Bulletin of the American Physical Society
64th Annual Meeting of the APS Division of Plasma Physics
Volume 67, Number 15
Monday–Friday, October 17–21, 2022; Spokane, Washington
Session BP11: Poster Session I: In-Person, Hall A (9:30-11:00am) and Virtual Poster Presentations (11:15am-12:30pm)
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Room: Exhibit Hall A and Online |
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BP11.00001: MFE: ANALYTICAL & COMPUTATIONAL Session Chairs: |
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BP11.00002: Active learning pipeline for surrogate models of gyrokinetic turbulence Jackson Burr, Thandikire Madula, Lorenzo Zanisi, Aaron Ho, Jonathan Citrin, Vignesh Gopakumar, Stanislas Pamela Model-based plasma scenario optimization often excludes reduced-order gyrokinetic models, e.g. QuaLiKiz, deeming them too slow for highly iterative applications. Previously, QLKNN, a feed-forward neural network (NN) surrogate model of QuaLiKiz, has shown a factor 104 prediction speedup which enables its use in optimization. However, the training set generation still demanded considerable computational resources due to its size. Moreover, the QLKNN-jetexp-15D dataset only a minority of unstable points (<30% per turbulent mode) and may have oversampled regions. Such brute-force approaches are not feasible for more computationally-intensive models. |
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BP11.00003: Bayesian Equilibrium Reconstruction for General Fusion Demonstration Plant Aaron Froese, Ryan Zindler, Matt Herunter, Calum Macdonald, Todd Chisholm, Daymon Krotez, Myles Hildebrand, Brian Kelly, Emily Love, Alex Mossman, Meritt Reynolds General Fusion is designing a magnetized target fusion reactor to compress a toroidal plasma inside a liquid metal cavity and heat it to fusion conditions. Plasma properties are inferred using Bayesian statistics by comparing measurements from our spherical tokamak targets to artificial diagnostic signals from a table of precalculated equilibria. Equilibria are assigned probabilities based on the least-squares fit to diagnostics, temporal constraints such as decaying helicity, and the linear stability of the plasma configuration calculated with RDCON. Measurements from Mirnov probes, interferometers, polarimeters, and Thomson scattering are included as fit constraints. Equilibria are generated using the FLAGSHIPS Grad-Shafranov solver as a 2nd-order finite element solution on an unstructured mesh. Outputs include the current, pressure, temperature, and density profiles with their probability distributions shown as 2D histograms. We present fits to a wide range of test cases and real shots showing a large set of equilibria that fall inside the measurement uncertainties, providing high levels on confidence in the accuracy of the method. We also show how our framework is used to design probe placement in the Fusion Demonstration Plant to facilitate reconstruction accuracy. |
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BP11.00004: Data-Driven Prediction and Control of Alfvén Eigenmodes at DIII-D Azarakhsh Jalalvand, Ralph Kube, Mark D Boyer, Alvin V Garcia, Max Austin, Geert Verdoolaege, William W Heidbrink, Egemen Kolemen We have previously developed a data-driven model based on reservoir computing networks (RCNs) to detect, classify, and localize Alfvén eigenmodes in a database of over 1000 DIII-D discharges. The model looks at 40 Electron Cyclotron Emission (ECE) signals, sampled at 500kHz, to distinguish AE activities such as Low-frequency modes (LFMs), Beta-induced Alfvén eigenmodes (BAE), Reversed-Shear Alfvén eigenmodes (RSAE), and Toroidal Alfvén eigenmodes (TAE). |
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BP11.00005: Capturing finite Larmor radius effects with an implicit, asymptotic preserving full-orbit integrator for particle-in-cell schemes Lee Ricketson, Luis Chacón While gyrokinetics is extremely useful for simulations of strongly magnetized plasmas, there is growing interest in full-orbit simulations when the gyrokinetic ordering breaks down. We present an implicit time-stepping scheme for charged particles that recovers the drift- and gyrokinetic limits when stepping over the gyroperiod while converging to the resolved orbit with small time-steps. The scheme preserves the exact total energy conservation enjoyed by recently developed implicit PIC schemes [1]. Development proceeds in three stages. Firstly, we review prior work that modified Crank-Nicolson to capture the drift-kinetic limit by introducing an effective magnetic-drift force [2]. Next, to handle finite Larmor radius effects, we evaluate the electric field at equispaced points on an approximate gyro-orbit, keeping total energy conservation by an analogous modification of the current deposition. Full-orbit convergence is maintained by adaptive selection of the number and location of these points, depending on time-step size and local field structure. Finally, we introduce a strategy of alternating large and small time-steps that dramatically relaxes the time-step constraints on the scheme, along with a corresponding adaptive stepping strategy. Tests on single-particle motion in complex field configurations demonstrate the ability to step over the gyration time-scale and recover correct dynamics -- even with field structure at the gyroradius scale -- along with strict conservation properties. |
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BP11.00006: Matlab-based Free-boundary Equilibrium Solver for Fast Control-oriented Predictions Xiao Song, Brian Leard, Eugenio Schuster A free-boundary equilibrium solver for axisymmetric tokamak geometries has been developed based on the finite-difference and Picard-iteration methods in a rectangular computational area. The solver can run either in direct mode, where external coil currents are prescribed, or in indirect mode, where desired plasma boundaries with or without X points are prespecified to find the needed coil currents. The equilibrium solution is made consistent with nominal plasma parameters, such as the total plasma current (Ip), poloidal beta (bp) or safety factor (q) on a specified flux surface. To benchmark the mathematical correctness and accuracy of the solver, numerical solutions are compared to analytic fixed-boundary solutions. Furthermore, these numerical solutions are benchmarked against those produced by another numerical solver based on the finite-element and Newton-iteration methods in triangular grids. The equilibrium solver is being coupled with the Control Oriented Transport SIMulator (COTSIM) within a Matlab/Simulinkâ environment in its path to become a fast tokamak flight simulator enabling pulse design, model-based scenario optimization, and assessment of performance of control solutions in closed-loop simulations before experimental implementation. |
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BP11.00007: Comparison of Qubit Lattice Algorithms for the Ampere-Faraday Equations with the full set of Maxwell equations. Linda D Vahala, George Vahala, Jack Gabriel, Abhay K Ram, Min Soe It is common to consider just the Faraday-Ampere curl equations when studying the propagation of waves in plasmas, with the two divergence equations being treated as initial conditions. However, in numerical computations (e.g., MHD simulations) the effects of discretization can plague the simulation since the constraint div B = 0 can only satisfied approximately. Thus, most MHD codes require divergence cleaning throughout the simulation, even if initially div B = 0. We compare Qubit Lattice Algorithms (QLAs) for the curl-curl Maxwell system with that for the full set of Maxwell equations. A QLA consists of an interleaved sequence of unitary collision-stream operations on a set of qubits with appropriate Hermitian potential operators [1]. In 2D the curl-curl subset requires 6 qubits/lattice node while the full Maxwell system requires 8 qubits/lattice node. We compare the two representations by studying the scattering of an electromagnetic pulse by a 2D scalar dielectric cylinder or cone with large refractive index gradients. The scattered fields have a complex structure arising from internal reflections within the dielectric. |
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BP11.00008: Accelerated JFNK via compressed sensing of near-sparse Jacobians Daniel Raburn, Allan H Reiman The Jacobian-free Newton-Krylov (JFNK) method is a powerful method for root-finding of black-box nonlinear continuous multidimensional real-valued functions. Recently developed enhancements to the conventional JFNK algorithm are presented, with emphasis on cases where the function evaluations are the dominant cost. In particular, the use of a novel approach to compressed sensing to reconstruct a sparse (or near-sparse) Jacobian matrix using only information from the available subspace, for use as a dynamic preconditioner, has been demonstrated to provide a significant speed-up in relevant cases. Results of the new JFNK code applied to TFTR MHD equilibria using the Princeton Iterative Equilibrium Solver (PIES) are also presented. |
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BP11.00009: In search of long-time stability with neural network surrogates of Fokker-Planck collision operator solvers Michael Churchill, Choongseok Chang, Todd Munson, Hong Zhang Collisional transport is a critical physical process in the edge of tokamak plasmas, yet for kinetic simulations with multiple ion species numerically solving for collisional transport are expensive. Previous work [1] showed the promise of using machine learning to train a surrogate for the numerical Fokker-Planck-Landau collision solver used in the edge turbulence code XGC. An encoder-decoder neural network was trained on a large dataset from XGC, with soft-constraints in the optimization loss to enforce conservation properties. This resulted in a surrogate which for single-time predictions on a test set gave acceptable conservation errors (1e-4). However, when using the ML model in the full XGC simulation over multiple timesteps, instabilities invariably occurred. Here we probe the ability of neural networks to produce stable, asymptotically correct solutions to a simpler collisional system, that of a bi-Maxwellian distribution function collisionally relaxing to an isotropic Maxwellian. We show the benefits of new operator learning models, such as the Fourier Neural Operator (FNO), in generalizing. We also show the benefits of imposing hard constraints to enforce conservation properties, and explore more directly the use of entropy functions to further constrain solutions. |
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BP11.00010: Advances in TRANSP: modular, modernized and future-oriented code for tokamak plasmas Alexei Pankin, Amrita Bhattacharya, Joshua A Breslau, Vinicius N Duarte, Laszlo Glant, Mariya Goliyad, Marina Gorelenkova, Mario L Podesta, Gopan Perumpilly, Francesca M Poli, Jai Sachdev, George J Wilkie, Xin Zhang We report progress in the modernization and improvement of a physics basis of TRANSP [https://doi.org/10.11578/dc.20180627.4], a time dependent equilibrium and transport code. The TRANSP code is used for the interpretive analysis of tokamak discharges, scenario development and experiment planning. The state-of-the-art models for heating and transport are utilized in the code. Recently, many of these models are reimplemented in TRANSP as stand-alone libraries with independent inputs. This effort on TRANSP modernization separates the TRANSP kernel from individual components, simplifies the development, maintenance, debugging and CI. The ITER Integrated Modeling & Analysis Suite (IMAS) is selected as an interface between TRANSP and these components. In this work, we also report successful coupling of TRANSP to the IMAS ITER database with simulations running with input derived directly from the IMAS database. At this time, we demonstrate TRANSP coupling to IMAS for several diagnostics such as interferometer and RF modules such as TORBEAM. Other developments reported in this talk include: (1) progress in the core-edge coupling; (2) impurity transport modeling; (3) performance improvements. |
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BP11.00011: Non-physical Asymptotic Behavior in the Modified Form of the Gyrokinetic Poisson Equation Used in the Split-Weight Scheme Benjamin J Sturdevant, Luis Chacon, Robert Hager, Michael Churchill, Amil Sharma, Seung-Hoe Ku, Choongseok Chang The split-weight scheme [1,2] is a commonly used numerical technique for treating kinetic electrons in magnetized plasmas, based on a splitting of the electron distribution function into adiabatic and non-adiabatic parts. For consistency with the original equations, the operator applied to the electrostatic potential in the Gyrokinetic Poisson equation must be modified to account for the adiabatic density contribution. In the absence of discrete effects, this modification to the operator is exactly accounted for in the dynamics of the non-adiabatic density. Numerically, however, this may not be the case, and problematic asymptotic behaviors may be forced on the solution due to the nature of the modified operator. Here, we present an asymptotic analysis of the modified form of the Gyrokinetic Poisson equation, suggesting the presence of non-physical boundary layers in the solution. We demonstrate how this behavior can show up in XGC simulations when a newly developed axisymmetric solver is used, driving numerical instabilities. Finally, we explore mitigation methods. |
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BP11.00012: Performance Analysis and Improvement of an Unstructured Mesh Gyrokinetic Particle-in-cell Code for Exascale Fusion Plasma Simulations Chonglin Zhang, Gerrett Diamond, Cameron W Smith, Mark S Shephard We report on efforts to improve the performance of a recently developed unstructured mesh gyrokinetic particle-in-cell (PIC) code, XGCm, for modeling fusion plasma (Zhang et. al, APS DPP Meeting 2021, PP11.00053). XGCm executes all steps on GPU accelerators, and exhibits good performance and portability. It builds on the Omega and PUMIPic libraries that perform mesh and particle related operations. This provided us with advantages of supporting distributed meshes and better memory usage and locality, while it does pose performance challenges in operations involving interprocess communications and the interaction between particles and mesh fields. To improve the performance, we analyzed the time costs of major components within the code using realistic test problems. This process identified that the key routines to improve were the particle search operation, which finds the mesh element each particle belongs to, and the particle migration operation, where each particle is put onto the correct mesh element and its information transferred to the correct MPI rank. With the improvements made, XCGm is as performant as XGC for delta-f PIC calculations while also able to support distributed meshes. |
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BP11.00013: Qubit Lattice Algorithm for electromagnetic wave scattering from scalar dielectric media Min Soe, George Vahala, Linda D Vahala, Abhay K Ram A Qubit Lattice Algorithm (QLA) consisting of an interleaved sequence of unitary streaming and collision non-commuting operators which together with an appropriate set of potential operators is a discrete representation of a set of continuum equations. Using an 8-spinor representation [1], we have developed an initial value QLA for Maxwell equations to study the scattering of spatially confined electromagnetic pulses by inhomogeneous 2D scalar dielectric objects. For homogeneous media, there is a direct analogy between Maxwell equations and the Dirac equation for a free particle, with the corresponding 4-qubit QLA fully unitary. In its simplest forms, the inhomogeneous 8-qubit QLA introduces a Hermitian operator. Numerical simulations show that the scattering of an initial 1D pulse by dielectric cylinders and cones show multiple internal reflections and subsequent refractions into the surrounding vacuum region. The refractions are not 1D as they are affected by the geometry of the scatterer. QLA simulations show new magnetic field components in the scattered field so that div B = 0. |
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BP11.00014: Formulation of Maxwell Equations in a Magnetized Plasma Amenable to Quantum Computing Efstratios Koukoutsis, Panagiotis Papagiannis, Kyriakos Hizanidis, Abhay K Ram, George Vahala In order to take advantage of the highly anticipated speedup offered by quantum computers over the classical ones, it is necessary for a quantum reformulation of classical topics in plasma physics. We are particularly interested in studying the propagation and scattering of electromagnetic waves by density fluctuations in fusion plasmas. We construct a Schrödinger representation of Maxwell equations for wave propagation in plasmas that admits unitary evolution operator, and incorporates methods from passive media theory and pseudo-Hermitian quantum dynamics [1]. The formulation establishes novel insights into the treatment of linear, dispersive, wave propagation in inhomogeneous plasmas, and the development of quantum lattice algorithms. We will present our theoretical model and discuss the symmetries associated with the generator for wave propagation, and the approach for implementing the model on a quantum computer with optimal error scaling. |
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BP11.00015: Application of extended magnetohydrodynamic model to plasma-vacuum systems Makoto Hirota It is well-known that the magnetohydrodynamic (MHD) equations are derived from the two-fluid equations by assuming quasi-neutrality and neglecting the Hall and electron-inertia effects. This MHD approximation is invalid, for instance, when plasma density becomes extremely low and Alfven velocity approaches infinity. The plasma-vacuum boundary is therefore difficult to treat within the framework of standard MHD. This problem is attempted to be resolved by using extended MHD (XMHD) model that include Hall terms and electron inertia. Although the electron inertial length is often negligible in plasma region, it is inversely proportional to the square root of density and, hence, electron inertia becomes the most dominant in vacuum region. By introducing electron viscosity as well and imposing physically appropriate boundary conditions, the whole plasma-vacuum system can be governed by the XMHD equations. Existence of cylindrical plasma equilibria surrounded by vacuum magnetic field and a conducting wall are investigated by solving the XMHD equations. Numerical schemes needed for XMHD simulation are also presented and demonstrated. |
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BP11.00016: Validation of Petra-M full-wave simulations against LAPD experiments Mark Zhang, Syun'ichi Shiraiwa, Nicola Bertelli Loss of RF heating power to the parasitic slow-wave in the plasma edge is a prominent challenge in ICRF heating for fusion devices. Plasma waves launched from a single strap RF antenna in the Large Plasma Device (LAPD) can be simulated using Petra-M, a C++ based finite element full-wave solver. Petra-M analysis is based on MFEM, an open source C++ FEM library. Experiments performed in the LAPD and Petra-M analysis under fast wave conditions agreed well with each other. Current investigations in Petra-M attempt to simulate slow as well as mixed (slow and fast wave modes) wave conditions with plasma conditions of ne~1018-1019m-3, Te~1-10eV, and B0~0.1-0.18T. Slow waves are difficult to resolve via finite element analysis methods due to a limit on computing power when small mesh sizes are required. Mixed conditions also require small mesh sizes in slow wave propagation regions. The goal of this investigation is to find a means of computing the Petra-M wave model so that a comparison with LAPD data can be made. |
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BP11.00017: Implementation and verification of a new model collision operator in gyrokinetic code COGENT Alexey R Knyazev, Mikhail Dorf, Sergei I Krasheninnikov Impurity transport in the tokamak plasma is a topic of great importance in fusion research. On the one hand, the radiation losses from high-Z impurities at the core plasma can fatally hinder the performance of fusion devices. On the other hand, impurities close to the edge help reduce the heat fluxes to the device's walls. Although many aspects of the impurity transport theory, such as local neoclassical theory, are now well developed, understanding global impurity transport remains a challenge and requires numerical simulation tools. The development and implementation of such collision operators is a subject of active research. While the Fokker - Plank operator derived from the first principle does, in principle, result in the highest fidelity simulation, the high computational cost makes its use impractical for many applications of interest. An alternative approach is to construct a model operator that, while simpler and faster to compute, still models the collision process reasonably well. |
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BP11.00018: Elliptical corrections to the gyroaveraging operation in gyrokinetic simulations in high E-field-gradients Xin Zhi Tan, Davide Curreli, Robert Hager, George J Wilkie, Seung-Hoe Ku, Choongseok Chang In gyrokinetic Particle-in-Cell codes, a particle is treated as a charged "ring" subject to a force from the effective potential representing the averaged value over the ring. Thanks to gyroaveraging, a particle's charge is split into N portions and projected onto a circular gyro-ring of size equal to one Larmor radius at equidistant gyro angles. However, in a region with large electric field gradients, like plasma quasi-neutral sheath and steep edge pedestal, the particle orbit departs from being circular, deformed by the presence of the electric field and of the E-field shear. At those locations, the use of circular ring may not be accurate assumption, and elliptical corrections may be applied. In this work, we quantify the deviation from circular orbits by analyzing the full-orbit trajectory of particles inside the quasi-neutral sheath using the hPIC code, a full-orbit Particle-in-Cell code developed at Illinois. The orbit ellipticity is then obtained by fitting the particle trajectory to an ellipse after projection onto the plane perpendicular to the B-field in the moving ExB frame. The ellipse parameters (eccentricity, minor and major axes) are characterized under a range of plasma conditions spanning over the conditions normally encountered in the near-surface region of tokamaks. The correction factors are tabulated in a form convenient for implementations in gyrokinetic PIC codes such as XGC. |
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BP11.00019: Enabling Multiscale Particle-in-Cell simulations using PUMI Multi-Block Boundary Layer Meshes in hPIC2 Md Fazlul Huq, Vignesh Vittal-Srinivasaragavan, Logan Meredith, Onkar Sahni, Davide Curreli In order to simulate large plasma domains including boundary regions of high-field-gradient, such as plasma sheaths formed in front of material surfaces, we have incorporated a Multi-Block Boundary Layer (MBBL) mesh in the hPIC2 Particle-in-Cell code. MBBL mesh is part of the PUMI mesh infrastructure developed at RPI. MBBL mesh allows to merge together multiple blocks with either uniform cell spacing, or geometrically graded boundary layer type spacing, thus enabling large freedom of sampling. We tested the MBBL mesh capability on a rectified Scrape-Off Layer (SOL) problem, and performed a number of semi-analytical verification of the PIC results against a fluid solution. Simulations were performed for a range of domain sizes ranging from 100 Debye lengths to 1 million Debye lengths (~33 m) with both uniform and block-structured MBBL meshes. We show that for MBBL meshes, the code allows the solution of even larger plasma domains, spanning over a full connection length (~100 m). When hPIC2 is run with dynamic coupling to the RustBCA sputtering code, it facilitates the investigation of impurity production at the divertor plates under simplified (rectified) SOL conditions. |
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BP11.00020: Data-driven surrogate modeling of hPIC ion energy-angle distributions for high-dimensional sensitivity analysis of plasma parameters’ uncertainty Mohammad Mustafa, Pablo Seleson, Davide Curreli, Cory D Hauck, Miroslav Stoyanov, David E Bernholdt The quantification of wall erosion due to plasma-surface interactions requires the determination of the energy-angle distribution of the ions accelerated through the plasma sheath and impacting on the material surfaces. However, such calculations are computationally expensive and thus a surrogate model is desired. Several challenges arise when attempting to construct a surrogate model for the ion energy-angle distribution (IEAD) computed using hPIC. Challenges include: high computational cost of particle-in-cell (PIC) codes; high dimensionality of physical parameters affecting the IEAD; and significant variation of IEAD support over the range of physical parameters. To effectively address these issues, a data-driven surrogate model strategy was developed. The strategy utilizes sparse grids in the parameter space and coordinate transformations in the energy-angle phase space. The surrogate model showed a significant reduction in computation time and was used to draw samples necessary to perform global sensitivity analysis (SA) for the ions’ energy and angle moments at the plasma-material interface. SA reveals a strong dependency of the moments on the electron-to-ion temperature ratio and intermediate dependency on the magnetic field inclination angle, whereas the dependencies on the magnetic field magnitude and plasma density are less significant. |
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BP11.00021: Overview of NIMROD modeling at the University of Wisconsin-Madison Carl R Sovinec, Brian S Cornille, Urvashi Gupta, Andrew D Ingram, Karsten J McCollam, Sanket A Patil, Alexandre P Sainterme, Grant A Tillinghast The NIMROD code [1] has been applied to investigate macroscropic dynamics in many plasma configurations. Current efforts at UW-Madison include developing an efficient representation for stellarators and applications to RFPs, tokamaks, and spherical-tokamak startup. The stellarator development, NIMSTELL, is a major refactoring to use a 3D representation of the geometry and of the equilibrium/steady-state fields [2]. It also uses H(curl) elements for vector potential so that the magnetic divergence constraint is satisfied to roundoff. The RFP study includes pressure dynamics to investigate the pressure-curvature drive and energy transport in the presence magnetic relaxation, according to the visco-resistive MHD model. Our recent tokamak simulations consider RE confinement [3] and transient-induced disruptions in MST tokamak discharges. We also implemented a reduced model of RE effects on magnetic-field evolution. The Pegasus study restarts our previous investigation of local helicity injection [4], now tailored for conditions in the Pegasus-III upgrade. [1] Sovinec, et al., JCP 195, 355; [2] Sovinec and Cornille, BAPS 66(13); [3] Cornille, et al., PoP 29, 052510; [4] O'Bryan, et al.; PoP 19, 080701. |
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BP11.00022: A Newton-Krylov Method for Simultaneous Semi-Implicit Time-advance of Extended MHD with Kinetic Closures Joseph A Spencer, Eric D Held, Joseph R Jepson The Chapman-Enskog like drift kinetic equations [1] provide kinetic closures to fluid equations and extends to the long mean free path regime of magnetized plasmas. Tight coupling between the fluid equations and drift kinetic equations demands a careful treatment of the time-centering to implicitly advance the full system of equations over large time steps. The fluid advance in NIMROD is numerically stabilized by a semi-implicit approach to allow for timesteps large compared to the compressional Alfven wave propagation time. In this approach, the center-of-mass flow is staggered in time from the remaining fluid quantities. Building on the success of this leap-frog method we center the electron and ion velocity distribution functions such that one is advanced simultaneously with the ion flow and the other is advanced simultaneously with the remaining fluid quantities. Preliminary results are presented that focus on the collisional effects of the Spitzer thermalization problem and the collisional/free-streaming effects of temperature flattening across a growing magnetic island. |
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BP11.00023: Unitary Qubit Lattice Algorithms for Electromagnetic Scattering in Anisotropic Dielectric Media George Vahala, Linda D Vahala, Abhay K Ram, Min Soe, Efstratios Koukoutsis, Kyriakos Hizanidis A fully unitary representation of the Faraday-Ampere subset of Maxwell equations has been developed recently for a medium represented by an anisotropic permittivity tensor [1]. Using pseudo-Hermitian theory[1], an appropriate metric is found in which the Faraday-Ampere equations take on a fully Hermitian form. The corresponding transformation leads to a Dyson map that yields a fully unitary representation of the curl-Maxwell equations in the standard Hilbert space. We are developing a unitary Qubit Lattice Algorithm (QLA) for this new representation, devising the required sequence and form of the interleaved sequence of unitary collision-stream operators on a chosen set of qubits. We first consider a simple splitting of the similarity Dyson transformation. While this splitting results in a QLA which is not fully unitary, the QLA simulates electromagnetic scattering in a tensor anisotropic dielectric media. Our earlier studies were restricted to scalar dielectric media. QLA simulations will be presented for both 1D and 2D scattering from tensor dielectric media and eventually in a cold plasma dielectric media. A fully unitary QLA is required for direct implementation on quantum computers. |
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BP11.00024: Equilibrium Solver using Physics-Informed Neural Networks Byoungchan jang, Alan Kaptanoglu, Matt Landreman Magnetohydrodynamic (MHD) equilibrium codes are vital tools in the field of plasma physics. Often, a large number of equilibrium calculations are required for uncertainty quantification, stellarator optimization, and other inverse problems. Surrogate equilibrium solvers, such as Physics-Informed Neural Networks (PINNs), present an opportunity for addressing this class of computationally intensive problems. Here, we present initial results with PINN surrogates for the Grad-Shafranov equation. We explore the parameter space by varying the size of the model, number of collocation points, and boundary conditions, in order to map various tradeoffs (e.g., reconstruction error and computational speed). |
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BP11.00025: Sonic-flow effects on tungsten impurities using the global gyrokinetic PIC code XGC Amil Sharma, Julien Dominski, Choongseok Chang The usual gyrokinetic ordering [1] orders the E x B drift speed to be small compared to the thermal particle speed. This ordering is not satisfied within many edge, scrape-off-layer, impurity-containing, and strongly-rotating plasmas. However, gyrokinetic equations exist that allow the presence of sonic flows by ordering the vorticity to be small [2]. The equations use the symplectic representation of gyrokinetics, which results in implicit equations. We discuss the implementation of sonic-flow gyrokinetic equations in XGC, based on the existing impurity simulation capability within XGC [3]. We present preliminary results of the effects of sonic flows on tungsten impurities using a model plasma. |
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BP11.00026: MFE: ENERGETIC PARTICLES
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BP11.00027: Anomalous transport and losses of energetic particles in fusion plasmas Diego Del-Castillo-Negrete, David Zarzoso Instabilities can significantly reduce the confinement of energetic particles (EP) thus limiting the performance of fusion devices. In this presentation we study EP anomalous transport and losses in the presence of energetic geodesic acoustic modes (EGAMs) and tearing modes, using the recently developed Toroidal Accelerated Particle Simulator (TAPAS) code. It is shown that even if EGAMs are axisymmetric and non-turbulent, a chaotic channel from the inner region to the edge of the tokamak is created leading to losses of counter-passing EP. Also, numerical evidence is presented of trapping-induced super-diffusion, leading to asymmetric transport and a net toroidal torque. The impact of single-helicity (m=2, n=1) tearing modes on fusion-born alpha-particles transport is also studied including island rotation. In qualitative agreement with previous simulations and observations in TFTR, DIII-D and AUG tokamaks, it is shown that the density profile can exhibit a global modification leading to significant alpha particles losses. This is due to the fact that, although the magnetic field is integrable, the alpha particles can exhibit chaotic dynamics and anomalous exit time statistics. |
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BP11.00028: Alpha Particle Loss Measurements During JET's 2021 DT Campaign Phillip J Bonofiglo, Vasili Kiptily, Ziga Stancar, Viktor Goloborodko, Mario L Podesta, Sergei Sharapov, Remi Dumont, David Keeling, Michael Fitzgerald, James Oliver, Elena De La Luna, Ashwin Patel, Jeronimo Garcia Olaya, Laszlo Horvath, Ivor Coffey Alpha particle confinement is crucial for sustaining burning plasmas and designing future reactor concepts. A multitude of MHD instabilities can lead to wave-particle interactions and transport alpha particles outward from the plasma. These processes are detrimental to plasma self-heating and require further study. JET's 2021 DT-campaign provides new opportunities for alpha particle experiments in ITER-like plasmas with state-of-the-art energetic particle diagnostics and advanced modeling capabilities. This work will present alpha particle loss measurements from JET's Faraday cup fast ion loss detector array and scintillator probe with supporting measurements from neutron and gamma ray diagnostics. Losses from low frequency MHD activity are examined with comments on alpha transport, confinement, and heating in the bump-on tail distribution and ``afterglow" scenarios. The measurements are paired with ORBIT-kick simulations with fast ion distributions provided from TRANSP/NUBEAM to fully describe and quantify the loss mechanisms. Through modeling, differences among the fusion born alphas and beam born species are highlighted. The presentation will conclude with suggestions for ITER experimentation and alpha confinement with regards to the JET observed mode activity. |
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BP11.00029: Low frequency Alfvénic activity in ST40: assessment of stability and likelihood for nonlinear frequency chirping Vinicius N Duarte, Nikolai N Gorelenkov, James Bland, Mario L Podesta, Stanley M Kaye, Peter Buxton, marco sertoli, Michele Romanelli, Mikhail Gryaznevich We present analyses of low-frequency Alfvénic instabilities in the ST40 spherical torus high field plasmas, with simultaneous neutral beam heating due to two sources at 25keV and 55keV. Given the limitation on internal measurements, the plasma profiles for the TRANSP and NUBEAM simulations have been estimated using an integrated analysis of the available line-of-sight integrated measurements and volumetric integrals. NOVA/NOVA-C [Gorelenkov et al, Phys. Plasmas 6, 2802 (1999)]) analysis indicates that the most unstable modes are found to be core-localized n=1 BAAE eigenmodes with mixed acoustic and electromagnetic Alfvénic polarization (Gorelenkov et al, Phys. Lett. A 370, 70 (2007)). The global transport analysis combined with the eigenmodes' stability indicates that BAAEs are strongly unstable and that there is a greater tendency for bursty chirping response as the level of background micro-turbulence decreases in time. Those predictions are shown to be consistent with the experimental data. This finding is interpreted in terms of the suppression of coherent phase-space structures that support chirping when the resonant fast ion dynamics is dominated by frequent stochastic, orbit-decorrelating events. |
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BP11.00030: Validating Quasi-linear simulations of a single Alfven eigenmode in a tokamak Nikolai N Gorelenkov, Vinicius N Duarte, Michael Van Zeeland The oscillatory behavior of a single unstable toroidicity-induced Alfvénic mode (TAE) observed in DIII-D experiments [M. Van Zeeland et al, Nucl. Fusion Nucl. Fusion 61 (2021) 066028] and excited by suprathermal beam ions is investigated numerically. One goal of this study is to validate the quasilinear approach used in recently developed Resonance Broadened Quasilinear code RBQ [N.N. Gorelenkov, Duarte, Phys. Lett. A 386 (2021) 126944]. We are showing that the realistic time dependence of fast ion growth rate is essential to reproduce the observed overshoot phase emerging within a few milliseconds after the start of NBI blip. Another goal is to quantify the TAE oscillations in the saturated state. The comparison helps to understand the multiscale intermittency observed in experiments and predicted in simulations. An interplay between the growth, damping rates and the effective scattering frequency in RBQ simulations exhibits a predator-prey behavior of the mode amplitude evolution. Additionally, studied beam blip experiments exhibit a rapidly changing drive which needs to be factored into simulations. |
Author not Attending |
BP11.00031: Pre-Universe-"Dawn"(PUD) First Plasma-Waves/Heavy/Mass-ive-Proton-Plasmons VS. Relatively Mass-"less"-Electron-Plasmons Interactions With Siegel BAES Acoustic-Phonons(aka Much-Later "BAOS") via Matsubara/Siegel G...P-Ontology E Carl-Ludwig Siegel, Marvin Antonoff, Norman Rostoker, Joquin Luttinger, Jan de Boer, Peter Egelstaff, Norman March, Albert Overhauser, Herman Chernoff, Frederic Young PUD first plasma-waves/(PWS):(relatively)-heavy/mass-ive-proton-plasmons VS. (relatvely)-mass-“less”-electron-plasmons interactions with Kaiser-Tatro-Siegel BAES acoustic-phonons [much later “Silk”/“Shapiro”/“Tegmark” baryon-acoustic-oscillations”(“BAOS”) PWS/plasmons dispersion-relations generic-analytics(GA) via Salam-Matsubara/Siegel(SMS)[J.Non-Xline-Solids 40,453(80);Ferroelectrics(81);Statphys-13(77);Intl.Conf./Lattice-Dynamics(77), M. Balkanski ed.,Flammaron(78)] G...P-ontology within “hierarchical-nested-ontologieS”(HNOS)-Sequence (HNOSS). G...P Dispersion-rel-ationS interactions/scatterings/inter-sections:UP- |
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BP11.00032: Experimental comparison of ion cyclotron emission in the LHD stellarator and DIII-D tokamak Jeff B Lestz, Kenji Saito, Shuji Kamio, Hiroe Igami, Kunihiro Ogawa, Masaki Osakabe, William W Heidbrink, Genevieve H DeGrandchamp, Steve Vincena Ion cyclotron emission (ICE) is ubiquitously observed at integer harmonics of the cyclotron frequency of fast ions present in magnetic fusion devices such as tokamaks and stellarators. Due to the ease of detection, ICE has the potential to serve as a passive fast ion diagnostic suitable for harsh burning plasma environments, so long as this collective instability is sufficiently well understood. To this end, dedicated experiments have been performed on the LHD stellarator and DIII-D tokamak to determine the sensitivity of ICE to magnetic configuration, fast ion distribution and species (H and D), and fundamental plasma parameters including magnetic field strength, electron density, and the thermal ion species mix (H, D, and 3He). Whereas ICE in DIII-D is observed uniformly on all toroidally-separated probes, ICE in LHD exhibits a strong toroidal localization, indicating a major difference in eigenmode structure and propagation. In both tokamak and stellarator configurations, ICE is most commonly emitted near the plasma edge, though core emission is also possible in spherical tokamaks such as NSTX(-U) and L-mode DIII-D plasmas. The dependence of the saturated ICE amplitude on plasma parameters will be discussed. |
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BP11.00033: Regulation of Alfven eigenmodes by microturbulence in fusion plasmas Pengfei Liu, Xishuo Wei, Zhihong Lin, Guillaume R Brochard, Gyungjin Choi, William W Heidbrink, Javier H Nicolau, George McKee Meso-scale Alfven eigenmodes (AE) and microturbulence in tokamak plasmas can strongly couple despite the scale separation. Energetic particle (EP) scattering by the microturbulence can affect phase space dynamics in nonlinear AE-EP interactions. Zonal flows can be generated/damped by, and in turn, suppress both the AE and microturbulence. AE and driftwave can have direct mode-mode coupling. Understanding these cross-scale interactions requires global integrated simulations incorporating multiple physical processes. In this work, reversed shear Alfven eigenmodes (RSAE) in the DIII-D tokamak is found to saturate through zonal flows in global GTC [1] simulations using gyrokinetic thermal and fast ions and drift kinetic electrons. The RSAE amplitude and EP transport are much higher than experimental levels at the nonlinear saturation, but quickly diminish to very low levels after the saturation if background microturbulence is artificially suppressed. In contrast, in simulations coupling micro-meso scales, the RSAE amplitude and EP transport decrease drastically at the initial saturation but later increases to the experimental levels in a quasi-steady state due to regulation by the thermal ion temperature gradient (ITG) microturbulence. The quasi-steady state EP transport is larger for a stronger microturbulence. The EP radial scattering by the microturbulence is much more effective than Coulomb collisions in destroying EP coherent structures to maintain the quasi-steady state. The RSAE amplitude from gyrokinetic simulations agree, for the first time, very well with the DIII-D ECE and BES measurements [2]. GTC simulations of AE and microturbulence interactions in ITER operational scenarios will also be presented. |
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BP11.00034: Alfvén eigenmode critical-gradient predictions of alpha particle and NBI ion transport in ITER scenarios integrated with microturbulence Eric M Bass, Ronald E Waltz, William W Heidbrink, Christopher G Holland The TGLF-EP+Alpha critical-gradient model of Alfvén eigenmode-driven energetic particle (EP) transport is used to predict transport of fusion alpha particles and 1 MeV beam ions in two ITER scenarios: a hydrogen baseline (without fusion alphas) and a deuterium-tritium steady state. This work is part of a larger cross-code DOE EP milestone project. This 1D transport model combines critical-gradient AE-driven transport with EP transport driven by thermal particle-driven microturbulence predicted using the TGLF gyro-Landau fluid model. The TGLF model, with higher resolution to correctly treat AEs, also provides the crucial AE critical gradient used in the TGLF-EP+Alpha transport model. Predictions are compared against two associated DIII-D cases chosen to closely match anticipated q profiles of the ITER cases. AE spectra from global, linear GYRO simulations are shown to contextualize findings from the local transport models. We find larger EP redistribution in the steady-state case than previously reported for the ITER Kinsey case due to a 2.5 times higher fusion rate, and thus stronger mode drive, in the present case. |
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BP11.00035: Gyrokinetic simulation of energetic particle driven toroidal Alfven eigenmodes in micro-turbulence Yang Chen, Jeff Candy, Scott E Parker We present nonlinear simulations of the evolution of energetic particles (EP) driven Reverse Shear Alfven |
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BP11.00036: Preliminary identification and characterization of nonlinear wave-wave, wave-beam, and wave-particle interactions in beam-driven tokamak plasma Gregory Riggs, Mark E Koepke, William W Heidbrink, Michael Van Zeeland, Donald A Spong We present the analysis of 18 DIII-D shots heated by neutral-beam injection (NBI). [Typical plasma parameters are n~2x1013 cm-3, T~1keV.] As energetic ions seeded by NBI resonate at the frequencies of various Alfven eigenmodes (AEs), we observe rich toroidal Alfven eigenmode (TAE) activity as these weakly-damped modes are driven. Both steady and modulated beam power have been investigated. Statistical techniques were used to benignly filter out the polluting effect of edge-localized modes (ELMs) in the observed fluctuation spectra. Guided by recent simulations [Spong et al 2021; Nucl. Fusion 61, 116061] which identify nonlinear coupling between TAEs and zonal flows, we seek to correlate the observed nonlinear interaction between ensembles of AEs and lower-frequency MHD modes with coincident perturbations in the fast-ion distribution function. Evidence for energy exchange due to this coupling is given by higher-order spectral techniques. In particular, we report on the evolution of consistent bicoherent features in magnetic fluctuation data. |
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BP11.00037: DISRUPTIONS Session Chairs: |
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BP11.00038: Overview of Disruption Event Characterization and Forecasting (DECAF) Research Steven A Sabbagh, Young-Seok Park, Juan D Riquezes, John Berkery, Jalal Butt, Matthew Tobin, Veronika Zamkovska, Jun Gyo Bak, M. J. Choi, Hyunsun Han, Jayhyun Kim, Woong Chae Kim, Jinseok Ko, Won-Ha Ko, Jongha Lee, Jeongwon Lee, Si-Woo Yoon, Mark D Boyer, Keith Erickson, Mario L Podesta, Jongsoo Yoo, Fred M Levinton, Matt Galante, Christopher Ham, Sam Gibson, Andrew Kirk, Lucy Kogan, David Ryan, Andrew J Thornton, Andrea Piccione, Yiannis Andreopoulos Physics-based disruption event characterization and forecasting (DECAF) research determines the relation of events leading to plasma disruption and aims to provide early warning for disruption avoidance. Offline analysis accesses data from several tokamaks (e.g. KSTAR, MAST/-U, NSTX/-U, ASDEX-U, DIII-D) to best understand, validate, and extrapolate models and to consider the key question of event and disruption correlation vs. causality. Fully automated analysis of large datasets is possible with initial results showing true positive rates over 99%. Real-time (r/t) DECAF has started on KSTAR. Experiments produced over 50 plasmas that are forecast with 100% accuracy in r/t, some triggering controlled plasma shutdown or disruption mitigation. Warnings were issued well before (>0.5s) the expected disruption. R/t magnetics, Te profiles from electron cyclotron emission (ECE), 2D Te fluctuation data from ECE imaging, and velocity profile acquisition are installed. An r/t MSE system has been built. Research supporting DECAF is shown including resistive stability evaluation at high non-inductive current fraction and innovative counterfactual machine learning application to MHD stability limits. *This research is supported by U.S. DOE grants DE-SC0020415, DE-SC0018623, and DE-SC0021311. |
Author not Attending |
BP11.00039: Confinement state characterization modules for DECAF Jalal Butt, Steven A Sabbagh, Jack Berkery, Veronika Zamkovska, Juan D Riquezes, Young-Seok Park, Matthew Tobin High-confinement mode (H-mode) is an operational regime in which future reactors will likely operate, including ITER. H-mode is characterized by broad, elevated kinetic profiles with steep edge gradients resulting from the formation of an internal transport barrier. Transitions from H-mode to low-confinement (L-mode) have previously been identified as part of some event sequences that lead to plasma termination, hence making its characterization of interest in understanding disruptions. We present an implementation of new confinement modules for DECAF – a code that resolves, characterizes, and forecasts event chains that lead to plasma disruption. The confinement events take as input various plasma signals, including electron temperature, Dα, plasma stored energy, energy confinement time. The events are validated on a database of H- and L-mode plasmas in KSTAR and NSTX. Primary confinement modules are currently being examined for real-time implementation on KSTAR, commencing utilization of the newly installed rt- electron cyclotron emission diagnostic as part of the machine’s rt-DECAF implementation. Finally, using the DECAF event chain analysis framework, we present preliminary results on the extent of correlation and causality of confinement back-transitions with disruptions. |
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BP11.00040: DECAF Code Multi-device Investigation of Disruption Timing and Categorization Indicated by Abnormal Variations in the Plasma Vertical Position and Current Veronika Zamkovska, Steven A Sabbagh, John Berkery, Young-Seok Park, Juan D Riquezes, Jalal Butt, Matthew Tobin, Jun-Gyo Bak, Jayhyun Kim, Jinseok Ko, K. D Lee, Siwoo Yoon, Lucy Kogan, Keith Erickson Plasma disruption in tokamaks is a multi-step process in which the loss of plasma vertical position control and the quenching of the plasma current are typically among the last events preceding plasma deconfinement. Deviation from a normal waveform of either of these two parameters has served in various forms as an indicator of the disruption onset in the past. The present non-uniformity of disruption time definitions across the tokamak community brings ambiguity in cross-comparisons of various predictor performances. Here, we present a systematic study of abnormal plasma current and vertical position waveforms and evaluate their capacity to serve as disruption onset indicators. The study is conducted with the DECAF code, on multi-year and device databases with a focus on KSTAR, MAST/-U and NSTX/-U tokamaks. The frequency of occurrence of different types of abnormal waveforms and the disruption categories that they define will be presented in the context of the operational spaces of each device. Interconnection of the abnormal waveforms will be discussed as well. Results obtained hereby might serve to define a reliable indicator of the disruption onset. *This research was supported by the U.S. Department of Energy under grants DE-SC0020415, DE-SC0018623 and DE-SC0021311. |
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BP11.00041: A multi-tokamak comparative study of methods for detecting and predicting disruptivity of vertical displacement events Matthew Tobin, Steven A Sabbagh, Jack Berkery, James M Bialek, Jalal Butt, Veronika Zamkovska, Young-Seok Park, Juan D Riquezes Vertical displacement events (VDEs) in tokamaks involve large displacements of the plasma magnetic axis from the vessel plane of symmetry, often leading to disruptions. These events are particularly dangerous for their potential to cause damage to plasma-facing components, as well as large forces on the vessel due to halo currents generated during the disruption that run through the plasma and vessel. Detection and control of these events and mitigation or avoidance of a potential disruption is crucial, and is often achieved through either real-time equilibrium reconstructions or real-time comparisons of magnetic probe measurements. For example, external flux loops typically located above and below the midplane of the tokamak are employed to monitor the displacement and velocity of the plasma magnetic axis. Using the DECAF code, we compare these two detection approaches in terms of their reliability and accuracy in predicting disruptions of the plasma. Further, we present results of a comparative study between VDEs on KSTAR and NSTX indicating critical metrics and thresholds for predicting these events and their propensity to result in disruption. |
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BP11.00042: CQL3D Fokker-Planck modelling of runaway electrons in the DIII-D tokamak at reactor-relevant electron temperatures Juan F Caneses Marin, Robert W Harvey, Yuri V Petrov In this contribution, we model the formation of Runaway-Electrons (REs) in the DIII-D tokamak at reactor-relevant electron temperatures (1-12 keV) using the Bounce-Averaged Fokker-Planck (FP) code CQL3D. Thermal Quench (TQ) events are initiated with Ar pellet injection to create REs where the TQ times are taken from recent DIII-D experiments [1]. FP calculations are coupled to the Ampere-Faraday (AF) equations to study the self-consistent conversion of pre-disruption thermal current to RE current as a function of the pre-disruption electron temperature. The impact of these results are discussed together with future steps towards improved FP modelling of RE production via pellet injection in tokamak plasmas. |
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BP11.00043: Effects of Modified Radial Transport Model on Runaway Electron Current Yuri V Petrov, R.W. Harvey, C. C Kim, L. L Lao The classical formula for the radial transport of electrons in perturbed magnetic field [1] has been modified to have a lower radial diffusion for high-energy electrons. Different energy dependence factors are tested for a DIII-D shot with Neon shattered pellet injection. The modeling is done with the CQL3D bounce-averaged Fokker-Planck (FP) code [2,3] coupled to the 3D extended MHD code NIMROD [4]. Time-dependent data on plasma profiles (Ohmic current density, temperatures, toroidal electric field, densities of all ionization states of Neon, magnetic field fluctuation, etc.) is read from NIMROD and mapped to CQL3D grids. The CQL3D advances the FP solution for electrons, with adjustment of electric field when the REs appear, in such a way as to maintain a nearly constant current density during thermal quench. Based on the survey results, a range in the magnitude and shape of the radial diffusion coefficient is determined that is consistent with the RE current observed in the experiment. |
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BP11.00044: Modeling of multistage disruption mitigation scenarios and runaway electrons with the DTRAN/CQL3D codes A.Yu. Pigarov, Yu.V. Petrov, R.W. Harvey Successful disruption mitigation in tokamaks includes safe quenching of plasma thermal energy (TQ), plasma current (CQ), and non-thermal/relativistic runaway electron (RE) fractions; that requires multistage mitigation scenarios (MMS) based on successive controlled mass injections (or RF waves, MHD events). For advanced modeling of such MMS, CompX is developing the integrated modeling package including: 1D multielement multispecies flux-surface-average plasma transport code DTRAN; atomic physics code CRAMD-RE; GSE magnetic equilibrium library EQLIB; and common CDC framework. The dynamics of velocity distribution functions (VDF) is simulated with kinetic 2V-1.5D Fokker-Planck code CQL3D+GENRAY. Here we present the DTRAN modeling results on SPI+MGI MMS for DIII-D leading to various low-temperature partially-ionized (LTPI) Ar-D-mixture plasma conditions at the end of CQ phase including RE-plateaus. The effects of a VDF RE-tail, anomalous transport, molecular chemistry (MAR, ICN, vibrational kinetics), line radiation (and the opacity), and evolving geometry on LTPI plasma performance are highlighted. Conditions for establishing a quasi-stationary VDF in RE-plateaus are discussed. |
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BP11.00045: Magnetohydrodynamic Modeling of Shattered Pellet Injection and Impurity Dynamics Brendan C Lyons, Nathaniel M Ferraro, Stephen C Jardin, Charlson C Kim, Joseph T McClenaghan, Lang L Lao, Ryan M Sweeney, Nick C Hawkes, Gabor Szepesi, Jayhyun Kim, Sangjun Lee, Michael LEHNEN Future tokamaks require disruption mitigation to prevent machine damage. Predictive models are needed to project these systems to future devices. We present an overview of disruption-mitigation modeling with the M3D-C1 MHD code. M3D-C1 has been coupled to a coronal model for impurities and a state-of-the-art model for pellet ablation. A 3D benchmark with NIMROD for an injected pellet shows that the codes agree on the peak radiated power as well as thermal-quench (TQ) and current-quench time scales, giving confidence in predictive modeling by both codes. Simulations of JET with realistic SPI plumes of pure-Ne and Ne-D2 pellets show a competition of time scales between pellet propagation and outside-in radiative collapse. At low injection speeds, the two pellets have similar TQ dynamics; at high speeds, the mixed pellet travels further before complete TQ. Other topics considered include single vs. dual-symmetric injection on KSTAR, validation of DIII-D SPI TQ modeling with experiment and EFIT reconstructions, predictive ITER simulations in L- and H-modes, and a comparison of coronal and collisional-radiative impurity models for disruption mitigation. |
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BP11.00046: Cooling flow regime of a plasma thermal quench Yanzeng Zhang, Jun Li, Xianzhu Tang A large class of Laboratory, Space, and Astrophysical plasmas is nearly collisionless. When a localized energy or particle sink, e.g., in the form of a radiative cooling spot, is introduced into such a plasma, it can trigger a plasma thermal quench (TQ). Notice that injecting neon pellets to force a core TQ through radiation is ITER's standard approach of mitigating the thermal load of an incoming thermal quench in the event of a major disruption. Here we show that the electron thermal conduction in such a nearly collisionless plasma follows the convective energy transport scaling in itself or in its spatial gradient, due to the constraint of ambipolar transport. As the result, a robust cooling flow aggregates mass toward the cooling spot and the TQ of surrounding plasma takes the form of four propagating fronts that originate from the radiative cooling spot, along the magnetic field line. The slowest one, which is responsible for deep cooling, is a shock front. For the TQ in a tokamak, these fronts will turn the core TQ into four phases, each of which has its unique physics and duration. Specifically, the nearly collisionless TQ is governed by a fast scaling $T_{e\parallel}\propto t^{-2}$, while the collisional TQ is described by a slow scaling $T_{e\parallel}\propto t^{-2/5}$. |
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BP11.00047: KORC Modeling of Wall Heating by Avalanche Runaway Electrons During a Final Loss Event in DIII-D Matthew T Beidler, Diego Del-Castillo-Negrete, Daisuke Shiraki, Eric M Hollmann, Larry R BAYLOR This work extends the recent modeling of runaway electron (RE) mitigation in Ref. [1] by including an avalanche RE source in the Kinetic Orbit Runaway electrons Code (KORC). We find that REs produced by the avalanche source are the primary contributor to transient surface heating of plasma-facing components (PFCs). The magnitude of the calculated heating is comparable to that for DIII-D graphite tile ablation and features of the simulated PFC surface heating qualitatively agree with infrared imaging of the first wall tiles in DIII-D only when the avalanche source is included. The KORC simulations presented in this work evolve a distribution of tracer RE guiding center orbits using a time series of experimental reconstructions of the electromagnetic fields. Fokker-Planck and large-angle collisions with the effects of partially-ionized impurities are employed assuming uniform and constant plasma and impurity profiles with magnitudes inferred from experimental observations. To calculate the PFC surface heating due to RE deposition, we have extended the 1D model from Ref. [2] to include the energy dependence of the deposition length scale. [1] Beidler et al., Phys. Plasmas 27, 112507 (2020) [2] Martín-Solís et al., Nucl. Fusion 54, 083027 (2014) |
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BP11.00048: Development of KORC-NIMROD couplings toward hybrid kinetic-fluid runaway electron mitigation modeling Omar E Lopez, Matthew T Beidler, Diego Del-Castillo-Negrete, Valerie A Izzo Unmitigated runaway electrons (REs) threaten the achievable performance in ITER, and there is a pressing need for predictive modeling of RE mitigation via shattered pellet injection. In the post-disruption phase, most of the current is carried by the REs instead of the cold, background plasma. Modeling needs to evolve the full distribution function for the kinetic REs self-consistently with a magnetohydrodynamic (MHD) model for the background plasma. This work presents advances and plans for the implicit coupling of the Kinetic Orbit Runaway electrons Code (KORC) with the nonlinear MHD code NIMROD. For the NIMROD to KORC one-way coupling, we are building upon NIMROD’s RE tracer orbits [1] to incorporate the optimized particle-pushers and robust collision operators developed in KORC [2], which include Fokker-Planck and large-angle collision operators that account for partially-ionized impurities. To couple back KORC to NIMROD, we calculate the fluid RE current using a previously developed PIC scheme [3] to deposit REs onto NIMROD’s finite element grid. |
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BP11.00049: Extended MHD Modeling of Disruption Mitigation in SPARC and NSTX-U Nathaniel M Ferraro, Andreas Kleiner, Matthew L Reinke, Ryan M Sweeney, Brendan C Lyons Reactor-scale tokamaks must be designed to withstand the large forces and thermal loads associated with disruptions. To characterize these forces and loads, fully three-dimensional magnetohydrodynamic (MHD) simulations of mitigated and unmitigated disruptions in NSTX, NSTX-U, and SPARC model discharges have been performed using the M3D-C1 extended-MHD code. In these simulations, whether mitigated or unmitigated, the thermal quench ultimately proceeds from magnetohydrodynamic instabilities in the current sheet that forms as the edge of the plasma cools, consistent with previous calculations. In the SPARC simulations, poloidally and toroidally localized gas injection sources are included in order to calculate the spatial distribution of radiation on the plasma facing components. Ionization, recombination, and radiation from injected gas is calculated self-consistently with the MHD evolution using a coronal non-equilibrium model based on KPRAD. M3D-C1 implements spatially resolved models of the first wall, vacuum vessel, and passive plates to calculate halo currents and eddy currents. Ports are treated as regions of anisotropic resistivity in an axisymmetric model of the vessel. |
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BP11.00050: Runaway electron x-ray emission during the startup of MST tokamak plasmas Courtney L Johnson, Luis F Delgado-Aparicio, Aubrey Houser, Noah C Hurst, Patrick D VanMeter, Diego Del-Castillo-Negrete, minglei yang, Brett E Chapman, Novimir A Pablant, Kenneth W Hill, Manfred L Bitter, Oulfa Chellai, Tullio Barbui, John P Wallace, Karsten J McCollam, Cary B Forest Energetic electron emission has been observed during the startup (∼0-10 ms) of reproducible tokamak plasmas (Ip = 40-60 kA, ne < 0.05-0.2 x 1019 m-3) produced at the Madison Symmetric Torus (MST). The multi-energy soft x-ray (ME-SXR) pinhole camera provides brightness measurements of the bremsstrahlung radiation given off by the suprathermal runaway electrons (RE’s) with space (Δr/a≈2%), time (∼1 ms), and energy resolution. Motivated by an ITPA Joint Analysis task, the effects of prefill gas pressure, applied electric field, and current ramp-up rate on the startup of MST tokamak plasmas were investigated with a specific focus on the RE emission. Resonant magnetic perturbations (RMPs) with m=1, 2, and 3 fields were applied with different amplitudes, phases, and times to explore the suppression of these RE’s during startup. Preliminary results suggest that RE acceleration is decreased at sufficiently high pressures, but the consistent presence of RE emission indicates that RE generation is a robust feature of MST tokamak plasma startup. A new gating capability was tested using the versatile PILATUS3 detector to improve the time-resolution of the x-ray measurement from 0.5 kHz to 2 kHz and 4 kHz, providing a more complete picture of the RE emission during the breakdown and startup of the plasma. |
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BP11.00051: RF Current Condensation via Top Launch ECCD for Island Stabilization Elena Litvinova Mitra, Allan H Reiman, Lanke Fu, Richard Nies, Nathaniel Fisch Radio frequency (RF) current drive can be used in tokamaks to reduce disruptions by stabilizing islands. In this project, we study the particular effects of plasma positioning and shaping on the RF current condensation by coupling the EFIT equilibrium solver to the OCCAMI code (Of Current Condensation Amid Magnetic Islands) and applying the resulting code to top launch electron cyclotron current drive (ECCD) stabilization of islands in DIII-D tokamak plasmas. |
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BP11.00052: Simulations of Neoclassical Tearing Mode Growth with Realistic Wall Boundary Conditions Eric C Howell, Jacob R King, James D Callen, Robert J La Haye Nonlinear MHD simulations study the mechanisms via which neoclassical tearing modes (NTMs) lock and trigger disruptions using reconstructions of DIII-D ITER Baseline Scenario discharges [La Haye R. J., et al., Nucl Fusion 2022]. Simulations build on NIMROD development that enables NTM modeling [Howell E.C., et al., Phys Plasmas 2022]. Previous simulations use a close-fitting conducting wall at the separatrix which has two major impacts on NTM dynamics: 1) The braking torque that arises due to the decay of wall eddy currents is absent. 2) The close proximity of the wall strongly stabilizes the edge tearing modes which alters the mode coupling. Here, simulations use a wall approximating DIII-D's vacuum vessel with both resistive and conducting boundary conditions. An applied perturbation seeds a growing m/n=2/1 NTM. As the NTM grows large it destabilizes higher-n core modes which degrade the core magnetic surfaces. We present analysis of the simulation as it progresses through the thermal quench and report on parameter scans varying the wall resistivity. |
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BP11.00053: Study of D2 Line Emission after Massive D2 Injection into Runaway Electron Plateaus in DIII-D Eric M Hollmann, Jeffery L Herfindal, Daisuke Shiraki, Robert S Wilcox, Adam McLean, Alexander Pigarov Massive injection of D2 gas into runaway electron (RE) plateaus is of interest as a possible method to reduce the severity of RE-wall strikes in ITER, motivating the study of the physics of these RE plateaus. Measurements of visible and UV D and D2 line brightnesses in DIII-D indicate that D Ly-α is strongly (>10x) trapped. Self-consistent collisional-radiative modeling including D2 line opacity and both thermal and non-thermal electron impact indicates that the D2 band radiation is largely untrapped. This allows D2 band radiation to become the dominant (>2x) power radiation channel. The modeling indicates that D2 band radiation is caused by RE-impact excitation, with thermal electron impact nearly completely negligible. Initial fits to D2 band structures indicate rotational temperatures of order 3000 - 4000 K, reasonably (within 2x) close to kinetic temperatures predicted by a 1D diffusion model. |
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BP11.00054: Runaway Electron Amplification in Tokamak Disruptions Jonathan Arnaud, Chris McDevitt Runaway electron (RE) generation during a tokamak disruption poses a significant concern to the longevity of plasma facing components. More specifically, amplification of REs by the avalanche mechanism provides a means of converting current carried by near bulk electrons into RE current. The present work focuses on evaluating the efficiency of the avalanche process in tokamak geometry for plasmas with large electric fields and significant impurity content, conditions typical of a tokamak disruption. It is found that the efficiency of the avalanche process depends sensitively on the collisionality of electrons near the critical energy to run away. The presence of impurities plays a multifaceted role in this process. While high-Z impurities increase the collisionality of the overall plasma, they also significantly increase the critical energy to run away, thus decreasing the collisionality near the critical energy to runaway. In contrast, larger quantities of impurities lead to a larger electric field, due to the increase in radiation. The impact of these partially offsetting processes on the net efficiency of the avalanche mechanism will be addressed by integrated drift kinetic simulations of tokamak disruptions. |
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BP11.00055: Marginal stability constraint on runaway electron distribution Dmitrii I Kiramov, Boris Breizman High-frequency kinetic instabilities of the strongly anisotropic runaway electrons can enhance the pitch-angle scattering of the runaways significantly. This wave-induced scattering can easily prevail over runaway scattering on high-Z impurities. |
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BP11.00056: Measurement of Whistler-like Waves in the Madison Symmetric Torus (MST) Tokamak Plasma* Abdulgader F Almagri, Mark A Thomas, Allyson M Sellner, Brett E Chapman, Luis F Delgado-Apariciop, Noah C Hurst, Steve F Oliva, Alex S Squitieri, Paul Wilhite, Cary B Forest Experiments and simulations show Whistler waves can be driven by runaway electrons, RE, which in a predator-prey fashions stabilize these RE. High frequency magnetic fluctuation measured in MST reveal multiple coherent modes.. Multipole single-turn coils are used to measure magnetic fluctuation and wave number spectra. Whistler-like magnetic fluctuations up to 3.4 GHz have been observed. Magnetic fluctuation and x-ray intensity in the range of 5 to 100 keV show a strong correlation. Both signals show alternating bands of high and low activities. The highest frequency measured is 3.4 GHz in the range of the local electron cyclotron frequency, 3.4 GHz. The amplitude of this mode is modulated at about 200 MHz. A new high frequency probe that measures the parallel and perpendicular fluctuation simultaneously is used to determine the wave polarization.. Using two-point correlation method, and are measured. Signals are digitized at 12.5 GHz with 5 GHz bandwidth. The target Plasma has , , , -2. The fluctuation amplitude of these frequency lines decrease with increased density and are absent at 0.4x1013 cm-3.. The polarization, wave numbers, and other properties of these waves will be discussed |
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BP11.00057: Investigating the Nature of a Hollow Radial Profile of Runaway Electrons During Tokamak Disruptions Aubrey V Houser, Noah C Hurst, Courtney L Johnson, Luis F Delgado-Aparicio, Augustus Azelis, Brett E Chapman, Abdulgader F Almagri, Karsten J McCollam, John S Sarff, Cary B Forest Understanding the creation and transport of runaway electrons in tokamak plasmas is vital for the safety and preventing machine damage during plasma disruptions. We use a Multi-energy Soft X-Ray (ME-SXR) camera on the Madison Symmetric Torus (MST) to probe the radial distribution of low-energy photon emission between 2-3 and 40keV (using a 450 μm silicon detector) which is characteristic of fast electrons up to 100 keV. Low-density plasmas are tailored using a density ramp-down to ~10●1018 m-3, and disruptions occur due to a programmed ramp-down of the toroidal field. The exposure of the ME-SXR camera is gated to allow for finer temporal resolution of the runaway electron behavior during the rapid plasma termination. Preliminary evidence of a hollow radial profile of x-ray emission during the termination is discussed, including the possible role of a pre-existing fast electron population. Ongoing work is described in which runaway acceleration in MST is modeled using the Fokker-Planck code CQL3D, and ME-SXR signals are predicted using a synthetic diagnostic. |
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BP11.00058: Linear and Nonlinear Simulations of Tokamak Discharges with Fluid Runaway Electrons in NIMROD. Alexandre P Sainterme, Carl R Sovinec A reduced fluid model for runaway electrons (REs) is incorporated in the time advance of the NIMROD code. REs are treated as a distinct fluid species that flows with a velocity consisting of a large prescribed parallel component and a perpendicular component given by the E cross B drift. There is a volumetric source density for REs given by the background density and parallel electric field via the Dreicer mechanism [Connor and Hastie, NF 15, 415], and a source representing the avalanche RE generation [Rosenbluth and Putvinski, NF 37, 1355]. Like the JOREK model presented in Ref. [Bandaru, et al., PRE 99, 063317] and the M3D-C1 model in Ref. [Liu et al., PoP 27, 092507], the RE density evolution couples to the MHD equations via Ohm's law in under the assumption that the RE current does not contribute to the resistive electric field. The NIMROD code has the capability to perform both linear and nonlinear calculations with the RE model. Linear calculations of an m=2, n=1 tearing mode in both cylindrical and toroidal geometry confirms prior findings that the presence of RE current introduces rotation of the eigenmode structure in the poloidal plane [Liu]. We also present 3D, nonlinear simulations of MST tokamak discharges with REs. |
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BP11.00059: Antenna-driven Compressional Alfven Eigenmodes in Relativistic Electron Beam Plasmas Hari P Choudhury, Alexander F Battey, Carlos A Paz-Soldan, Andrey Lvovskiy, Tsuyoshi Akiyama Compressional Alfven Eigenmodes (CAEs) are a kinetic instability observed in tokamak plasmas with significant ion heating power. While CAEs are typically excited by a fast ion population, recent work has reported that they can also be driven by a runaway electron (RE) population following a plasma disruption (Chang Liu et al 2021 Nucl. Fusion 61 036011). Whether naturally occurring or driven by an antenna these modes have the potential to deconfine the RE population. During recent DIII-D discharges, CAEs were driven using a low-power ICRF antenna, located on the low-field side, in both pre- and post-disruption plasmas. Waves were launched for a range of frequencies from 0.1 MHz to 10 MHz and were observed to excite multiple wave harmonics, as shown in frequency spectrograms of magnetic fluctuations, in both the pre-disruption and RE plasma. The dependence of the low frequency cut-off on several plasma parameters, such as toroidal field and plasma density, will be presented; and a comparison will be made between those conditions that support the propagation of the driven mode post-disruption and those conditions in which no modes propagate. The results of this study will improve the fundamental understanding of CAEs and how they may deconfine the RE population. |
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BP11.00060: Simulation of DIII-D disruption process with pellet injection and runaway electrons using M3D-C1 code Chen Zhao During a tokamak disruption, electrons can runaway and be accelerated to high energies, potentially damaging the first wall. To predict the occurrence and consequences of runaway generation during a disruption, we have developed a runaway electron (RE) module for the M3D-C1 code. This fluid RE model is fully coupled to the bulk plasma and pellet model. It utilizes an implicit time advance with sub-cycling that allows runaway velocities approaching the speed of light. Both the Dreicer and avalanche source terms are included, and we have verified their implementation by performing benchmarks with the JOREK code. We have computed the whole non-linear disruption process starting from the beginning of a single pellet injection to the time that runaway electron current plateau has been formed. This process includes both thermal quench and current quench phases with RE beam in disruption. Such a simulation is challenging due to multi-scale physics. M3D-C1 runs for a DIII-D discharge 177053 reveal detailed dynamics of the runaway current density and the electromagnetic field structure, in particular the role of the electric field in the runaway evolution. |
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BP11.00061: MFE: POWER HANDLING Session Chairs: |
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BP11.00062: Improvements in wall conditioning and performance throughout the phase I of WEST operations Alberto Gallo, David Douai, Nicolas Fedorczak, Thierry Alarcon, Vivien Anzallo, Clarisse Bourdelle, Sebastijan Brezinsek, Eric Caprin, Matthieu De Combarieu, Corinne Desgranges, Pascal Devynck, Annika Ekedahl, Jonathan Gaspar, Christophe Guillemaut, Remy Guirlet, James Paul Gunn, Julien Hillairet, Thierry Loarer, Patrick Maget, Pierre Manas, Philippe Moreau, Francis-Pierre Pellissier, Emmanuelle Tsitrone, Jerome Bucalossi The tungsten (W) Environment in Steady-state Tokamak (WEST) is the only superconducting EU device with metallic plasma-facing components (PFC). The main goal of WEST is to test actively cooled, ITER-like, W diverter PFC under a steady state heat load of qdiv~10 MWm-2. In campaigns 1 and 2 no glow discharge boronization (GDB) was performed, to study W PFC all installed at once. After a challenging commissioning, frequent deuterium (D2) glow discharge cleaning (GDC) led to pulses up to ~10 s, lower hybrid power up to PLH~2.4 MW, and central density up to n~1.5e19 m-2, but with high impurity content, radiated fraction frad>0.8, and qdiv~0 MWm-2. During campaign 3, besides D2 and helium GDC, diborane (B2D6) GDB was first deployed, significantly opening the operational space: improved startup conditions and lower oxygen content allowed for long pulses (>30 s) at more than twice the density ( n~3.5e19 m-2), with higher injected power (PLH~5 MW), lower frad~0.6, and qdiv~2.5 MWm-2. Large use of GDC and GDB in campaign 4, with a renewed GD system in campaign 5, pushed performance further: WEST achieved minute-long pulses with better LH coupling and qdiv~6 MWm-2. W content remains high and the spectral brightness of light impurities sputtering W (mainly oxygen and carbon) rises back to pre-GDB levels after a few long pulses. |
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BP11.00063: Benchmark Collisional-Radiative Modeling of Fusion-Relevant Plasmas Mark C Zammit, James T Sanchez, Christopher J Fontes, James Colgan, Nathan Garland, Xianzhu Tang The collisional-radiative modeling of impurity elements relevant to magnetic fusion is a complex process involving an array of assumptions and methods with respect to atomic structure and processes. Data from such models exist, but ambiguities may form concerning approximations used within each model and to where resulting data is applicable. Out of these ambiguities arises the need for benchmarking studies detailing specific model methods and approximations, and where simplifications can be applied. |
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BP11.00064: Benchmarking an improved atom and molecule neutral fluid model in UEDGE with DEGAS2 Menglong Zhao, Thomas D Rognlien, Marvin E Rensink, Andreas Holm, Maxim Umansky, George J Wilkie A fluid neutral model is regularly used in UEDGE to simulate neutral gas transport. An improved neutral model was recently implemented in UEDGE. The new model solves for an atom temperature (Ta) separate from that of the ions, as opposed to the default neutral model that solves for a mean temperature of ions and atoms. The new model thus identifies that the atom temperature can be substantially different from the ion temperature. The implementation is verified using the Method of Manufactured Solution [1]. The simulation results show that for comparatively low collisional edge plasmas, the atom temperature can be much lower than ion temperature and thus lead to reduced atom penetration into the core region. Validation of the new model is also required. Therefore simulation results with the new atom temperature equation are compared to results from the kinetic neutral model of DEGAS 2 in various geometries. |
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BP11.00065: Using GITR to simulate and predict performance of silicon carbide as first-wall material in DIII-D. Aritra De, Zachary J Bergstrom, Jerome Guterl, Stefan A Bringuier, Tyler Abrams, Dmitry L Rudakov A. Dea, Z. Bergstromb, J. Guterlb, S. Bringuierb, T. Abramsb and Dmitry Rudakovc |
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BP11.00066: SOLPS-ITER modelling of Liquid Lithium Divertor for a Fusion Nuclear Science Facility (FNSF) MD SHAHINUL ISLAM, Jeremy D Lore, Smolentsev, Sergey, Charles E Kessel The scrape-off layer heat flux width (λq) is an important parameter for the plasma facing components in fusion devices because it can determine the peak energy flux to the divertors. Here, we have investigated the impact of λq on the divertor and upstream plasma conditions for the Fusion Nuclear Science Facility (FNSF) with fast flowing liquid lithium (Li) divertors. The anomalous radial transport values, χ⊥e,i = 1.0 m2/s and D⊥ = 0.3 m2/s are used as a base case, resulting in λq mapped to the outer midplane of 3-4 mm. The radial transport values are modified to provide three different λq. The main gas puffing and neon (Ne) seeding rate are then adjusted to maintain the upstream electron separatrix density ~ 1020 m-3 and Li is sourced into the system. The Li ion concentration is increased in the upstream region as λq is reduced, while the electron temperature (Te) profile becomes narrower. Consequently, Li escapes along the periphery regions and transports toward the upstream region due to lower Te. The effect of Li sourcing location and private flux region PFC geometry will be presented. Coupling between the liquid Li MHD heat transfer code and SOLPS has been performed, and the radial profile of evaporated flux is imposed according to the liquid metal (LM) surface temperature. Divertor plasma parameters are significantly affected for the higher evaporation Li divertor. |
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BP11.00067: Kinetic modelling of plasma parallel transport in open systems with Ion Cyclotron Radio-frequency and Neutral beam heating scenarios Atul Kumar, Juan F Caneses Marin, Cornwall H Lau, Richard H Goulding In this work, the hybrid Particle-In-Cell code: PICOS++ [1] is applied to study plasma transport in two different open magnetic geometries. The analyses include the effects of: (1) finite fully-absorbing boundaries for the particles, (2) volumetric particle sources, (3) Fokker-Plank Collision operator and (4) Radio-Frequency (RF) heating. RF heating on a divertor simulator: Material Plasma Exposure eXperiment (MPEX) is studied to understand ion heating using fundamental ion cyclotron resonance and its associated parallel transport. Calculations show that RF heating creates ion temperature anisotropy and strongly modifies the plasma density and parallel flow leading to significant drop in density near the target region. This density drop near the target in MPEX is found to saturate with higher RF power. Furthermore, the effect of Neutral Beam Injection (NBI) on the parallel electric field and plasma confinement in an Axisymmetric Magnetic mirror geometry has been investigated. It is found that the presence of NBI enhances the confinement of warm ions in a mirror plasma system. A sensitivity scan of source temperature, neutral beam energy, mirror ratio and mirror length are also performed to study their impact on plasma confinement time in mirror geometry. |
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BP11.00068: Towards a MPEX Digital Twin Cornwall H Lau, Richard Archibald, Mark R Cianciosa, Markus Eisenbach, Atul Kumar, Jeremy D Lore, Yury Osetskiy, German D Samolyuk, Juergen Rapp, Tim Younkin, Eva Zarkadoula The Material Plasma Exposure eXperiment (MPEX) is a currently constructed linear plasma device to test materials, including irradiated materials, to fusion divertor reactor relevant fluxes and fluences. This paper will show the high level plan and initial results towards the development of a MPEX digital twin to accelerate the commissioning of MPEX. Radio frequency (RF) source and heating models, plasma, neutral and impurity transport models, and plasma-material interaction (PMI) models are combined and coupled together to calculate the plasma and impurity fluxes from MPEX engineering parameters. These coupled models will first be validated on the existing Proto-MPEX experimental results before eventual extrapolation to MPEX. Initial results show the importance of core power absorption for helicon waves, parallel pressure gradients in predicting plasma flows, role of oxygen in predicting impurity transport, and importance of direct atomistic modeling in understanding ion penetration depth and reflection yields. Coupling all these models together appear necessary to predict source and heating, transport of main plasma, and transport of impurities in understanding the experimental measurements of plasma and impurity flux at the Proto-MPEX target. |
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BP11.00069: Disentangling volumetric power and momentum losses in the JET-ILW scrape-off layer Bartosz Lomanowski, Jae-Sun Park, Leena Aho-Mantila, Mathias Brix, Mathias Groth, Christophe Guillemaut, Christopher Lowry, Stefan Marsen, Andrew G Meigs, Marco Wischmeier A large variation in the measured volumetric power, (1-fcooling), and momentum, (1-fmom), loss factors has been observed in theJET-ILW scrape-off layer (SOL), leveraging spectroscopic target electron temperature measurements and JET’s unique capability for separating the main-ion-driven net dissipation effects from impurity radiation. SOLPS-ITER and EDGE2D-EIRENE fluid-neutral edge plasma simulations have been carried out to decompose the dominant momentum and power loss channels in unseeded, high recycling and low recycling nitrogen seeded seeded L-mode scenarios. The simulations show that while momentum losses in the unseeded cases are dominated by atom-molecule-plasma interactions, a similar momentum loss trend is obtained for the low recycling nitrogen seeding scan, consistent with experiment, due to a combination of poloidal viscosity, radial transport and atom-plasma interactions, even in the absence of significant molecular densities at the target. The steeper power loss trend in the low recycling nitrogen seeding scan results in a factor of three reduction in the (1-fcooling)/(1-fmom) ratio, demonstrating for the first time the variation in this important parameter in the context of two point model separatrix density scaling and SOL-pedestal integration. |
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BP11.00070: Observation of Edge Harmonic Oscillations in JET-ILW Deuterium,Tritium and DT plasmas. Emilia R Solano, P Buratti, JM Fontdecaba, D Brunetti, Eleonora Viezzer, J Hobirk, S Silburn Long-lived EHOs that suppress ELMs have been reported in co-NBI plasmas in JET, with a Carbon wall [1,2]. Here we report on recent observations of transient EHOs in Deuterium, Tritium and DT plasmas in the JET-ILW, with Be walls and a W divertor. EHOs are observed in early phases of hybrid plasmas (co-NBI injection) and they delay the arrival of the 1st ELM, but are typically destroyed as gas is added to deliberately initiate an ELMy phase [3]. Modes are typically n=1, edge localised, with at least an n=2 harmonic, sometimes more. They are generally observed at low collisionality, as expected from the exfernal mode model [4]. Transient QH-modes with duration of up to 500 ms have also been reported in AUG with a full W wall, both with co and counter NBI [6]. In AUG EHOs appear in the low density, high temperature branch, with the pedestal close to the kink-peeling boundary. Future work in both JET and AUG aims at investigating access conditions, extending the QH-mode to stationarity, and determining whether it can be a viable operating regime for future fusion devices. [1] E. R. Solano et al, Phys. Rev. Lett. 104 185003 (2010) [2] E. R. Solano et al, 45th EPS Conf. on Plasma Physics, Prague, P4.1044 (2018) [3] C Challis et al, 48th EPS Conf. on Plasma Physics, Online (2022) Poster 287. [4] D. Brunetti et al., Phys. Rev. Lett. 122, 155003 (2019).[5] E. Viezzer et al, 47th EPS Conf. on Plasma Physics, Online, (2021) P1.1054 |
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BP11.00071: Towards real-time detachment control using reduced models derived from the SOLPS-ITER code Jeremy D Lore, Sebastian De Pascuale, John Canik, MD SHAHINUL ISLAM, Paul Liau, Jae-Sun Park, Birdy Phathanapirom, Ben Russo Time-dependent SOLPS-ITER simulations are used to develop reduced models for real-time control of the boundary plasma. This approach extends beyond typical linear control used on present-day tokamaks, offering the potential to respond to rapid transient behavior in addition to avoiding time-consuming tuning procedures. SOLPS-ITER is run to determine the plasma response to fuel ion and impurity seeding gas inputs. The full 2D simulation output is reduced to a set of experimentally measurable upstream and downstream quantities with the implementation of synthetic diagnostics, to test control of fully observable and limited access systems. Data-driven methods that identify sparse interpretable (non-black box) dynamic models are applied, including DMD, SINDy, and a novel kernel-based method to reduce sensitivity to noise. The system nonlinearity is stronger for impurity seeding as compared to fuel ion puffing, as well as when the divertor plasma approaches detached conditions, highlighting the need for model-based control. Model-predictive feedback control with adaptive retraining has been demonstrated and used to virtually control a DIII-D discharge and has also been recently implemented for simulating control of a hydrogen ITER plasma. |
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BP11.00072: Reversed-direction 2-point modeling applied to divertor conditions in DIII-D Jacob H Nichols, Peter C Stangeby, Adam McLean, John Canik, Auna L Moser, Morgan W Shafer, Huiqian Wang, Jonathan G Watkins A predictive form of the extended 2-point model known as the “reverse 2-point model”, Rev2PM, is applied to a range of detachment levels in the open lower divertor of DIII-D. It is found that the experimentally measured electron temperature (Te) and pressure (pe) at the divertor entrance can be calculated within 30% from target measurements, if and only if a posteriori corrections for convective heat flux are included in the model. Unlike the standard 2-point model, the Rev2PM calculates upstream SOL quantities (such as separatrix Te and pe) from target conditions (such as Te and parallel heat flux), with volumetric power and momentum losses depending solely on target Te. The Rev2PM is tested against a database of DIII-D inter-ELM DTS measurements, built from a series of 6 MW, 1.3 MA, LSN H-mode discharges with varied main ion density, drift direction, and nitrogen puffing rate. Measured target Te ranged from 0.4-25 eV over this database, and upstream Te ranged from 5-60 eV. Poor agreement is found between upstream measurements and Rev2PM calculations that assume purely conductive parallel heat transport. However, introducing a posteriori corrections to account for convective heat transport brings the Rev2PM calculations within 30% of the measured upstream values across the dataset. These corrections imply that up to 99% of the parallel heat flux is carried by convection in detached conditions in the DIII-D open lower divertor, though further work is required to assess any potential dependencies on device size or divertor closure. |
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BP11.00073: SOLPS-ITER Wide Grid implementation in different divertor geometries Ivan Paradela Perez, Jeremy D Lore, MD SHAHINUL ISLAM Simulations of DIII-D SAS divertor and MAST-U Super X configuration using the Wide Grid version of SOLPS-ITER with kinetic neutral transport are compared with standard SOLPS-ITER 3.0.8 simulations , and with simulations with 9-point-stencil fluid neutrals. |
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BP11.00074: Time-dependent SOLPS-ITER simulation for KSTAR target flux bifurcation analysis Jae-Sun Park, Jeremy D Lore, Sebastian De Pascuale, Jin Myung Park Extensive tokamak boundary plasma studies have been conducted using the SOLPS-ITER code package including 2D fluid plasma and a kinetic neutral solver, and have generally focused on time-independent solutions. SOLPS-ITER code is inherently capable of time-dependent simulations. In addition, with recently developed features such as time-varying gas throughput, it can be applied to feedforward simulation, and feedback control through the IPS integrated modeling environment with system identification. A feedforward SOLPS-ITER simulation was performed for the target flux bifurcation observed in the KSTAR density ramp experiment, which is a dynamic problem. The observed bifurcation time scale was in good agreement with the value obtained from simulation within a factor of 2, and the core penetration of X-point radiation observed through the bolometer was also reproduced. Accordingly, the cause of bifurcation was explained through the two-point formatting equation. With data-driven system identification via DMD and SINDy, feedback control of upstream density using IPS was demonstrated and the validity of the model subject to bifurcation was tested. |
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BP11.00075: Microstructural Evolutions in Helium Irradiated Dispersoid Strengthened Tungsten Alloys Chase C Hargrove, Xing Wang, Trevor F Marchhart, Ashrakat H Saefan, Jean Paul Allain Tungsten is a candidate material for the divertor region of fusion tokamak reactors due to its high melting point, low coefficient of linear thermal expansion, high sputter threshold, and low tritium retention. Transition metal carbide additions by spark-plasma sintering (SPS) has been shown to increase the recrystallization temperature of W with no increase to deuterium retention. High energy helium particles implant themselves in near–surface(nm) regions of tungsten, stabilizing vacancies and coalescing to nanometer–sized bubbles. The growth of He bubbles from incident plasma at elevated temperatures has been observed in W-TiC, W-TaC, and W-ZrC samples, but the effects of the microstructure on the migration of helium warrants further study. Kesternich et al showed the preferential trapping of He for TiC precipitates can be altered by recrystallization at elevated temperatures resulting in a dislocation-sparse microstructure.Samples of W-TaC, W-TiC, and W-ZrC are fabricated via SPS and held at 1600°C in an inert atmosphere to alleviate internal stresses within the microstructure and grow grains. Samples are then irradiated with He to a 3 x 1016/cm2 fluence at 800°C and characterized via scanning electron microscopy (SEM). |
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BP11.00076: Surface chemistry analysis of lithiated porous tungsten under deuterium irradiation Camila Lopez Perez, Hanna Schamis, Jean Paul Allain High-Z materials such as tungsten-based alloys and alloy composites are attractive for use as PFCs because of their low sputtering yield, high melting point, and high thermal conductivity [1]. However, the use of these high-Z PFCs poses challenges during transient event operation such as dust generation, surface melting, cracking, and droplet ejection [2]. A solution to protect the plasma from high-Z emission is to coat them with a liquid low-Z metal (e.g. lithium) in the liquid state to continually replenish Li and therefore maintain a low-Z plasma interface while tolerating both high steady-state and transient heat fluxes in the high-duty cycle environment of a fusion reactor [3]. A lithium coating was deposited on three porous tungsten substrates. Sample 1 was irradiated while Li was solid, sample 2 while Li was liquid, and sample 3 after Li had resolidified. All samples were irradiated with D2+ with a fluence of 1016/cm2. In-vacuo X-ray Photoelectron Spectroscopy (XPS) and Thermal Desorption Spectroscopy (TDS) were performed on the samples following D2+ irradiation. The work described here identifies the impact of intrinsic impurities (H2O, O2, C) on the surface chemistry of lithium films under D+ exposure. Analysis of in-vacuo XPS data is correlated to emission channels of D2+ species from TDS and compared to previous Li-O- D2+ interaction studies done on porous and non-porous substrates such as TZM, carbon and tungsten. |
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BP11.00077: Effect of magnetic topology and injection location in DIII-D real-time wall conditioning experiments Florian Effenberg, Alessandro Bortolon, Federico Nespoli, Darin R Ernst, Heinke G Frerichs, Florian M. Laggner, Jeremy D Lore, Rajesh Maingi, Yuhe Feng Modeling with EMC3-EIRENE reveals the role of the parallel impurity forces, including the scrape-off layer (SOL) main ion flows, on the edge transport of injected material and ionized impurities. New analysis compares impurity powder injections in DIII-D lower single null, upper single null, and double null configurations with plasma edge transport and dust migration and ablation modeling. Materials in powder and granular form have been injected into various divertor configurations for real-time wall conditioning, ELM control, and divertor power exhaust mitigation at DIII-D. Changes in the divertor configuration lead to a re-direction of SOL flows associated with changing drag forces acting on the injected material favoring conditioning of plasma-facing components on either the low field side or the high field side. Poloidal shifts of the injection location can also modify the penetration depths and trajectories of injected materials in the plasma boundary. Such changes ultimately affect the local deposition of materials on plasma-facing components, which is critical for active conditioning and replenishment of functional coatings in future long-pulse scenarios. |
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BP11.00078: Calculation of material erosion and ion-shadowed area at rough graphite and silicon carbide divertor surfaces Shota Abe, Charles H Skinner, Andrew H Liu, Jhovanna Garcia, Zihan Lin, Stefan A Bringuier, Tyler Abrams, Bruce E Koel We present a computational investigation of material erosion and ion-shadowed areas as a function of the ion incident angle for rough graphite and silicon carbide divertor surfaces. Surface roughness affects erosion, material deposition, and, hence, plasma-facing component lifetime. Ion angle distributions (IADs) for D plasmas on the NSTX-U and DIII-D divertors were calculated by an equation-of-motion model that traces ion trajectories in the sheath. Then the effective sputtering yields and ion-shadowed area fractions are calculated by a Monte Carlo micro-patterning and roughness code that applies the calculated IADs to surface topographic data obtained from confocal microscopy of rough graphite and SiC surfaces from NSTX-U and DIII-D. The calculations find that the effective sputtering yields, the sputtering pattern, and the shadowed area are determined by the detailed surface topology. The mean surface inclination angle was found to be a useful parameter to estimate the local ion incident angle from the calculated IADs. We report global empirical formulas for the surface erosion and the shadowed area fraction from the main D ions for rough surface configurations of the divertor. |
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BP11.00079: Low-recycling liquid-metal "divertorlets" concept for heat exhaust in divertors of fusion reactors Francisco J Saenz, Zhen Sun, Brian R Wynne, Jabir Al-Salami, Egemen Kolemen Liquid metal flows are promising for heat exhaust in divertors of fusion devices and continuous operation at the reactor scale [1]. Fast flows are intended to remove all of the heat captured by liquid metals, but they have risk of splashing and formation of liquid-metal pileups due to intense MHD drag [2]. Slow flows may suffer liquid metal evaporation for the increased exposure time of the liquid metal to the plasma. |
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BP11.00080: In Situ Tritium Separation and Hydrogen Isotope Pumping for Liquid Metal Divertor Applications Brian R Wynne, Francisco J Saenz, Zhen Sun, Egemen Kolemen A liquid metal centrifuge is being developed for the extraction of deuterium and tritium from lithium inventory in a closed-loop liquid metal system. Dilute solutions of lithium tritide (LiT) and lithium deuteride (LiD) will form when the temperature of the mixture of deuterium and tritium in lithium is reduced. The large density differences of LiD and LiT compared to pure liquid lithium will then be utilized for the separation into an enriched slurry, which can be later broken down through electron beam heating. [1] The magnetic centrifuge system is being designed based on an electromagnetic liquid metal (EMLM) pumping method. The magnetohydrodynamic (MHD) effects of Lorentz forces are implemented for liquid metal circulation, with externally applied magnetic fields and current driving the flow. A centrifuge system is constructed and optimized at Princeton Plasma Physics Laboratory, first tested with galinstan (67% Gallium, 20.5% Indium, and 12.5% Tin) separating crystal impurities. Simulations are performed to characterize performance of the galinstan centrifuge, and compared to experimental results. The next iteration will be a system for liquid lithium, running experiments at University of Illinois Urbana-Champaign for lithium hydride (LiH) separation using the density differences between Li and LiH. |
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BP11.00081: A New Workflow for Simulating X-point target and Snowflake Divertors in SOLPS-ITER cyd Cowley, Adam Q Kuang, David Moulton, Jeremy D Lore, John Canik, Maxim Umansky, Michael Wigram, Sean B Ballinger, Bruce Lipschultz Alternative divertor configurations such as snowflakes or X-point targets may be crucial for reducing steady-state heat loads for reactor tokamaks, providing strong motivation for their extensive study. However, to date, the snowflake and X-point target have not been simulated extensively in codes with kinetic treatment of neutrals such as SOLPS-ITER. This is primarily because the SOLPS-ITER grid builder CARRE cannot be applied to such divertors, and the physics modules of SOLPS-ITER are not expecting such geometries. Though code modifications have been made to allow for snowflake simulations previously (Pan O et al. Plasma Physics and Controlled Fusion. 2020.), the generalisation of these changes has been challenging. |
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BP11.00082: Energy and particle balance during plasma detachment in alternative divertor configurations Rebecca L Masline, Sergei I Krasheninnikov Comprehensive studies of energy and particle balances in the transition to plasma detachment in alternative divertor configurations are shown. Numerical simulations are performed with the 2D code suite SOLPS 4.3, using an up-down, disconnected double null grid with narrow, tightly baffled long poloidal leg divertors at the outer lower target and outer upper target. A density scan is performed using the "closed gas box" model, where the tunable parameter in the simulations is the total number of deuterium particles in the simulation space and all other parameters are held fixed, including a constant input power and trace neon impurity radiation, to assess the physics of the transition to detachment in the system as the density increases. Three main aspects of the physics of divertor detachment are addressed: the distribution of heat flux and other plasma parameters between the four divertors as each divertor transitions to detachment, the criteria for the local onset of divertor detachment in each of the divertors, and the role of neutrals and fluxes to the walls in the transition to the detached regime. These results are compared to the existing understanding of the physics of the transition to plasma detachment in standard divertors. |
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BP11.00083: Comparison of divertor and main wall recycling dynamics during ELMs Roman Smirnov, Maxim Umansky, Sergei I Krasheninnikov Plasma recycling on material surfaces of tokamaks plays essential role in SOL plasma transport via various processes involving neutrals. The plasma-material interfaces are usually described using constant recycling coefficient in tokamak plasma modeling studies. This approach, which ignores the dynamic material response to changing plasma conditions, however, can be insufficient when large plasma transient events, such as ELMs, are considered. In this work, we perform dynamic 2D plasma-wall simulations using coupled plasma transport code UEDGE and wall reaction-diffusion code FACE. The simulations are conducted for different initial states of the divertor plasma and for the material parameters approximating tungsten. The ELMs are emulated by varying in time the edge plasma cross-field transport coefficients and heating power. The obtained results demonstrate that the dynamic plasma recycling at the divertor target and the main wall can have disparate effects during ELM depending on the ELM size, the initial plasma and material conditions. It is shown that in attached divertor plasma regime, large ELMs can lead to desorption of significant amounts of hydrogen from the divertor target, while the hydrogen is simultaneously reabsorbed by the wall material in the far SOL regions. The interplay between the divertor and wall recycling effects on plasma recovery in inter-ELM period will be also examined. |
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BP11.00084: Lithium Alloy Creation for the Advancement of Liquid Metal Plasma Facing Components Giovanni Diaz, Cody Moynihan, Steven Stemmley, James Bramble, David N Ruzic The interest in using liquid lithium as a plasma facing component (PFC) in fusion reactors has grown in recent years due to the PFC’s self-healing surface, and low hydrogen recycling. However, the liquid PFC is hindered by its relatively high vapor pressure (about 1Pa at 800K). This hinderance introduces relatively high Z material into the bulk plasma, potentially decreasing the reactor’s efficiency. Yet, this decrease may be mitigated by using a lithium alloy: such as tin lithium. With liquid tin’s substantially lower vapor pressure (about 10nPa at 800K), these alloys may limit the vapor pressure of the liquid PFC while keeping the benefits of liquid lithium. |
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BP11.00085: Distillation Column for Hydrogen Removal in Liquid Lithium PFC Systems Cody Moynihan, Steven Stemmley, David N Ruzic Tritium trapping in liquid lithium plasma-facing components remains one of the major counterarguments to the use of lithium in fusion devices. This trapping could contribute to tritium inventory concerns and the loss of the low recycling boundary. As such, it is crucial to develop technology for the removal of hydrogen and other impurity species. These systems can prevent lithium saturation, reduce corrosion of materials, and limit the clogging of distribution systems. At the Center for Plasma-Material Interactions (CPMI), a distillation column has been developed to thermally treat the liquid lithium and remove the hydrogenic species. |
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BP11.00086: Assessment of the sources of uncertainty for the validation of wall erosion models in the WEST tokamak Ananthi Renganathan, Davide Curreli, Sophie Blondel, Jon T Drobny, Wendy A Garcia, James Paul Gunn, Alyssa L Hayes, Jeremy D Lore, Ane Lasa Esquisabel, Logan Meredith, Emmanuelle Tsitrone, E.A. Unterberg, Brian D Wirth Quantifying wall erosion in tokamaks is fundamental for determining the impurity sources leading to plasma contamination and assessing the lifetime of plasma-facing components. In order to validate the modeling results on wall erosion obtained from the PSI-2 suite of codes and facilitate successful use of their predictive capabilities for reactor-relevant conditions, we first need to assess the effect the uncertainties have on the modeling results in existing tokamaks. A coupled hybrid particle-in-cell code, hPIC2, with a binary collision approximation code, RustBCA, is used to determine the wall erosion of select few locations in the WEST tokamak, namely a reciprocating collector probe placed in the SOL, and the surface of the RF limiter in front of the ICRH actuator. We have analyzed the effect of three significant sources of uncertainty on the predicted wall erosion: (1) Actual plasma impurity composition, which includes both intrinsic and extrinsic impurities such as oxygen, carbon, copper, residual gases, etc. 2) Charge state distribution of the impurities, and 3) Inverse Photon Efficiency (S/XB), which is finally used for the conversion of sputtering fluxes into observed spectral radiance. |
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BP11.00087: Plasma Line Emission Measurements for Assessment of Tungsten Sputtering on the Radio Frequency Plasma Interaction Experiment Kaitlyn Butler, John B Caughman, Curtis Johnson, E.A. Unterberg, Davis C Easley, David C Donovan Filterscopes are being used to measure the line emissions from plasma material interactions of a biased tungsten electrode in the Radio Frequency Plasma Interaction Experiment (RF PIE). A 2.54 cm diam tungsten electrode is exposed to a helium or deuterium-argon plasma generated via electron cyclotron resonance at 2.45 GHz (density 5e17/m3, temp 4-5 eV) and biased with either DC or RF voltages up to 550 V. Ratios of He lines at 667.8 nm, 706.5 nm, and 728.1 nm are being used to determine changes to the electron density and temperature near the electrode due to biasing conditions and are compared with the local parameters measured with a double Langmuir probe. The W I line at 400.9 nm is being measured for comparison with results from a 1-meter Czerny-Turner spectrometer. Filters with various bandwidths are being used to determine their effectiveness at filtering out the emission from nearby helium or argon lines. Multiple viewing chords are being used to determine the axial variation in front of the electrode. Tungsten emission as a function of bias voltage is observed to start near the threshold energy for helium (~100 eV) and increase in a way that is consistent with the expected sputter yield. Experimental details, as well as application of tungsten filterscope techniques for DIII-D and WEST, will be presented. |
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BP11.00088: Radio Frequency Driven Plasma Material Interactions of Reactor Relevant Materials John B Caughman, Kaitlyn Butler, Curtis Johnson, E.A. Unterberg, Davis C Easley, David C Donovan The interaction of radio frequency (RF) sheaths with fusion reactor relevant materials (e.g., tungsten) is being studied on the Radio Frequency Plasma Interaction Experiment (RF PIE). The RF PIE consists of an electron cyclotron resonance plasma source (2.45 GHz, 5 kW) with a biased and heated RF electrode. Helium and/or deuterium plasmas (density of ~1e18/m3, electron temperature of 4-5 eV) are being used to explore sheath formation on tungsten surfaces at temperatures up to 850 C and biases up to 500 V. An increase in the electron temperature on magnetic field lines connected to the electrode has been observed and depends on the grounding of the RF-driven electrode. The changes in helium line ratios measured with a filterscope are being compared to Langmuir probe measurements and modeling predictions to characterize this sheath interaction. The erosion of the tungsten surface as a function of bias conditions is also being studied spectroscopically. Tungsten line emission intensity is different for DC versus RF bias for similar plasma conditions and average ion energy, which is likely due to the calculated broadening of the ion energy distribution due to RF. The effect of this broadening on the expected sputtering yield is being determined. Experimental details, as well as tungsten nano-fuzz growth under certain bias conditions, will be presented. |
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BP11.00089: Validation of prompt versus local tungsten redeposition using target geometry and magnetic field scans Davis C Easley, Timothy R Younkin, Ezekial A Unterberg, Curtis A Johnson, Atul Kumar, David C Donovan Using the 3D Monte-Carlo Global Impurity TRansport (GITR) code, we examine differences in the redeposition pattern for tungsten (W) surfaces with a particular view toward ex situ diagnostic methods for discriminating the dominating redeposition mechanisms. Our modeling results show that W redeposition is primarily geometrically-driven (promptly redeposited) or electrostatically-driven (locally transported within the pre-sheath). We have demonstrated how the dominant redeposition type evolves under changes in key plasma parameters and present initial modeling results comparing W redeposition mechanisms in different magnetic field strengths (i.e., 0.7T and 2.2T, corresponding to future experiments planned at CTH and DIII-D, respectively). The distinction in redeposition mechanism is inferred using exact patterning of the source isotopic W which provides sub-mm spatial accuracy of the resultant deposition. By scanning target geometries as well sheath conditions, the GITR redeposition patterns show distinct spatial regions for sputtered material that is geometric- versus electrostatic-driven. These techniques lay the foundation for determining these mechanisms experimentally and for comparing ex situ with in situ diagnostics, all to provide better predictive high-Z sputtering models. |
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BP11.00090: Structural characterization and deuterium ion irradiation effects of tantalum as an absorbing first wall material Danah Velez, Mykola Ialovega, Marcos X Navarro, Kumar Sridharan, Hwasung Yeom, Tyler Dabney, Jay K Anderson, Cary B Forest, Oliver Schmitz
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BP11.00091: Calculation and measurement of D+, D2+, and D3+ fraction in KAERI ion beam irradiation facility by D collisional-radiative model and ExB probe Kil-Byoung Chai, Duck-Hee Kwon, Changmin Shin, Wonho Choe Ion beam irradiation facility was developed using an Applied-Field MPD thruster to study divertor engineering such as the evaluation of plasma facing materials [1, 2]. The AF-MPD thruster was chosen because it can produce high-density plasmas which is necessary for achieving high particle flux as the divertor region. The D ion flux measured by a Langmuir probe was 1×1023 m-2s-1 when the plasma was ignited by 5 kW input power. The electron temperature at the downstream region is in the range of 4-5 eV and the electron density is in the range of (1-4)×1018 m-3. The energy of the D ion beam was measured as 15-18 eV by a Retarding Potential Analyzer. In the D plasmas, both atomic and molecular ions (D+, D2+, and D3+) are generated. Thus, it is important to know the fraction of D+, D2+, and D3+ for obtaining precise D particle flux. In order to calculate the fraction of D+, D2+, and D3+, we developed a D collisional-radiative (CR) model including D, D2, D+, D2+, and D3+ species. Our model predicts that D+ ions are dominated over D2+ and D3+ in our plasmas. To confirm the calculated results, we plan to build an ExB probe: this probe can distinguish ions having different charge-to-mass ratio. The details and preliminary results of the ExB probe will be shown in the paper. |
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BP11.00092: Molten Tin Droplet Ejection in the Presence of a Hydrogen Plasma James Bramble, Cody Moynihan, Steven Stemmley, Giovanni Diaz, Jackson Stermer As the fusion community works to find a way to mitigate the high heat and particle flux onto the first wall and divertor region, liquid metals have been gaining traction as a potential material for those two regions. Some of the biggest benefits of utilizing a liquid metal wall are its ability to self-repair any damage caused by transient events in the plasma, as well as the ability of a liquid metal wall to trap escaped fuel and waste material thereby promoting a lower recycling regime in the edge plasma regions. However, there are multiple liquid metals being considered for use as PFCs in future fusion devices: Tin, Lithium, Lead-Lithium, Tin-Lithium… etc. It is therefore important to investigate these liquid metal PFC candidates to determine the benefits and hazards of each individual liquid metal to the fusion device as well as the fusion plasma. This work builds on an observation made in the semiconductor industry by ASML, a company using molten tin as an EUV source, who noticed that if the tin is molten in a hydrogen plasma environment, tin droplets are ejected, or spit, from the tin surface. This was confirmed by some preliminary work which has shown that ejected tin droplets range in size from tens of nanometers to hundreds of microns. If tin is used in future fusion devices, the fusion plasma will cause tin to spit thereby contaminating the core fusion potentially causing increased power losses. This work characterizes the size and spatial distribution of the tin droplets that are ejected from the molten tin surface over a range of pressures and powers, thereby showing that tin should not be considered as a PFC for fusion devices. |
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BP11.00093: ICF: Z-PINCH Session Chairs: |
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BP11.00094: Energetics of Triple-Nozzle Gas-Puff Z Pinches on the 1-MA COBRA Generator Eric S Lavine, Alexander Rososhek, William M Potter, Jay S Angel, Euan Freeman, Chiatai Chen, David A Hammer, Bruce R Kusse Gas-puff z-pinches (GPZPs) are efficient sources of intense x-rays or neutrons and are of general interest for magneto-inertial fusion studies. Here we present preliminary results of an energy-inventory analysis for triple-nozzle GPZPs on the 1-MA, 220-ns rise time COBRA generator at Cornell university for both axially magnetized and unmagnetized implosions. The total energy coupled to the plasma is inferred from current and voltage traces while spatially resolved plasma parameters such as flow velocity, temperature, and density are measured at different times across highly repeatable implosions using Thomson scattering and laser interferometry. This enables a calculation of kinetic and internal energies. Directed kinetic energy is also estimated from the radial implosion trajectory and initial mass distribution, assuming the mass is accreted as in a snowplow. Radiated energy is measured using calibrated photoconducting detectors (PCDs) and a bolometer. By including a means of discriminating between thermal and non-thermal broadening of the Thomson scattering spectra, we demonstrate that some energy resides in non-directed turbulence which mediates dissipation in the collisionless shock. Evidence of shock reflected ions in the Thomson scattering signal is also presented. |
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BP11.00095: Development of Schlieren Imaging and Interferometry to Diagnose Density Profiles in a DPF Sophia Rocco, Clement S Goyon, Brian H Shaw, Christopher M Cooper, Steven F Chapman, Andrea E Schmidt The MJOLNIR (MegaJOuLe Neutron Imaging Radiography) dense plasma focus (DPF) at LLNL is designed to perform neutron radiography of dynamic events. The DPF (2.6 MA, 1 MJ stored energy) consists of two coaxial electrodes, which generate a plasma sheath by ionizing deuterium gas. The sheath implodes on the axis in a z-pinch geometry. When the pinch breaks apart, it produces a beam of ions that impacts the "target", a region of the sheath assembled on axis past the pinch (n_e ~1e19/cm^3). The beam-target interaction produces a neutron burst. A laser interferometry diagnostic will measure the electron density of the pinch and target regions; allowing us to infer the ion density in the target region, study dynamics during implosion to optimize beam generation in the pinch region, and. compare with hybrid fluid-kinetic particle-in-cell stimulations to verify models. Our implementation of the interferometer began with a Schlieren imaging system, the results of which we present here. The Schlieren technique allows us to image density gradients in the plasma, putting upper and lower bounds on the density and showing small-scale features and structure in the plasma. LLNL-ABS-836612 |
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BP11.00096: Locating restrikes in the MJOLNIR Dense Plasma Focus Paul C Campbell, Christopher Cooper, Steven F Chapman, Luis Frausto, Anthony J Link, Clement S Goyon, Andrea E Schmidt A dense plasma focus (DPF) is a compact coaxial plasma gun which completes its discharge as a z-pinch. The MJOLNIR (MegaJOuLe Neutron Imaging Radiography) DPF at LLNL is designed for flash neutron radiography and has achieved neutron yields up to 3.8E11 neutrons/pulse at 2.5 MA peak current with 1 MJ of stored energy. We hypothesize that current is being diverted from the pinch (also referred to as restrikes) and lowering the neutron yield based on the correlation between current traces and yield. For shots with smaller inductive current dips (and smaller yields) restrikes need to be added in simulation to attain the best match to the experimental data. This suggests that restrikes are occurring somewhere in the DPF head and are causing lower neutron yields. 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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BP11.00097: Measuring Characteristic Differences between High- and Low-Performing Discharges on the MegaJoule Neutron Imaging Radiography (MJOLNIR) DPF Andrea E Schmidt, Enrique Anaya, Michael G Anderson, Justin R Angus, Paul C Campbell, Steven F Chapman, Christopher M Cooper, Luis Frausto, Clement S Goyon, Drew P Higginson, Sheng Jiang, Anthony J Link, Don Max, Matthew M McMahon, Sophia V Rocco, James K Walters A dense plasma focus (DPF) is a compact coaxial plasma gun which completes its discharge as a Z-pinch, producing short (<100 ns) pulses of ions, X-rays, and/or neutrons. LLNL recently constructed and brought into operation a new device, the MJOLNIR (MegaJOuLe Neutron Imaging Radiography) DPF, which is designed for flash neutron radiography. This device has achieved neutron yields of up to 4.1e11 neutrons/pulse at 3.3 MA peak current and 1 MJ stored energy. Higher stored energy (up to 2 MJ) commissioning is underway. LLNL runs particle-in-cell (PIC) simulations of DPF discharges in the Chicago code, and has gained significant insight into the various physical factors that influence neutron yield. Optical diodes and the framing camera have enabled run-down and run-in velocity measurements of the plasma sheath. We present measurements from the optical diodes, framing camera, current traces, and voltage probe that are consistent with low-performance shots being plagued by early-in-time current restrikes. |
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BP11.00098: Temporal variance of timing fiducials on the MJOLNIR dense plasma focus Christopher Cooper, Enrique Anaya, Michael G Anderson, Steven F Chapman, Paul C Campbell, Owen B Drury, Shane M Evans, Luis Frausto, Clement S Goyon, Drew P Higginson, Anthony J Link, Don Max, Sophia V Rocco, Andrea E Schmidt, Kurt Walters Timing fiducials and shot metadata are analyzed to investigate temporal variation and correlations on the MJOLINR dense plasma focus (DPF). The DPF must synchronize the neutron flash to an external experiment and its neutron imaging system by minimizing temporal variation. |
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BP11.00099: Design and Alignment of Neutron Time-of-Flight Shadowbar Detector to Gate a Neutron Camera on the MJOLNIR Dense Plasma Focus. Shane M Evans, Shane M Evans, Christopher Cooper, Clement S Goyon, Andrea E Schmidt, Amanda E Youmans The neutron time-of-flight (n-ToF) measures the time response of the incident x-ray and neutrons generated by the dense plasma focus (DPF). A shadowbarred detector isolates the prompt neutrons from the scattered neutrons in order to gate a neutron camera for flash neutron radiography, of only the prompt neutrons. To achieve this, an array of four n-ToF detectors, two of which are shadowbarred with 25cm of polyethylene, have been set up 2 meters from the DPF. The avalanche photodiodes are in two identical pairs with 10x different gains for high dynamic range. Data from the DPF trains the scaling and subtraction algorithm to produce the profile of the prompt neutrons. Using alignment lasers, the shadowbar must be spatially aligned with a precision of 1 cm and 1 degree to accurately obscure the DPF. |
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BP11.00100: Improved recent simulations of nozzle gas flow and gas-puff z-pinch implosions with recesses in the Weizmann z-pinch* Varun Tangri, John L Giuliani, Arati Dasgupta, Alexander L Velikovich, Tal Queller, Eyal Kroupp, Yitzhak Maron Recent measurements [1] 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. New simulations of the oxygen pinch will be presented that address some of these inconsistencies. Simulations of magnetic field evolution using the 2D radiation-magneto-hydrodynamic code, MACH2-TCRE are presented in two steps as follows. In the first step, initial density is modeled the by neutral gas-flow through nozzles. In the second step, the density profile from the previous step is used as initial condition for simulating the gas-puff implosion. It is shown that simulating the detailed nozzle geometry and outflow significantly improves the comparison of magnetic field radial distribution, temperature and spectroscopic data between the measurements and the pinch simulations. Density and magnetic field in the anode recess will also be compared with experiments. |
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BP11.00101: The effect of pre-ionization on gas puff Z-pinch experiments on a linear transformer driver Apsara M Williams, Fabio Conti, Samantha Fong, Maria Pia Valdivia Leiva, Farhat N Beg Z-pinches are intense X-ray and neutron sources [1]. Neutral gas used for gas puff Z-pinch experiments is ionized when the voltage applied across the A-K gap exceeds some minimum value given by the Paschen curve for the experimental configuration. This type of ionization is statistical, resulting in shot-to-shot variation in current. Externally pre-ionizing the gas puff is presumed to improve experimental reproducibility by providing an established current path [1]. Pre-ionization has also been shown to increase compression ratio, decrease instability and increase X-ray yield [2,3]. The CESZAR LTD (500kA, 150ns) experimental platform at UCSD has been fitted with a custom-built preionizer. Ne hollow gas puff was imploded on a solid-fill D2 target. Here we present a pre-ionizer design for the CESZAR current driver and report the effect of preionization on experimental reproducibility, compression ratio, stability and X-ray as well as neutron yields. |
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BP11.00102: Hall Instability Driven Seeding of Helical Magneto-Rayleigh-Taylor Instabilities in Axially Premagnetized Thin-Foil Liner Z-pinch Implosions Jeff M Woolstrum, Charles E Seyler, Ryan D McBride Helical magneto-Rayleigh-Taylor instability (MRTI) structures have been observed in z-pinch-driven liner implosion experiments with a pre-imposed axial magnetic field. We show that the formation of these helical structures can be described by a Hall magnetohydrodynamical (HMHD) model. We used the 3D extended magnetohydrodynamics simulation code PERSEUS (which includes Hall physics) [C. E. Seyler and M. R. Martin, Phys. Plasmas 18, 012703 (2011)] to study these helical instabilities and show that a Hall interchange instability in low-density coronal plasma immediately surrounding the dense liner is responsible for producing helically oriented effects in the magnetic field and current density within the coronal layer. This seeds the helical pitch angle of the MRTI even when other proposed helical seeding mechanisms are either not present in the experiments or not accounted for in the simulations. For example, this mechanism does not require low-density power-feed plasmas to be swept in from large radius or the development of electrothermal instabilities. The Hall Instability is thus a new, independent explanation for the origin of the helical instabilities observed in axially premagnetized liner experiments. Simulation results supporting this mechanism are presented. |
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BP11.00103: Investigation of edge ablation in magnetic anvil cells Matthew Evans, James Young, Reed C Hollinger, Shoujun Wang, Jorge J Rocca, Pierre-Alexandre Gourdain The magnetic anvil cell (MAC) is a platform that uses a z-pinch configuration to compress matter into a WDM regime using a pulsed-power driver. The MAC platform uses a dielectric coating, or damper, to quench plasma ablation and allows magnetic pressure to build up just outside the sample. To further develop and diagnose this platform, we need to probe beneath the dense sample surface at peak compression. Specifically, we use a bright x-ray source to examine the material’s edge and determine if the compression is uniform. To perform this experiment, we used the Low Amperage System for Small Implosion Experiments (LASSIE), which is a compact pulsed-power driver designed by the XSPL team at the University of Rochester. LASSIE is a low inductance Linear Transformer Driver (LTD) capable of delivering 250 kA peak currents with a risetime of 200 ns. LASSIE was transported to the Laboratory for Advanced Lasers and Extreme Photonics (L-ALEPH) at Colorado State University and coupled to the outside of the laser’s test chamber. We report on the results comparing coated and bare aluminum wires of 250-500 µm that were probed with the x-rays from the ALEPH laser. |
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BP11.00104: Z-pinch simulations using the 5N-moment multi-fluid plasma model with Braginskii transport Yu Takagaki, Uri Shumlak The axisymmetric Z pinch is numerically investigated using the 5N-moment multi-fluid plasma model via the Washington Approximate Riemann Plasma (WARPXM) code [U. Shumlak et al., Comput. Phys. COmmun. 182, 1767 (2011)]. WARPXM, developed at the University of Washington, is a high-order-accurate finite element code that uses a discontinuous Galerkin (DG) spatial representation. The Z-pinch initial conditions satisfy a two-fluid (ion and electron) Bennett equilibrium with uniform temperature and axial velocity for each species such that $T_{i} = T_{e}$ and $u_{iz} = - u_{ez}$. The growth rates for a $m = 0$ sausage instability using the ideal 5N-moment two-fluid model can be larger than the growth rates obtained using the ideal MHD model. Due to the initially uniform temperature and axial velocity, the Braginskii viscosity stress tensor $∏ ∝ \nabla \vec{u}$ and conductive thermal heat flux $\vec{h} ∝\nabla T$ are found to only weakly suppress the $m = 0$ sausage instability. However, the frictional force related to the resistivity $\vec{R}_{\alpha \beta} ∝ \vec{J}$ induces electric fields that exhibit strong stabilizing effects by producing a radially sheared flow $∂_{r} u_{z}$. The applicability of 5N-moment multi-fluid plasma model in the high-temperature and weakly collisional fusion plasma will be discussed. |
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BP11.00105: Dense Plasma Focus Simulations at LLNL Anthony J Link, Rick Anaya, Michael G Anderson, Justin R Angus, Paul C Campbell, Steven F Chapman, Christopher M Cooper, Owen B Drury, Clement S Goyon, Drew P Higginson, Luis Frausto, Sheng Jiang, Don Max, Matthew M McMahon, Sophia V Rocco, Kurt Walters, Amanda E 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 and results from a reduced physics model will be presented for shots utilizing the new MJOLNIR powerflow upgrade. |
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BP11.00106: Plasma formation sourced from initial condition perturbations on high-current-density conductors Maren W Hatch, Thomas J Awe, Edmund P Yu, Brian T Hutsel, Mark A Gilmore The electrothermal instability (ETI) is a Joule heating-driven instability that drives runaway heating in conductors driven to high current density and generates azimuthally correlated temperature and density perturbations in solid state metal. ETI may seed magneto Rayleigh-Taylor (MRT) instability growth in current-carrying, fuel-filled metallic liners used in magnetic direct drive fusion targets, reducing the stagnation pressure and temperature of the fuel. Previous z-pinch experiments examined growth of ETI from 99.999% pure aluminum rods by monitoring characterized micron-scale engineered defects (ED) machined into the rod surface. ED drive local current density amplification which drives early surface plasma formation. Informed design and material alterations have helped to better understand these high-current density explosions. The emission evolution of axially vs. azimuthally oriented ED pairs of varying size/separation has been studied. Sinusoidal perturbations, which are theorized to amplify current density, have been studied to determine how the varying ratio of amplitude over wavelength (A/λ) drives surface heating and plasma formation. Experimental data will be compared with 3D-MHD simulations. |
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BP11.00107: ICF: MAGNETO INERTIAL FUSION Session Chairs: |
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BP11.00108: An ERAU plasma experiment relevant to MHD instability and magnetized reconnection study and its application to ion heating in adiabatic compression Byonghoon Seo, Christopher M Lamb, Xuanye Ma, Katariina Nykyri We introduce a plasma experiment facility in the physical sciences department at Embry-Riddle Aeronautical University (ERAU). A newly installed plasma gun, planned diagnostic instruments, and experimental plans will be presented. This facility provides students, plasma physics and engineering communities with various opportunities in the central Florida area. This new laboratory experiment is developed to specialize in the study of magnetohydrodynamics instability, magnetic reconnection, and the development of experimental diagnostic instruments. In addition, this experiment will be explored in the context of adiabatic compression to observe ion heating during the magnetic reconnection process and secondary adiabatic compression. As a new experimental facility developed by an assistant professor at ERAU, invaluable discussion and input are desired. |
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BP11.00109: Turbulence augmented applied magnetic field in compressions Seth Davidovits The application of a magnetic field to inertial confinement fusion implosions can relax ignition criteria, which may help otherwise marginal implosions ignite. Such applied fields may be augmented by the presence of (non-radial) flows in compressions, either intentionally or not. Here we study, in a simplified simulation setup, the compression and heating of MHD turbulence and the resulting kinematic dynamo dynamics. In particular we show mechanisms which raise the possibility of various benefits for implosions with applied field: enhanced growth of applied magnetic field during the compression; localization of this enhanced field to a hot spot; and the generation there of a stochastic magnetic field with increased thermal conduction suppression relative to the uniform-applied-field case. |
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BP11.00110: Magnetized target plasma collision experiments for PLX: Diagnostics and Results Andrew Case, Edward Cruz, Marco Luna, Robert Becker, Adam Cook, Douglas Witherspoon HyperJet Fusion is building magnetized hydrogen plasma target formation guns for the PLX plasma liner-on-target plasma jet magneto-inertial fusion (PJMIF) scaling experiment at LANL. The target is made by stagnating multiple magnetized plasma jets. In order to reduce risk, a two-jet collision experiment is underway at HyperJet Fusion’s Virginia facility using two target guns to evaluate the collision dynamics of the magnetized hydrogen plasma jets. To diagnose the jets and the merged target plasma we measure velocity, Ti, density, and magnetic field. The diagnostics are interferometry, movable B-dot probe array, spatially resolved photodiodes, high speed imaging, and time resolved spectroscopy, both high resolution (for temperature and velocity) and survey spectroscopy (for line ratios and impurities). The impurity measurements are critical due to the impact on Te during plasma compression. The initial level of impurities in two-gun collided experiments is ~3% as inferred from broadband visible spectroscopy, which may cause excessive radiation losses during upcoming compression experiments. A third chord has been added to the interferometer to measure the line integrated density of the second jet. We present data on the density and magnetic field evolution of the colliding plasmas as well as time-resolved spectroscopic measurements showing that the full 4-jet target system should be able to reach the necessary parameters of density, temperature and embedded magnetic field. |
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BP11.00111: Magnetized Plasma Gun Development for the PLX PJMIF Project Edward Cruz, Andrew Case, Adam Cook, Marco Luna, Robert Becker, Franklin D Witherspoon We present a description of the engineering and technical development of magnetized plasma target guns for the Plasma Liner Experiment (PLX) project [1,2,3]. Each target gun incorporates a high power, pulsed magnet coil designed to provide linked magnetic flux between gun electrodes in the plasma formation region such that the resultant hydrogen plasma jet exits the gun with an embedded magnetic field. Individual target gun performance achieved goals of magnetized hydrogen plasma jets with ∼3 x 1014 cm-3 density, ∼100 km/s velocity, and embedded field of ∼1 kG, but the resultant jets had an higher-than-expected level of impurities from the ceramic insulator, resulting in ∼3% impurity fraction in two-gun collision experiments. This impurity fraction must be reduced to limit radiation losses during near-term target compression experiments at PLX. More detailed target modeling also revealed that increased jet velocity was needed to achieve the desired target stagnation temperature for the integrated experiment at LANL. Two-jet collision experiments are ongoing in effort to address these issues, with the goal of merging magnetized dueterium plasma jets with velocities of ∼140 km/s to form a magnetized target plasma with ≤0.5% impurity species, diagnosing stagnation parameters and comparing to simulations. |
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BP11.00112: Magnetized Plasma Gun Optimizations for Higher Velocity for the PLX PJMIF Project Franklin D Witherspoon, Andrew Case, Edward Cruz In plasma jet driven magneto-inertial fusion (PJMIF), an array of discrete supersonic plasma jets is used to form a spherically imploding plasma liner, which then compresses a magnetized plasma target to fusion conditions[1,2]. The central target is formed by stagnating multiple magnetized plasma jets. Magnetized coaxial plasma guns have been developed by adding a bias field coil to the previously developed contoured gap plasma liner gun. We have achieved goals of magnetized hydrogen plasma jets with ~3 x 1014 cm-3 muzzle density, 100 km/s velocity, and embedded fields of ~1 kG. Two-jet collision experiments at HyperJet indicated the need for velocities of order 140 km/s to achieve sufficient stagnation temperatures. Current gun modeling efforts are focused on increasing velocity to 140 km/s via optimization of the electrode profiles, pfn, and operating parameters. We provide an overview of the Mach2 modeling effort to achieve this increase. |
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BP11.00113: PLX-BETHE: Target Formation and Integrated Experiments for Plasma-Jet Driven Magneto-Inertial Fusion Samuel J Langendorf, Feng Chu, John P Dunn, Andrew L LaJoie, Mark A Gilmore, Franklin D Witherspoon, Andrew Case, Edward Cruz, Jason Cassibry, Aalap C Vyas An overview of research conducted in the Plasma Liner Experiment (PLX) BETHE collaboration is presented, encompassing experimental studies of supersonic spherically imploding plasma liners on PLX, development of compatible compact toroid (CT) target plasma formation and injection methods, and modeling and simulation efforts in support of the above. In addition, methods pursued to improve the synchronization and control of the 36 individual plasma jets on PLX, including high voltage triggering, individual gas puff injection control, and early-time wide-angle imaging, are discussed, and the impacts of these approaches on jet-to-jet timing and liner uniformity are presented.
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BP11.00114: Formation of Plasmas with Tangled Magnetic Fields as Target Plasma for Magneto-Inertial Fusion Feng Chu, Andrew L LaJoie, Samual Langendorf, Joseph R Olson, Karsten J McCollam Plasmas with highly tangled magnetic fields have drawn interest in multiple physics disciplines, such as fundamental plasma physics and astrophysics. Specifically for magneto-inertial fusion (MIF), plasmas containing a tangled magnetic field have been proposed as a novel fusion fuel target plasma, which is quasi-adiabatically compressed and heated by heavy imploding shell or "linear" to achieve thermonuclear conditions. In this work, we present experiments attempting to form plasmas with tangled magnetic fields by colliding compact toroid (CT) plasmas with a coarse grid structure at the Big Red Ball (BRB) Facility at Wisconsin Plasma Physics Laboratory (WIPPL). The topology of the magnetic field perturbed by the grid is measured using a 3-axis Bdot probe array and plasma electron temperature is inferred using a multi-tip Langmuir probe. |
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BP11.00115: Measurements of Plasma Liner Parameters and Uniformity at the Plasma Liner Experiment (PLX) Andrew Lajoie, Feng Chu, Samual Langendorf, Jason Cassibry, Aalap C Vyas, Mark A Gilmore The Plasma Liner Experiment (PLX) at LANL studies the formation and properties of supersonic spherically imploding plasma liners, used in the plasma-jet-driven magneto-inertial fusion (PJMIF) concept. The present campaign on PLX focuses on assessing recent system upgrades aimed at enabling an improved degree of liner uniformity by means of tuning each individual gun's parameters to account for systematic deviations. Here we provide initial results of various diagnostics over a range of operating conditions and over the entire implosion duration. These diagnostics include spatially resolved visible light spectroscopy to determine electron temperatures, multi-chord interferometry to determine line-integrated electron densities, and fast visible imaging to view both the individual jets' and liner's macroscopic characteristics. Comparisons of these properties will be made with simulations from the smooth particle hydrodynamics code SPFMax to better constrain the liner's overall uniformity and properties. |
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BP11.00116: Three Dimensional Simulations of Two Magnetized Jets Merging Aalap C Vyas, Jason Cassibry, Douglas Witherspoon, Samuel J Langendorf, Andrew Case, Edward Cruz The PLX BETHE project has conducted a series of experiments involving the collision of two jets to study the scaling of peak temperature and the production of magnetic fields. A three dimensional numerical model Smooth Particle Fluid with MAXwell equation solver (SPFMax) has been utilized to support these experiments. These simulations included radiation, thermal conduction, and an electromagnetic field solver based on a combination of transmission line theory and Biot Savart's law. Peak stagnation temperatures at the collisional interface between two plasma jets monotonically increases with jet velocity and molecular weight. Modeling of 100 km/s hydrogen jets give agreement with experimental data in which the temperature reaches 10-12 eV. Simulations with Deuterium and Helium at 140 km/s can reach 50 eV at stagnation. Recent two jet experiments have included solenoid coils to promote jet magnetization, where a peak 0.1 T field was observed at the collisional interface, several times that of individual jets prior to collision. SPFMax modeling of these jets reproduce the peak magnetic field, and we explore methods for amplifying the field at stagnation. |
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BP11.00117: Computational Scaling Laws for Plasma Jet Driven Magneto-inertial Fusion Jason Cassibry, Aalap C Vyas, Samuel J Langendorf, Franklin D Witherspoon
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BP11.00118: PIC simulations of liner-fuel compression in PLX Chuang Ren, Han Wen, Eddie C Hanson, Samuel J Langendorf, David Michta, Petros Tzeferacos OSIRIS Particle-in-Cell modeling of liner-fuel compression in Plasma Liner Experiment [PLX, Hsu et al. IEEE Transaction on Plasma Science 40, 1287 (2012)] will be presented. These 1D simulations show that hydrogen fuel compression and heating can be achieved with an impinging Xenon liner and with significant liner-fuel interpenetration. FLASH simulations show similar liner slowdown and fuel heating even though the MHD code does not allow the interpenetration. Numerical issues in the PIC simulations will also be discussed. |
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BP11.00119: Kinetic study of shock formation in colliding plasma jets Petr Cagas, James L Juno, Ammar Hakim, Samuel J Langendorf, Bhuvana Srinivasan Understanding shock formation in colliding plasma jets is crucial for many plasma applications, e.g., inertial confinement fusion (ICF). Here, we use the fully kinetic Vlasov model in the Gkeyll simulation framework (https://gkeyll.readthedocs.io) to study the effects of collisional models (Fokker-Planck operator and some of its simplifications) and the degrees of freedom in the velocity space. These approaches have various levels of precision but also computational cost. Therefore, it is essential to choose the right tool for the task and improve its numerical implementation using novel algorithmic approaches. We will show a comparison of these models and details of their implementation to investigate shocked versus shock-mitigated regimes for the colliding jets. |
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BP11.00120: ICF: HYDRODYNAMICS Session Chairs: |
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BP11.00121: Investigation of converging ultra-fast jets in cylindrical implosions: A new platform to study complex hydrodynamic effects relevant to inertial confinement fusion Pericles S Farmakis, Joshua P Sauppe, Yingchao Lu, Brian M Haines, Riccardo Betti, Petros Tzeferacos We present the results of a computational study investigating an experimental platform that can furnish new insights on the stability of inertial confinement fusion (ICF) implosions. This novel design concept puts particular emphasis on the generation of very high Mach number jets, which are similar to flows observed in certain ICF target designs. The platform has been designed and modeled using FLASH, a highly versatile, parallel, adaptive mesh refinement, finite-volume Eulerian, radiation-magnetohydrodynamics code with extended physics capabilities. A directly driven, open-ended cylindrical ablator is manufactured with a series of carefully designed conical protrusions. These jet-generating features give a high degree of control over the characteristics on the inwardly propagating jet flows, their speed, collimation, etc., and the open geometry of the cylinder gives us a clear window to observe the flows over the entire implosion history. The behavior of this kind of converging flow, in the context of ICF, is still not well understood. This platform opens up the possibility of studying converging ultrafast jet propagation over a large parameter space, and it can be used to inform the design of ICF targets that may exhibit jetting phenomena. |
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BP11.00122: Quantifying and reducing uncertainty in ICF experiments using optimal experimental design Codie Y Fiedler Kawaguchi, Kirk A Flippo, Elizabeth C Merritt, Alexander M Rasmus, Xun Huan, Eric Johnsen High Energy Density (HED) science is the study of the behavior of material under extreme LA-UR-22-26870 |
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BP11.00123: Instability growth mitigation in double -shell planar experiments using graded density layer and bilayer inner shell Sasi Palaniyappan, David J Stark, Eric N Loomis, Evan S Dodd, Joshua P Sauppe, Elizabeth C Merritt, Willow Wan, Derek W Schmidt, Tana Morrow, Wendi Sweet, Hongwei Xu, Haibo Huang The double-shell platform is a volume ignition concept that takes advantage of low convergence volumetric burn (inner shell CR ~10) at the expense of reduced gain using a high-Z (W) metal pusher. Though low convergence implosions are expected to be more stable, the high Atwood numbers at the foam-pusher interface in double-shell designs makes them susceptible to instability growth that can feed through the pusher causing high-Z material mix into the fuel. Thus, stabilizing the fuel-pusher interface is crucial to achieve a stable double-shell implosion. Typically, a low-Z (Be) tamper layer on top of the high-Z pusher is used to reduce the abrupt jump in Atwood number and reduce instability growth. A graded density layer, where the density gradually increases from Be density (facing the foam cushion) to full W density (facing the DT fuel) is expected to suppress the instability growth more effectively than a Be/W bilayer due to the gradually smoothed Atwood number. We have tested this idea at the OMEGA laser facility using a planar experiment with a halfraum drive. The results show that both the bilayer and graded layer are effective in mitigating a pre-imposed 35um wavelength perturbation. However, the results are inconclusive between the bilayer and graded layer for the 35um wavelength perturbation. |
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BP11.00124: Modeling Plasma Kinetic Effects in ICF Targets Jan Velechovsky, Erik L Vold Inertial Confinement Fusion (ICF) targets consist of multiple materials. During target compression, these materials undergo significant acceleration causing these materials to mix. Direct Numerical Simulations (DNS) of whole targets are prohibitively expensive due to the 3-Dimensional (3D) nature of the flow and initially low fluid viscosity. Therefore, ICF targets are modelled using inviscid Euler equations coupled with sub-grid closure mix models and with other models for relevant physics such as heat transport. We compare the results of Los Alamos National Laboratory (LANL) mix models denoted BHR and LWN to DNS of the Deceleration Rayleigh-Taylor Instability (DRTI) between a Carbon ablator and Deuterium fuel inside an ICF target. DRTI occurs around the time of targets maximal compression resulting in mixing of hot plasmas when kinetic effects on mixing are significant. These kinetic effects are directly accounted for in LANL hydrodynamic code xRAGE and therefore xRAGE is used to run DNS of DRTI. We demonstrate that the significance of plasma kinetic effects is underestimated in 2D simulations compared to 3D simulations. Next, we show how to account for plasma kinetic effects in LANL mix models. The LWN mix model is particularly suitable for such accounting. |
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BP11.00125: ICF: INDIRECT DRIVE Session Chairs: |
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BP11.00126: The effect of rate of rise to peak power on x-radiation drive in hohlraums at the National Ignition Facility Nicholas Aybar, Stephan A MacLaren, Marilyn B Schneider, Edward V Marley, Hui Chen, Denise E Hinkel, Christine M Krauland, Duane A Liedahl, Tod Woods, Maylis m Dozieres, Jeremy Huckins, Nobuhiko Izumi, Otto L Landen, Weston Montgomery, John D Moody, Katya Newman, Steven Ross, Nathaniel B Thompson, Scott Vonhoff Modern hohlraum simulations of inertial confinement fusion (ICF) experiments must incorporate empirical multipliers on the laser input power to match experimental data. The laser pulse has a low-power picket, and a long, low-power trough before rising to peak power, and each portion of the laser pulse incorporates separate multipliers. To understand the physical mechanisms involved in the discrepancies, a two-shot campaign investigated the effect of the rate of rise to peak power on the resulting x-radiation drive. The experiments used a ViewFactor hohlraum (truncated hohlraum, cut open at ~75% of its length) to measure the x-radiation drive as observed by the target on standard hohlraums by viewing the ViewFactor hohlraum interior through the “open” end, without a laser entrance hole. A secondary goal is to measure the charge state of gold in the bubble region using gold L band spectroscopy as a first step in the development of a diagnostic for electron temperature distributions in the multi-KeV regime. The experimental configuration will be described, and results will be discussed and compared to simulations. |
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BP11.00127: Understanding the enhanced hohlraum drive that follows high yield Mordecai D Rosen, Michael S Rubery The 1.35 MJ yield shot N210808 at the National Ignition Facility began a new era in enhanced hohlraum heating. The capsule imploded after the drive laser was off, and thus during a period of time in which the signal from the Dante instrument (that measures hohlraum drive via x-ray output through the laser entrance hole) was dropping in time. After the capsule produced its high yield, the Dante signal rose, implying a non-laser source of hohlraum heating. This observation is the first of its kind. We discuss here the many possible "suspects" that may have caused this enhanced hohlraum heating. We identify the most likely cause. This understanding may allow future shots to be optimized to increase this heating enhancement. We also point out that in future, even higher yield shots, another phenomenon may also contribute to enhanced hohlraum heating. |
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BP11.00128: High speed plasma species interpenetration and implications in hohlraums Erik L Vold, Jan Velechovsky, Brian M Haines The effect of high speed interpenetrating plasma species on the transport and collisionality in Inertial Confinement Fusion (ICF) hohlraum physics is examined. The AMR multi-species radiation hydrodynamic code, xRage, includes low speed fluid models for plasma transport including species mass diffusion, viscous effects in momentum and species thermal equilibration. Corrections for high speed plasma species flows are recently added to the code, based on work by Burgers (1969), Schunk (1977) and in a recent review (Hunana, Gomez, Tenerani,,et.al. (2022). The high speed species flows reduce the collisionality and species coupling thus increasing species interpenetration (runaway effect) and reducing species thermal equilibration rates. The high speed correction increases with the ratio of the species drift speeds relative to thermal speed and for a ratio of order unity, this reduces momentum coupling by about 40% and thermal coupling by about 60%. The change in collisionality is examined in test problems including studies in ICF indirect-drive hohlraum physics where interpenetrating plasma moves inward from the hohlraum inner surface and outward from the capsule surface during laser irradiation. |
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BP11.00129: Investigation of plasma flow and interface dynamics in Au-foam lined hohlraums at OMEGA Skylar G Dannhoff, Patrick J Adrian, Timothy M Johnson, Jacob A Pearcy, Graeme D Sutcliffe, Chikang Li In indirect drive inertial confinement fusion (ICF) experiments, laser interactions with the hohlraum wall generate dense, high-Z blowoff. The blowoff can contribute to asymmetric capsule drive by shifting laser absorption areas, preventing beams from reaching the inner hohlraum wall, and stagnating too quickly on the hohlraum axis. The most effective attempts to tamp this high-Z blowoff include the use of a gas fill and exploration of non-cylindrical hohlraum geometries, but even these configurations have drawbacks. Within the last few years, another promising alternative has been demonstrated through simulations and experiment at Lawrence Livermore National Laboratory: using inner-wall, high-Z foam linings to tamp the wall blowoff. We are further studying Au-foam-lined hohlraum dynamics through experiments at OMEGA. Proton and x-ray radiography will be used to reconstruct the self-generated electric and magnetic fields in hohlraums lined with ~200 um thick, ~30-40 mg/cc Au-doped CH foam. These measurements will reveal the associated plasma flow and interface dynamics during the hohlraum drive and contribute to the physics understanding and optimization of high-Z foam linings in hohlraums. |
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BP11.00130: Mitigating LPI and gold bubble expansion using ultra low density foams Mikhail Belyaev We consider designs for indirect drive that partially fill the hohlraum with an ultra-low density foam (1.0 mg/cc SiO2 aerogel). We compare the foam-filled designs with standard gas-filled hohlraums, paying particular attention to LPI and gold bubble expansion. We find that the best designs for mitigating both LPI and gold bubble expansion use a combination of high-Z foam and low-Z gas. The placement of the foam at the location where the outer beams strike the wall tamps the expansion of the gold bubble into the hohlraum. This widens the channel between the capsule and the wall, allowing propagation of the inners to the hohlraum waist for more time. The foam design has significantly lower inner beam SRS than the gas-only design, which is achieved via the presence of high-Z material in the foam. The high-Z atoms lead to a greater inverse-brem absorption rate, increasing the electron temperature and Landau damping in the region of high SRS gain. This results in reduced SRS gains and reflectivities, as simulated using FLIP and pF3D. SBS is kept in check via low-Z atoms in the foam, which facilitate efficient Landau damping of ion acoustic waves. |
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BP11.00131: Generating uniform high-Z plasmas on the OMEGA and NIF laser facilities for radiative properties studies Gregory E Kemp, Edward V Marley, Mark E Foord, Robert F Heeter, Denise E Hinkel, Mark J May, Mehul V Patel, Howard A Scott, Marilyn B Schneider Previous efforts to obtain benchmarking data for atomic-kinetics modeling of non-local thermodynamic equilibrium (non-LTE) plasmas by direct laser heating of tamped high-Z foils have successfully demonstrated uniform, sub-critical density, multi-keV electron temperature Au plasmas. Such conditions are relevant for understanding the influences of coronal plasmas in inertial confinement fusion hohlraums – i.e., the “Au bubble” which influences hohlraum drive symmetry and generates undesirable capsule preheat via M-band line-radiation – but reaching higher densities of relevance to the LTE wall conditions (where most of the heated hohlraum mass is located) is nontrivial as the high-Z sample does not heat uniformly until it becomes sub-critical throughout. We discuss the potential risks and benefits of using x-rays as an alternative heating source to isochorically heat tamped Au foils to hohlraum-wall-relevant plasma conditions using multi-keV line-radiation from laser driven, sub-critical density, Ag nanowire foam x-ray sources. We present radiation-hydrodynamic simulations studying the high-Z plasma evolution and sensitivity to target/x-ray drive design, along with preliminary designs for experiments on both the OMEGA and NIF laser facilities.
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BP11.00132: Neutron emission from light-gas gun projectile driven targets Zoran D Pesic, Guy C Burdiak, Jonathan Skidmore, Rosie Barker, Emilio Escauriza, Joshua Read, Nicolas-Pierre L Niasse, Timothy Ringrose, Hugo W Doyle, Nicholas Hawker Projectile fusion concept represents a promising avenue for achieving ignition and a significant fusion yield. As a part of the fusion targets development program, First Light Fusion (FLF) uses two-stage light gas to accelerate projectiles up to 6.5 km/s. The initial drive pressure which is in order of 100 GPa is amplified to compress a capsule with DD or DT gas mixture to densities and temperatures relevant to achieve fusion. The target design is a key aspect in FLF approach and is optimized using codes developed at FLF [https://firstlightfusion.com/assets/uploads/images/First-Light-Fusion-Nevarro-modelling-white-paper.pdf] |
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BP11.00133: New capabilities for faster, higher fidelity simulations in HYDRA* Michael M Marinak, Chris R Schroeder, Milan Holec, Britton Chang, Mehul V Patel, Howard A Scott We discuss several new capabilities in HYDRA which enable higher fidelity simulations which also complete faster. A multi-resolution advection method avoids small time step limits near mesh singularities. We show examples where it enables high resolution capsule simulations to complete in just a fraction of the previous run time. A linear response matrix (LRM) method for non-local thermodynamic equilibrium (NLTE) now enables tabular NLTE opacities and equations of state. For hohlraum simulations in which steady state NLTE is a good approximation, LRM tables largely eliminate the time spent calculating NLTE kinetics inline. This enables hohlraum simulations to complete significantly faster and allows NLTE models of any level of complexity to be used. Several improvements to HYDRA’s polar SN multigroup radiation transport method enable higher accuracy on complex meshes. A novel unlocked-step method is combined with the existing differencing operator to minimize oscillations and improve accuracy in high optical depth zones. A Positivity Preserving Method ensures non-negative solutions in all circumstances and enables faster convergence to solution. |
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BP11.00134: Experimental measurements of yield amplification in burning and near-ignited plasmas David J Schlossberg, Alison R Christopherson, Steve A MacLaren, Alex B Zylstra, Annie L Kritcher, Omar A Hurricane, Bogdan Kustowski, Otto L Landen, Arthur Pak, Joseph E Ralph, James S Ross, Benjamin Bachmann, Kevin L Baker, Richard M Bionta, Noah W Birge, Daniel T Casey, Laurent Divol, David N Fittinghoff, Maria Gatu Johnson, Edward P Hartouni, Matthias Hohenberger, Shahab Khan, Alastair S Moore, Katya Newman, Michael S Rubery, Chris Weber, Christopher V Young Previous design changes of inertial confinement fusion implosions have led to MJ-range production of fusion yield on the National Ignition Facility. These fusion plasmas have significant self-heating due to alpha-particle energy deposition, and exhibit non-trivial burn propagation into the dense DT-ice fuel layer. This self-heating drives additional yield production, termed "yield amplification", and ultimately leads to a runaway phenomenon. This process has been observed in several recent HYBRID-E target designs, notably the shot N210808 and its precursor N210307. In order to quantify the performance gain due to this yield amplification, we conducted a pair of experiments replicating those two burning-plasma shots but using a fuel layer dudded with hydrogen which effectively "turns off" the yield amplification. Results from this set of burn-on and burn-off implosions will be presented and discussed, and briefly compared with post-shot simulations and modeling. Values for the yield amplification of N210808 and N210307 will be presented, and we'll discuss trends in the no-alpha DSR with yield-amplification. |
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BP11.00135: Potential Impact of Inner Shell Plug Characteristics on Double Shell Capsule Implosions John Kuczek, Brian M Haines, Joshua P Sauppe Double shell capsules were first conceptualized almost four decades ago [4] as an alternative approach to inertial confinement fusion experiments. The double shell target consists of a low-Z outer ablator surrounding a high-Z inner shell [5,4,2]. Two potential mechanisms can be used to fill the inner shell with fuel: a fill tube, or a drill hole and plug. Simulations with fill tubes have shown unwanted contamination early on in the implosion process [1]. Two plug concepts have been considered: a pyrofuze plug made of an aluminum and palladium alloy, and autogenous welding of a plug composed of the same high-Z material as the inner shell. |
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BP11.00136: Studies of multi-ion and kinetic effects in shock-driven and ablatively-driven implosions at OMEGA Tucker E Evans, Patrick J Adrian, Neel Kabadi, Graeme D Sutcliffe, Jacob A Pearcy, Benjamin L Reichelt, Cody W Chang, Skylar G Dannhoff, Arijit Bose, Brandon J Lahmann, Cody E Parker, Maria Gatu Johnson, Chikang Li, Richard D Petrasso, Johan A Frenje, Enac Gallardo-Diaz, Roberto C Mancini, Christian Stoeckl, Riccardo Betti, Andrew Sorce, Joe Katz, James P Knauer, David Weiner, Mark Bedzyk, Hong W Sio Two experiments at OMEGA are discussed, focusing on the impact of multi-ion and kinetic effects on the shock-convergence and compression phases of an Inertial Confinement Fusion (ICF) implosion. Such effects are known to significantly impact the final yield of an ICF implosion. The first experiment involved shock-driven implosions with varying Knudsen numbers from fully kinetic to hydro-like behavior. The second experiment involved compressively-driven implosions with varying combinations of shell thickness and laser drive used to produce different shock strengths and to probe conditions when the implosion transitions from the shock to compression phase. In both cases, data from the Particle X-ray Temporal Diagnostic (PXTD) and the Neutron Temporal Diagnostic (NTD) provided information about particle emission histories for DD-neutron, DT-neutron and D3He-proton reactions, referenced against spectral information from CR-39-based diagnostics and time-of-flight diagnostics. Comparison of the time-resolved data from these experiments with theory and simulation informed an analysis of the role of kinetic and multi-ion effects in ICF implosions. |
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BP11.00137: Interpenetration and Kinetic Mix in Weakly Collisional, Fully-ionized Plasma Jets William Riedel, Nathan Meezan, Drew P Higginson, Matthias Hohenberger, Mark A Cappelli, Siegfried H Glenzer Laser-driven "inverted corona" fusion targets have attracted interest as a low-convergence neutron source and as a platform for studying kinetic physics. These targets consist of a fuel layer lined along the interior surface of a hollow or gas-filled plastic hohlraum. The plasma streams generated in vacuum targets are initially nearly collisionless as they converge, leading to wide interaction length scales and long interaction time scales as the jets interpenetrate. With the inclusion of a low-density gas fill, ejected particles from the shell can pass far into the gas before colliding, leading to significant mixing across the gas-shell interface. Such interactions are difficult to accurately model using standard hydrodynamic simulations, which assume high collisionality. Instead we model the system using a kinetic-ion, fluid-electron hybrid particle-in-cell (PIC) approach. Simulations demonstrate significant kinetic effects (interpenetration, beam-beam fusion, and weakly collisional electrostatic shocks) that are mediated by collisional processes and can be tuned by changing the initial fill pressure of the gas. Using two-dimensional simulations we also investigate compression symmetry, hotspot velocity, and directional differences in neutron spectra, as well as make comparison with x-ray emission images. |
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BP11.00138: Double cylinder experiments on OMEGA for study of Rayleigh-Taylor instability growth on a classically unstable interface Rebecca Roycroft, Joshua P Sauppe, Paul A Bradley, Sasi Palaniyappan, Alexandria Strickland, Saba Goodarzi The double cylinder experimental platform is designed as an analogue to the double shell inertial confinement fusion capsule in order to study hydrodynamic instability growth on the inner shell, the outer surface of which is classically Rayleigh-Taylor unstable during the acceleration phase. We present results from recent experiments at the OMEGA laser facility. These experiments were designed as a proof-of-principle for the platform, using the same cylinder exterior dimensions and direct-drive beam configuration as previous single cylinder experiments. In these experiments, three sets of targets were fielded: no machined perturbations (smooth), a sinusoidal mode-10 perturbation on the inner cylinder, and a mode-20 perturbation on the inner cylinder. The primary diagnostic was a gated x-ray framing camera which imaged the backlit inner cylinder on-axis for 16 frames over a time window of 1 ns for each shot. A second side-lit radiograph captured 1 image per shot, diagnosing axial uniformity. We investigate the energy transfer efficiency between outer and inner cylinders, and we compare the perturbation growth between mode-10 and mode-20. We compare marker trajectories and measured Rayleigh-Taylor spike growth with radiation-hydrodynamics simulations and linear theory. |
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BP11.00139: Continuum kinetic modeling of cathode plasma sheath in Z-pinch Noah Reddell, Uri Shumlak, Iman Datta, Peter Stoltz, Eric T Meier Continuum kinetic model simulations of plasma dynamics are challenged by the high dimensionality and computational expense of the Vlasov equation in up to six dimensions of space and velocity. Nevertheless, such modeling is crucial for capturing plasma physics associated with strong deviations from local thermodynamic equilibrium and other departures from fluid model approximations. This work presents a model and two-species (ion/electron) results from simulations of cathode to plasma interaction across a plasma sheath with implications important to Z-pinch formation and compression. The research includes work to accelerate and map an existing high order discontinuous Galerkin implementation to the latest GPU-accelerated supercomputers. An overview of the computational approach on massively-parallel GPU systems is presented. |
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BP11.00140: Low Z Impurity Seeding in KSTAR H-mode Plasmas Junghoo Hwang, Jae-Sun Park, Matthias Bernert, Richard Pitts, Yoon Seong Han, Haewon Shin, Junhyeok Yoon, Hyungho Lee, Suk-Ho Hong, Wonho Choe Low Z impurity seeding experiments using nitrogen and neon were recently carried out in KSTAR. The discharges were in H-mode with a total heating power of 3.5 MW. Maximum achieved total radiation fractions (frad,tot = Prad,tot/Pheat) were about 80% for N and 50% for Ne by the impurity seeding rate ramp-up. N showed a larger radiated power fraction in the divertor region (= Prad,div/Prad,tot) compared to Ne with the same frad,tot, and also showed a larger reduction in the particle and heat fluxes onto the outer target than Ne. The inner target particle flux remained nearly constant and this in/out detachment asymmetry opposite to most other devices was also reported in KSTAR L-mode discharges. An experiment at higher heating power (6.5 MW) was performed in the 2022 campaign and the outer target particle flux reduction was obtained by Ne seeding. Numerical simulations using the SOLPS-ITER code of the moderate power discharges were performed. The simulations qualitatively reproduced the experimentally observed radiation behaviors of N and Ne, although both species dissipated the particle flux onto the outer target efficiently (by a factor of 2). Analysis of impurity transport in the divertor will be presented to provide an explanation of the different behaviors between N and Ne. |
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