Bulletin of the American Physical Society
60th Annual Meeting of the APS Division of Plasma Physics
Volume 63, Number 11
Monday–Friday, November 5–9, 2018; Portland, Oregon
Session PI2: Turbulent Transport |
Hide Abstracts |
Chair: Saskia Mordijck, College of William & Mary Room: OCC Oregon Ballroom 203 |
Wednesday, November 7, 2018 2:00PM - 2:30PM |
PI2.00001: Predict first: turbulent transport validation within integrated modeling on JET and ASDEX Upgrade Invited Speaker: Clarisse Bourdelle Integrated modelling is extensively carried out on JET and ASDEX Upgrade pulses applying the first-principle-based quasilinear turbulent transport model QuaLiKiz [www.qualikiz.com, Citrin PPCF2017] within JINTRAC [Romanelli PFR2014]. For the first time, the evolution of density, rotation and temperature profiles for electrons and multiple ions (including Tungsten) is modelled within a flux-driven transport code over multiple confinement time along with the self-consistent prediction of the current diffusion, heat sources, radiation and magnetic equilibrium, revealing the complex interactions and multiple nonlinearities at play. Agreement between the predicted profiles and the measured ones is obtained in all channels, including the time evolution of W 2D profiles, for various hybrid and baseline H modes in both JET [Breton NF 2018] and ASDEX Upgrade. The transition between the LOC and the SOC regimes is also reproduced. In JET, the core W accumulation is shown to be reinforced by NBI central particle source and NBI torque. Applying ICRH can prevent W accumulation. The impact of the boundary conditions, at the pedestal top or at the LCFS, is investigated using uncertainties produced by Gaussian process regression techniques. Based on this successful integrated modelling, extrapolations to higher power and longer pulses are carried out to prepare the upcoming JET DT campaign. In ASDEX Upgrade, the modeling is used to assess the impact of neoclassical, turbulent and MHD driven transport on avoidance of central W accumulation. A surrogate model of QuaLiKiz, 4 orders of magnitude faster than the original model, has been produced through a neural network regression of 3x108 flux calculations over 9 input dimensions. Presently, a proof-of-principle 4D version is implemented in the control-oriented fast tokamak simulator RAPTOR for simultaneous heat and particle transport [Felici NF 2018]. |
Wednesday, November 7, 2018 2:30PM - 3:00PM |
PI2.00002: Accounting for Saturation Efficiency in Quasilinear Transport Models Invited Speaker: Garth G Whelan Ion Temperature Gradient instability (ITG) is a major contributor to turbulent transport in tokamaks. Plasma turbulence has numerous linear eigenmodes per wavenumber, most of which are stable. ITG saturates through nonlinear energy transfer involving zonal flows, scattering energy to higher radial wavenumber stable and ustable modes. Finite normalized plasma pressure beta significantly reduces ITG transport. We investigate a modified Cyclone Base Case where quasilinear estimates underpedict the stabilization due to the impact of nonlinear physics. We probe the cause of enhanced stabilization and measure of the importance of stable modes in energy dissipation and transport. At low toroidal wavenumber, stable modes increase energy production relative to the unstable mode by changing phase relations, while they cause energy dissipation at higher wavenumbers. Transport is also enhanced by stable modes at low wavenumber. This does not affect nonlinearly enhanced stabilization however. The transport reduction occurs because nonlinear energy transfer becomes more efficient with beta as the interaction time between modes becomes more resonant. This is measured by the triplet correlation time, given by the difference in frequencies between the unstable mode, stable mode and zonal flow. A quasilinear model scaled with triplet correlation time correctly matches nonlinear transport. We repeat this analysis with parameters from several experimental discharges, including a JET and an ASDEX Upgrade case. Stable mode effects were significantly different in each of them, but only varied significantly with beta for the JET case. In cases where beta did not change stable mode physics, including the triplet correlation lifetime improved transport estimates. |
Wednesday, November 7, 2018 3:00PM - 3:30PM |
PI2.00003: Understanding Cold-Pulse Dynamics in Tokamak Plasmas Using Local Turbulent Transport Models Invited Speaker: Pablo Rodriguez-Fernandez A long-standing enigma in plasma transport has been resolved by the modeling of cold-pulse experiments conducted on the Alcator C-Mod and DIII-D tokamaks with a local turbulent transport model, TGLF-SAT1 [1]. The model is able to capture the full dynamics of cold-pulse experiments, demonstrating that the existence of nonlocal transport phenomena is not necessary for explaining the behavior and time scales of cold-pulse experiments in tokamak plasmas [2]. Observed for more than twenty years, controlled edge cooling of low-density plasmas triggers a core electron temperature increase on time-scales faster than an energy confinement time, which appear to challenge the local transport paradigm encapsulated in electromagnetic drift-wave turbulent transport models. The quasilinear model TGLF-SAT1 includes a new saturation rule, motivated by recently uncovered cross-scale turbulence coupling, that captures the nonlinear upshift (Dimits shift) of the critical gradient, higher stiffness, and enhanced importance of TEM transport, which are important for reproducing the cold pulse dynamics. For Alcator C-Mod laser blow-off (LBO) cold-pulse experiments, TGLF-SAT1 is able to quantitatively capture the prompt onset of the core electron temperature inversion, with a magnitude that is qualitatively consistent with experimental trends, as well as the disappearance of cold pulse dynamics at high-density. New experiments conducted at DIII-D, guided by predictive analysis to identify plasma conditions that should exhibit temperature inversions, and actuated by a new LBO system, confirm the predicted cold pulse regime and provides evidence of fast density perturbation dynamics using a high-resolution profile reflectometer. |
Wednesday, November 7, 2018 3:30PM - 4:00PM |
PI2.00004: Full-F gyrofluid simulation of large-amplitude instabilities, vortices and turbulence Invited Speaker: Alexander Kendl The standard (“delta-f”) method to split dynamical fields into stationary background profiles and small fluctuations is not applicable to large fluctuation levels, as they for example appear in the edge and scrape-off-layer (SOL) region of magnetized fusion plasmas. “Full-F” gyrokinetic models, which avoid this splitting, are presently developed but pose challenges on computability and costs. Gyrofluid models based on full-F gyrokinetics are much less expensive, but still contain (or may approximately model) relevant physics for edge/SOL turbulent transport. This allows detailed numerical investigations into the basic physics of drift instabilities, vortex dynamics, turbulence and flows in magnetized plasmas, and efficient application to coupled edge/SOL turbulent transport studies in tokamaks and stellarators. Recent results obtained in our group illuminate the mechanisms of FLR effects on vortex interactions and vorticity dynamics in drift wave turbulence. Large fluctuations and steep pressure gradients have been shown to affect the evolution of zonal flows and geodesic acoustic modes, and cause symmetry breaking in the propagation of SOL blobs and holes. The transition of character from delta-f to full-F turbulence is analysed by 3D and 2D model scenarios and by detailed coupled computations of tokamak edge/SOL electromagnetic drift wave turbulence. The relevance for interpretation of SOL profiles is discussed. Our approach includes self-consistent interaction of (multiple) isotopic or impurity species with plasma edge turbulence. A more exotic fundamental physics application analyses the impact of instabilities and ion impurities on transport in planned magnetized electron-positron plasma experiments. |
Wednesday, November 7, 2018 4:00PM - 4:30PM |
PI2.00005: On Multi-Scale Interactions Among Microturbulence, Tearing Modes, and Zonal Flows Invited Speaker: Zachary R Williams Analytic theory and gyrokinetic simulations show that turbulence-regulating zonal flows are weakened by radial magnetic field fluctuations as a consequence of particle streaming along radial fields and shorting out cross-flux-surface potential differences. Two prominent sources of radial magnetic field fluctuations are studied here, resonant magnetic perturbations (RMPs) in tokamaks and tearing modes in reversed-field pinches (RFPs). This work focuses on understanding the inherently multi-scale nature of the interplay of microturbulence, zonal flows, and tearing modes and its effect on transport. This interplay is studied with gyrokinetics to model DIII-D tokamak and MST RFP plasmas. An imposed magnetic perturbation that mimics a tearing mode increases the level of trapped-electron-mode turbulence to a level consistent with fluctuation and transport measurements in MST plasmas. This motivated a dedicated experiment on DIII-D to study the impact of varying RMP amplitude on turbulence in inboard-limited L-mode plasmas. Highlights of the theory-experiment comparison are presented. To study the self-consistent multi-scale interaction of the tearing mode physics, nonlinear simulations containing both tearing mode (driven from equilibrium current gradients) and microinstability scales are performed in a slab geometry. The system is characterized by distinct microinstability- and tearing-dominated regimes. Within the microturbulence-dominated phase, the slow tearing mode growth corresponds directly to a decay in zonal flow and a corresponding increase in the electrostatic turbulence amplitudes. For the tearing-dominated regime, we discuss the possibility of gradient-enhanced tearing caused by the microturbulence, as well alterations to saturated island structure. |
Wednesday, November 7, 2018 4:30PM - 5:00PM |
PI2.00006: Theoretical requirements for calculating heavy impurity transport in rotating plasmas Invited Speaker: Jeff Candy Toroidal plasma flow shear is known to have a profound stabilizing effect on drift-wave turbulence and radial transport. In practice, gyrokinetic theory and simulation operate almost exclusively in the weak-rotation limit, retaining only the ExB flow, Coriolis drift and toroidal rotation shear. Proper treatment of sonic rotation, however, requires inclusion of centrifugal effects, which are quadratic in the Mach number. In 1998, Sugama derived a comprehensive formulation of gyrokinetic theory including sonic rotation and associated centrifugal terms valid for general electromagnetic perturbations. We show that implementation of this complete formulation is critical for the study of heavy impurity transport. In particular, turbulent fluxes of tungsten at finite Mach number are heavily modified by the new terms, even though deuterium ions and electrons are mostly unaffected. To this end, we discuss implications for core tungsten accumulation in a reactor, and remark that for realistic tungsten modeling both turbulent and neoclassical transport must be considered. These claims are based on neoclassical NEO simulations together with nonlinear CGYRO simulations, and suggest that tungsten transport calculations with existing reduced transport models may be unreliable. In addition, we discuss a new approach for the implementation of ExB flow shear. This is different than the previous rotation terms and cannot be treated simply or directly in a flux-tube. In the past, ExB shear has been simulated using either non-periodic boundary conditions or with a discontinuous wavenumber shift method. We report on the development of a new algorithm that is continuous and can treat the shear with spectral accuracy. This new method sheds light on recent gyrokinetic code disagreements. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700