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Yang S, Park JK, Jeon Y, Logan NC, Lee J, Hu Q, Lee J, Kim S, Kim J, Lee H, Na YS, Hahm TS, Choi G, Snipes JA, Park G, Ko WH. Tailoring tokamak error fields to control plasma instabilities and transport. Nat Commun 2024; 15:1275. [PMID: 38341448 DOI: 10.1038/s41467-024-45454-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2023] [Accepted: 01/23/2024] [Indexed: 02/12/2024] Open
Abstract
A tokamak relies on the axisymmetric magnetic fields to confine fusion plasmas and aims to deliver sustainable and clean energy. However, misalignments arise inevitably in the tokamak construction, leading to small asymmetries in the magnetic field known as error fields (EFs). The EFs have been a major concern in the tokamak approaches because small EFs, even less than 0.1%, can drive a plasma disruption. Meanwhile, the EFs in the tokamak can be favorably used for controlling plasma instabilities, such as edge-localized modes (ELMs). Here we show an optimization that tailors the EFs to maintain an edge 3D response for ELM control with a minimized core 3D response to avoid plasma disruption and unnecessary confinement degradation. We design and demonstrate such an edge-localized 3D response in the KSTAR facility, benefiting from its unique flexibility to change many degrees of freedom in the 3D coil space for the various fusion plasma regimes. This favorable control of the tokamak EF represents a notable advance for designing intrinsically 3D tokamaks to optimize stability and confinement for next-step fusion reactors.
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Affiliation(s)
- SeongMoo Yang
- Princeton Plasma Physics Laboratory, Princeton, NJ, 08543, USA.
| | - Jong-Kyu Park
- Princeton Plasma Physics Laboratory, Princeton, NJ, 08543, USA
- Department of Nuclear Engineering, Seoul National University, Seoul, 08826, South Korea
| | - YoungMu Jeon
- Korea Institute of Fusion Energy, Daejeon, Republic of Korea
| | | | - Jaehyun Lee
- Korea Institute of Fusion Energy, Daejeon, Republic of Korea
| | - Qiming Hu
- Princeton Plasma Physics Laboratory, Princeton, NJ, 08543, USA
| | - JongHa Lee
- Korea Institute of Fusion Energy, Daejeon, Republic of Korea
| | - SangKyeun Kim
- Princeton Plasma Physics Laboratory, Princeton, NJ, 08543, USA
| | - Jaewook Kim
- Korea Institute of Fusion Energy, Daejeon, Republic of Korea
| | - Hyungho Lee
- Korea Institute of Fusion Energy, Daejeon, Republic of Korea
| | - Yong-Su Na
- Department of Nuclear Engineering, Seoul National University, Seoul, 08826, South Korea
| | - Taik Soo Hahm
- Department of Nuclear Engineering, Seoul National University, Seoul, 08826, South Korea
| | - Gyungjin Choi
- Department of Nuclear Engineering, Seoul National University, Seoul, 08826, South Korea
| | - Joseph A Snipes
- Princeton Plasma Physics Laboratory, Princeton, NJ, 08543, USA
| | - Gunyoung Park
- Korea Institute of Fusion Energy, Daejeon, Republic of Korea
| | - Won-Ha Ko
- Korea Institute of Fusion Energy, Daejeon, Republic of Korea
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Kim EJ, Thiruthummal AA. Stochastic Dynamics of Fusion Low-to-High Confinement Mode (L-H) Transition: Correlation and Causal Analyses Using Information Geometry. ENTROPY (BASEL, SWITZERLAND) 2023; 26:17. [PMID: 38248143 DOI: 10.3390/e26010017] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/20/2023] [Revised: 12/17/2023] [Accepted: 12/20/2023] [Indexed: 01/23/2024]
Abstract
We investigate the stochastic dynamics of the prey-predator model of the Low-to-High confinement mode (L-H) transition in magnetically confined fusion plasmas. By considering stochastic noise in the turbulence and zonal flows as well as constant and time-varying input power Q, we perform multiple stochastic simulations of over a million trajectories using GPU computing. Due to stochastic noise, some trajectories undergo the L-H transition while others do not, leading to a mixture of H-mode and dithering at a given time and/or input power. One of the consequences of this is that H-mode characteristics appear at a smaller input power QQc as a second peak. The coexisting H-mode and dithering near Q=Qc leads to a prominent bimodal PDF with a gradual L-H transition rather than a sudden transition at Q=Qc and uncertainty in the input power. Also, a time-dependent input power leads to increased variability (dispersion) in stochastic trajectories and a more prominent bimodal PDF. We provide an interpretation of the results using information geometry to elucidate self-regulation between zonal flows, turbulence, and information causality rate to unravel causal relations involved in the L-H transition.
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Affiliation(s)
- Eun-Jin Kim
- Centre for Fluids and Complex Systems, Coventry University, Coventry CV1 2TT, UK
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3
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Hollerbach R, Kim EJ. Effects of Stochastic Noises on Limit-Cycle Oscillations and Power Losses in Fusion Plasmas and Information Geometry. ENTROPY (BASEL, SWITZERLAND) 2023; 25:e25040664. [PMID: 37190453 PMCID: PMC10137813 DOI: 10.3390/e25040664] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/22/2023] [Revised: 04/01/2023] [Accepted: 04/13/2023] [Indexed: 05/17/2023]
Abstract
We investigate the effects of different stochastic noises on the dynamics of the edge-localised modes (ELMs) in magnetically confined fusion plasmas by using a time-dependent PDF method, path-dependent information geometry (information rate, information length), and entropy-related measures (entropy production, mutual information). The oscillation quenching occurs due to either stochastic particle or magnetic perturbations, although particle perturbation is more effective in this amplitude diminishment compared with magnetic perturbations. On the other hand, magnetic perturbations are more effective at altering the oscillation period; the stochastic noise acts to increase the frequency of explosive oscillations (large ELMs) while decreasing the frequency of more regular oscillations (small ELMs). These stochastic noises significantly reduce power and energy losses caused by ELMs and play a key role in reproducing the observed experimental scaling relation of the ELM power loss with the input power. Furthermore, the maximum power loss is closely linked to the maximum entropy production rate, involving irreversible energy dissipation in non-equilibrium. Notably, over one ELM cycle, the information rate appears to keep almost a constant value, indicative of a geodesic. The information rate is also shown to be useful for characterising the statistical properties of ELMs, such as distinguishing between explosive and regular oscillations and the regulation between the pressure gradient and magnetic fluctuations.
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Affiliation(s)
- Rainer Hollerbach
- Department of Applied Mathematics, University of Leeds, Leeds LS2 9JT, UK
| | - Eun-Jin Kim
- Centre for Fluid and Complex Systems, Coventry University, Priory St, Coventry CV1 5FB, UK
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Yan Z, McKee GR, Schmitz L, Gohil P, Haskey S. Turbulence characteristics and flow dynamics impacts on the H-mode transition in favourable magnetic geometry with lower power threshold. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2023; 381:20210240. [PMID: 36587824 DOI: 10.1098/rsta.2021.0240] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/14/2022] [Accepted: 11/02/2022] [Indexed: 06/17/2023]
Abstract
The L-H transition power threshold (PLH) in favourable magnetic geometry (ion ∇B drift pointing towards X-point) is much lower than in the unfavourable magnetic geometry (ion ∇B drift pointing away from X-point) on multiple tokamaks. In a systematic experiment on DIII-D, the ion ∇B drift direction was changed continuously from the unfavourable to favourable configuration during plasma discharges. During such process, the input neutral beam power was kept constant at a value that was above PLH for favourable configuration, but lower than PLH for unfavourable configuration. Toroidal field and plasma current were also kept constant and there was little change in the edge electron density ne and electron temperature Te profiles. The density fluctuation amplitude was reduced approaching the transition, while a large increase of turbulence Reynolds stress and flow shear were simultaneously observed. The turbulence decorrelation rate was found to increase as the ion ∇B drift direction was moving towards the favourable configuration, but the flow shear also increased and exceeded the turbulence decorrelation rate. These measurements demonstrate an important correlation between turbulence and turbulence-driven flow and a lowering of PLH, provide insights into the underlyingphysics behind the hidden parameters and inform a more complete physics-based model of the L-H transition power threshold. This article is part of a discussion meeting issue 'H-mode transition and pedestal studies in fusion plasmas'.
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Affiliation(s)
- Z Yan
- Department of Engineering Physics, University of Wisconsin - Madison, Madison, WI 53706, USA
| | - G R McKee
- Department of Engineering Physics, University of Wisconsin - Madison, Madison, WI 53706, USA
| | - L Schmitz
- Department of Physics and Astronomy, University of California - Los Angeles, Los Angeles, CA 90095, USA
| | - P Gohil
- General Atomics, San Diego, CA 92121, USA
| | - S Haskey
- Princeton Plasma Physics Laboratory, Princeton, NJ 08536, USA
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Diamond PH, Singh R, Long T, Hong R, Ke R, Yan Z, Cao M, Tynan GR. How the birth and death of shear layers determine confinement evolution: from the L → H transition to the density limit. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2023; 381:20210227. [PMID: 36587820 DOI: 10.1098/rsta.2021.0227] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/24/2022] [Accepted: 11/05/2022] [Indexed: 06/17/2023]
Abstract
Electric field profile structure-especially its shear-is a natural order parameter for the edge plasma, and characterizes confinement regimes ranging from the H-mode (Wagner et al. 1982 Phys. Rev. Lett. 49, 1408-1412 (doi:10.1103/PhysRevLett.49.1408)) to the density limit (DL) (Greenwald et al. 1988 Nucl. Fusion 28, 2199-2207 (doi:10.1088/0029-5515/28/12/009)). The theoretical developments and lessons learned during 40 years of H-mode studies (Connor & Wilson 1999 Plasma Phys. Control. Fusion 42, R1-R74 (doi:10.1088/0741-3335/42/1/201); Wagner 2007 Plasma Phys. Control. Fusion 49, B1-B33 (doi:10.1088/0741-3335/49/12b/s01)) are applied to the shear layer collapse paradigm (Hong et al. 2017 Nucl. Fusion 58, 016041 (doi:10.1088/1741-4326/aa9626)) for the onset of DL phenomena. Results from recent experiments on edge shear layers and DL phenomenology are summarized and discussed in the light of L [Formula: see text] H transition physics. The theory of shear layer collapse is then developed. We demonstrate that shear layer physics captures both the well known current (Greenwald) scaling of the DL (Greenwald 2002 Plasma Phys. Control. Fusion 44, R27-R53 (doi:10.1088/0741-3335/44/8/201); Greenwald et al. 2014 Phys. Plasmas 21, 110501 (doi:10.1063/1.4901920)), as well as the emerging power scaling (Zanca, Sattin, JET Contributors 2019 Nucl. Fusion 59, 126011 (doi:10.1088/1741-4326/ab3b31)). The derivation of the power scaling theory exploits an existing model, originally developed for the L [Formula: see text] H transition (Diamond, Liang, Carreras, Terry 1994 Phys. Rev. Lett. 72, 2565-2568 (doi:10.1103/PhysRevLett.72.2565); Kim & Diamond 2003 Phys. Rev. Lett. 90, 185006 (doi:10.1103/PhysRevLett.90.185006)). We describe the enhanced particle transport events that occur following shear layer collapse. Open problems and future directions are discussed. This article is part of a discussion meeting issue 'H-mode transition and pedestal studies in fusion plasmas'.
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Affiliation(s)
- Patrick H Diamond
- Department of Physics, University of California San Diego, La Jolla, CA, USA
| | - Rameswar Singh
- Department of Physics, University of California San Diego, La Jolla, CA, USA
| | - Ting Long
- Center for Fusion Science, Southwestern Institute of Physics, Chengdu, People's Republic of China
| | - Rongjie Hong
- Department of Physics and Astronomy, University of California Los Angeles, CA, USA
| | - Rui Ke
- Center for Fusion Science, Southwestern Institute of Physics, Chengdu, People's Republic of China
| | - Zheng Yan
- Department of Engineering Physics, University of Wisconsin Madison, Madison, WI, USA
| | - Mingyun Cao
- Department of Physics, University of California San Diego, La Jolla, CA, USA
| | - George R Tynan
- Department of Mechanical and Aerospace Engineering, University of California San Diego, CA, USA
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6
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Schmitz L. Turbulence and E × B flow correlations across the L-H transition in DIII-D deuterium and hydrogen plasmas. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2023; 381:20210237. [PMID: 36587817 DOI: 10.1098/rsta.2021.0237] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/08/2022] [Accepted: 09/26/2022] [Indexed: 06/17/2023]
Abstract
The isotope dependence of the low- to high confinement-mode (L- to H-mode) transition power threshold PLH presents significant challenges for the initial (non-nuclear) hydrogen operations phase of the international thermonuclear experimental reactor (ITER). Here, we examine the isotope dependence of turbulence and E × B flow correlation properties in the L-mode edge plasma, leading up to the L-H transition. At marginal auxiliary power (near PLH), turbulence is initially suppressed periodically during limit cycle oscillations (LCO) that precede the transition to sustained H-mode confinement. We present evidence that the long-range (toroidal) correlation of the E × B edge plasma flow across the LCO phase is much weaker in hydrogen than in deuterium in the DIII-D tokamak, congruent with the higher threshold power PLH required to access LCO and H-mode in hydrogen. Concomitantly, the time required to initially quench edge turbulence via localized edge E × B flow shear is significantly longer in hydrogen (1-1.5 ms) than in deuterium (approx. 100 µs). No toroidal long-range correlation of the turbulence amplitude is observed, in agreement with expectations based on the relatively short poloidal turbulence correlation length. Radial edge turbulence and flow correlation lengths are longer in deuterium than in hydrogen plasmas as one would expect from 'naïve' gyro-Bohm isotope transport scaling, despite the substantially higher thermal flux across the last closed flux surface in hydrogen before the L-H transition. This article is part of a discussion meeting issue 'H-mode transition and pedestal studies in fusion plasmas'.
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Affiliation(s)
- Lothar Schmitz
- Department of Physics and Astronomy, University of California Los Angeles, Los Angeles, CA 90095, USA
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7
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Kim EJ, Hollerbach R. A stochastic model of edge-localized modes in magnetically confined plasmas. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2023; 381:20210226. [PMID: 36587818 DOI: 10.1098/rsta.2021.0226] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/07/2022] [Accepted: 06/24/2022] [Indexed: 06/17/2023]
Abstract
Magnetically confined plasmas are far from equilibrium and pose considerable challenges in statistical analysis. We discuss a non-perturbative statistical method, namely a time-dependent probability density function (PDF) approach that is potentially useful for analysing time-varying, large, or non-Gaussian fluctuations and bursty events associated with instabilities in the low-to-high confinement transition and the H-mode. Specifically, we present a stochastic Langevin model of edge-localized modes (ELMs) by including stochastic noise terms in a previous ODE ELM model. We calculate exact time-dependent PDFs by numerically solving the Fokker-Planck equation and characterize time-varying statistical properties of ELMs for different energy fluxes and noise amplitudes. The stochastic noise is shown to introduce phase-mixing and plays a significant role in mitigating extreme bursts of large ELMs. Furthermore, based on time-dependent PDFs, we provide a path-dependent information geometric theory of the ELM dynamics and demonstrate its utility in capturing self-regulatory relaxation oscillations, bursts and a sudden change in the system. This article is part of a discussion meeting issue 'H-mode transition and pedestal studies in fusion plasmas'.
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Affiliation(s)
- Eun-Jin Kim
- Fluid and Complex System Research Centre, Coventry University, Coventry CV1 2TT, UK
| | - Rainer Hollerbach
- Department of Applied Mathematics, University of Leeds, Leeds LS2 9JT, UK
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8
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Andrew Y, Bland J, Buxton P, Dnestrovskij A, Gryaznevich M, Kim EJ, Romanelli M, Sertoli M, Thomas P, Varje J. H-mode dithering phase studies on ST40. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2023; 381:20210225. [PMID: 36587816 PMCID: PMC9805817 DOI: 10.1098/rsta.2021.0225] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 06/01/2022] [Accepted: 09/28/2022] [Indexed: 06/17/2023]
Abstract
The dithering H-mode phase, characterized by oscillations, is generally observed at input power values close to the L-H transition power threshold and low plasma collisionalities (low electron density and/or high plasma temperature). Measurements to characterize the dithering phase are presented for the low aspect ratio, high magnetic field tokamak, ST40. The dithering phase oscillation frequency is observed between 400 and 800 Hz and demonstrates an inverse relationship with core plasma density. Dithering phase H-modes are documented across a nonlinear, low-density power threshold operational space, with signature low- and high-density branches. The minimum power threshold for dithering H-mode access is measured at a core, line average electron density of 4.7(±0.5) × 1019 m-3, close to a predicted value of 4.1(±0.4) × 1019 m-3 from multi-machine studies. ASTRA calculated values of power coupled to the ion species, at the dithering H-mode transition, exhibit a similar nonlinear dependence on density. This analysis points to the important contribution of the ion thermal channel to the L-H phase transition. The low-frequency plasma density and D-alpha dithers appear to be accompanied by sudden bursts of magnetohydrodynamic (MHD) activity. A simple model is tested to demonstrate a possible scenario of self-regulation among turbulence, zonal flows, pressure (density) gradient and MHD activities. This article is part of a discussion meeting issue 'H-mode transition and pedestal studies in fusion plasmas'.
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Affiliation(s)
- Yasmin Andrew
- Blackett Laboratory, Imperial College London, London SW7 2AZ, UK
| | - James Bland
- Tokamak Energy Ltd., 173 Brook Drive, Milton Park, Abingdon, UK
| | - Peter Buxton
- Tokamak Energy Ltd., 173 Brook Drive, Milton Park, Abingdon, UK
| | | | | | - Eun-jin Kim
- Fluid and Complex System Research Centre, Coventry University, Coventry CV1 2TT, UK
| | | | - Marco Sertoli
- Tokamak Energy Ltd., 173 Brook Drive, Milton Park, Abingdon, UK
| | - Paul Thomas
- Tokamak Energy Ltd., 173 Brook Drive, Milton Park, Abingdon, UK
| | - Jari Varje
- Tokamak Energy Ltd., 173 Brook Drive, Milton Park, Abingdon, UK
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9
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Estrada T, Hidalgo C. H-mode transition in the TJ-II stellarator plasmas. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2023; 381:20210229. [PMID: 36587823 DOI: 10.1098/rsta.2021.0229] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/25/2022] [Accepted: 05/09/2022] [Indexed: 06/17/2023]
Abstract
Since the first H-mode transitions were observed in TJ-II plasmas in 2008, an extensive experimental effort has been done aiming at better physics understanding of confinement transitions. In this article, an overview of the main findings related to the L-H transition in TJ-II is presented including how the radial electric field is driven, what are the possible mechanisms for turbulence suppression and what are the related temporal and spatial scales that can impact the transition. The trigger of the L-H transition in TJ-II plasmas is found to be more correlated with the development of fluctuating [Formula: see text] flows than with steady-state [Formula: see text] effects, pointing to the role played by zonal flows in mediating the transition. Experimental evidence supporting the predator-prey relationship between turbulence and flows as the basis for the L-H transition, found for the first time in TJ-II, reinforces this conclusion. Besides, the reduction in the turbulent transport at the transition is detected at the barrier region but also in a wider radial range with weak or even zero [Formula: see text] flow shear, which points to other mechanisms beyond the turbulence suppression by local sheared flows. This article is part of a discussion meeting issue 'H-mode transition and pedestal studies in fusion plasmas'.
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Affiliation(s)
- Teresa Estrada
- Laboratorio Nacional de Fusión, CIEMAT, 28040 Madrid, Spain
| | - Carlos Hidalgo
- Laboratorio Nacional de Fusión, CIEMAT, 28040 Madrid, Spain
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Rhodes TL, Michael CA, Shi P, Scannell R, Storment S, Pratt Q, Lantsov R, Fitzgerald I, Hall-Chen VH, Crocker NA, Peebles WA. Design elements and first data from a new Doppler backscattering system on the MAST-U spherical tokamak. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2022; 93:113549. [PMID: 36461471 DOI: 10.1063/5.0101848] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/03/2022] [Accepted: 09/25/2022] [Indexed: 06/17/2023]
Abstract
A new Doppler backscattering (DBS) system has been installed and tested on the MAST-U spherical tokamak. It utilizes eight simultaneous fixed frequency probe beams (32.5, 35, 37.5, 40, 42.5, 45, 47.5, and 50 GHz). These frequencies provide a range of radial positions from the edge plasma to the core depending on plasma conditions. The system utilizes a combination of novel features to provide remote control of the probed density wavenumber, the launched polarization (X vs O-mode), and the angle of the launched DBS to match the magnetic field pitch angle. The range of accessible density turbulence wavenumbers (kθ) is reasonably large with normalized wavenumbers kθρs ranging from ≤0.5 to 9 (ion sound gyroradius ρs = 1 cm). This wavenumber range is relevant to a variety of instabilities believed to be important in establishing plasma transport (e.g., ion temperature gradient, trapped electron, electron temperature gradient, micro-tearing, kinetic ballooning modes). The system is specifically designed to address the requirement of density fluctuation wavevector alignment which can significantly reduce the SNR if not accounted for.
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Affiliation(s)
- T L Rhodes
- Physics and Astronomy Department, University of California, Los Angeles, California 90098, USA
| | - C A Michael
- Physics and Astronomy Department, University of California, Los Angeles, California 90098, USA
| | - P Shi
- UKAEA/CCFE, Culham Science Centre, Abingdon, Oxfordshire, OX14 3DB, UK
| | - R Scannell
- UKAEA/CCFE, Culham Science Centre, Abingdon, Oxfordshire, OX14 3DB, UK
| | - S Storment
- Physics and Astronomy Department, University of California, Los Angeles, California 90098, USA
| | - Q Pratt
- Physics and Astronomy Department, University of California, Los Angeles, California 90098, USA
| | - R Lantsov
- Physics and Astronomy Department, University of California, Los Angeles, California 90098, USA
| | - I Fitzgerald
- UKAEA/CCFE, Culham Science Centre, Abingdon, Oxfordshire, OX14 3DB, UK
| | - V H Hall-Chen
- Institute of High Performance Computing, Singapore 138632, Singapore
| | - N A Crocker
- Physics and Astronomy Department, University of California, Los Angeles, California 90098, USA
| | - W A Peebles
- Physics and Astronomy Department, University of California, Los Angeles, California 90098, USA
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11
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Wang Z, Dai Z, Wang S. Nonlinear excitation of zonal flows by turbulent energy flux. Phys Rev E 2022; 106:035205. [PMID: 36266869 DOI: 10.1103/physreve.106.035205] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2022] [Accepted: 08/19/2022] [Indexed: 06/16/2023]
Abstract
The nonlinear excitation of zonal flows (ZFs) generated by the ion-temperature-gradient turbulence in a tokamak plasma is investigated by using the global gyrokinetic code nlt. It is found that ZFs are initially driven by the nonlinear self-interaction of the eigenmode. In the nonlinear saturation, the modulational instability becomes important, and its contribution to ZFs can finally be comparable to that of the self-interaction mechanism. More importantly, both types of nonlinear wave-wave interactions can be well described by the turbulent energy flux model.
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Affiliation(s)
- Zihao Wang
- Department of Engineering and Applied Physics, University of Science and Technology of China, Hefei 230026, China
| | - Zongliang Dai
- Department of Engineering and Applied Physics, University of Science and Technology of China, Hefei 230026, China
| | - Shaojie Wang
- Department of Engineering and Applied Physics, University of Science and Technology of China, Hefei 230026, China
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12
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Carralero D, Happel T, Estrada T, Tokuzawa T, Martínez J, de la Luna E, Cappa A, García J. A feasibility study for a Doppler reflectometer system in the JT-60SA tokamak. FUSION ENGINEERING AND DESIGN 2021. [DOI: 10.1016/j.fusengdes.2021.112803] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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13
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Nishizawa T, Almagri AF, Anderson JK, Goodman W, Pueschel MJ, Nornberg MD, Ohshima S, Sarff JS, Terry PW, Williams ZR. Direct Measurement of a Toroidally Directed Zonal Flow in a Toroidal Plasma. PHYSICAL REVIEW LETTERS 2019; 122:105001. [PMID: 30932630 DOI: 10.1103/physrevlett.122.105001] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/25/2018] [Revised: 02/16/2019] [Indexed: 06/09/2023]
Abstract
Zonal flow appears in toroidal, magnetically confined plasmas as part of the self-regulated interaction of turbulence and transport processes. For toroidal plasmas having a strong toroidal magnetic field, the zonal flow is predominately poloidally directed. This Letter reports the first observation of a zonal flow that is toroidally directed. The measurements are made just inside the last closed flux surface of reversed field pinch plasmas that have a dominant poloidal magnetic field. A limit cycle oscillation between the strength of the zonal flow and the amplitude of plasma potential fluctuations is observed, which provides evidence for the self-regulation characteristic of drift-wave-type plasma turbulence. The measurements help advance understanding and gyrokinetic modeling of toroidal plasmas in the pursuit of fusion energy.
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Affiliation(s)
- T Nishizawa
- Department of Physics, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
| | - A F Almagri
- Department of Physics, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
| | - J K Anderson
- Department of Physics, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
| | - W Goodman
- Electrical Engineering Department, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
| | - M J Pueschel
- Institute for Fusion Studies, University of Texas at Austin, Austin, Texas 78712, USA
| | - M D Nornberg
- Department of Physics, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
| | - S Ohshima
- Institute of Advanced Energy, Kyoto University, Uji, Kyoto 611-0011, Japan
| | - J S Sarff
- Department of Physics, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
| | - P W Terry
- Department of Physics, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
| | - Z R Williams
- Department of Physics, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
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14
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Zoletnik S, Hu GH, Tál B, Dunai D, Anda G, Asztalos O, Pokol GI, Kálvin S, Németh J, Krizsanóczi T. Ultrafast two-dimensional lithium beam emission spectroscopy diagnostic on the EAST tokamak. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2018; 89:063503. [PMID: 29960560 DOI: 10.1063/1.5017224] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
A diagnostic instrument is described for the Experimental Advanced Superconducting Tokamak (EAST) for the measurement of the edge plasma electron density profile and plasma turbulence properties. An accelerated neutral lithium beam is injected into the tokamak and the Doppler shifted 670.8 nm light emission of the Li2p-2s transition is detected. A novel compact setup is used, where the beam injection and observation take place from the same equatorial diagnostic port and radial-poloidal resolution is achieved with microsecond time resolution. The observation direction is optimized in order to achieve a sufficient Doppler shift of the beam light to be able to separate from the strong edge lithium line emission on this lithium coated device. A 250 kHz beam chopping technique is also demonstrated for the removal of background light. First results show the capability of measuring turbulence and its poloidal flow velocity in the scrape-off layer and edge region and the resolution of details of transient phenomena like edge localized modes with few microsecond time resolution.
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Affiliation(s)
- S Zoletnik
- Wigner Research Centre for Physics, Budapest, Hungary
| | - G H Hu
- Institute for Plasma Physics, Chinese Academy of Sciences, Hefei, China
| | - B Tál
- Wigner Research Centre for Physics, Budapest, Hungary
| | - D Dunai
- Wigner Research Centre for Physics, Budapest, Hungary
| | - G Anda
- Wigner Research Centre for Physics, Budapest, Hungary
| | - O Asztalos
- Budapest University of Technology and Economics, Budapest, Hungary
| | - G I Pokol
- Budapest University of Technology and Economics, Budapest, Hungary
| | - S Kálvin
- Wigner Research Centre for Physics, Budapest, Hungary
| | - J Németh
- Wigner Research Centre for Physics, Budapest, Hungary
| | - T Krizsanóczi
- Wigner Research Centre for Physics, Budapest, Hungary
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15
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Barada K, Rhodes TL, Burrell KH, Zeng L, Bardóczi L, Chen X, Muscatello CM, Peebles WA. Quasistationary Plasma Predator-Prey System of Coupled Turbulence, Drive, and Sheared E×B Flow During High Performance DIII-D Tokamak Discharges. PHYSICAL REVIEW LETTERS 2018; 120:135002. [PMID: 29694164 DOI: 10.1103/physrevlett.120.135002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/25/2017] [Indexed: 06/08/2023]
Abstract
A new, long-lived limit cycle oscillation (LCO) regime has been observed in the edge of near zero torque high performance DIII-D tokamak plasma discharges. These LCOs are localized and composed of density turbulence, gradient drives, and E×B velocity shear damping (E and B are the local radial electric and total magnetic fields). Density turbulence sequentially acts as a predator (via turbulence transport) of profile gradients and a prey (via shear suppression) to the E×B velocity shear. Reported here for the first time is a unique spatiotemporal variation of the local E×B velocity, which is found to be essential for the existence of this system. The LCO system is quasistationary, existing from 3 to 12 plasma energy confinement times (∼30-900 LCO cycles) limited by hardware constraints. This plasma system appears to contribute strongly to the edge transport in these high performance and transient-free plasmas, as evident from oscillations in transport relevant edge parameters at LCO time scale.
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Affiliation(s)
- K Barada
- Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA
| | - T L Rhodes
- Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA
| | - K H Burrell
- General Atomics, P.O. Box 85608, San Diego, California 92186-5608, USA
| | - L Zeng
- Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA
| | - L Bardóczi
- Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA
| | - Xi Chen
- General Atomics, P.O. Box 85608, San Diego, California 92186-5608, USA
| | - C M Muscatello
- General Atomics, P.O. Box 85608, San Diego, California 92186-5608, USA
| | - W A Peebles
- Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA
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16
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Cziegler I, Hubbard AE, Hughes JW, Terry JL, Tynan GR. Turbulence Nonlinearities Shed Light on Geometric Asymmetry in Tokamak Confinement Transitions. PHYSICAL REVIEW LETTERS 2017; 118:105003. [PMID: 28339277 DOI: 10.1103/physrevlett.118.105003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/01/2016] [Indexed: 06/06/2023]
Abstract
A comprehensive study of fully frequency-resolved nonlinear kinetic energy transfer has been performed for the first time in a diverted tokamak, providing new insight into the parametric dependences of edge turbulence transitions. Measurements using gas puff imaging in the turbulent L-mode state illuminate the source of the long known but as yet unexplained "favorable-unfavorable" geometric asymmetry of the power threshold for transition to the turbulence-suppressed H mode. Results from the recently discovered I mode point to a competition between zonal flow (ZF) and geodesic-acoustic modes (GAM) for turbulent energy, while showing new evidence that the I-to-H transition is still dominated by ZFs. The availability of nonlinear drive for the GAM against net heat flux through the edge corresponds very well to empirical scalings found experimentally for accessing the I mode.
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Affiliation(s)
- I Cziegler
- York Plasma Institute, Department of Physics, University of York, Heslington YO10 5DD, United Kingdom
| | - A E Hubbard
- Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - J W Hughes
- Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - J L Terry
- Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - G R Tynan
- University of California San Diego, La Jolla, California 92093, USA
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17
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Li B, Wang XY, Sun CK, Zhou A, Liu D, Ma CH, Wang XG. Bifurcation and hysteresis of plasma edge transport in a flux-driven system. Phys Rev E 2016; 94:043201. [PMID: 27841586 DOI: 10.1103/physreve.94.043201] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2016] [Indexed: 11/07/2022]
Abstract
Transition dynamics and mean shear flow generation in plasma interchange turbulence are explored in a flux-driven system that resembles the plasma edge region. The nonlinear evolution of the interchange mode shows two confinement regimes with different transport levels. Large amplitude oscillations in the phase space of turbulence intensity and mean flow energy are observed and investigated. Both clockwise and counterclockwise oscillations occur during the transition between the two regimes. The Reynolds stress gradients are shown to play a critical role in the generation of mean sheared flows in the edge region. Both the forward and back transitions are simulated self-consistently and a significant hysteresis is found.
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Affiliation(s)
- B Li
- Fusion Simulation Center, State Key Laboratory of Nuclear Physics and Technology, School of Physics, Peking University, Beijing 100871, China
| | - X Y Wang
- Fusion Simulation Center, State Key Laboratory of Nuclear Physics and Technology, School of Physics, Peking University, Beijing 100871, China
| | - C K Sun
- Fusion Simulation Center, State Key Laboratory of Nuclear Physics and Technology, School of Physics, Peking University, Beijing 100871, China
| | - A Zhou
- Fusion Simulation Center, State Key Laboratory of Nuclear Physics and Technology, School of Physics, Peking University, Beijing 100871, China
| | - D Liu
- Fusion Simulation Center, State Key Laboratory of Nuclear Physics and Technology, School of Physics, Peking University, Beijing 100871, China
| | - C H Ma
- Fusion Simulation Center, State Key Laboratory of Nuclear Physics and Technology, School of Physics, Peking University, Beijing 100871, China
| | - X G Wang
- Department of Physics, Harbin Institute of Technology, Harbin 150001, China
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18
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Kobayashi T, Itoh K, Ido T, Kamiya K, Itoh SI, Miura Y, Nagashima Y, Fujisawa A, Inagaki S, Ida K, Hoshino K. Experimental Identification of Electric Field Excitation Mechanisms in a Structural Transition of Tokamak Plasmas. Sci Rep 2016; 6:30720. [PMID: 27489128 PMCID: PMC4973265 DOI: 10.1038/srep30720] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2015] [Accepted: 07/06/2016] [Indexed: 11/09/2022] Open
Abstract
Self-regulation between structure and turbulence, which is a fundamental process in the complex system, has been widely regarded as one of the central issues in modern physics. A typical example of that in magnetically confined plasmas is the Low confinement mode to High confinement mode (L-H) transition, which is intensely studied for more than thirty years since it provides a confinement improvement necessary for the realization of the fusion reactor. An essential issue in the L-H transition physics is the mechanism of the abrupt "radial" electric field generation in toroidal plasmas. To date, several models for the L-H transition have been proposed but the systematic experimental validation is still challenging. Here we report the systematic and quantitative model validations of the radial electric field excitation mechanism for the first time, using a data set of the turbulence and the radial electric field having a high spatiotemporal resolution. Examining time derivative of Poisson's equation, the sum of the loss-cone loss current and the neoclassical bulk viscosity current is found to behave as the experimentally observed radial current that excites the radial electric field within a few factors of magnitude.
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Affiliation(s)
- T. Kobayashi
- National Institute for Fusion Science, Toki 509-5292, Japan
| | - K. Itoh
- National Institute for Fusion Science, Toki 509-5292, Japan
- Research Center for Plasma Turbulence, Kyushu University, Kasuga 816-8580, Japan
| | - T. Ido
- National Institute for Fusion Science, Toki 509-5292, Japan
| | - K. Kamiya
- National Institutes for Quantum and Radiological Science and Technology, Naka 311-0193, Japan
| | - S.-I. Itoh
- Research Center for Plasma Turbulence, Kyushu University, Kasuga 816-8580, Japan
- Research Institute for Applied Mechanics, Kyushu University, Kasuga 816-8580, Japan
| | - Y. Miura
- Japan Atomic Energy Agency, Tokai 319-1184, Japan
| | - Y. Nagashima
- Research Center for Plasma Turbulence, Kyushu University, Kasuga 816-8580, Japan
- Research Institute for Applied Mechanics, Kyushu University, Kasuga 816-8580, Japan
| | - A. Fujisawa
- Research Center for Plasma Turbulence, Kyushu University, Kasuga 816-8580, Japan
- Research Institute for Applied Mechanics, Kyushu University, Kasuga 816-8580, Japan
| | - S. Inagaki
- Research Center for Plasma Turbulence, Kyushu University, Kasuga 816-8580, Japan
- Research Institute for Applied Mechanics, Kyushu University, Kasuga 816-8580, Japan
| | - K. Ida
- National Institute for Fusion Science, Toki 509-5292, Japan
- Research Center for Plasma Turbulence, Kyushu University, Kasuga 816-8580, Japan
| | - K. Hoshino
- National Institutes for Quantum and Radiological Science and Technology, Naka 311-0193, Japan
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19
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Xu GS, Wan BN, Wang HQ, Guo HY, Naulin V, Rasmussen JJ, Nielsen AH, Wu XQ, Yan N, Chen L, Shao LM, Chen R, Wang L, Zhang W. Low-to-High Confinement Transition Mediated by Turbulence Radial Wave Number Spectral Shift in a Fusion Plasma. PHYSICAL REVIEW LETTERS 2016; 116:095002. [PMID: 26991181 DOI: 10.1103/physrevlett.116.095002] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/22/2014] [Indexed: 06/05/2023]
Abstract
A new model for the low-to-high (L-H) confinement transition has been developed based on a new paradigm for turbulence suppression by velocity shear [G. M. Staebler et al., Phys. Rev. Lett. 110, 055003 (2013)]. The model indicates that the L-H transition can be mediated by a shift in the radial wave number spectrum of turbulence, as evidenced here, for the first time, by the direct observation of a turbulence radial wave number spectral shift and turbulence structure tilting prior to the L-H transition at tokamak edge by direct probing. This new mechanism does not require a pretransition overshoot in the turbulent Reynolds stress, shunting turbulence energy to zonal flows for turbulence suppression as demonstrated in the experiment.
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Affiliation(s)
- G S Xu
- Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031, People's Republic of China
| | - B N Wan
- Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031, People's Republic of China
| | - H Q Wang
- Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031, People's Republic of China
| | - H Y Guo
- Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031, People's Republic of China
- General Atomics, P.O. Box 85608, San Diego, California 92186-5608, USA
| | - V Naulin
- PPFE, Department of Physics, Technical University of Denmark, DK 2800 Kongens Lyngby, Denmark
| | - J Juul Rasmussen
- PPFE, Department of Physics, Technical University of Denmark, DK 2800 Kongens Lyngby, Denmark
| | - A H Nielsen
- PPFE, Department of Physics, Technical University of Denmark, DK 2800 Kongens Lyngby, Denmark
| | - X Q Wu
- Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031, People's Republic of China
| | - N Yan
- Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031, People's Republic of China
- PPFE, Department of Physics, Technical University of Denmark, DK 2800 Kongens Lyngby, Denmark
| | - L Chen
- Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031, People's Republic of China
| | - L M Shao
- Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031, People's Republic of China
| | - R Chen
- Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031, People's Republic of China
| | - L Wang
- Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031, People's Republic of China
| | - W Zhang
- Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031, People's Republic of China
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20
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Hillesheim JC, Delabie E, Meyer H, Maggi CF, Meneses L, Poli E. Stationary Zonal Flows during the Formation of the Edge Transport Barrier in the JET Tokamak. PHYSICAL REVIEW LETTERS 2016; 116:065002. [PMID: 26918997 DOI: 10.1103/physrevlett.116.065002] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/21/2015] [Indexed: 06/05/2023]
Abstract
High spatial resolution Doppler backscattering measurements in JET have enabled new insights into the development of the edge Er. We observe fine-scale spatial structures in the edge Er well with a wave number krρi≈0.4-0.8, consistent with stationary zonal flows, the characteristics of which vary with density. The zonal flow amplitude and wavelength both decrease with local collisionality, such that the zonal flow E×B shear increases. Above the minimum of the L-H transition power threshold dependence on density, the zonal flows are present during L mode and disappear following the H-mode transition, while below the minimum they are reduced below measurable amplitude during L mode, before the L-H transition.
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Affiliation(s)
- J C Hillesheim
- CCFE, Culham Science Centre, Abingdon, Oxon OX14 3DB, United Kingdom
| | - E Delabie
- Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA
| | - H Meyer
- CCFE, Culham Science Centre, Abingdon, Oxon OX14 3DB, United Kingdom
| | - C F Maggi
- CCFE, Culham Science Centre, Abingdon, Oxon OX14 3DB, United Kingdom
| | - L Meneses
- Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal
| | - E Poli
- Max-Planck-institut fur Plasmaphysik, Garching, Germany
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21
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The Dynamics of Core and Outer Micro-turbulence During the L–I–H Confinement Transition on the EAST Superconducting Tokamak. JOURNAL OF FUSION ENERGY 2015. [DOI: 10.1007/s10894-015-9949-9] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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22
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Cao GM, Li YD, Li Q, Zhang XD, Sun PJ, Wu GJ, Hu LQ. The Dynamics of Short-Scale Turbulent Fluctuations During The H–L Back Transition in The EAST Superconducting Tokamak. JOURNAL OF FUSION ENERGY 2015. [DOI: 10.1007/s10894-015-9861-3] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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23
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Bardóczi L, Bencze A, Berta M, Schmitz L. Experimental confirmation of self-regulating turbulence paradigm in two-dimensional spectral condensation. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2014; 90:063103. [PMID: 25615202 DOI: 10.1103/physreve.90.063103] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/13/2013] [Indexed: 06/04/2023]
Abstract
Turbulent transport in magnetic fusion plasmas can be significantly suppressed by Reynolds-stress-induced zonal flows, allowing effective plasma confinement. We present experimental evidence of spatiotemporal correlation between small-scale turbulence-induced Reynolds stress and large-scale zonal flow production in the E×B driven hydrodynamic spectral condensation. We show that Reynolds stress is generated effectively by anisotropic vorticity structures possessing collective tilt angle. The maximum amplitude of the tilt, the Reynolds stress, and the mean zonal flow production coincide with the transition time of the velocity field, indicating a key role of turbulence-induced Reynolds stress in the condensation of the flow. The analysis of the energy transfer between turbulence and zonal flow shows coherent oscillations with π/2 phase delay, thus indicating a predator-prey-like interaction between zonal flow and turbulence.
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Affiliation(s)
- L Bardóczi
- University of California, Los Angeles, Los Angeles, California 90095, USA
| | - A Bencze
- Wigner RCP, EURATOM Association, 1121 Budapest, Hungary
| | - M Berta
- Széchenyi István University, EURATOM Association, 9026 Győr, Hungary and Institute of Plasma Physics AS CR, v.v.i., 18200 Prague, Czech Republic
| | - L Schmitz
- University of California, Los Angeles, Los Angeles, California 90095, USA
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24
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Zeng L, Peebles WA, Doyle EJ, Rhodes TL, Crocker N, Nguyen X, Wannberg CW, Wang G. Performance and data analysis aspects of the new DIII-D monostatic profile reflectometer system. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2014; 85:11D843. [PMID: 25430256 DOI: 10.1063/1.4889775] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
A new frequency-modulated profile reflectometer system, featuring a monostatic antenna geometry (using one microwave antenna for both launch and receive), has been installed on the DIII-D tokamak, providing a first experimental test of this measurement approach for profile reflectometry. Significant features of the new system are briefly described in this paper, including the new monostatic arrangement, use of overmoded, broadband transmission waveguide, and dual-polarization combination/demultiplexing. Updated data processing and analysis, and in-service performance aspects of the new monostatic profile reflectometer system are also presented. By using a raytracing code (GENRAY) to determine the approximate trajectory of the probe beam, the electron density (ne) profile can be successfully reconstructed with L-mode plasmas vertically shifted by more than 10 cm off the vessel midplane. Specifically, it is demonstrated that the new system has a capability to measure ne profiles with plasma vertical offsets of up to ±17 cm. Examples are also presented of accurate, high time and spatial resolution density profile measurements made over a wide range of DIII-D conditions, e.g., the measured temporal evolution of the density profile across a L-H transition.
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Affiliation(s)
- L Zeng
- Physics and Astronomy Department, University of California, Los Angeles, California 90095, USA
| | - W A Peebles
- Physics and Astronomy Department, University of California, Los Angeles, California 90095, USA
| | - E J Doyle
- Physics and Astronomy Department, University of California, Los Angeles, California 90095, USA
| | - T L Rhodes
- Physics and Astronomy Department, University of California, Los Angeles, California 90095, USA
| | - N Crocker
- Physics and Astronomy Department, University of California, Los Angeles, California 90095, USA
| | - X Nguyen
- Physics and Astronomy Department, University of California, Los Angeles, California 90095, USA
| | - C W Wannberg
- Physics and Astronomy Department, University of California, Los Angeles, California 90095, USA
| | - G Wang
- Physics and Astronomy Department, University of California, Los Angeles, California 90095, USA
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25
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Guo ZB, Diamond PH, Kosuga Y, Gürcan ÖD. Elasticity in drift-wave-zonal-flow turbulence. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2014; 89:041101. [PMID: 24827182 DOI: 10.1103/physreve.89.041101] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/05/2013] [Indexed: 06/03/2023]
Abstract
We present a theory of turbulent elasticity, a property of drift-wave-zonal-flow (DW-ZF) turbulence, which follows from the time delay in the response of DWs to ZF shears. An emergent dimensionless parameter |〈v〉'|/Δωk is found to be a measure of the degree of Fickian flux-gradient relation breaking, where |〈v〉'| is the ZF shearing rate and Δωk is the turbulence decorrelation rate. For |〈v〉'|/Δωk>1, we show that the ZF evolution equation is converted from a diffusion equation, usually assumed, to a telegraph equation, i.e., the turbulent momentum transport changes from a diffusive process to wavelike propagation. This scenario corresponds to a state very close to the marginal instability of the DW-ZF system, e.g., the Dimits shift regime. The frequency of the ZF wave is ΩZF=±γd1/2γmodu1/2, where γd is the ZF friction coefficient and γmodu is the net ZF growth rate for the case of the Fickian flux-gradient relation. This insight provides a natural framework for understanding temporally periodic ZF structures in the Dimits shift regime and in the transition from low confined mode to high confined mode in confined plasmas.
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Affiliation(s)
- Z B Guo
- WCI Center for Fusion Theory, NFRI, Daejeon 305-333, South Korea
| | - P H Diamond
- WCI Center for Fusion Theory, NFRI, Daejeon 305-333, South Korea and CMTFO and CASS, University of California, San Diego, La Jolla, California 92093, USA
| | - Y Kosuga
- IAS and RIAM, Kyushu University, Kasuga 816-8580, Japan
| | - Ö D Gürcan
- LPP, Ecole Polytechnique, CNRS, Palaiseau Cedex 91128, France
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26
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Yan Z, McKee GR, Fonck R, Gohil P, Groebner RJ, Osborne TH. Observation of the L-H confinement bifurcation triggered by a turbulence-driven shear flow in a tokamak plasma. PHYSICAL REVIEW LETTERS 2014; 112:125002. [PMID: 24724655 DOI: 10.1103/physrevlett.112.125002] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/26/2013] [Indexed: 06/03/2023]
Abstract
Comprehensive 2D turbulence and eddy flow velocity measurements on DIII-D demonstrate a rapidly increasing turbulence-driven shear flow that develops ∼100 μs prior to the low-confinement (L mode) to high-confinement (H mode) transition and appears to trigger it. These changes are localized to a narrow layer 1-2 cm inside the magnetic boundary. Increasing heating power increases the Reynolds stress, the energy transfer from turbulence to the poloidal flow, and the edge flow shearing rate that then exceeds the decorrelation rate, suppressing turbulence and triggering the transition.
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Affiliation(s)
- Z Yan
- University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
| | - G R McKee
- University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
| | - R Fonck
- University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
| | - P Gohil
- General Atomics, PO Box 85608, San Diego, California 92186-9784, USA
| | - R J Groebner
- General Atomics, PO Box 85608, San Diego, California 92186-9784, USA
| | - T H Osborne
- General Atomics, PO Box 85608, San Diego, California 92186-9784, USA
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27
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Kobayashi T, Itoh K, Ido T, Kamiya K, Itoh SI, Miura Y, Nagashima Y, Fujisawa A, Inagaki S, Ida K, Hoshino K. Spatiotemporal structures of edge limit-cycle oscillation before L-to-H transition in the JFT-2M tokamak. PHYSICAL REVIEW LETTERS 2013; 111:035002. [PMID: 23909334 DOI: 10.1103/physrevlett.111.035002] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/26/2013] [Indexed: 06/02/2023]
Abstract
In this Letter, we report analyses of spatiotemporal dynamics of turbulence and structure in the limit-cycle oscillation (LCO) that precedes an L-to-H transition. Zonal flows are not observed during LCO, and the oscillation is the periodic generations or decays of barrier with edge-localized mean flow. Oscillatory Reynolds stress is found to be too small to accelerate the LCO flow, by considering the dielectric constant in magnetized toroidal plasmas. Propagation of changes of the density gradient and turbulence amplitude into the core is also observed.
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Affiliation(s)
- T Kobayashi
- Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, Kasuga 816-8580, Japan.
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28
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Cheng J, Dong JQ, Itoh K, Yan LW, Xu M, Zhao KJ, Hong WY, Huang ZH, Ji XQ, Zhong WL, Yu DL, Itoh SI, Nie L, Kong DF, Lan T, Liu AD, Zou XL, Yang QW, Ding XT, Duan XR, Liu Y. Dynamics of low-intermediate-high-confinement transitions in toroidal plasmas. PHYSICAL REVIEW LETTERS 2013; 110:265002. [PMID: 23848884 DOI: 10.1103/physrevlett.110.265002] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/11/2013] [Indexed: 06/02/2023]
Abstract
The dynamic features of the low-intermediate-high-(L-I-H) confinement transitions on HL-2A tokamak are presented. Here we report the discovery of two types of limit cycles (dubbed type-Y and type-J), which show opposite temporal ordering between the radial electric field and turbulence intensity. In type-Y, which appears first after an L-I transition, the turbulence grows first, followed by the localized electric field. In contrast, the electric field leads type-J. The turbulence-induced zonal flow and pressure-gradient-induced drift play essential roles in the two types of limit cycles, respectively. The condition of transition between types-Y and -J is studied in terms of the normalized radial electric field. An I-H transition is demonstrated to occur only from type-J.
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Affiliation(s)
- J Cheng
- Southwestern Institute of Physics, Chengdu 610041, People's Republic of China
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29
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Vlad M. Ion stochastic trapping and drift turbulence evolution. Phys Rev E 2013; 87:053105. [PMID: 23767641 DOI: 10.1103/physreve.87.053105] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2012] [Revised: 02/02/2013] [Indexed: 11/07/2022]
Abstract
Test modes on turbulent magnetized plasmas are studied taking into account the stochastic ion trapping or eddying that characterizes the E×B drift in the background turbulence. It is shown that ion trapping provides an important physical mechanism for the complex nonlinear processes in drift turbulence evolution: generation of large-scale correlations and of zonal flow modes.
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Affiliation(s)
- Madalina Vlad
- National Institute of Laser, Plasma and Radiation Physics, Bucharest, Romania.
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Miki K, Diamond PH, Hahn SH, Xiao WW, Gürcan ÖD, Tynan GR. Physics of stimulated L→H transitions. PHYSICAL REVIEW LETTERS 2013; 110:195002. [PMID: 23705712 DOI: 10.1103/physrevlett.110.195002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/26/2013] [Indexed: 06/02/2023]
Abstract
We report on model studies of stimulated L→H transitions. These studies use a novel reduced mesoscale model. Studies reveal that L→H transitions can be triggered by particle injection into a subcritical state (i.e., P<P(Thresh)). Particle injection alters the edge mean flow shear via changes of density and temperature gradients. The change of edge mean flow shear is critical to turbulence collapse and the subsequent stimulated transition. For low ambient heating, strong injection is predicted to trigger a transient turbulence collapse. We predict that repetitive injection can maintain the turbulence collapse and so sustain a driven H-mode-like state. The total number of particles required to induce a transition by either injection or gas puffing is estimated. Results indicate that the total number of injected particles required is much smaller than that required for inducing a transition by gas puffing. Thus, we show that internal injection is more efficient than gas puffing of comparable strength. We also observe that zonal flows do not play a critical role in stimulated transitions.
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Affiliation(s)
- K Miki
- WCI Center for Fusion Theory, National Fusion Research Institute, Daejeon 305-333, Republic of Korea
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31
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Birkenmeier G, Ramisch M, Schmid B, Stroth U. Experimental evidence of turbulent transport regulation by zonal flows. PHYSICAL REVIEW LETTERS 2013; 110:145004. [PMID: 25167000 DOI: 10.1103/physrevlett.110.145004] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/26/2012] [Indexed: 06/03/2023]
Abstract
The regulation of turbulent transport by zonal flows is studied experimentally on a flux surface of the stellarator experiment TJ-K. Data of 128 Langmuir probes at different toroidal and poloidal positions on a single flux surface enable us to measure simultaneously the zonal flow activity and the turbulent transport in great detail. A reduction of turbulent transport by 30% during the zonal flow phase is found. It is shown that the reduction process is initiated by a modification in the cross phase between density and electric field followed by a reduction in the fluctuation levels, which sustain low transport levels on larger time scales than the zonal flow lifetime.
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Affiliation(s)
- G Birkenmeier
- Institut für Plasmaforschung, Universität Stuttgart, Pfaffenwaldring 31, 70569 Stuttgart, Germany and Max-Planck-Institut für Plasmaphysik, EURATOM-Assoziation, Boltzmannstr. 2, 85748 Garching, Germany
| | - M Ramisch
- Institut für Plasmaforschung, Universität Stuttgart, Pfaffenwaldring 31, 70569 Stuttgart, Germany
| | - B Schmid
- Institut für Plasmaforschung, Universität Stuttgart, Pfaffenwaldring 31, 70569 Stuttgart, Germany
| | - U Stroth
- Institut für Plasmaforschung, Universität Stuttgart, Pfaffenwaldring 31, 70569 Stuttgart, Germany and Max-Planck-Institut für Plasmaphysik, EURATOM-Assoziation, Boltzmannstr. 2, 85748 Garching, Germany
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