Bulletin of the American Physical Society
62nd Annual Meeting of the APS Division of Plasma Physics
Volume 65, Number 11
Monday–Friday, November 9–13, 2020; Remote; Time Zone: Central Standard Time, USA
Session PP12: Poster Session: Magnetic Confinement: Other (2:00pm - 5:00pm)On Demand
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PP12.00001: Moment approach to the ion parallel flow for toroidal plasmas Jeong-Young Ji, Eric Held The ion parallel flow in a magnetized plasma can be obtained by solving the ion drift kinetic equation. Although ion-electron collisions modify the ion transport equation, studying the ion equation alone provides insights into the mathematical structure for the responses (transport) and sources (thermodynamic drives). In this work the ion drift kinetic equation is solved by the general moment method. For axisymmetric magnetic geometry, the magnetic field and parallel moments are expanded in Fourier series and a system of algebraic equations for the Fourier coefficients of moments is constructed. The algebraic system is solved to express the density, temperature, and flow velocity in terms of the radial derivatives of pressure and temperature. The behavior of the ion parallel flow is compared to the standard theory and carefully investigated when the inverse aspect ratio approaches zero. The ion distribution function is also constructed from the moment solution. [Preview Abstract] |
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PP12.00002: A Fully Implicit Particle-in-Cell Method for the Symplectic Formulation of Electromagnetic Gyrokinetics. Luis Chacon, Seung-Hoe Ku, Amil Sharma, Choog-Seock Chang, Benjamin Sturdevant, Mark Adams A fully implicit particle-in-cell (PIC) method based on the work of G. Chen and L. Chac\'{o}n [1] has been developed to study gyrokinetic electromagnetic modes in tokamak plasmas. A fully implicit time discretization scheme overcomes stability issues due to the inductive component of the electric field in the sympletic formulation of gyrokinetics [2] while avoiding a well-known ``cancellation problem'' associated with the Hamiltonian formulation of gyrokinetics [3]. We present our efforts to construct an effective preconditioner for this system, starting from an electron fluid model and accounting for additional effects due to the numerics of the PIC method. Application of the preconditioner requires the solution of a linear system of equations resulting from the discretization of a coupled PDE system. We present a multigrid strategy for solving the linear system based on semi-coarsening and block smoothing. Finally, we will present numerical results to validate our scheme, including the simulation of the ITG-KBM transition [4] and long wavelength Alfven waves, which has been problematic with previous approaches. [1] G. Chen, L. Chacon, Comput. Phy. Comm. 197, 73-87, 2015. [2] J.V.W. Reynders, Ph.D. thesis, Princeton University, 1992. [3] J.C. Cummings, Ph.D. thesis, Princeton University, 1995. [4] T. Gorler, N. Tronko, et al., Phys. Plasmas, 23, 072503, 2016. [Preview Abstract] |
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PP12.00003: Exact energy-momentum conservation laws for the symplectic gyrokinetic Vlasov-Maxwell equations Alain Brizard A new representation of electromagnetic gyrokinetic Vlasov-Maxwell theory is presented in which the gyrocenter equations of motion are expressed solely in terms of the perturbed electric and magnetic fields. In this representation, the gyrocenter symplectic (Poisson-bracket) structure and the gyrocenter Jacobian contain electric and magnetic perturbation terms associated with the standard first-order gyrocenter polarization and magnetization terms that traditionally appear in the gyrokinetic Maxwell equations. In addition, the gyrocenter polarization drift now appears explicitly in the gyrocenter velocity. The self-consistent symplectic gyrokinetic Vlasov-Maxwell equations are derived from a variational principle, which yields exact energy-momentum conservation laws (through the Noether method) that are verified explicitly. An exact toroidal canonical angular momentum conservation law is also derived explicitly under the assumption of an axisymmetric background magnetic field. [Preview Abstract] |
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PP12.00004: Moving fusion energy into the big and fast data lane Ralph Kube, Michael Churchill, Jong Youl Choi, Ruonan Wand, CS Chang, Scott Klasky A wide array of diagnostics are routinely used to measure pulsed plasma discharges in tokamaks.Diagnostics with the highest spatial and temporal resolutions readily produce data streams upward of 1 GByte/s. Reducing such large volume, high-velocity high-dimensional data time-series into analysis results available to scientists in near real-time allows to accelerate scientific discovery. Here we present Delta, a novel framework that leverages computational resources of remote high-performance compute facilities to analyze data streams from plasma diagnostics in near real-time. As a demonstration, we use Delta to calculate a suite of spectral analysis routines using data from the KSTAR ECE diagnostic on Cori, a Cray XC-40 supercomputer operated at NERSC. The ECE diagnostic samples Te fluctuations on a 24 by 8 pixel grid at two toroidal locations with a rate of about 1 MHz. Our experiments show that we can consistently stream the entire 5GB large dataset with up to 500 MB/sec from KSTAR to Cori and perform the entire analysis suite in about 5 minutes. A web-based live dashboard visualizes the analysis in near real-time. Finally, we discussing ongoing efforts to incorporate variational auto encoders in Delta to compress the data stream and perform outlier detection. [Preview Abstract] |
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PP12.00005: Numerical Study of Two-Fluid Transonic Equilibria Luca Guazzotto, Riccardo Betti In axisymmetric plasmas ``transonic'' equilibria are equilibria, in which the poloidal macroscopic velocity of the plasma is larger than a characteristic velocity ($\sim C_{sp}=C_s B_p/B$) in the edge region of the plasma and smaller than $C_{sp}$ in the central region. Theoretical ideal MHD analysis proved that the two regions are separated by a contact discontinuity on a critical magnetic surface. Except for one point in the poloidal cross section, plasma density, pressure and velocity have finite jumps between the two sides of the discontinuity. Since there is no macroscopic flow perpendicular to the discontinuity due to the frozen-in law, the discontinuity can exist at steady state without energy dissipation or increase of entropy. Numerical solutions of the equilibrium equations confirmed the theoretical results. It is unknown whether the transonic discontinuity still exists in a two-fluid model of the plasma or is replaced by a narrow boundary layer, since in this model magnetic field and plasma velocity do not reside on the same family of surfaces. We explore for the first time the properties of transonic equilibria in a two-fluid model with numerical tools adapted to include dedicated routines based on the ones designed for the solution of the MHD transonic problem. [Preview Abstract] |
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PP12.00006: Stability analysis of implicit and fractional-step algorithms for plasma-neutral coupling Sina Taheri, Uri Shumlak, Jacob R King Interactions between plasma and neutral species can largely alter the dynamic behavior of magnetically confined devices and having a tractable plasma-neutral model helps to study these effects. A previous work [Taheri, APS-DPP 2016] incorporated a reacting plasma-neutral model presented by E.T. Meier and U. Shumlak [Meier, PoP 2012] in NIMROD code [Sovinec, JCP 2004] to include electron-impact ionization, reactive recombination and resonant charge exchange. However, the atomic physics terms in this model are highly nonlinear and may cause numerical instabilities in simulations. Two separate algorithms for atomic physics terms, namely implicit Crank-Nicolson and fractional-step with Strang splitting, are used in this research to ensure stability in handling these nonlinear terms. The Strang splitting utilizes a stiff ODE solver to advance the nonlinear source terms. Linearized plasma-neutral system is analyzed with von Neumann's method to show the stability of each algorithm. In addition, the accuracy and stability of the algorithms are compared on a battery of nonlinear test cases. [Preview Abstract] |
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PP12.00007: Novel Hybrid Reactor Concepts Based on Ignitor Technology and Physics M. Ciotti, B. Coppi, R. Gatto, F. Panza, A. Cardinali The line of compact high field experiments developed with the Alcator and the Frascati Torus Programs has produced well confined plasmas with record high densities that make them particularly suitable as neutron sources. The technology and physics developed, along this line, for the Ignitor Program have been suggested by E. P. Velikhov (2019) as the basis for a D-T (Deuterium-Tritium) hybrid reactor with Th (Thorium) as its fissile component. Given the very high densities that can be sustained a suggestion (Anonymous, 2019) was made that a D-D (Deuterium-Deuterium) neutron source could also be adopted as reaching ignition conditions is not needed and pulsed operation is acceptable in both cases. A comprehensive analysis is underway to identify an optimal set of parameters and components for a D-T based system and to extend the relevant results to a possible D-D system. Recent advances made in areas related to fission reactors (e.g. molten salts blankets) have an important role in this analysis. [Preview Abstract] |
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PP12.00008: Fast Poincar\'e maps for magnetic fields using symplectic neural networks Qi Tang, Joshua Burby Field-line Poincar\'e maps are powerful tools for analyzing the global behavior of magnetic fields in magnetic fusion devices. In some special cases, the Poincar\'e map may be derived by hand, but in most practical applications the map is approximated by numerically integrating the streamlines for the magnetic field. We present a new method for computing approximate Poincar\'e maps based on a novel neural network architecture called the H\'enon Network. A H\'enon Network is trained in a supervised fashion by showing it results from fourth-order Runge-Kutta field-line following simulations. After training, the network's input-to-output mapping gives an exactly-flux-conserving (i.e. symplectic) approximation of the Poincar\'e map. Moreover, evaluating such a neural approximation of the Poincar\'e map is orders of magnitude faster than evaluating an approximation based on field-line following. [Preview Abstract] |
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PP12.00009: A kinetics-only delta-f (KODF) method for modeling warm plasma waves Thomas Jenkins, David Smithe A new delta-f particle-in-cell method, kinetics-only delta-f (KODF), is presented. In conventional delta-f methods, perturbations around a known analytic equilibrium are modeled; statistical noise is reduced since the particles model only perturbations and not the equilibrium itself. In KODF, we generalize this concept to incorporate cold linear plasma waves into the known (quasi)analytic plasma behavior. The perturbations modeled by KODF PIC methods are thus nonlinear, finite-temperature perturbations atop cold linear waves whose evolution can be modeled without the noise associated with a PIC model. We demonstrate the implementation of KODF in the VSim particle-in-cell code. VSim’s semi-implicit FDTD methods [D. N. Smithe, PoP 14, 056104 (2007)] are used to model the fluid behavior of cold plasma waves, and source terms that arise from these waves (e.g., from gradients of cold current or charge densities, or from quasilinear terms) appear in the KODF weight evolution equation to drive and evolve responsive warm plasma effects. We explore the noise-reduction capabilities of the KODF algorithm and its ability to model waves of interest in RF heating scenarios (e.g. mode-converted IBWs). [Preview Abstract] |
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PP12.00010: Benchmarking Chapman-Enskog-Like (CEL) Kinetic Results in NIMROD Joseph Jepson, Chris Hegna, Eric Held, Brendon Lyons In the simplified regime of axisymmetric geometry and fixed magnetic field, steady-state results for the neoclassical, poloidal flow constant are compared between NIMROD and DK4D [1]. These quantities are obtained by evolving the Chapman-Enskog-like drift kinetic equation (CEL-DKE) [2] in NIMROD to steady state, and then taking appropriate moments of the non-Maxwellian part of the distribution. The full CEL approach differs from a traditional delta-f approach in that the lowest-order Maxwellian evolves according to n, T, and \mathbf{V}, which may be advanced using NIMROD's fluid model. The CEL-DKE results are also compared to analytics, as well as to previous results obtained using NIMROD's delta-f DKE implementation [3]. Future work will include using the CEL implementation in NIMROD to better understand the role of island formation in ELM supression by RMPs. [1] B. C. Lyons, S. C. Jardin, and J. J. Ramos, Phys. Plasmas \textbf{22}, 056103 (2015). [2] J. J. Ramos, Phys. Plasmas \textbf{18}, 102506 (2011), [3] E. D. Held, et al., Phys. Plasmas \textbf{22}. 032511 (2015). [Preview Abstract] |
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PP12.00011: Interpreting Doppler backscattering with beam tracing and reciprocity in tokamak geometry Valerian Hall-Chen, Felix Parra, Jon Hillesheim We use beam tracing (Torbeam\footnote{E. Poli et al., \textbf{Comput. Phys. Commun} 136(1-2), 90-104, (2001)} as well as a newly written code) and the reciprocity theorem\footnote{E.Z. Gusakov et al., \textbf{PPCF}, 46(7), 1143, (2004)} to derive a model for the backscattered power of the Doppler Backscattering (DBS) diagnostic. Our model works for both the O-mode and X-mode in tokamak geometry. We present the analytical derivation of our model, providing an understanding of how the DBS signal is localised and the quantitative effect of the mismatch angle. Consequently, one can now correct for the attenuation due to mismatch, avoiding the need for empirical optimisation. We then use our model to determine the wavenumber resolution and find different results from the widely-accepted formula\footnote{M. Hirsch et al., \textbf{PPCF}, 43(12), 1641, (2001)}. [Preview Abstract] |
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PP12.00012: Magnetized Edge Plasma Fluid Simulation Using High-Order Finite Elements Ilon Joseph, Milan Holec, Chris Vogl, Ketan Mittal, Andris Dimits, Alex Friedman, Tzanio Kolev, Mark Stowell, Xueqiao Xu, Ben Zhu, Tom Manteuffel, Ben Southworth A novel finite element approach is developed and applied to magnetized edge plasma simulation. The multiscale nature of the problem makes edge plasma physics simulations challenging due to the fast timescales associated with electric conductivity, thermal conduction, Alfven waves, and sound waves. Strong anisotropy in a magnetized plasma generates multiple spatial scales due to the formation of sharp boundary layers and filamentary structures that are aligned with the magnetic field lines. We are exploring the use of the MFEM framework, a highly scalable software library used for large-scale simulations to address these challenging physical, geometric, and numerical issues. Strategies for refining and adapting meshes near X-points caused by divertors and magnetic islands, as well as external walls, are being developed through adaptive mesh refinement, mesh optimization, high-order discretization, and high-order curved meshes. We have begun development of both linear and nonlinear solvers for the plasma fluid equations, including preconditioning strategies and block preconditioning strategies that address the combination of the shear Alfven wave, advection by the ExB flow, and anisotropic diffusion. [Preview Abstract] |
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PP12.00013: Fast convergence methods for calculating the magnetic field from coils Caoxiang Zhu, Nick McGreivy, Stuart Hudson Calculating the magnetic field from coils using the Biot-Savart law is required for numerous plasma physics applications. One of the most-used strategies is to approximate the (filamentary) coils with N straight segments and then use the Hanson-Hirshman expression (Hanson & Hirshman, Phys. Plasmas, 9(10):4410, 2002) to compute the field produced by each segment. The Hanson-Hirshman expression efficiently calculates the exact field from a straight filamentary segment and is only singular on the segment itself. However, the piecewise-linear approximation to a generally smooth coil filament results in a discontinuous tangent vector, and thus only quadratic convergence is obtained with respect to N. In this presentation, we introduce fast, higher-order approximations for calculating the magnetic field from coils that exploit a continuous tangent. The convergence of the magnetic field calculation from circular coils, D-shaped TF coils and stellarator non-planar coils can be significantly improved with negligible extra computation cost. [Preview Abstract] |
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PP12.00014: A One-Dimensional Multi-Region Multi-Timescale Burning Plasma Dynamics Model for Tokamaks Zefang Liu, Weston Stacey Fusion burning plasma with $\alpha $-heating brings forth demands for research moving from the equilibrium to dynamics. When radiation and transport are included, the plasma core cannot be modeled independently. Electron cyclotron radiation from the fusion $\alpha $-heating in the core can have a rapid response to temperature increases and heat the edge, while Coulomb collisions will distribute energy between ions and electrons on relatively long timescales. Such fast and slow phenomena will couple the plasma core with the edge. A one-dimensional multi-region multi-timescale transport model will be developed to simulate burning plasma dynamics in tokamaks. Regions such as the core, edge, scrape-off layer (SOL), and divertor will be modeled, where the electron cyclotron radiation, impurity radiation, and bremsstrahlung will be considered. The confinement time and transport parameters will be computed theoretically and tuned by the experimental data from DIII-D. More edge effects, including ion orbit loss, MARFEs, and ELMs, and the delayed effects of burn control mechanisms will be introduced to the model later. This model will be used for developing the optimal burning control algorithms for tokamaks in the future. [Preview Abstract] |
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PP12.00015: 2D Lagrangian Code for Resistive Evolution of Plasma Equilibrium and Its Application to MTF Studies at General Fusion Ivan Khalzov, Ryan Zindler, Michel Laberge 2D Lagrangian code is developed in General Fusion (GF) for simulations of resistive plasma dynamics in magnetized target fusion (MTF) systems. The goal of these simulations is to model GF plasma experiments and to guide the design of MTF reactor, in which liquid metal liner compresses compact toroid plasma. We adopt the method of Grad and Hogan [PRL 24 (1970) 1337], who showed that at the resistive timescale the tokamak-like plasma goes through a sequence of equilibria, which are linked together through the resisitive diffusion of the poloidal and toroidal magnetic fluxes and the transport phenomena in the plasma. At every time step the code alternates between solving the 2D Grad-Shafranov equilibrium equation and the 1D flux-averaged transport equations. The main advantage of this code is its speed: the time step is limited by a large resistive diffusion timescale and not by a small Alfven timescale as in usual MHD codes. The code is Lagrangian in the sense that the numerical mesh follows the flux surfaces. Lagrangian nature of the code allows for its coupling with moving boundaries of plasma domain, which is especially useful in modeling MTF reactor. Comparison of simulations with ongoing GF experiments and results of MTF reactor design optimization will be presented. [Preview Abstract] |
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PP12.00016: Application of Equation-Free Projective Integration to Gyrokinetic Turbulence Simulations in XGC Benjamin Sturdevant, Robert Hager, Lee Ricketson, Paul Tranquilli, Choong-Seock Chang, Jeffery Hittinger, Scott Parker An improved multi-scale time integration method based on equation-free projective integration [1] has been recently developed for accelerating kinetic simulations [2]. Previously, the method was applied to the 4D gyrokinetic particle-in-cell code XGCa and was shown to accurately reproduce neoclassical ion heat transport due to microscopic guiding-center orbital dynamics under Coulomb collisions, while achieving a computational speed up of over 4x compared to brute force time stepping. In this work, we present our efforts to extend the method to the 5D gyrokinetic turbulence code XGC-1 to study the combined effects of turbulence, neoclassical physics, and heat sources on the transport timescale. In addition, algorithmic aspects of the method will be explored using simpler kinetic test problems in 1D-1V. We will present comparisons with other algorithms for addressing long-timescale integration including parallel-in-time. [1] I.G. Kevrekidis, C.W. Gear, J. Hyman, P. Kevrekidis, O. Runborg, and C. Theodoropoulos, Comm. Math. Sci. 1 (4) (2003) 715-762. [2] B. Sturdevant, S. E. Parker, C. S. Chang, and R. Hager, Physics of Plasmas 27, 032505, 2020. [Preview Abstract] |
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PP12.00017: Control-Oriented Core-SOL-Divertor Model to Address Integrated Burn and Divertor Control Challenges in ITER Vincent Graber, Eugenio Schuster Burn control in ITER will require careful regulation of the core-plasma's density and temperature while guaranteeing safe operation of the divertor. Satisfying performance objectives in the plasma core is challenging due to the core's sensitivity to both the conditions and the requirements in the scrape-off-layer (SOL) and divertor regions. First, SOL-divertor conditions determine the strength to which deuterium-tritium recycling fuels the core. This could be particularly important in ITER where there might be limits on the level of tritium that can be supplied externally. Second, the SOL-divertor conditions prescribe the intensity to which intrinsic impurities (W and He) and puffed impurities (needed to achieve detachment) pollute the plasma core. Third, the ability to maintain some level of detachment depends strongly on the separatrix density and the power flowing into the SOL from the core. Clearly, core-control objectives will need to be balanced with divertor-control objectives. In this work, the phenomena outlined above are described by using a control-oriented core-SOL-divertor model. The model consists of three components: (1) the energy and density transport equations of the core-plasma, (2) neutral particle balances in the divertor region, and (3) a two-point model that relates the plasma conditions at some upstream separatrix position to that at the divertor target. Using this core-SOL-divertor model, the coupled burn and divertor control challenges faced by ITER can be investigated. [Preview Abstract] |
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PP12.00018: The ITER-Core Turbulent Plasma Diagnostics Based on the Synergy of Stimulated Raman and Brillouin Scattering V. Alexander Stefan A novel plasma diagnostic method\footnote{ R. Prater et. al., APS-DPP-2009, (BAPS.2009.DPP.NO4.11); V. A. Stefan, APS-DPP-2019, GP10.00091}$^{\mathrm{,}}$\footnote{ Evgeny Pavlovich Velikhov, private (tel.) communication, May, 2019; V. Alexander STEFAN, \textit{Nonlinear Electromagnetic Radiation Plasma Interactions}, (S-U-Press, 2008). \par } is proposed based on the synergy of stimulated Raman and Brillouin scattering. A nonlinear electron-Bernstein mode is excited in a 4-wave parametric coupling$^{\mathrm{.}}$. The synergy between stimulated Raman and Brillouin scattering is analyzed. The scatterings off electron Bernstein mode is analyzed for the gyrotron frequency of 170GHz; X-Mode and O-Mode power of \quad 24 MW CW; on-axis B-field of \quad 10T.$^{\mathrm{\thinspace }}$The stimulated scattering in the electron cyclotron frequency range of the X-Mode and O-Mode driver with the ITER plasma lead to the appearance of suprathermal electrons and dragged by them accelerated ions at the plasma edge with the parameters directly dependent on the plasma parameters in the core of the ITER. Plasma diagnostic in the core region, (ion temperature), can be performed by the diagnostics of suprathermal electrons and accelerated ions at the edge plasma. [Preview Abstract] |
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PP12.00019: Collective Alfv\'{e}nic fast ion transport evaluation using Landau closure models Donald Spong, Jacobo Varela, Luis Garcia, Yashika Ghai, Mike Van Zeeland Energetic particle (EP) instabilities related to various EP resonances with Alfv\'{e}n waves are known to drive enhanced levels of transport in both tokamaks and stellarators. The prediction of this transport and its long-term intermittency characteristics are important goals for both the ignition margin of fusion systems, as well as first wall protection. While various evaluations of single particle confinement in the presence of Alfven activity have been made, relatively little has been done based upon self-consistent stability models to assess the collective transport that is driven by the evolving phase relations of the fast ion density perturbations with the potential and magnetic field fluctuations. This transport can be readily assessed using the FAR3d nonlinear model which uses Landau closure methods to incorporate the wave-particle resonances that drive EP instabilities. Applications have been made to several well-diagnosed DIII-D discharges. EP transport flows in both 1D and 2D are diagnosed, and an erosion of EP density gradients leading asymptotically to a critical gradient limit is observed. [Preview Abstract] |
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PP12.00020: Prediction of isotopic effects in neutral beam experiments in DIII-D Eric Bass, Ronald Waltz, Michael Van Zeeland The TGLF-EP$+$Alpha$^{\mathrm{1,2}}$ model of energetic particle (EP) transport is used to predict the transport-limited profile of neutral beam injection (NBI) ions in DIII-D discharges with hydrogen isotopes with super-Alfv\'{e}nic EPs. When NBI mass is reduced, increased Alfv\'{e}n Mach number is destabilizing to Alfv\'{e}n eigenmodes (AEs) but decreased slowing-down time is stabilizing. The TGLF-EP$+$Alpha critical gradient model$^{\mathrm{3}}$ treats both effects self-consistently. We consider two shear-reversed scenarios: and . Across beam powers, a hydrogen beam into a hydrogen plasma increases AE transport over the all-deuterium reference. Competing effects roughly cancel with a hydrogen beam into a deuterium plasma.$\backslash^{\mathrm{1}}$He Sheng and R. E. Waltz, Nucl. Fusion 56, 056004 (2016)He Sheng, R.E. Waltz, and G.M. Staebler, Phys. Plasmas 24, 072305 (2017)$\backslash $super 3R. E. Waltz and E. M. Bass, Nucl. Fusion 54, 104006 (2014) [Preview Abstract] |
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PP12.00021: An Improved Gyrofluid Model to Study Energetic Particles Instabilities Yashika Ghai, Donald A. Spong, Jacobo Varela, Luis Garcia Energetic particle (EP) driven Alfv\'{e}n instabilities have been extensively studied for fusion devices to evaluate the device first wall heat load as well as to plan experimental scenarios. EP instabilities arise when fast ions from the neutral beam injectors undergo resonant interactions with the Alfv\'{e}n waves. Models based on gyro-Landau fluid moment closure have been used to model the stability of fast ions in such studies. Precise emulation of kinetic effects for the fast ions in a fluid model requires a reasonable truncation of the gyrofluid moment equations hierarchy. We have developed a gyro-fluid model comprised of six moment equations for fast ions derived by taking velocity moments of the gyrokinetic equation with electromagnetic fluctuations while considering a velocity dependent drift frequency. We optimize our gyrofluid model with the gyrokinetic response function to study instability of Alfv\'{e}n eigenmodes. Unlike the velocity averaged drift frequency gyro-fluid models currently in use for EP instabilities, the velocity dependent drift frequency leads to coupling with higher order moments and hence presents the opportunity for a new optimal closure technique. [Preview Abstract] |
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PP12.00022: Features of energetic particle transport in the after-glow phase of the JET plasma discharges A. A. Teplukhina, F. M. Poli, M. Podesta, P. J. Bonofiglo, J. Yang, M. Sertoli, N. C. Hawks, D. L. Keeling, C. S. Collins, R. J. Dumont Reliable projections from existing JET DD plasmas are required to develop a scenario allowing to observe alpha-particle driven modes in DT plasmas (R. J. Dumont et al, 2018 Nucl. Fus. 58 082005). Favourable conditions to observe Alfven Eigenmodes (AE) driven by alpha particles include reducing mode damping by beam ions and maintaining minimum q at high values to destabilize modes. We focus on optimization of the JET NBI heating scheme to ensure fast slowing down of beam ions along with elevated q profiles. With the TRANSP code, we analyse the after-glow phase of JET DD high performance plasma discharges. Uncertainties in computed plasma parameters are assessed depending on modelling assumptions. Modelling of fast ion transport is improved by including orbital dependence of transport coefficients computed by the reduced ``kick'' model (M. Podest\`a et al, 2014 PPCF 56 055003). TRANSP simulation results are the starting point for investigation of AE destabilization in the planned JET DTE2 discharges and linear analysis of AE stability with the NOVA-K code. [Preview Abstract] |
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PP12.00023: Nonlinear Evolution of Instabilities due to Drag and Large Effective Scattering Jeff Lestz, Vinicius Duarte, Nikolai Gorelenkov, Roscoe White Energetic-particle-driven instabilities exhibit a broad range of nonlinear behavior in fusion plasmas, including steady state solutions, frequency chirping, bursting, chaos, etc. The role of drag in chirping has been explored extensively, but its effect on the more ubiquitous steady state solutions has not been thoroughly investigated. The electrostatic bump on tail problem is studied analytically in order to determine the effect of drag on steady state solutions near marginal stability ($1 - \gamma_d/\gamma_L \ll 1$) when effective collisions are large ($\nu_\text{eff} \gg \gamma$). A new analytic solution is derived in this common tokamak regime, demonstrating that drag increases the saturation amplitude and introduces a shift in the oscillation frequency by modulating the saturated wave envelope. Remarkably, a quasilinear diffusion equation for $\delta f$ naturally emerges from the nonlinear system when $\nu_\text{eff} \gg \gamma$, even for a single, isolated resonance. Due to a broken symmetry, drag shifts the wave-particle resonance lines and can even split them into many new sidebands. Excellent agreement is found between all analytic results and 1D Vlasov simulations. Methods for future experimental validation of these fundamental plasma physics predictions are discussed. [Preview Abstract] |
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PP12.00024: Energetic trapped ion losses driven by resonant NTMs Hugo Ferrari, Ricardo Farengo, Pablo Garcia-Martinez, Cesar Clauser The (2,1) neoclassical tearing mode (NTM) has been proposed as a candidate to explain the larger than expected losses of high energy ions produced during neutral beam injection in ASDEX-U (1). Although the numerical simulations performed so far to study the effect of NTMs on energetic ions have reproduced several features observed in experiments, the agreement is not completely satisfactory. In this work we study the effect of NTMs on the confinement of energetic ions produced by NBI injection using FOCUS (2), a full orbit code that includes the time dependent perturbed electric and magnetic fields during NTM instabilities. To calculate the perturbed fields a reconstruction technique that includes the experimental information available (3,4) is employed. The main result of this study is that when the frequency of the NTM matches the precession frequency of the trapped particles, the losses significantly increase. Simulations also show that the main losses correspond to trapped particles. (1) M. Garcia-Munoz et. al., Nucl. Fus. 47, L10 (2007). (2) C. F. Clauser et al. Comput. Phys. Comm. 234, 126 (2019). (3) R. Farengo et al, Plasma Phys. Control. Fusion,025007 (2012). (4) V. Igochine et al, Nucl. Fus. 43 1801 (2003). [Preview Abstract] |
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PP12.00025: Global Alfven eigenmode (GAE) simulations for NSTX(-U) and DIII-D Elena Belova, Neal Crocker, Shawn Tang, Jeff Lestz, Eric Fredrickson Numerical study of global Alfv\'{e}n eigenmodes (GAEs) in the sub-cyclotron frequency range explains observed GAE frequency scaling with beam parameters in experiments across different devices. GAEs are frequently excited during neutral beam injection (NBI) in the National Spherical Torus Experiment (NSTX/NSTX-U), as well as other beam-heated devices such as MAST and DIII-D. These modes are driven unstable through the Doppler shifted cyclotron resonance with the NBI ions, and can be excited in ITER due to super-Alfv\'{e}nic velocities and strong anisotropy of the beam ions. Numerical simulations using the HYM code have been performed to study the excitation of GAEs in the NSTX, NSTX-U and most recently for DIII-D. Simulation results match the experimentally observed unstable GAEs in the NSTX-U and NSTX. New simulations for typical DIII-D plasma and beam parameters demonstrate that high-frequency modes with $\omega /\omega _{ci}$\textasciitilde 0.6, previously identified as compressional Alfv\'{e}n eigenmodes (CAEs), have in fact shear Alfven polarization and are identified as GAEs. Simulation results match the observed frequencies and estimated toroidal mode numbers. Nonlinear simulations show broadening of the GAE mode structure at saturation, and the scaling of saturation amplitude with the beam parameters. [Preview Abstract] |
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PP12.00026: An Integrated Model for Fast Ion Losses in JET Plasmas Supported by Measurement P. J. Bonofiglo, M. Podesta, V. Kiptily, V. Goloborodko, A. Horton, P. Beaumont, F. E. Cecil, C. Giroud As JET's 2021 DT-campaign approaches, the development of fully integrated fast ion transport models is needed to better examine future alpha confinement and losses. JET's 2019-2020 deuterium campaign was used as a testbed for examining fast ion confinement and transport where MeV scale ICRH heated deuterium NBI ions, as well as DD-fusion products, acted as proxies for DT-alpha particles. This presentation details the development of a predictive model for fast ion losses in JET deuterium plasmas supported by measurement. Fast ion loss measurements are reported via an array of Faraday cup fast ion loss detectors which have recorded losses due to MHD activity, including: tearing modes, kink modes, sawteeth, and fishbone modes. Analytic representations for the perturbations are used as input into the reduced transport ORBIT-kick model which calculates transport matrices for use in TRANSP/NUBEAM. The NUBEAM computed fast ion distributions are biased against the distribution assembled from reverse-orbit integrating ions from a synthetic loss detector providing a weight for the modeled particles, relative to a detection event, for comparison to measurement. [Preview Abstract] |
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PP12.00027: Fast ion transport in presence of magnetic islands Julio Martinell, Leopoldo Carbajal, Rodrigo Saavedra The presence of fast ions in current and future magnetic fusion experiments is commonplace including NBI and alpha particles from fusion reactions. They are expected to be well confined in order to deliver their energy before escaping the plasma. MHD perturbations usually produce magnetic islands which affect plasma confinement and they are regarded as deleterious. However, there is some evidence that rational surfaces may be related to the presence of transport barriers in devices such as stellarators [1]. Therefore, it is interesting to study the influence of magnetic islands on fast ions. In this work we present Monte Carlo simulations on the transport of ions based on two different codes that use guiding center motion and full orbit computations in toroidal geometry. The presence of the islands is included by adding a magnetic perturbation at a rational surface. The flux of particles is then analyzed from the inner plasma region across the island as function of the island width and the particle energy. Results will be presented showing that the transport across the island can be actually reduced for some particular cases, relative to the no-island case, indicating a sort of transport barrier. [1] D. Lopez-Bruna et al. Euro. Phys. J. 82, 65002 (2008) [Preview Abstract] |
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PP12.00028: Simulation of MHD Instabilities with Runaway Electron Current using M3D-C1 Chen Zhao, Chang Liu, Stephen Jardin, Nathaneil Ferraro Runaway electrons can be generated in a tokamak during the start up, during normal operation and during a plasma disruption. To predict the consequences of runaway generation during a disruption, it is necessary to consider resonant interactions of runaways with the bulk plasma. Here we consider the interactions of runaways on low mode-number tearing modes, the nonlinear effect of runaways on low beta sawteeth and the runaway current generation during disruption. For this study, we have developed a fluid runaway electron model for the 3D MHD code M3D-C1. The code employs high-order C1 continuous finite elements in 3 dimensions. It can be switched into reduced MHD or full MHD, linear or non-linear, cylindrical or toroidal geometry. The code allows localized mesh adaptation around certain rational surfaces so that it can better resolve the near-singular behavior of the runaway electron current in the inner layer region. We have reproduced the reduced-MHD linear tearing mode results (with runaway electrons) in a circular cylinder presented in previous studies. This work is also extended to full MHD. We also have carried out the result of nonlinear low-beta sawteeth with runaways and the runaway current generation during disruption using DIII-D parameters. [Preview Abstract] |
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PP12.00029: NIMROD Modeling of Transient-Induced NTM E.C. Howell, J.R. King, S.A. Kruger, J.D. Callen, R.J. La Haye Extended MHD NIMROD simulations are used to study a neoclassical tearing mode (NTM) induced by an external magnetic perturbation pulse. Simulations use a kinetic reconstruction of a DIII-D ITER baseline scenario discharge and include experimental flow profiles inferred from Charge Exchange Recombination (CER) measurements. In the simulation, a n$=$1 external magnetic perturbation, containing a broad poloidal spectrum, is applied as a 1 ms pulse. The perturbation initially generates a slowly growing m/n$=$2/1 seed island. Following the pulse, high-n core modes are destabilized in a sequence. Initially the 6/5, 5/4, and 4/3 modes go unstable. The 6/5 and 5/4 modes saturate as the 4/3 mode grows to large amplitude, and the 3/2 mode is destabilized. As the 3/2 mode grows to a large amplitude, the 4/3 mode saturates while the 2/1 NTM seed island transitions to a phase of rapid growth and becomes dominant. An analysis of the radial induction equation will be presented to investigate how the nonlinear mode interactions drive the increased 2/1 growth. [Preview Abstract] |
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PP12.00030: Interpretable data-driven disruption predictors to trigger avoidance and mitigation actuators on different tokamaks Cristina Rea, Kevin Montes, Wenhui Hu, Jayson Barr, Keith Erickson, Robert Granetz, QiPing Yuan, Dalong Chen, Biao Shen, Bingjia Xiao This contribution details advancements of interpretable data-driven algorithms for disruption prevention across different tokamaks and in response to ITER needs. The Disruption Prediction via Random Forest (DPRF) algorithm is currently in use in both the DIII-D [1] and EAST PCS. DPRF predicts impending disruptions in real-time, while simultaneously identifying the drivers of the disruptivity through local measures of interpretability, i.e. feature contributions. DPRF performances on both devices allow predictions and contributions to be computed in less than 200us. On DIII-D, DPRF includes real-time calculations of peaking factors for temperature, density and radiation profiles. Such profile-based indicators prove to be relevant metrics in impurity accumulation events leading to disruptions in scenarios close to ITER baseline. Preliminary studies of DPRF integration with a proximity controller architecture [2] for continuous plasma state optimization on DIII-D will also be discussed. On EAST, DPRF was trained using high-density disruptive data, and it shows an accurate alarm rate (\textgreater 85{\%}) on real-time data, up to 1s prior to the disruption. DPRF was also used to trigger EAST mitigation system in dedicated experiments. [1] C. Rea et al 2019 Nucl. Fusion 59 096016; [2] J. Barr et al IAEA FEC 2020. [Preview Abstract] |
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PP12.00031: Machine Learning methods for forecasting error-field locking in tokamak plasmas Cihan Akcay, John Finn, Dylan Brennan The resonant interaction of a rotating tokamak with an error field can lead to locking, one of the leading causes of disruptions. Here, we train a series of machine learning (ML) classifiers to predict locking events, as a real-time forecasting tool for disruptions. We use a simple coupled third order ODE model to represent the interaction of the magnetic perturbation with the error field, in order to rapidly generate the training data for the ML algorithms. This model qualitatively captures the characteristic locking and unlocking bifurcations. The dependent variables of the ODE are the magnitude of the reconnected magnetic flux, its phase relative to the error field, and the plasma rotation, all at the mode rational surface. These three \textit{order parameters} completely characterize locked and unlocked states and form the features of the ML training. The \textit{control parameters} are the magnitude of the error field and the rotation frequency associated with the momentum source that maintains the plasma rotation in the absence of a magnetic perturbation. We use ML methods to classify locked and unlocked states, and to estimate the probability of locking in the region of control parameter space with hysteresis, where both locked and unlocked states co-exist. [Preview Abstract] |
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PP12.00032: Detection of Disruption Precursors with Semi-Supervised Learning Kevin Montes, Jinxiang Zhu, Cristina Rea, Robert Granetz This contribution presents a novel application of a label spreading\footnote{Zhou D. et al., Advances in Neural Information Processing Systems 16, 321-328 (2004)} algorithm to detect disruption precursors in a large dataset, given few manually labeled examples. A high detection accuracy ($>$85\%) for H-L back transitions is demonstrated on a dataset of hundreds of discharges with manually identified events for which $<$3\% of the transitions are labeled. Since the only necessary inputs are a dataset of 0D signals sufficient for manual detection of the event and a few recorded times at which the event occurs, this technique can in principle be used to detect a large variety of precursor events in a disruption database. As an example, the same algorithm is used to detect radiative collapses and initially rotating locked modes with high accuracy, despite their different dynamics and prevalence in the dataset. This implies that the construction of large event databases can be accelerated, automatically detecting new events with increasing fidelity as the user adds manually labeled data. This kind of disruption precursor data can improve the ability to train and interpret machine learning-based prediction algorithms, which rely on datasets too large to completely assemble by hand. [Preview Abstract] |
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PP12.00033: Numerical Simulation of the Hot-Tail Runaway Electron Production Mechanism Using CQL3D and Comparison with Analytical Methods Yu. V. Petrov, P. B. Parks, R. W. Harvey The hot tail mechanism of runaway electron (RE) production [1] is the primary source of RE in the case of rapidly cooling tokamak plasma. Quantifying this mechanism is very important as it can provide most of the post-thermal-quench (TQ) current, or a seed current for the secondary source of RE through the avalanche mechanism. An analytic model which omits pitch-angle scattering is often used in literature for estimating the hot tail RE density [2], though a thorough numerical verification of its validity has not been performed. In the present study, we use the CQL3D bounce-averaged Fokker-Planck code [1,3] to test the limits of validity of the model. In particular, we examine the cases of Z$=$1 and Z$=$18 ions, for sets of different initial temperature, density, electric field and the characteristic time of temperature decay. This is a more extensive comparison than in [4]. We show that for Z$=$1 plasma, CQL3D results closely match the model with spherical critical-speed boundary in phase space. For Z$=$18 case, the model over-estimates the RE density by factor of 2-10, comparing to CQL3D runs that include pitch-angle scattering. [1] R.W. Harvey, V.S. Chan, S.C. Chiu et al., Phys. Plasmas \textbf{7}, 4590 (2000). [2] H.M. Smith and E. Verwichte, Phys. Plasmas \textbf{15}, 072502 (2008). [3] R.W. Harvey and M.G. McCoy, www.compxco.com/cql3d.html. [4] A. Stahl, O. Embreus, et al., Nucl. Fus. \textbf{56}, 112009 (2016). [Preview Abstract] |
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PP12.00034: Sideways wall force and thermal quench in JET disruptions Henry Strauss, Stephen Jardin Two critical issues in tokamak disruptions are the asymmetric wall force produced during the current quench (CQ) and the thermal load during the thermal quench (TQ). Simulations of asymmetric wall force during disruptions with M3D were consistent with JET data. These results have been extended with M3D-C1 simulations and compared with additional JET data. The results confirm decrease of asymmetric wall force with CQ time, when the CQ time is less than the resistive wall penetration time. The asymmetric wall force and impulse were calculated with the Noll formula for shots in the JET ILW 2011-2016 disruption database, and compared with simulations. It is shown that vertical displacement events (VDE) scrape off plasma and cause $q$ to reach unity, destabilizing $(1,1)$ kink mode which causes the asymmetric wall force. Recent simulations of thermal quench have been carried out. The TQ has two phases: a rapid broadening of the temperature profile, and a slow loss of heat from the plasma. The slow phase can depend on wall resistivity. Magnetic perturbations at the plasma edge can increase in magnitude, increasing parallel thermal conduction and thermal load from disruptions. A longer resistive wall time reduces this effect. [Preview Abstract] |
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PP12.00035: Development of a Reduced Fluid Model for Runaway Electrons in NIMROD Simulations A. P. Sainterme, C. R. Sovinec, Ge Wang A reduced fluid model for runaway electrons is incorporated into the NIMROD code. Runaway electrons are treated as a distinct fluid species that flows with a velocity consisting of a large parallel component and a perpendicular component arising from an $\mathbf{E}\times\mathbf{B}$ drift. There is a source density for the runaway species given by the local background density and parallel electric field via the Dreicer mechanism. The runaway evolution couples to the MHD equations via Ohm's law and the momentum evolution in accordance with the assumption that the runaway species does not contribute to the resistive electric field, similar to the work presented in Bandaru, et al. [Bandaru, et al., PRE 99, 063317(2019)]. An iterative scheme ensures the nonlinear continuity equation for the runaway number density advance reaches a converged solution. Further iterations between the magnetic field, temperature, and runaway number density are used to achieve a consistent solution for the change to each quantity within a time step. Simulations in cylindrical geometry demonstrate the implementation of the source mechanism and parallel advection. [Preview Abstract] |
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PP12.00036: Overview of two disruption research projects on DIII-D and MST B.E. Chapman, A.F. Almagri, B.S. Cornille, D.J. Den Hartog, N.C. Hurst, K.J. McCollam, M.D. Pandya, J.S. Sarff, C.R. Sovinec, D.L. Brower, J. Chen, R. Yoneda, W.X. Ding Two projects have recently been initiated on DIII-D and MST to further the understanding of disruptions in tokamak plasmas. Both projects focus on internal measurement of the magnetic fluctuations that play a key role in disrupting plasmas. The initial targets of the project on DIII-D have been the onset of tearing modes that can lead to disruption and the post-disruption runaway electron plateau. The project on MST, which has relatively recently begun operating as a tokamak, has a singular focus on the physics of the thermal quench. Internal measurement of magnetic fluctuations on DIII-D is made possible by Faraday-effect polarimetry, and both polarimetry and a rugged, multi-point insertible magnetic probe are utilized on MST. Measurements with these diagnostics can reveal dynamics not detectable by sensing coils at the plasma boundary. A primary goal of these projects is comparison of the measurements to the results of 3D nonlinear MHD computation. That is with the goals of validating the modeling and improving predictive capability for ITER. Here we will present an overview of and initial results from these projects. Work supported by U.S.D.O.E. [Preview Abstract] |
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PP12.00037: Polarization measurements of post-disruption runaway electron synchrotron emission in DIII-D Z. Popovic, E.M. Hollmann, D. Del-Castillo-Negrete, I. Bykov, R.A. Moyer, J.L. Herfindal, D. Shiraki, N.W. Eidietis, C. Paz-Soldan, A. Lvovskiy Visible synchrotron emission by runaway electrons (REs) has been studied with spectra and images to gain insight on RE dynamics and energy in several devices. RE pitch angle in post-disruption RE plateaus is important for radial transport loss of REs, current dissipation, and deposition of RE kinetic energy into the wall during final loss. A slow (\textasciitilde 100 ms) decrease of synchrotron brightness is usually observed during RE plateau, which is interpreted as dropping pitch angle for relativistic (\textgreater MeV) REs due to slowly evolving impurity content (and decreasing pitch angle scattering). If massive D2 injection is done, there is a more rapid purge of Ar out of RE plateau and a much faster drop of synchrotron brightness (\textasciitilde 20 ms). The brightness depends on pitch angle and RE density, so investigating polarization ratios (vertical/horizontal $=$ Pz/Px) is a way of isolating pitch angle. Initial analysis indicates that the ratio depends on pitch angle. This is supported by drop in Pz/Px from \textasciitilde 10 to about 3 during D2 MGI. The observation Pz/Px \textgreater 1 is consistent with earlier observations [Tinguely 2019]. Comparisons of full orbit (KORC) and guiding center (SOFT) simulations of the polarization will be given. [Preview Abstract] |
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PP12.00038: Whistler waves driven by runaway electrons have been observed on the Madison Symmetric Torus (MST) tokamak plasma. A. F. Almagri, B. E. Chapman, N. C. Hurst, S. Oliva, A. S. Squitieri, P. Van Meter, P. Wilhite, C. B. Forest Whistler waves driven by mildly relativistic runaway in tokamak discharges have been observed in MST. The waves are detected with high frequency insertable magnetic probe and the runaway electrons are monitored with high time resolution x-ray detector. The probe consists of two poloidal and two toroidal single turn coil. The two poloidal coils and the two toroidal coils are re separated by 4 mm. The probe signals are digitized at 5 GHz. The target Plasma has a toroidal field of 1.38 kG and 64 kA for plasma current. Plasma density scanned from 0.007x10$^{\mathrm{13}}$ to 0.4x10$^{\mathrm{13}}$ cm$^{\mathrm{-3}}$. For these plasmas, the edge safety factor is 1.8, f$_{\mathrm{ce\thinspace }}=$2.5 GHz, and f$_{\mathrm{ci}}=$1 MHz. At density of 0.007x10$^{\mathrm{13}}$ cm$^{\mathrm{-3}}$, discrete magnetic fluctuation lines appear at many frequencies. The lowest line appears at 12f$_{\mathrm{ci}}$. Higher frequency lines observed in MST plasma may be due to improved coupling to the wave. These discrete frequency lines decrease in amplitude as the plasma density is increased. A spectrogram of the magnetic fluctuations show a band like structure. These bands of discrete frequencies are totally absent at plasma density of 0.4x10$^{\mathrm{13}}$ cm$^{\mathrm{-3}}$. The two poloidal coils are used to estimate the perpendicular wave number. At the 12 MHz , at 22 MHZ , and at about 60 MHz . X-ray pulses from 3 keV up to 30 keV where detected in a perpendicular chord. Spectrogram of the x-ray pulses shows band like structure similar to the magnetic fluctuations. These results will be presented and results of the parallel wave numbers will be shown as well. [Preview Abstract] |
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PP12.00039: Physics and Machine Learning Based Approaches to Stability Analysis and Control on DIII-D Rory Conlin, Joseph Abbate, Keith Erickson, Alexander S. Glasser, Egemen Kolemen We have developed a neural network to predict the evolution of plasma profiles on confinement time scales (200 ms) using experimental data from DIII-D. This machine learning model can be used to predict future values of the profiles in real time using available diagnostic measurements and a set of proposed actuator inputs. This predictive model can be used for real time model predictive control of the plasma profiles. We demonstrate a first of its kind controller using this neural network and show its ability to accurately control the profiles in tests on DIII-D. We also demonstrate the use of real time physics based stability analysis using a parallel implementation of the STRIDE code, and its use for predicting ideal MHD instabilities. When combined together, the physics based stability analysis and machine learning based controller allow for the possibility of actively controlling the plasma to mitigate and prevent instabilities before they happen. Work supported by US DOE under DE-FC02-04ER54698, DE-AC02-09CH11466 and DE-SC0015878. [Preview Abstract] |
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PP12.00040: Improving the sub cycling technique with delta-f kinetic electron physics in XGC Pallavi Trivedi, Julien Dominski, Seung-Hoe Ku, Aaron Scheinberg, Choong-Seock Chang, Junyi Cheng, Yang Chen, Scott Parker The High-Fidelity Whole Device Modeling (WDM) project models the whole device of tokamaks with core and edge gyrokinetic simulations coupled together. Successful core-edge coupled simulation of DIII-D like plasma including the X-point has been achieved with adiabatic electrons [wdmapp.pppl.gov]. Currently, the work on coupled simulations with kinetic electrons is ongoing. The difficulty in coupling the edge gyrokinetic code XGC with the core gyrokinetic codes GENE or GEM arises due to the use of different numerical schemes for pushing electrons. For instance, XGC sub-cycles the electrons using a direct delta-f scheme for evolving electron weights, whereas both GENE and GEM, in their original version, push the electrons consistently with the field using a reduced delta-f weight evolution equation for evolving electron weights. In order to have the possibility of evolving the electrons with the same reduced delta-f equations, this reduced delta-f scheme for electron weight evolution has been implemented in XGC, as will be presented. This particular scheme is also being optimized on GPU using advantages of the Particle-in-Cell(PIC) representation. XGC kinetic electron physics with the reduced delta-f equaiton is cross-verified against the gyrokinetic code GEM. [Preview Abstract] |
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PP12.00041: Particle-In-Cell simulation of ion beam extraction Regis John, David Caron, Earl Scime An Object-Oriented Particle-In-Cell simulation is developed using OOPIC Pro to model the extraction of a plasma generated by an RF source through an aperture of size 5mm by 5mm. The extraction field is created by a biased wafer outside of the source chamber. For comparison to the model results, measurements of the ion velocity distribution function are obtained with a confocal laser induced fluorescence diagnostic system. The extraction geometry creates ion beamlets used in advanced semiconductor fabrication. The objective of the simulation is to identify (and then validate) the experimental conditions that optimize beamlet formation. [Preview Abstract] |
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PP12.00042: TRANSP: status and plans to bring the golden standard into the silicon age Francesca Poli, Joshua Breslau, Laszlo Glant, Marina Gorelenkova, Jai Sachdev TRANSP is a time-dependent 1.5D equilibrium and transport solver, used for modeling of tokamak plasma discharges and experimental planning. TRANSP incorporates state of the art heating/current drive sources and transport models, implemented in a solver (PT-SOLVER) that is especially suited to treat stiff turbulence transport. With increasing number of users worldwide and with the upcoming ITER era, TRANSP is facing a new challenging: reducing the computational burden without compromising the physics fidelity. While upgrading physics capabilities is still a priority, the focus is shifting towards the modernization of the code and the re-factoring of its modules for new computer architectures and to enable collaborations (modularization). We describe the plans forward for physics upgrades and for modernizing and modularizing TRANSP, including running the code on a laptop and on the cloud, and with the need for a whole device model code that provides at the same time high fidelity physics models and computational efficiency. [Preview Abstract] |
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