Bulletin of the American Physical Society
64th Annual Meeting of the APS Division of Plasma Physics
Volume 67, Number 15
Monday–Friday, October 17–21, 2022; Spokane, Washington
Session NO07: Turbulence and Transport in Toroidal DevicesLive Streamed
|
Hide Abstracts |
Chair: Alessandro Marinoni, MIT Room: 401 ABC |
Wednesday, October 19, 2022 9:30AM - 9:42AM Author not Attending |
NO07.00001: Phase dynamics and locking of large-scale modes in edge plasmas Sara Moradi, Johan Anderson, Matthias Hoelzl, Andres Cathey Turbulence is often characterized by energetic couplings between different scales of a flow. However, in the context of turbulence driven transport, such as the case of magnetically confined fusion plasmas typical flow structures are identified by dominant modes and the global turbulent state is approximated by a superposition of linear contributions (waves in general). These theoretical studies consider the amplitudes of the fluctuating quantities but disregard the dynamics of the phases by using the so-called random-phase approximation (RPA) for which the existence of a Chirikov-like criterion for the onset of wave stochasticity is assumed. |
Wednesday, October 19, 2022 9:42AM - 9:54AM |
NO07.00002: Study of the impact of ion temperature perturbations on the inferences of incremental electron thermal diffusivity Audrey Saltzman, Pablo Rodriguez-Fernandez, Rachel Bielajew, Nathan T Howard, Anne E White In the study of electron perturbative heat transport, electron incremental diffusivity, χince , is often used in validating transport models. Experimental χince are typically inferred by assuming that a perturbation in the electron heat flux only has a dependence on the ∇Te, not ∇Ti (Creely et al., 2016). However, multi-scale simulation work has showed that, in plasmas with very stiff ITG transport, even small changes in ∇Ti can impact the electron heat flux (Howard et al., 2018). We take profiles from an electron-heated L-mode plasma on ASDEX Upgrade as the initial condition in our simulations, and apply perturbations. With the TGLF transport model, we find ∇Ti has a similarly strong effect to ∇Te on the electron heat flux regardless of the direction of propagation for the dominant long-wavelength instability. Work is on-going to use time-dependent, self-consistent transport modeling with TRANSP and ASTRA to test the impact of the ion temperature evolution on calculated χince . We perform scans of the strength of the heat pulses and the plasma conditions to test the regimes in which ignoring the ion channel in the inference of χince is a valid approach. |
Wednesday, October 19, 2022 9:54AM - 10:06AM |
NO07.00003: Zonal flow screening in negative triangularity tokamaks Rameswar Singh, Patrick H Diamond Negative triangularity (NT) discharges exhibit reduced fluctuations and improved confinement, as compared to positive triangularity (PT). Zonal flow shear de-correlates the turbulence eddies. This, in turn, reduces the radial transport and improves confinement. So zonal flow is a natural 'suspect' responsible for improved confinement in NT. Neoclassical screening sets the strength of zonal flow shear for fixed drive and damping. Here, we compare zonal flow screening in PT and NT. Orbit calculations show that the radial excursions of trapped particles are reduced in NT, as compared to PT. Yet surprisingly, the neoclassical dielectric susceptibility actually increases with decreasing triangularity, such that the susceptibility is higher for NT than for PT. This is because the reduction in neoclassical polarization by shrinking the banana width is offset by the increase in neoclassical polarization by the enhancement of trapped fraction for NT. As a result, the zonal flow screening length is actually enhanced for NT, as compared to PT. Hence, the zonal flow residual is smaller for NT than for PT. Results from gyrokinetic simulations support the analytic calculations. This suggests that core transport improvement in NT cannot be attributed to simple elements of zonal flow physics. |
Wednesday, October 19, 2022 10:06AM - 10:18AM |
NO07.00004: Zonal Flow Generation in Gyrokinetic-Ion Electron-Temperature-Gradient Turbulence Simulations Stefan Tirkas, Haotian Chen, Gabriele Merlo, Scott E Parker Understanding nonlinear saturation mechanisms of electron-scale turbulence is important for predicting electron heat transport in tokamak plasmas. In fluid models, the zonal flow generation by electron-temperature-gradient (ETG) turbulence is shown to be much weaker than that of similar ion-scale ITG turbulence. This leads to the expectation of a saturated state that is characterized by radially-elongated streamers at electron gyroradius scales. However, gyrokinetic electron simulations have seen that zonal flow (ZF) modes can contribute to long timescale behavior by breaking up these streamers and leading to less radially-elongated eddies. A weak-turbulence, toroidal, gyrokinetic-electron theory [Haotian Chen et al 2021 Nucl. Fusion 61 066017] has shown that as the ETG spectrum cascades downward, a stronger Navier-Stokes type nonlinearity couples ETG and ZF modes in electron-scale simulations, thus allowing for relevant ZF generation and ETG regulation. Here, we present electron-scale continuum gyrokinetic simulations with both single-mode ETG and full-spectrum ETG results showing strong support of this previous theoretical result. We specifically look at the strength of ZF generation by ETG modes at the intermediate scale between the ion and electron scales, as well as the role of collisionality in affecting the strength of the saturated ETG turbulence. We find that zonal flows driven by intermediate-scale ETG turbulence may be responsible for regulating electron heat-flux transport levels. |
Wednesday, October 19, 2022 10:18AM - 10:30AM |
NO07.00005: Transport prediction using gyrokinetic simulations with in situ quasilinear model Justin Walker, David R Hatch, Gabriele Merlo, Cole D Stephens First-principles, nonlinear solutions of the gyrokinetic equation are computationally expensive, particularly in the high-gradient, strongly-shaped H-mode pedestal. For predictions of transport, quasilinear models have the ability produce results using linear solutions at a fraction of the cost. Typically, these quasilinear models are applied to linear gyrokinetic or gyrofluid simulations post-hoc. In this work, we present the results from an in situ quasilinear model incorporated into the gyrokinetic code GENE as a replacement for the nonlinear coupling term in initial value calculations. We envision two major applications: (1) global simulations where different instabilities may be active in different regions of the radial domain, and (2) scenarios where many unstable modes coexist, for example, some stellarator scenarios. |
Wednesday, October 19, 2022 10:30AM - 10:42AM |
NO07.00006: Database study of turbulent electron temperature fluctuation measurements at ASDEX Upgrade Christian Yoo, Rachel Bielajew, Garrard D Conway, Klara Höfler, Pedro Molina Cabrera, Pablo Rodriguez-Fernandez, Branka Vanovac, Anne E White Turbulent transport plays a central role in determining energy and particle confinement times in tokamaks. The correlation electron cyclotron emission (CECE) diagnostic installed on the ASDEX Upgrade (AUG) tokamak measures broadband, long-wavelength (kθρs ≤ 0.3) electron temperature fluctuations, yielding insight into turbulence-driven transport. In this work, an automated method for the analysis of CECE data is being applied to thousands of discharges at AUG in order to build a large-scale experimental turbulence database. The database provides a unique opportunity to search for large-scale trends in turbulent electron temperature fluctuation levels over a wide range of parameter space and allows for direct comparisons with cutting-edge numerical models. The database is used to investigate the physics of tokamak plasma turbulence, including studying the effects of collisionality and gradients on the turbulence measured by the CECE diagnostic. |
Wednesday, October 19, 2022 10:42AM - 10:54AM |
NO07.00007: Confinement in Mixed Isotope Plasmas with Constant ELM Frequency in JET-ILW Damian B King, Eleonora Viezzer, Matteo Baruzzo, Elena De La Luna, Jeronimo Garcia Olaya, Ephrem Delabie, Wojech Gromelski, rafael henriques, Jon C Hillesheim, Laszlo Horvath, Krassimir Kirov, Morten Lennholm, Costanza F Maggi, Mikhail Maslov, Ash Patel, Philip A Schneider, Ridhima Sharma, Tom Wilson Over recent years a series of dedicated experiments have been performed on JET to study the effect of plasma isotope on plasma parameters in an ITER-like wall. These experiments have included plasmas with a single main isotope of H, D or T and mixtures such as HD, HT and ultimately DT. The effective mass of the plasma can have several different effects on plasma parameters e.g., confinement, L-H transition power and ELM frequency. |
Wednesday, October 19, 2022 10:54AM - 11:06AM |
NO07.00008: Insights on divertor turbulence from first-principle modelling and comparison with experiments Diego Sales de Oliveira, Davide Galassi, Christian Theiler, Nicola Offeddu, Curdin Wuthrich, Kyungtak Lim, Davide Mancini, Paolo Ricci, Yinghan Wang, Claudia Colandrea, Sophie Gorno, Kenneth Lee, Holger Reimerdes, Cedric K Tsui The effect of turbulence in broadening the target heat flux profile and its precise contribution to the power exhaustion handling in tokamak plasmas are not fully understood. Previous studies have shown that fluctuations, fluxes, and scale lengths in the scrape-off layer are strongly influenced by field-aligned filaments (or blobs) [1]. Recently, the validation of the first full-size 3D edge turbulence simulations of a diverted TCV plasma revealed considerable discrepancies in the divertor and at the targets in comparison to the experiments [2]. In particular, the absence of divertor-localized blobs, small circular structures observed by Gas Puffing Imaging along the divertor leg for sufficiently high values of plasma current and which, according to simplified estimates, contribute significantly to target profile broadening [3]. In this contribution, we present progress on the understanding of turbulent transport around the X-point and in the divertor region using simulations carried out with GBS, a 3D flux-driven, global, two-fluid turbulence code including a kinetic equation for neutrals [4], and comparisons with experiments. By performing a plasma current scan with the simulations, we address the condition for the formation of divertor-localized blobs and quantify the contribution of divertor turbulence on the cross-field transport. These results are compared with high-resolution measurements across the divertor of similar plasmas in TCV provided by the X-point GPI system [3] and a reciprocating divertor probe array [5]. |
Wednesday, October 19, 2022 11:06AM - 11:18AM |
NO07.00009: Energy transfer of trapped electron turbulence in tokamak fusion plasmas Lei Qi The first principle gyrokinetic simulations[1,2,3] of trapped electron turbulence in tokamak fusion plasmas demonstrate the energy transfers from the most linearly unstable modes at high to intermediate via parametric decay process in a short period of linear-nonlinear transition phase. Dominant nonlinear wave-wave interactions occur near the mode rational surface . In fully nonlinear turbulence, inverse energy cascade occurs between a cutoff wave number and with a power law scaling , while modes with are suppressed. The numerical findings show fair agreement with both the weak turbulence theory[4,5] and realistic experiments on Tore Supra tokamak[6]. |
Wednesday, October 19, 2022 11:18AM - 11:30AM |
NO07.00010: Turbulence and Transport in Negative and Positive Triangularity M.J. Pueschel, J.M. Duff, J. Ball, S. Coda Triangularity δ is investigated via gyrokinetic simulations of ion-temperature-gradient-driven (ITG) modes. Large negative δ < −0.5 leads to a reduction in growth, as local magnetic shear dis-aligns modes from the region of bad curvature. At large positive δ > 0.5, the local shear forces the mode to finite radial wavenumber, reducing transport efficacy. This is confirmed by nonlinear simulations, which show that while zonal flows are stronger at δ > 0, their impact is comparable regardless of δ sign due to higher saturation efficiency at δ < 0. Analysis of extreme-δ experiments on TCV with δ ≈ ±0.6 shows to which degree such desirable effects can be achieved in experiment, and which properties apply to trapped-electron-mode (TEM) turbulence. |
Wednesday, October 19, 2022 11:30AM - 11:42AM |
NO07.00011: Core Turbulence and Transport Dependence on Isotope Mass in Dimensionally Similar H-Mode Plasmas on DIII-D George R McKee, Kathreen E Thome, Zheng Yan, Kshitish Kumar Barada, Darin R Ernst, Nathan T Howard, Tomas Odstrcil, Tom Osborne, Terry L Rhodes, Lothar Schmitz The global energy confinement time is approximately 80% higher in low-rotation H-mode Deuterium (D) plasmas compared with dimensionally similar Hydrogen (H) plasmas, indicating an isotopic dependence that significantly exceeds that in the empirical scaling relation, τE~M0.19. Correspondingly, both electron and ion thermal diffusivity are nearly twice as high in H than D across much of the radius. Long-wavelength (ion-gyroscale) turbulence characteristic differences may partially explain the large transport differences. Spatiotemporal measurements of long-wavelength density fluctuations obtained with BES demonstrate the surprising result that the turbulence amplitude is lower in H than in D plasmas, in contrast to the higher transport, however other characteristics are consistent with higher transport. The turbulence radial correlation lengths are larger in the H-plasma (2.5 cm) compared to D (1.5 cm), consistent with larger turbulent step size, and the H and D wavenumber spectra differ, suggesting different turbulence modes. Comparisons with gyrokinetic simulations will be performed to identify underlying mechanisms for the isotope dependence, and implications for D-T plasmas in ITER. |
Wednesday, October 19, 2022 11:42AM - 11:54AM |
NO07.00012: TJ-II observations of nonlinear wave-wave coupling in play during Alfven-Eigenmode:Turbulence:Zonal-Flow interactions Mark E Koepke, Filip Papoušek, Marion Ochando, Carlos Hidalgo, Boudewijn van Milligen, Gregory Riggs TJ-II Flexible Heliac, a stellarator, has a major radius of 1.5 m, averaged minor radius 0.2 m, B field of 1 T, and a high degree of configuration flexibility (rotational transform spans 0.9 to 2.5). Time series of probe signals are presented from 11 TJ-II shots fueled by neutral-beam injection (NBI). Typical parameters for both electrons and ions are density = 10^19 m^-3 and core temperatures are Te = 300 eV and Ti = Te/2. Energetic ions, seeded by NBI, resonate at a given Alfven eigenmodes (AE) frequency and toroidal Alfven eigenmode (TAE) activity arises. One probe, from one Langmuir probe array, and 8 radially incremented probes, from a second array, measure floating potential at separate toroidal and poloidal positions. We observe, analyze (by the bispectrum), and confirm nonlinear, incommensurate-frequency, wave-wave coupling signatures and document the cross-bi-phase between AE (200kHz) and broadband turbulence (20kHz) on TJ-II in terms of the interaction's role in establishing Long-Range Correlations and in generating zonal flows in fusion-relevant plasma. No other fusion-relevant facility can simultaneously examine these issues. These results lead us to hypothesize that interactions between coexisting zonal flow and broadband turbulence may rely on AE dynamics. |
Wednesday, October 19, 2022 11:54AM - 12:06PM |
NO07.00013: Preceding propagation of turbulence pulses at heat avalanche events Naoki Kenmochi, Katsumi Ida, Tokihiko Tokuzawa, Ryo Yasuhara, Hisamichi Funaba, Hiyori Uehara, Daniel J Den Hartog, Ichihiro Yamada, Mikiro Yoshinuma, Yuki Takemura, Hiroe Igami Plasma transport cannot be explained only by local models, and non-local transport effects must be considered. In this study, the Large Helical Device (LHD) is used to clarify the spatio-temporal characteristics of avalanche and turbulence spreading phenomena, which have been identified as a cause of non-local transport. An electron internal transport barrier (e-ITB) collapse phenomenon is targeted to induce large observable turbulence spreading phenomena. In the LHD, when thermal avalanche phenomena accompanying the collapse of the e-ITB occur, both turbulence and thermal pulses are generated near the foot of the e-ITB and propagate to the peripheral region faster than the diffusion time, but the propagation speed of turbulence pulses is about 10 km/s, which is faster than that of thermal pulses, which is about 1.5 km/s. Existing models estimate that both heat and turbulence propagate at a speed of about 1 km/s, but the turbulence pulse propagates more than an order of magnitude faster than this prediction.The results of this study indicate the existence of a phenomenon that cannot be explained by existing models, namely, the simultaneous propagation of avalanches and turbulence, and provide important insight into the physical mechanism of non-local transport. |
Wednesday, October 19, 2022 12:06PM - 12:18PM |
NO07.00014: A statistical approach to investigate plasma dynamics in gyrokinetic simulations of stellarator turbulence Johan Anderson, Aristeidis D Papadopoulos Turbulent dynamics in stellarator plasmas is investigated by a geometrical method. Gyrokinetic simulations of ITG mode driven turbulence in the core-region of the stellarator W7-X, with realistic quasiisodynamic topologies using the GENE software are considered. The turbulent states are approximated by probability distribution functions where distances between thermodynamic states can be computed according the thermodynamic length methodology which allows the use of a Riemannian metric on the phase space. The geometric methodology is suitable in order to understand stochastic processes involved in e.g. order-disorder transition, where a sudden increase in distance is expected. In gyrokinetic plasma turbulence simulations avalanches, e.g. of heat and particles, are often found and in this work this novel method for detection is investigated. Previously [1,2] 1D versions have been investigated however this falls short in identification of coherent modes. The Hurst exponent, the Information Length and the Dynamic Time is computed from the 2D time series. Based on these measures the transport features of large scale modes can be investigated, identified by a sudden increase in information. |
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