Bulletin of the American Physical Society
63rd Annual Meeting of the APS Division of Plasma Physics
Volume 66, Number 13
Monday–Friday, November 8–12, 2021; Pittsburgh, PA
Session ZO08: MFE: Turbulence and Transport IIOn Demand
|
Hide Abstracts |
Chair: Chris Holland, University of California - San Diego Room: Rooms 317-318 |
Friday, November 12, 2021 9:30AM - 9:42AM |
ZO08.00001: The role of passing electrons in long-wavelength electrostatic instabilities in the small electron-to-ion mass ratio limit Michael Hardman, Felix I Parra, Ching Chong, Toby Adkins, Michail Anastopoulos-Tzanis, Michael Barnes, David Dickinson, Jason F Parisi, Howard R Wilson Microinstabilities with binormal wavenumbers at scales of the ion gyroradius evolve with frequencies comparable to the ion transit frequency. Passing electrons are often assumed to play a negligible role in long-wavelength modes: it is argued that the rapid free streaming of electrons along magnetic field lines leads to an adiabatic passing electron response in the limit of small electron-to-ion mass ratio. However, gyrokinetic simulations of electrostatic1,2 and electromagnetic3 (micro-tearing) modes reveal that the passing electron response can drive instability. The small electron-to-ion mass ratio limit of electrostatic gyrokinetics is obtained, revealing a novel branch of electrostatic modes driven purely by the passing electron response in narrow layers near rational flux surfaces. The width of the layer is set by electron free streaming, finite Larmor radius and finite orbit width physics in the collisionless regime, and by a balance of perpendicular and parallel diffusion in the collisional regime. Scaling predictions are compared to numerical simulations with favourable results for the theory. Finally, the extension of the theory to the electromagnetic case is considered, with possible relevance for the description of micro-tearing modes. |
Friday, November 12, 2021 9:42AM - 9:54AM |
ZO08.00002: Assessing Zonal-Flow Impact in Turbulence Simulations MJ Pueschel, J.M. Duff, Benjamin Faber Zonal flows saturate turbulence, lower transport levels, and are ubiquitous in fusion plasmas. Common non-invasive methods of determining zonal-flows importance in a nonlinear simulations are a visual inspection of contours in the perpendicular plane or an evaluation of the shearing rate. It will be discussed how these approaches can fail to answer the question of zonal-flow impact correctly. Direct evaluation of nonlinear energy transfer and the evaluation of transfer efficiency via triplet correlation times provide more reliable results. |
Friday, November 12, 2021 9:54AM - 10:06AM |
ZO08.00003: Spectrally accurate global-local gyrokinetic simulations of turbulence in tokamak plasmas Denis A St-Onge, Felix I Parra, Michael Barnes We develop a novel approach to gyrokinetics where multiple flux-tube simulations are coupled together in a way that consistently incorporates global profile variation while allowing the use of Fourier basis functions, thus retaining spectral accuracy. By doing so, the need for Dirichlet boundary conditions typically employed in global simulation, where fluctuations are zeroed at the radial boundaries, is obviated. This results in a smooth convergence to the local periodic limit as ρ∗ → 0. In addition, our scale-separated approach allows the use of transport-averaged sources and sinks, offering a more physically motivated alternative to the standard sources based on Krook-type operators. Having implemented this approach in the flux-tube code stella, we study the role of transport barriers and avalanche formation in the transition region between the quiescent core and the turbulent pedestal, as well as the efficacy of intrinsic momentum generation by radial profile variation. Finally, we investigate the role of zonal flows in mitigating the effects of turbulence spreading, and determine whether the Dimits shift can persist in a global setting. |
Friday, November 12, 2021 10:06AM - 10:18AM |
ZO08.00004: Comparing reduced delta-f and direct total-f gyrokinetic models in view of their core-edge coupling with the XGC code Pallavi Trivedi, Julien Dominski, Seung Hoe Ku, Choongseok Chang The High-Fidelity Whole Device Modeling (WDM) project aims to model the whole device of tokamaks with core-edge coupled gyrokinetic simulation models [wdmapp.pppl.gov]. The coupling of core reduced delta-f and edge total-f gyrokinetic models could enable a significant speed-up of the whole device modeling simulations. Thus, it is interesting to compare these models in the core plasma and in the edge pedestal, in view of their coupling. Both of these models differ mainly due to presence of the zeroth order term in the right hand side of the total-f gyrokinetic equation. This zeroth order term is responsible for driving a radial electric field associated with GAM-like oscillations. To investigate the coupling of these models, the subsequent expensive gyrokinetic 3D turbulence simulations have been performed starting from an already saturated gyrokinetic axisymmetric equilibria (collisions are not included). This work has also been extended to couple different axisymmetric and turbulent models available in XGC. It is shown that the radial electric field and its drive have to be taken care of consistently while coupling different models together. Furthermore, a comparison of reduced delta-f and total-f models with the heat source has also been discussed, by running gradient-driven and flux-driven simulations. |
Friday, November 12, 2021 10:18AM - 10:30AM |
ZO08.00005: Plasma profile and magnetic topology self-organization with total-f gyrokinetic KBM turbulence Choongseok Chang, Robert Hager, Seung-Hoe Ku Kinetic ballooning modes (KBMs) in the first stability regime may set the upper bound of plasma performance in a fusion reactor and needs to be understood at kinetic level. The total-f electromagnetic gyrokinetic code XGC is used to study for the first time how the plasma profile evolves to self-organize with the KBM saturation. The self-organization involves magnetic reconnection and island formation around the mode rational surfaces, and neoclassical and zonal flows. Unlike in a reduced delta-f simulation, the total-f growth rates of KBMs are abated to be much smaller than the linear growth rates due to rapid "giving-in" of the plasma slope around the mode rational surfaces. The saturated radial transport fluxes are found to be not much greater than those from ITG/TEM turbulence. Modification of the magnetic surface topology around the mode rational surfaces caused by KBMs could affect other important physics, such as the energetic particle instability and confinement. |
Friday, November 12, 2021 10:30AM - 10:54AM |
ZO08.00006: Kinetic Ballooning Mode turbulence in low-average-magnetic-shear equilibria Ian J McKinney, MJ Pueschel, Chris C Hegna, Benjamin Faber, Akihiro Ishizawa, Paul W Terry Optimizing for turbulent transport in high-β stellarators requires understanding of electromagnetic (EM) turbulence in 3D magnetic geometries. In this work, we report studies of kinetic ballooning mode (KBM) turbulence in low-average-magnetic-shear (s) equilibria, namely HSX, Heliotron-J, and a circular tokamak. EM flux-tube simulations of HSX using the gyrokinetic code GENE show that the onset of KBM instability at low ky occurs at a value of normalized plasma pressure βKBM that is nearly an order of magnitude smaller than the MHD ballooning limit βMHD. Both Heliotron-J and a low-s tokamak exhibit behavior similar to HSX with respect to βKBM. Regardless, saturation of nonlinear simulations of HSX with βKBM<β<βMHD is achievable and results in lower heat fluxes than the electrostatic case, even though KBMs contribute significantly to the nonlinear state. |
Friday, November 12, 2021 10:54AM - 11:06AM |
ZO08.00007: TEM turbulence in simulation and experiment in the HSX stellarator Jason Smoniewski, Gavin M Weir, MJ Pueschel, Joseph N Talmadge, Benjamin Faber, Ian J McKinney, Konstantin M Likin, David T Anderson The geometric flexibility of stellarator experiments offers an opportunity to optimize the magnetic field for reduced turbulent transport. The reliability of such optimization depends on the ability of simulations to accurately predict turbulence in existing devices, and few validation studies have been performed for the stellarator. Here, the first comparison of experimental measurements to nonlinear simulations of the TEM at experimental parameters in a stellarator is presented. The magnetic-field flexibility of the Helically Symmetric eXperiment is exploited to investigate Trapped Electron Mode (TEM) turbulence in quasi-helically symmetric (QHS) and degraded-symmetry (Mirror) configurations. The experimental heat flux shows that anomalous transport is larger in the Mirror configuration at the mid-radius when temperature and density profiles are matched. While linear growth rates are not predictive of overall turbulence, general aspects of experimental transport are captured by nonlinear simulations. The heat flux and density fluctuation amplitude in simulation reproduce a stronger dependence on the density gradient, and the simulated heat flux matches measurements within experimental uncertainties. This confirms that ▽n-driven TEM turbulence is the dominant source of anomalous transport in HSX. |
Friday, November 12, 2021 11:06AM - 11:18AM Not Participating |
ZO08.00008: Effect of MHD on Gas Puff Induced Cold Pulse Propagation in ADITYA-U Tokamak Tanmay Macwan, Suman Dolui, Kaushlender Singh, Ankit Kumar, Joydeep Ghosh, Rakesh Tanna, Suman Aich, Rohit Kumar, Kumarpalsinh A Jadeja, Kaushal M Patel, Umesh Nagora, Kirankumar Patel, Malay B Chowdhuri, Ranjana Manchanda, Shishir Purohit, Sameer Kumar, Raju Daniel, Manoj Gupta, Surya Pathak, Abhijit Sen Cold pulse propagation has been recently studied and characterized with short gas puff of fuel H2 gas in ADITYA-U tokamak, each gas puff injecting ~ 1017-1018 molecules. The edge temperature shows a sharp decrease while the core temperature increases promptly, faster than energy confinement time. The occurrence of the cold pulse is preceded by an even faster rise in the chord averaged density. The increase in the density is attributed to an increase in the inward pinch velocity and a decrease in the ion obit loss in ADITYA-U. In this work, the effect of MHD modes on the density rise is studied. A parametric study is undertaken with the variation of MHD mode amplitude, chord averaged density, amount of injected neutrals and toroidal magnetic field. The density rise is observed to occur much faster in the presence of significant MHD activity. The study has relevance to the overall fueling efficiency in presence of MHD activity. |
Friday, November 12, 2021 11:18AM - 11:30AM |
ZO08.00009: Explaining the lack of power degradation of the energy confinement in the wide pedestal quiescent H-mode via transport modelling Saeid Houshmandyar, Keith H Burrell, Michael R Halfmoon, Brian A Grierson, Joseph Mcclenaghan, Gary M Staebler, Rongjie Hong, David R Hatch, Lei Zeng, Max E Austin The large Shafranov shift resulting from increased near-zero-torque injected beam power (PNBI) in the wide pedestal quiescent H-mode (WPQH) stabilizes turbulence and enables high-confinement ELM-free plasmas. Compared to the standard QH-mode, WPQH is characterized by formation of a wider and higher pedestal, and strong broadband fluctuations in the pedestal. However, unlike conventional H-modes where the energy confinement time reduces with increasing heating power, WPQH modes do not show power degradation of the energy confinement, posing a riddle. As the PNBI was increased, reduced transport, as well as increased core diamagnetic E×B shear rate are observed, suggesting the formation of an ion internal transport barrier (ITB). In this work, TGLF code was used to predict the ITB and its stability analysis. The energy confinement time calculated from the new constructed equilibria with the modelled profiles show insensitivity to the increased PNBI; these modelled profiles use the TGYRO transport solver with TGLF/TRANSP matched energy fluxes. Linear stability analysis reveals that drift-wave instabilities in the core are stabilized by E×B shear, the Ti/Te ratio and the Shafranov shift; the latter was found to have the strongest effect on the turbulence suppression. |
Friday, November 12, 2021 11:30AM - 11:42AM |
ZO08.00010: Comprehensive experimental turbulence measurements for scale-resolved multichannel gyrokinetic code validation Klara Höfler, Tobias Görler, Tim Happel, Pascale Hennequin, Pedro A Molina Cabrera, Michael G Bergmann, Rachel Bielajew, Garrard D Conway, Pierre David, Rainer Fischer, Antonia Frank, Carsten Lechte, Rachael M McDermott, Philip A Schneider, Ulrich Stroth, Anne E White, the ASDEX Upgrade Team Turbulence is the main driver of heat transport which deteriorates the performance of fusion reactors. To design turbulence optimised devices, simulation codes need to be validated by experiments. Validation work has already been done for a single or a small number of turbulence parameters, showing agreement but also highlighting areas where disagreement helps point to new physics discoveries. |
Friday, November 12, 2021 11:42AM - 11:54AM |
ZO08.00011: A 2D gyrofluid model for coupled toroidal ITG/ETG multiscale turbulence and its comparison to gyrokinetics Manaure Francisquez, Darin R Ernst, Daniel R Reynolds, Cody J Balos To study cross-scale interactions and provide a practical test-bed for multi-rate and multi-scale algorithms, we have formulated a reduced 2D toroidal nonlinear gyrofluid model with full FLR effects via Bessel functions. A modified Poisson equation simulates the electron response at both ion and electron scales. These equations are implemented in a pseudo-spectral code with adaptive additive multi-rate Runge-Kutta time integration using the ARKODE[1] library, providing more robust time integration than a naive CFL-constrained RK stepper, with specified accuracy and IMEX hyperviscosity. Toroidal ITG mode linear growth rates are very close to 2D GENE gyrokinetic results for Cyclone-like parameters. Unlike Hasegawa-Mima like models, toroidal ITG and ETG modes are simultaneously unstable. Nonlinear simulations using this reduced model also closely match GENE toroidal ITG heat fluxes and even its nonlinear critical temperature gradient when using a particular closure. In the parameter regime in which the 2D approximation is justified, zonal flows are very strong. Multi-scale simulations are presented, qualitatively comparing 2D phenomena to published 3D results. |
Friday, November 12, 2021 11:54AM - 12:06PM |
ZO08.00012: Effect of turbulence on the neoclassical momentum fluxes Javier Maurino, Felix I Parra Díaz Although the origin of the phenomenon is not fully understood, several experimental tokamak plasmas have been observed to rotate toroidally without any external input of parallel (i.e. approximately toroidal) momentum. This self-induced rotation can bring positive aspects to the tokamak design, such as the stabilisation of MHD tearing modes or the generation of an intrinsic current. |
Friday, November 12, 2021 12:06PM - 12:18PM |
ZO08.00013: A Learned Fluid Closure for Phase Mixing Applied to a Turbulent Gradient-Driven Gyrokinetic System in Simple Geometry Akash Shukla, David R Hatch, Craig Michoski, William D Dorland We present a new method for formulating closures that learn from kinetic simulation data. We apply this method to phase mixing in a simple gyrokinetic turbulent system - temperature gradient driven turbulence in an unsheared slab. The closure is motivated by the observation that in a turbulent system the nonlinearity continually perturbs the system away from the linear solution, thus demanding versatility in the closure scheme. The closure, called the learned multi-mode (LMM) closure, is constructed by, first, extracting an optimal basis from a nonlinear kinetic simulation using singular value decomposition (SVD). Subsequent nonlinear fluid simulations are projected onto this basis and the results are used to formulate the closure. We compare the closure with several other closures schemes over a broad range of the relevant 2D parameter space (collisionality and gradient drive). We find that the turbulent kinetic system produces phase mixing rates much lower than the linear expectations. In contrast with the other closures, the LMM closure is able to capture this reduction. In comparisons of heat fluxes, the LMM closure exhibits errors substantially lower than the other closures. |
Friday, November 12, 2021 12:18PM - 12:30PM |
ZO08.00014: Polarization and magnetization laws in collisional and turbulent transport processes Hideo Sugama, Seikichi Matsuoka, Masanori Nunami Global simulations of collisional and turbulent plasma transport are now vigorously conducted based on gyrokinetic equations using the gyrocenter coordinates that are derived from the Lie transformation method. Such gyrokinetic equations possess conservation properties which are suitable for global and long-time transport simulations. It is well-known that the finite distance between particle and gyrocenter positions generates so-called polarization and magnetization laws, which relate the density and mean velocity of particles to those of gyrocenters, respectively. These relations are important for using gyrokinetic simulation results to correctly evaluate particle transport as well as to accurately calculate the charge density and the electric current in Poisson and Ampère equations which are required to self-consistently determine electromagnetic fields in the simulation. In the present study, expressions of polarization and magnetization laws including effects of collisions and gyroradius scale electromagnetic turbulence are presented. It is shown that collisional effects appear in the magnetization law as an additional term representing the classical particle flux of second order in the normalized gyroradius parameter which becomes influential in transport time scale. The turbulent parts of Poisson and Ampère equations obtained here are verified to agree with the gyrokinetic Poisson and Ampère equations derived in earlier works using the WKB representation. |
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