Bulletin of the American Physical Society
58th Annual Meeting of the APS Division of Plasma Physics
Volume 61, Number 18
Monday–Friday, October 31–November 4 2016; San Jose, California
Session CM9: Mini-Conference: New Developments in Algorithms and Verification of Gyrokinetic Simulations IIMini-Conference
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Chair: David Hatch, University of Texas Room: 211 CD |
Monday, October 31, 2016 2:00PM - 2:25PM |
CM9.00001: New developments in algorithms and verification in the particle-in-cell code XGC C.S. Chang, S. Ku, R. Hager, S. Parker, Y. Chen, E. Yoon Recent algorithm developments for electrostatic and electromagnetic simulations in the edge gyrokinetic code XGC1 will be reported, together with their verification activities. Topics to be discussed include Lagrangian-Eulerian hybrid algorithm, fully nonlinear multispecies Fokker-Planck collision algorithm, and implicit electromagnetic simulation algorithm. These developments enabled study of edge blobby turbulence, divertor heat-flux width, edge transport bifurcation, electromagnetic instabilities, RMP physics, etc. on extreme scale computers, which would have been difficult otherwise. [Preview Abstract] |
Monday, October 31, 2016 2:25PM - 2:50PM |
CM9.00002: Comparison of Implicit Multiscale Full Kinetics to Gyrokinetics Scott Parker, Benjamin Sturdevant, Yang Chen Recent progress has been made developing full kinetic Lorentz force ion dynamics using implicit multiscale techniques [1]. It is now possible to capture low-frequency physics along with finite Larmor radius (FLR) effects with a fully kinetic multiscale delta-f particle simulation. The utility of such a model is to be able to verify gyrokinetics in situations where the smallness of the ordering parameters are under question. Additionally, such a model can help identify what higher order terms in gyrokinetics might be important. Orbit averaging and sub-cycling are utilized with an implicit particle time advance based on variational principles. This produces stable and accurate ion trajectories on long time scales. Excellent agreement with the gyrokinetic dispersion relation is obtained including full FLR effects. Ion Bernstein waves are easily suppressed with the implicit time advance. We have developed a global toroidal electrostatic adiabatic electron Lorentz ion code. We will report our linear results benchmarking Lorentz ions with gyrokinetics for the Cyclone base case. We will also present our progress on ion including drift-kinetic electrons and electromagnetic perturbations. [1] B.J. Sturdevant, S.E. Parker, Y. Chen, and B. Hause, J. Comput. Phys., 316 519 (2016). [Preview Abstract] |
Monday, October 31, 2016 2:50PM - 3:15PM |
CM9.00003: Advanced validation of local and global gyrokinetic codes: effects of the magnetic equilibrium G merlo, O Sauter, S Brunner, A Burkel, J Dominski, E Lanti, L Villard, Y Camenen, F Casson, W Dorland, E Fable, T Goerler, E Sonnendrucker, F Jenko, D told, A Peeters The large availability of computational resources, together with significant improvements in both simulations models and diagnostic capabilities, have more and more allowed the possibility of carrying out a one-to-one comparison between gyrokinetic simulations and microturbulence measurements. This, however, demands for more sophisticated and comprehensive validation and verification efforts of existing gyrokinetic codes. As one further step in this direction, we have developed a series of benchmarks focusing our attention on the effect of realistic magnetic geometry provided by ideal MHD equilibrium solvers, which is an essential requirement in order to model specific experimental conditions. A first series of tests have been successfully carried out by the GENE, GS2 and GKW codes [G. Merlo {\it et al.} PoP {\bf 23} 2016]. Details and critical points of this exercise will be discussed. The extension of these tests to global gyrokinetic codes, an ongoing effort currently involving the GENE and ORB5 codes, will be discussed as well. [Preview Abstract] |
Monday, October 31, 2016 3:15PM - 3:30PM |
CM9.00004: Gyrokinetic-neoclassical study of the bootstrap current in the H-mode pedestal Robert Hager, C. S. Chang, S. Ku, E. S. Yoon, E. F. D'Azevedo, P. H. Worley Since existing bootstrap current formulas are based on assumptions that are valid only under core plasma conditions, we developed an improved bootstrap current formula for the steep H-mode pedestal based on simulations with the gyrokinetic-neoclassical particle-in-cell code XGCa [R. Hager, C.S. Chang, Phys. Plasmas 23, 042503 (2016)] using a fully nonlinear, multi-species Fokker-Planck-Landau collision operator. The new formula is much more accurate than the widely used formula by Sauter et al. [O. Sauter et al., Phys. Plasmas 6, 2834 (1999)], which deviates by about 24.8 percent from XGCa results. The new bootstrap current formula is applied to electromagnetic stability calculations with a version of gyrokinetic code XGC1 that uses gyrokinetic ions and fluid electrons. Two significant findings from this XGCa study of the bootstrap current are the significant contribution of trapped electrons to the total current and the finite orbit width effects that generally decrease the bootstrap current compared to the prediction from conventional neoclassical theories and simulations. We also present the numerical implementation and results of verification studies of our nonlinear collision operator. [Preview Abstract] |
Monday, October 31, 2016 3:30PM - 3:55PM |
CM9.00005: $\delta$f gyrokinetics for the scrape-off layer transport Qingjiang Pan, Frank Jenko, Daniel Told Edge plasmas present a few challenges for gyrokinetic simulations that are absent in tokamak cores. Among them are large amplitudes of fluctuations and plasma-wall interactions in the open field line region. Recently, the widely-used core-turbulence code GENE, which applies $\delta$f-splitting technique, is extended to simulate open systems with large electrostatic deviations from the background plasmas. With inclusion and proper discretization of the parallel nonlinear term, $\delta$f-splitting causes no extra fundamental difficulty in handling large deviations. The loss of particles to the wall is accounted by using logical sheath boundary, which is implemented in the context of finite-volume method. The extended GENE is benchmarked for the well-established parallel transport in the scrape-off layer (SOL) during edge-localized modes (ELMs). The parallel heat flux deposited onto the divertor target due to the ELM pulse is compared with previous simulation results and shows good agreement. [Preview Abstract] |
Monday, October 31, 2016 3:55PM - 4:20PM |
CM9.00006: Advanced Discontinuous Galerkin Algorithms and First Open-Field Line Turbulence Simulations G. W. Hammett, A. Hakim, E. L. Shi New versions of Discontinuous Galerkin (DG) algorithms have interesting features that may help with challenging problems of higher-dimensional kinetic problems. We are developing the gyrokinetic code Gkeyll based on DG. DG also has features that may help with the next generation of Exascale computers. Higher-order methods do more FLOPS to extract more information per byte, thus reducing memory and communications costs (which are a bottleneck at exascale). DG uses efficient Gaussian quadrature like finite elements, but keeps the calculation local for the kinetic solver, also reducing communication. Sparse grid methods might further reduce the cost significantly in higher dimensions. The inner product norm can be chosen to preserve energy conservation with non-polynomial basis functions (such as Maxwellian-weighted bases), which can be viewed as a Petrov-Galerkin method. This allows a full-$F$ code to benefit from similar Gaussian quadrature as used in popular $\delta f$ gyrokinetic codes. Consistent basis functions avoid high-frequency numerical modes from electromagnetic terms. We will show our first results of $3x+2v$ simulations of open-field line/SOL turbulence in a simple helical geometry (like Helimak/TORPEX), with parameters from LAPD, TORPEX, and NSTX. [Preview Abstract] |
Monday, October 31, 2016 4:20PM - 4:45PM |
CM9.00007: Variational approach to low-frequency kinetic-MHD in the current-coupling scheme Cesare Tronci, Joshua Burby Hybrid kinetic-MHD models describe the interaction of an MHD bulk fluid with an ensemble of hot particles, which is described by a kinetic equation. When the Vlasov description is adopted for the energetic particles, different Vlasov-MHD models have been shown to lack an exact energy balance, unless non-inertial force terms are inserted in the kinetic equation. These force terms arise from fundamental approaches based on Hamiltonian and variational methods. In this work we apply Hamilton's variational principle to formulate new current-coupling kinetic-MHD models in the low-frequency approximation (i.e. large Larmor frequency limit). More particularly, we formulate current-coupling hybrid schemes, in which energetic particle dynamics are expressed in either guiding-center or gyrocenter coordinates. [Preview Abstract] |
Monday, October 31, 2016 4:45PM - 5:00PM |
CM9.00008: Energy Conserving Forms of Discontinuous Galerkin Algorithms, and Sparse Grid Methods Ammar Hakim, Greg Hammett, Eric Shi A hybrid discontinuous/continuous Galerkin scheme for gyrokinetic equations is presented. Discretizing the Poisson bracket form of the equations, along with a careful choice of basis functions allows conserving the total (particle+field) energy exactly, even with upwinding to reduce artificial oscillations. Straightforward use of tensor basis functions can get expensive in higher dimensions and high polynomial order. Savings might be possible by using basis sets that have fewer monomials and combining these with a version of sparse grid quadrature methods. For example, a tensor product of piecewise parabolic basis functions in 5D involves 243 basis functions per cell, but this drops to 21 basis functions if only second order monomials are needed. Enforcing continuity needed for energy conservation in configuration space might reduce the savings, but would still be a gain over Gaussian quadrature. Our version of sparse grid methods could use non-nested quadrature points as well as well as anisotropic basis. Energy conservation with use of reduced basis sets is discussed. [Preview Abstract] |
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