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 BO11: Magnetic Confinement: RF SciDACLive
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Chair: Greg Wallace, MIT |
Monday, November 9, 2020 9:30AM - 9:42AM Live |
BO11.00001: Recent Results from the SciDAC Partnership for Simulation of Fusion Relevant RF Actuators P. T. Bonoli, D. L. Green, E. D'Azevedo, N. Bertelli, A. Dimits, T. Kolev, D. N. Smithe, R. W. Harvey, J. R. Myra, M. S. Shephard, D. Curreli We present an overview of research related to the interaction of ICRF and LHRF power with the tokamak scrape-off layer (SOL) and core. We discuss the development and application of the RF full-wave solver Stix and the more general FEM analysis platform Petra-M, both based on the Modular Finite Element Framework (MFEM), highlighting work on matrix pre-conditioners, implementation of high fidelity geometric descriptions of ICRF antennas, and incorporation of a RF sheath boundary. We will discuss the development of a far-SOL fluid transport solver for equilibrium (Braginskii MFEM mini-app) and a turbulent (SOLT-3D code based on BOUT$++)$ model, including a RF ponderomotive force term, which can be calculated directly from the VSim FDTD plasma wave code. Results for the interaction of RF power with metallic surfaces will be presented, including PIC simulations of the ion energy-angle distributions at ICRH antennas in RF sheaths. We will also discuss novel applications of LHRF power for mitigating disruptions, extension of RF codes to mirror geometries, and implementation of RF codes on GPU's. [Preview Abstract] |
Monday, November 9, 2020 9:42AM - 10:06AM Live |
BO11.00002: Ponderomotive Density Modification via High Power Radio-Frequency Waves in the Scrape-Off Layer. (PhD Oral-24) Rhea Barnett, Colin Waters, David Green, Jeremy Lore, David Smithe, Jim Myra, Cornwall Lau, Bart Van Compernolle, Steve Vincena Maximising the energy transfer from ion cyclotron range of frequencies (ICRF) actuators to the core of fusion plasmas will be integral to reliable operation of devices such as ITER. Injected RF wave properties depend on and modify plasma properties such as density, leading to a coupled system that requires a self-consistent description. The role of the ponderomotive force on density redistribution during application of RF power in regions close to the actuator is of interest. Simulation results from a 1D (parallel to the confining magnetic field), coupled full-wave cold plasma RF and plasma transport solver are described and the results compared with experimental data from the Large Plasma Device (LAPD). Parallel gradients in the total electric field are also considered. Plasma transport and RF cold plasma parameters for which the ponderomotive force may drive significant density redistribution will be highlighted. [Preview Abstract] |
Monday, November 9, 2020 10:06AM - 10:18AM Live |
BO11.00003: Physics of simultaneous excitation of electrostatic slow mode and fast helicon waves Eun-Hwa Kim, Syun'ichi Shiraiwa, Nicola Bertelli, Bart Van Compernolle, Masayuki Ono The significance of parasitic coupling to the undesired slow waves for helicon wave excitation was quantified using the high-resolution full wave simulation code, Petra-M. RF current drive is expected to be a crucial current drive actuator in a fusion power plant and particularly useful for current profile control needed for an advanced tokamak reactor. In particular, helicon waves are thought to be promising since it can penetrate into reactor-grade high density core and drive off-axis current at higher efficiency. In experiments on helicon current drive in DIII-D and KSTAR near 500 MHz, both electrostatic slow and fast helicon waves can coexist, and since slow waves can only penetrate to n$_{\mathrm{e}}$ \textasciitilde 1 x 10$^{\mathrm{19}}$ m$^{\mathrm{-3}}$ they are not useful for core current drive. For this reason, it is important to understand the slow wave excitation. To properly treat the physics of simultaneous excitation of slow and fast waves, the state-of-the-art rf modeling codes with 3D realistic antenna and plasma geometry were utilized to handle the waves with different wavelength and polarization. In particular, sufficiently fine mesh sizes must be chosen to allow for short wavelength slow wave excitation. [Preview Abstract] |
Monday, November 9, 2020 10:18AM - 10:30AM Live |
BO11.00004: Recent progress in development of full torus size RF simulation on NSTX-U S Shiraiwa, N Bertelli, M Ono, C Lau, M Shephard High harmonic fast wave (HHFW) presents a unique challenge for the RF full wave simulation. These waves are excited using a geometrically complicated strap type antenna located close to the plasma surface. Unlike the regular fast waves, the number of straps tends to be large (12 at NSTX-U) for better wave directivity. Moreover, the relative size of wave length to the plasma is smaller and the wave field solution contains many wave oscillations. Resolving such a wave field is expensive especially for the 3D full wave simulations. We tackled this issue using a high order finite element basis. We use the Petra-M versatile FEM analysis platform and modeled HHFW propagation in the entire NSTX-U plasma with fully detailed 12 strap antenna included. The simulation results are compared with TORIC, AORSA, and 2D simulations on Petra-M, showing good agreement. In this talk we also report recent development in Petra-M platform. Potential advantages of high order finite element basis when taking the warm plasma effects into account is also discussed. [Preview Abstract] |
Monday, November 9, 2020 10:30AM - 10:42AM Live |
BO11.00005: Development of Impedance Sheath Boundary Conditions in Stix Finite Element RF Code Christina Migliore, John Wright, Mark Stowell, Paul Bonoli Ion cyclotron radio frequency range (ICRF) power plays an important role in heating and current drive in fusion devices. However, experiments show that in the ICRF regime there is a formation of a radio frequency (RF) sheath at the material and antenna boundaries that influences sputtering and power dissipation. Given the size of the sheath relative to the scale of the device, it can be approximated as a boundary condition (BC). Electromagnetic field solvers in the ICRF regime typically treat material boundaries as perfectly conducting, thus ignoring the effect of the RF sheath. Here we describe progress on implementing a model for the RF sheath based on the a finite impedance sheath BC formulated by J. Myra 2015 \textasciitilde $\backslash $footnote\textbraceleft J. Myra, et al., Phys. Plasmas 22, 062507 (2015)\textbraceright which provides a representation of the RF rectified sheath including capacitive and resistive effects. This research will discuss the results from the development of a parallelized cold-plasma wave equation solver Stix that implements this non-linear sheath impedance BC through the method of finite elements in pseudo-1D and pseudo-2D using the MFEM library [http://mfem.org]. [Preview Abstract] |
Monday, November 9, 2020 10:42AM - 10:54AM Live |
BO11.00006: LHCD Simulation Using Full-Wave/Fokker-Planck Iteration Samuel Frank, Jungpyo Lee, John Wright, Paul Bonoli Lower Hybrid Current Drive (LHCD), has been used as an efficient means of RF current drive and heating in tokamaks for approximately 40 years. However, in the weakly damped regimes present in most tokamak LHCD experiments, the raytracing/Fokker-Planck (FP) simulations of LHCD typically used to interpret experiments have had difficulty accurately predicting current drive efficiency and profiles precisely. One possible reason for the discrepancy present in these simulations may be the omission of full-wave effects such as interference or the breakdown of the WKB approximation. This work is focused on resolving these discrepancies and introduces an improved version of the high-performance full wave code TORLH coupled to the CQL3D FP code. The requirements for achieving good coupling and a stable iteration between the two codes are significantly more stringent than previously assumed, and their study has demonstrated the importance of previously overlooked timescales in the LHCD problem and given insight into the LHCD velocity gap problem. The implications of these results with respect to raytracing and full-wave Fokker-Planck modeling of LHCD will be discussed. [Preview Abstract] |
Monday, November 9, 2020 10:54AM - 11:06AM Live |
BO11.00007: Finite-Element Solution of a Vorticity Transport Model Including RF Antenna Effects and Application to Scrape-Off-Layer-Turbulence Simulations A.M. Dimits, M. Holec, I. Joseph, T. Rognlien, C.J. Vogel, M.V. Umansky, J. Myra, D. Smithe Radio-frequency (RF) heating and current drive are important for magnetic fusion devices. The associated antenna structures can result in large rectified sheath potentials and ponderomotive forces, which can drive large plasma flows. These can drive or suppress turbulence in the scrape-off layer (SOL), which can significantly affect the RF-wave coupling to and propagation in the plasma. To model the plasma flows with the complicated (material) boundary shapes and boundary conditions needed, a drift-reduced fluid model has been implemented in the COMSOL Multiphysics finite-element (FEM) package, and is also being implemented in the more scalable Modular Finite-EleMent (MFEM) package. Steady-state solutions have been obtained with model RF-antenna-structure boundaries, RF-sheath boundary conditions and ponderomotive force contributions, so far in a simplified two-dimensional, axisymmetric geometry. From these solutions are generated boundary conditions on a flux surface, which can then be used in BOUT$++$-based turbulence codes such as SOLT3D. The FEM-based implementations are being generalized to find steady solutions with complicated three-dimensional domains, boundaries, and ponderomotive sources. [Preview Abstract] |
Monday, November 9, 2020 11:06AM - 11:18AM Live |
BO11.00008: Development of SOLT3D model for tokamak edge plasma turbulence M.V. Umansky, B.I. Cohen, A.M. Dimits, J.R. Myra Progress is reported on development of a tokamak edge turbulence model SOLT3D, for studies of interaction of edge plasma turbulence and RF waves. The model is motivated by the 2D model SOLT [1], which, in spite of its relative simplicity, produced a number of encouraging results. SOLT3D, being developed in the BOUT++ framework [2], roughly follows the original SOLT physics model and design but includes the dimension along the magnetic field line and solves for parallel variations of plasma fields and electron dynamics along the magnetic field line. The model domain represents edge plasma region of a tokamak in a “rectified” geometry. The model supports basic linear instabilities relevant to SOL turbulence: drift-resistive-ballooning mode (DRBM) instability driven by the magnetic curvature and the radial gradient of plasma pressure, and the conducting-wall mode (CWM) instability driven by the end-plate sheath boundary conditions and the radial gradient of plasma temperature. Extensive testing of the model demonstrates verification of local and nonlocal linear dispersion relations and benchmarking against available nonlinear results. [1] Russell et al., Phys. Plasmas 22, 092311 (2015); [2] Dudson et al., Comput. Phys. Commun. 180, 1467–1480 (2009). [Preview Abstract] |
Monday, November 9, 2020 11:18AM - 11:30AM Live |
BO11.00009: FDTD Ponderomotive Source Terms for BOUT++ David Smithe, James Myra, Andris Dimits, Maxim Umansky In the past, we have used a fast-time-scale / slow-time-scale approach to derive the vector Ponderomotive force in the slow-time-scale fluid equations, due to a fast-time-scale RF excitation. An issue that had remained unresolved, involving the appearance, and possible cancelation of the Reynolds Stress / Dynamic Pressure, e.g., the rho*V*V tensor, has finally been resolved. Proper accounting for the additional contribution to the slow-time-scale velocity distribution, when the distribution contains a cold fluid “quiver” [1], reestablishes the term, in its usual and familiar form. Progress has also been made in the computational implementation of these terms as additions into the SOLT3D code, making effective use of the generality of the BOUT++ framework [2] to facilitate the new physics. The properly normalized Ponderomotive vorticity term is concatenated to the other data files, in NetCDF format, after a run of the FDTD code. A simple one-line addition to the code reads that data in, and puts it into a global variable. Then the global variable is inserted into the vorticity equation. Compiling and testing of the modified SOLT3D code is ongoing. [1] P. J. Catto & J. R. Myra, Phys Fluids B 1, 1193 (1989). [2] M. Umansky et al, CPC 180, 887 (2009). [Preview Abstract] |
Monday, November 9, 2020 11:30AM - 11:42AM Live |
BO11.00010: Particle-in-Cell Simulations of the Ion Energy-Angle Distributions at ICRH Antennas in RF sheaths Davide Curreli Magnetic fusion devices operating with ICRH (Ion Cyclotron Resonance Heating) antennas suffer from increased erosion at the material surfaces exposed to the plasma. The radio-frequency rectified sheath formed in front of the surfaces accelerates the ions to energies which can easily exceed the sputtering threshold, with consequent enhanced sputtering and impurity emission during RF operations. In order to characterize the ion energy-angle distribution (IEAD) of the particles impacting on the surface, we performed a sequence of Particle-in-Cell simulations using the hPIC code developed at Illinois. The simulations highlight the main features of the kinetic distributions of the ions impacting on the IRCH surfaces. The Ion Energy-Angle Distributions obtained from hPIC were used for a characterization of the sputtering behavior as a function of the RF cycle and for an estimate of the enhanced gross erosion due to RF-sheaths. [Preview Abstract] |
Monday, November 9, 2020 11:42AM - 11:54AM Live |
BO11.00011: An Adaptive Sparse-Grid Fokker-Planck Approach toRF Heating of Plasmas in Magnetic Mirrors Louis Wonnell, Juan Caneses, David Green, Diego Del-Castillo-Negrete, Lin Mu, Eduardo D'Azevedo, Tyler McDaniel, Harry Hughes The application of RF power to heat or control plasmas in magnetic mirror devices, together with losses at the device ends results in distribution which deviate from Maxwellian and requires kinetic simulation for quantitative prediction. However, as spatial dimensionality is added to the required 2 velocity dimensions, the Fokker-Planck equation describing the dynamics becomes more challenging to solve within available computational resources, especially for continuum / Eulerian (mesh-based) approaches. For this work, the merits of an adaptive sparse-grid approach are discussed in the context of the RF heating of plasma in a magnetic mirror configuration for a three-dimensional phase space involving two velocity dimensions and one spatial coordinate along the magnetic field line. This continuum approach is compared with Monte Carlo-based Fokker-Planck calculations and experimental data to determine the effectiveness and cost savings of the approach. [Preview Abstract] |
Monday, November 9, 2020 11:54AM - 12:06PM Live |
BO11.00012: GPU-based Computing of RF Propagation John Cary, Carl Bauer, Marc Durant, Tom Jenkins, David Smithe Tech-X has applied its GPU computing framework to ICRF propagation. This framework uses finite-difference methods for both modeling the antennas and the linear plasma response. This required developing robust cut-cell meshing including the ability to heal bad surfaces. The curved surfaces of the perfect conductor antennas are modeled by the Dey-Mittra algorithm, which has now been ported to GPUs. The linear-plasma-dielectric algorithm has been improved using the method of triads introduced by Bauer et al [1], and the implementation is underway. This talk will demonstrate the workflow from problem setup to visualization as well as show the results of convergence tests. [Preview Abstract] |
Monday, November 9, 2020 12:06PM - 12:18PM Live |
BO11.00013: CQL3D-GENRAY Simulations of Suppression of Impurity-Induced Current Quench Using LHCD in C-Mod R.W. (Bob) Harvey, Yu.V. Petrov, P.T. Bonoli, S. Shiraiwa, P.B. Parks In Alcator C-Mod lower hybrid current drive experiments (LHCD), Reinke [1] has examined discharges which undergo an abrupt thermal quench (TQ) to low Te due to radiation from incoming tungsten flake material. This is simulated using the coupled CQL3D Fokker-Planck/Ampere-Faraday [2] and GENRAY ray tracing codes, based on experimental traces of the background densities, temperatures, and one-turn voltage. Simulations show evolution of a quasilinear plateau on the electron distribution, and with onset of the TQ, a collisional decay of the plateau from lower to higher velocity ($\tau_{slow} \propto v^{3}}$) giving an inverted distribution, and consequently a self-consistent instability of the injected LH waves; this broadens the current profile by edge damping. The effect of broadening is similar to recently-reported MHD TQ healing in DIII-D discharges [3]. The LH C-Mod interpretation further supports a new, hopefully robust, disruption control approach. [1] M.L. Reinke \textit{et al}, Nucl. Fusion 59, 066003 (2019). [2] R.W. Harvey \textit{et al}., Nucl. Fusion 59, 106046 (2019) [3] X.D. Du \textit{et al}., Nucl. Fusion 59, 094002 (2019); X. D. Du, Personal communication (2020). [Preview Abstract] |
Monday, November 9, 2020 12:18PM - 12:30PM Live |
BO11.00014: Simulation Workflow for RF Fusion System Simulations Mark Shephard, Morteza Hakimi, Syun’ichi Shiraiwa Accurate RF simulations of fusion systems like ITER require the definition of high-fidelity analysis geometries that include antenna, reactor wall and physics region representations. This presentation will describe a workflow for the execution of adaptive high-performance FR fusion system simulations. The steps in the simulation workflow include; defeaturing of un-needed details from antenna CAD models; combining the antenna, reactor wall and physics components into a single analysis model geometry; applying physical attributes to the analysis model; automatically generating a graded mesh; and executing an adaptive finite element analysis that includes the application of a iterations of finite element solve, a posteriori error estimation, and mesh enrichment. To create this simulation workflow advanced geometry and meshing technologies from Simmetrix are combined with advanced RF simulation capabilities being developed by LLNL, PPPL and MIT. [Preview Abstract] |
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