Bulletin of the American Physical Society
55th Annual Meeting of the APS Division of Plasma Physics
Volume 58, Number 16
Monday–Friday, November 11–15, 2013; Denver, Colorado
Session UM9: Mini-Conference: Two-Fluid, Gyro-fluid and Hybrid Kinetic-fluid Models |
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Chair: Andris Dimits, Lawrence Livermore National Laboratory Room: Governor's Square 16 |
Thursday, November 14, 2013 2:00PM - 2:20PM |
UM9.00001: Overview of recent BOUT$++$ simulation and validation results X.Q. Xu A suite of two-fluid models has been implemented in BOUT$++$ for all ELM regimes and fluid turbulence. A suite of gyro-fluid models is under development for pedestal turbulence and transport. A suite of 3D neutral and impurity models is also under development for SMBI, recycling, gas puffing, and for sputtering from RF antennas and divertor plates. Progress in several key areas of research will be presented: upshift of PB instability thresholds due to background turbulence; ELM power deposition on the divertor plates; identification of top pedestal micro-turbulence zone for ELM spreading and pedestal peak gradient MHD zone for ELM crashing For a ballooning-dominated equilibrium, we find that both pressure gradient and pedestal density can control the transition from large ELMs to small ELMs. Small elms can be either resistive or ideal P-B modes; the density dependence of the Elm size is due to ion diamagnetic stabilization, not due to collisionality. The flux limited expressions of parallel thermal diffusivities show weak or no collisionality dependence, even in the SOL. A decrease of the ELM size with density is a natural consequence for ballooning modes. For a peeling-dominated equilibrium and for typical experimental scenarios with natural transition between peeling dominated and ballooning dominated equilibria during the pedestal buildup, the scaling characteristics of the ELMs size will also be presented. [Preview Abstract] |
Thursday, November 14, 2013 2:20PM - 2:40PM |
UM9.00002: An assessment of fluid closures based on gyrokinetic and hybrid simulations Akihiro Ishizawa, Shinya Maeyama, Tomo-Hiko Watanabe, Hideo Sugama, Noriyoshi Nakajima Fluid closures are investigated by means of the gyrokinetic model and a hybrid model consisting of the gyrokinetic equation for ions and fluid equations for electrons [1]. Effects of closure on the linear growth rate of kinetic ballooning modes (KBMs) are examined by increasing the number of fields from two-fields including density and parallel velocity to six-fields including parallel and perpendicular temperatures and heat fluxes in addition to the two-fields. The Landau closure [2] is good enough to evaluate the linear growth rate of KBM, on the other hand, the model should be modified to get a steady state in nonlinear evolution because of the conservation of quadratic quantity. The importance of ion current in the Ampere's law is also presented. It was expected that the contribution of ion current is much smaller than that of electron current because of large mass ratio, however it is found that the ion current is important for evaluating the growth rate of KBM.\\[4pt] [1] A. Ishizawa, et.al., Nuclear Fusion 53, 053007 (2013).\\[0pt] [2] M. Beer and G. Hammett, Phys. Plasmas, 4046 (1996) [Preview Abstract] |
Thursday, November 14, 2013 2:40PM - 3:00PM |
UM9.00003: A hybrid drive ignition model for inertial confinement fusion using spherical hohlraum-capsule target He Xian-Tu An indirect-direct hybrid drive ignition model for inertial confinement fusion is proposed: the fusion capsule in a spherical hohlraum with six laser entrances and radiation non-uniformity of a few in thousand is compressed first by indirect-drive x rays and then by direct-drive lasers. Numerical simulations show that the hybrid drive produces a higher-density plateau between radiation and electron ablation fronts separately generated by indirect-drive x rays and direct-drive lasers. Such a density plateau ahead of the imploding capsule under the indirect-drive temperature ablation produces a stationary piston-like high-pressure structure with pressure of hundreds Mbar, which drives an enhanced shock wave (ES). The ES fleetly moves towards the imploding capsule center and stops the indirect-drive shock multiple reflections at the interface of hot spot/main fuel, and thus hydrodynamic instabilities and the asymmetry amplification are prevented there. A rapid non-isobaric hot spot ignition before stagnation is performed. [Preview Abstract] |
Thursday, November 14, 2013 3:00PM - 3:20PM |
UM9.00004: Simulations of Edge Current Driven Kink Modes with BOUT$++$ code G.Q. Li, X.Q. Xu, P.B. Snyder, A.D. Turnbull, T.Y. Xia, C.H. Ma, P.W. Xi Edge kink modes (or peeling modes) play a key role in the ELMs. The edge kink modes are driven by peak edge current, which comes from the bootstrap current. We calculated sequences of equilibria with different edge current using CORSICA by keeping total current and pressure profile fixed. Based on these equilibria, with the 3-field BOUT$++$ code, we calculated the MHD instabilities driven by edge current. For linear low-n ideal MHD modes, BOUT$++$ results agree with GATO results. With the edge current increasing, the dominant modes are changed from high-n ballooning modes to low-n kink modes. The edge current provides also stabilizing effects on high-n ballooning modes. Furthermore, for edge current scan without keeping total current fixed, the increasing edge current can stabilize the high-n ballooning modes and cannot drive kink modes. The diamagnetic effect can stabilize the high-n ballooning modes, but has no effect on the low-n kink modes. Also, the nonlinear behavior of kink modes is analyzed. [Preview Abstract] |
Thursday, November 14, 2013 3:20PM - 3:40PM |
UM9.00005: Analysis of different responses of ion and electron in six-field two-fluid ELM simulations Chenhao Ma, Xueqiao Xu We report simulation results of a Landau-Fluid (GLF) extension of the BOUT++ six-field two-fluid Braginskii model which contributes to increasing the physics understanding of ELMs. Landau-Fluid closure can fill the gap for parallel dynamics between hot, collisionless pedestal region and cold, collisional SOL region in H-mode plasmas. Our goal is extending the classical parallel heat flux with Landau-Fluid closures and making comparisons with other closure models. Our simulations show that for weakly collisional pedestal plasmas, the calculated growth rate with Landau-Fluid closure introduces more effective damping on the peeling-ballooning modes than that with the classical thermal diffusivity. Further nonlinear simulation shows that ELM size with Landau-Fluid Closure is smaller than that with classical thermal diffusivity. We find an ELM crash has two phases: fast initial crash of ion temperature perturbation on the Alfven time scale and slow turbulence spreading. Turbulence transport phase is a slow encroachment of electron temperature perturbation due to the ELM event into pedestal region which is due to a positive phase shift around $\pi/2$ between electron temperature and potential on pedestal region while ion temperature is in-phase with potential. [Preview Abstract] |
Thursday, November 14, 2013 3:40PM - 4:00PM |
UM9.00006: Tokamak turbulence simulations using BOUT$++$ framework in core region S.S. Kim, X.Q. Xu, H. Jhang, Tongnyeol Rhee, P.W. Xi, P.H. Diamond, A. Dimits, M. Umansky, G.Y. Park Development of a self-consistent, core-edge integrated simulation capability is a long standing problem in fusion simulation program. Such capability would yield insight into questions related to global profile dynamics originating from L to H and internal transport barrier (ITB) transitions. Starting from a tokamak edge plasma simulation code, BOUT$++$ has evolved into a versatile framework that can be used to simulate a wide range of fluid models in complicated magnetic geometry. For the realization of the self-consistent core-edge coupled simulation, we developed a core gyro-Landau-fluid code using BOUT$++$ framework. The primary physics goal of this development is to realize ITB formation in the presence of non-resonant modes and to study effects of flat q-profile and rotation shear on core profile de-stiffening. Initial efforts focused on the self-consistent simulation of core ITG turbulence and code verification. Verification of the code was realized by comparing linear growth rates calculated from BOUT$++$ with those from gyrokinetic codes. Global nonlinear simulations using 3$+$1 fields model were performed for ITG turbulence. Details of the code development and preliminary physics results will be presented. [Preview Abstract] |
Thursday, November 14, 2013 4:00PM - 4:20PM |
UM9.00007: BOUT++ flux-driven simulation of edge transport barrier formation with sheared equilibrium flows G.Y. Park, S.S. Kim, T. Rhee, H.G. Jhang, P.H. Diamond, X.Q. Xu The BOUT++ three-dimensional electromagnetic turbulence simulation code [1] is used to study edge transport barrier (ETB) formation and its underlying dynamics. A set of reduced MHD equations is solved including the effects of both equilibrium shear and turbulence driven zonal flows. The form of equilibrium flow profiles can be either proportional to the equilibrium pressure gradient or analytically given. We have applied flux-driven boundary condition near the inner simulation boundary to inject a finite amount of heat flux into the simulation domain and reach the steady flux-driven states. It has been found that externally imposed equilibrium shear flow can trigger ETB formation. Large turbulence is observed to be generated near and propagate into the pedestal region and strongly suppressed there by the local equilibrium flow shear. It has also been found that actual ETB formation is significantly influenced by various effects, i.e., turbulence driven zonal flow and its damping rate, outgoing heat flux level, etc. Detailed dynamics of edge transport barrier formation and its parametric dependence on varying parameters (zonal flow damping rate, heat source and sink rates, etc) will be discussed. \\[4pt] [1] B.D. Dudson, et al., Comput. Phys. Commun. 180, 1467 (2009) [Preview Abstract] |
Thursday, November 14, 2013 4:20PM - 4:40PM |
UM9.00008: Peeling-Ballooning mode simulation in ``Snowflake'' divertor configuration using BOUT++ Jingfei Ma, Xueqiao Xu, Dmitri Ryutov, Maxim Umansky ``Snowflake'' divertor, one of the two innovative divertor concepts [1,2], was introduced to solve the issue of large heat loads on plasma facing components and the resulting material erosion, especially during ELMing H-mode, by spreading particle flux to two additional divertor plates. In our work, two-fluid code BOUT++ is used to conduct linear peeling-ballooning (P-B) mode simulations in both standard (SD) and snowflake (SF) divertor geometry generated from DIII-D ELMing H-mode equilibrium. The purpose of this work is to explore how the changes of edge magnetic topology due to implementation of SF geometry will affect P-B mode instabilities. The results are: (1) Linear P-B mode behaviors are greatly affected by magnetic shear at outer middle plane. The growth rate in SF geometry is larger due to the smaller local magnetic shear. (2)Due to the smaller local shear, global mode structures are more strongly ballooning (more radially extended yet less poloidally extended) in SF geometry for moderate toroidal mode numbers. (3) Diamagnetic drift provides stabilizing effects on P-B mode in SF geometry, but not in SD geometry.\\[4pt] [1] M.Kotschenreuther et al., 2004 IAEAFEC. IC/P6-43\\[0pt] [2] D.D. Ryutov, PHYSICS OF PLASMAS 14, 064502 (2007) [Preview Abstract] |
Thursday, November 14, 2013 4:40PM - 5:00PM |
UM9.00009: Development of PIC-Fluid hybrid scheme for impurity generation and transport in BOUT++ framework Xiaotao Xiao, Xueqiao Xu Impurity generation and transport are an important topic of research in burning plasmas in order to avoid a significant degradation of the fusion capabilities of a reactor device. It is a critical issue for RF experiments due to the phenomenon of rf-enhanced impurity generation. In tokamaks, the impurity transport is usually complicated by the combination of turbulent-driven transport and neoclassical transport, So developing the PIC module in BOUT++ framework, which simulates tokamak edge plasmas using fluid models, will enhance the capability to efficiently simulate both turbulence and neoclassical physics in realistic geometry. The research will be carried out mainly in two steps: a test particle module, in which the orbits is advanced in given background plasma with turbulent electromagnetic field from BOUT++ edge turbulence simulations to yield the spatial distribution of impurities in edge plasmas from given sources at the divertor plates and at the protection limiters near RF antennas; and then a PIC-fluid hybrid module, in which background plasma and the turbulent electromagnetic fields will change with the impurity particle sources. The main issues such as particle weighting and sorting scheme, the communication between the fluid and the PIC parts, are discussed. [Preview Abstract] |
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