describe the particle interactions in SCPs, which fundamentally differ from those in conventional weakly coupled plasmas. However, even the basic equation of states is yet to be verified by experiments. The main difficulty in SCP experiments is that very high energy should be confined both in space and time. We demonstrate a method to enhance the charge and energy confinement of strongly coupled plasmas produced by pulsed laser discharge by utilizing inhomogeneous supercritical fluids. We recently discovered that a single-component supercritical fluid, which is considered a homogeneous medium, can be prepared in a quasi-stable inhomogeneous state containing a dense population of nanometer-size liquid-like clusters and a small number of submicron-size droplets that survive for an hour [Nat. Commun., accepted]. In laser discharges of argon SCPs, it is observed that the clusters and droplets prolong the charge and energy relaxation time of the plasma up to about microseconds. This finding alleviates the problem of short timescales in strongly coupled plasma experiments and will allow measurements of plasma parameters for a more in-depth understanding of the charge and energy transport of strongly coupled plasma. |
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NP11.00152: Approaches towards cross-beam energy transfer for short laser pulses Kirill Lezhnin, Nathaniel J Fisch, Kenan Qu Processing ultra-intense laser pulses through stimulated Raman scattering in plasmas has shown promising results. With two counter-propagating pulses, backward Raman amplification can transfer the energy of a long pump pulse to a short and sharp seed pulse. The excited plasma waves mediate rapid energy transfer between laser pulses. We show, through 2D PIC simulations, that the plasma waves can also mediate energy transfer between two crossing beams through near-forward Raman scattering. In that case, as our 2D PIC simulations show, the energy transfer can also be mediated through filamentation instability. However, the extent to which this filamentation usefully combines beams, or disadvantageously destroys focusability, is a key question. |
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NP11.00153: Pump depletion in four-photon collinear laser frequency multiplication in plasma Vladimir M Malkin, Nathaniel J Fisch It was shown recently that exactly resonant four-photon scattering of collinear laser pulses in |
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NP11.00154: Characterization of Plasma for Raman Amplification Kyle R McMillen, Jessica Shaw, Dustin H Froula As the frontier of high-intensity lasers advances, the need for more efficient and damage-resistant compression gratings has become a significant cost and size constraint for advanced laser systems. Plasma-based amplifiers, which utilize a plasma's ability to sustain intensities orders of magnitude larger than traditional gratings, offer an alternative solution to the constraints of these gratings. Such plasma amplifiers utilize Raman amplification, a process in which stimulated Raman scattering (SRS) transfers energy from a long (~ns) pump pulse to a counter-propagating short (~100-fs) seed pulse through a resonantly driven electron plasma wave. However, depending on local plasma characteristics, namely the temperature and density, many phenomena can limit this process. Thermal variation within the plasma can lead to spontaneous SRS, detuning of the resonant plasma frequency, and shifts to the wave-breaking limit, all of which can lead to early or incomplete pump depletion. As such, careful characterization of the plasma parameter space is required to optimize Raman amplification. We will present the density and temperature characterization of plasmas for Raman amplification studies via density measurements and theory comparisons. |
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NP11.00155: Collisional and transport parameters of Cu in the Warm Dense Matter regime calculated using the Average Atom Model George M Petrov, Asher Davidson Collisional and transport parameters for Cu are computed using the Average Atom Model. Transition metals such as copper are difficult to model within the framework of the Average Atom Model due to the presence of a narrow band of 3d electrons that mix and hybridize with the broad 4s band of nearly-free electrons. With electron temperature increasing, the 3d electrons play a key role in the thermodynamics and transport properties of Cu [Z. Lin, et. al., Phys. Rev. B 77, 075133 (2008)]. In this work, the Average Atom Model was used to track the average energy of the 3d band and its evolution with electron temperature. At room temperature, its center is at ~6 electron-volts (eV), a few electron-volts below the Fermi energy, and with electron temperature increasing it sinks relative to it. At electron temperature of about 8 eV the energy of the 3d electrons leave the conduction band. A long-standing problem related to the average ion charge observed by conduction band electrons is addressed and successfully resolved. A work-around has been found that predicts the correct average ion charge, , by formally introducing a third group of electrons: quasi-bound electrons. Benchmarking with published data has been made that shows good agreement. |
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NP11.00156: Ultrashort pulsed laser atmospheric filament electrical conductivity and radius measurements by guided wave attenuation in an S-band waveguide and visible light imaging Edward L Ruden, Jennifer A Elle, Alexander C Englesbe, Adrian P Lucero, Erin A Thornton, James E Wymer, Andreas Schmitt-Sody A diagnostic is described and demonstrated to measure the electrical conductivity σ of the plasma filament left behind by an ultrashort pulsed laser's optical pulse after it has self-focused in air via the Kerr effect. The filament is formed by a 30 mJ Ti:sapphire laser pulse with a center wavelength of 800 nm with a linearly polarized 50 mm diameter approx. 50 fs long pulsed beam focused with a 300 cm focal length spherical mirror. It passes through holes in the middle of an S-band waveguide in the TE10 electric field direction. There is a transmitter at one end of the waveguide and a receiver at the other. The receiver signal is recorded with and (to record the effect of self-emission from the filament) without 3.2 GHz TE10 mode excitation from the transmitter. The dependence of the mode's measured attenuation (corrected for self-emission) on σ and filament radius R is determined by 3-D steady state electromagnetic simulations. R is measured by fast optical imaging. Measurements are made along a filament's length at a broad range of atmospheric pressures. |
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NP11.00157: High-energy-density Targets Fabricated by The University of Michigan Sallee Klein, dave Gillespie, Kwyntero Kelso, Heath J LeFevre, R P Drake, Carolyn C Kuranz The University of Michigan has the distinctive capability of fabricating targets for a wide variety of high-energy-density physics experiments. |
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NP11.00158: A Robust Algorithm for Orbital-Free Average Atom Models of Dense Plasmas Tyler J Dorsey, Michael S Murillo, Liam G Stanton Average atom models are the primary method for predicting equation of state (EOS) properties in plasmas. While the most high-fidelity models rely on orbital-based density functional theory (DFT) [1], orbital-free models are still in wide use due to both their computational efficiency as well well their ability to continuously exhaust the temperature-density space. The most popular orbital-free DFT is the Thomas-Fermi model [2]; however, this simplistic model can be systematically improved through gradient corrections, exchange-correlation effects, etc. While these more sophisticated models have been explored in the past [3], they are often poorly formulated due to ambiguity in the boundary conditions. Here, we derive the proper boundary conditions necessary in orbital-free average atom models and present a numerical investigation of the governing equations. EOS calculations are compared with data from both orbital-based methods and experiments. |
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NP11.00159: Isotope Effects on High-Pressure Water Heather M Pantell, Linda E Hansen, Grigoriy Tabak, Margaret F Huff, Gerrit Bruhaug, J. Ryan Rygg, Gilbert Collins Recent observations on superionic water reveal a rich phase behavior including dissociation, hydrogen melting, rapid hydrogen ion diffusion through an oxygen lattice, oxygen melting, and a transition from ionic to mostly electronic conduction. To better understand this complex phase diagram we explored its dependence on exchanging deuterium for hydrogen. D2O was precompressed in diamond-anvil cells and then compressed through laser-driven shocks on the OMEGA laser at the University of Rochester’s Laboratory for Laser Energetics. Shock velocity and temperature were measured using the velocity interferometer system for any reflector and streaked optical pyrometer diagnostics and used to determine mechanical, thermal, and transport properties of heavy water to 500 GPa. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0003856. |
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NP11.00160: High Repetition Rate Investigation of the Biermann Battery Effect in Laser Produced Plasmas Over Large Spatial Regions Jessica J Pilgram, Carmen G Constantin, Robert S Dorst, Marissa B Adams, Petros Tzeferacos, Peter V Heuer, Derek B Schaeffer, Marietta Kaloyan, Sofiya Ghazaryan, Christoph Niemann The Biermann Battery effect is a mechanism of magnetic field generation in both astrophysical phenomena and laser produced plasmas (LPPs). We present data from a high repetition rate (HRR) experiment examining the spatial structure and evolution of such fields. Data was taken at a repetition rate of 1 Hz over large volumetric regions producing detailed data sets containing thousands of points. Measurements show azimuthally symmetric magnetic fields with peak magnitudes of up to 60 G in our closest measurements, 7 mm from the target surface. The current densities in the system were determined by taking the curl of the measured magnetic fields. We additionally present optical Thomson scattering measurements of electron temperature and density within our system. |
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NP11.00161: Radiative heating and cooling of laboratory photoionized plasmas Jeffrey Rowland, Roberto C Mancini Recent measurements of the electron temperature in laboratory photoionized plasma experiments have shown significant discrepancies with predictions computed with astrophysical modeling codes1. However, simulations of the experiments performed with radiation-hydrodynamics codes have produced good temperature comparisons between theory and observation. For the conditions of the experiments, the heating and temperature of the photoionized plasmas mainly depend on radiative heating and cooling. In turn, the temperature impacts the level population distribution that determines the opacity and emissivity of the plasma. Hence, the electron temperature is a central parameter of photoionized plasmas that depends on external x-ray flux, atomic physics and density. We will discuss the differences in assumptions and approximations used in the physics models employed in the astrophysical and radiation-hydrodynamics modeling codes and how they can result in different temperature predictions. 1R. C. Mancini et al, Phys. Rev. E 101, 051201(R) (2020). |
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NP11.00162: A laser-driven experimental platform to study angular momentum transport in disk-jet transitions Francisco Suzuki-Vidal, George F Swadling, Chris Walsh, Mathieu Bailly-Grandvaux, Vicente Valenzuela-Villaseca We present the design of an experimental platform to produce supersonic, rotating plasmas on the OMEGA laser looking at studying astrophysical processes characteristic of accretion disks and jet launching. A rotating plasma is driven by the oblique collision of 6 simultaneous radially inward plasma outflows produced by laser irradiation of V-shaped targets made of CH, assembled in a circular array with an outer diameter of ∽15 mm. Each V-shaped target has an opening angle of 60○ and an offset angle of 5○. Axial pressure gradients lead to the formation of bipolar rotating jets normal to the plane of rotation. The rotation velocity will be measured using optical Thomson scattering and the plasma dynamics will be measured with time-resolved, self-emission X-ray imaging. We also present the expected plasma conditions in the experiments with numerical simulations with the 3-D MHD code Gorgon. |
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NP11.00163: Studying the collimation of outflows in radially converging plasmas from a 3D printed load Hannah R Hasson, Marissa B Adams, Matthew Evans, Imani Z West-Abdallah, James Young, David A Hammer, Bruce Kusse, William Potter, Pierre-Alexandre Gourdain We present new results as a continuation of a scaled laboratory study on the stability and collimation of astrophysical plasma outflows using the COBRA pulsed power driver at Cornell University [1]. In this new experimental campaign, we use the simplest version of the load hardware design in which the axial magnetic field component has been removed. Additionally, the spacings between the initial and return current paths have been increased in order to protect from parasitic current arcing. Our goal of this campaign is to scan across the time-evolution of the plasma’s structure with laser interferometry and extreme ultraviolet (XUV) imaging in order to find any indication that collimated outflows are present in our simplest 3D printed load design. We present evidence of an overdensity at the center of our converging flows from top-down and side-on viewpoints of the XUV images, as well as evidence of streams emerging from the plasma in the interferometry data. We also discuss the introduction of higher-Z wires into two of the six current paths. |
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NP11.00164: Influence of the azimuthal B-field distribution on the formation of the ring structures in the ion images on GIT-12 Vojtech Munzar, Daniel Klir, Alexander V Shishlov, Rustam K Cherdizov, Jakub Cikhardt, Fedor I Fursov, Volody A Kokshenev, Jozef Kravarik, Pavel Kubes, Nikolai E Kurmaev, Jakub Malir, Jan Novotny, Nikolai A Ratakhin, Karel Rezac Multi-MeV hydrogen ion beams are produced in the deuterium hybrid gas-puff 3-MA Z-pinch experiments on the generator GIT-12 [1]. Experimental ion images from the pinhole camera show characteristic ring-like structures. Several effects can participate in the formation of the rings. The effect of the spatial distribution of the ion source has already been discussed in [2]. The ions are also influenced by the azimuthal B-fields inside Z-pinch plasmas below the ion source. Recently, we measured these B-fields in the first Z-pinch-driven ion deflectometry experiments [3]. Based on the results, we use our ion-tracking simulations and investigate how B-field gradients affect the ring structures. In addition, we study other properties of the ion source. |
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NP11.00165: Ideal MHD and two-fluid axisymmetric free-boundary equilibrium Luca Guazzotto, Riccardo Betti The codes FLOW[1] and FLOW2[2] are ideal MHD and two-fluid axisymmetric equilibrium codes that allow for arbitrary rotation in the plasma. In their published implementation they can only run as fixed-boundary equilibrium codes. In this work we present an extension to free-boundary mode for both codes. The FREE-FIX[3] code is used to provide boundary conditions for the two equilibrium codes based on a desired plasma shape and on assigned coil geometry. Since magnetic surfaces (tangential to the magnetic field) and flow surfaces (tangential to the plasma rotation) are different in the two-fluid model, different positions for X-points and separatrix are calculated for each set of surfaces. Noting that the proper plasma edge definition has to be given in terms of flow surfaces, we investigate the shift in X-point, separatrix and strike points on the divertor between the two sets of surfaces. Magnetic surfaces calculated by FLOW are used as a reference for comparison with the ideal MHD model. We investigate the issue by running both codes in free-boundary mode for realistic plasma and coil geometries and comparing the magnetic surfaces obtained by FLOW and FLOW2 and the flow surfaces calculated by FLOW2. |
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