Frequency-Resolved Nonlinear Turbulent Energy Transfer into Zonal Flows in Strongly Heated<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>L</mml:mi></mml:math>-Mode Plasmas in the HL-2A Tokamak

Xu, M.; Tynan, G. R.; Diamond, P. H.; Mänz, P.; Holland, C.; Fedorczak, N.; Thakur, Saikat Chakraborty; Yu, J. H.; Zhao, K.J.; Dong, J. Q.; Cheng, J.; Hong, W.Y.; Yan, Lei; Yang, Qingwei; Song, X.M.; Yuan, Huan; Cai, Lijun; Zhong, W.L.; Shi, Z.B.; Ding, X.T.; Duan, X.R.; Liu, Y.

doi:10.1103/physrevlett.108.245001

Cited by 81 publications

(101 citation statements)

References 36 publications

(39 reference statements)

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“…The strongest change is observed in terms of a significantly lower SOL density in the Iphase, particularly on the HFS. This is in fact consistent with the majority of reports on the I -phase, where a clear drop in the D α intensity is seen 1,8,9,[17][18][19][20] prior to the main pulsing activity, for which strong evidence exists that it results from the predator-prey interplay between shear flows and small-scale turbulence. By observing in Fig.…”

Section: Discussionsupporting

confidence: 91%

“…[1][2][3][4][5][6][7][8][9][10][11][12][13] While this interaction is primarily important in the confined plasma, several observations have been made that relate the L-H transition to properties of the scrape-off layer (SOL), 14,15 neutrals, or even the wall. 16 It is thus possible that theories and models based on turbulence-flow interaction alone will be incomplete when it comes to predicting the L-H power threshold in future devices such as ITER.…”

Section: Introductionmentioning

confidence: 99%

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Direct observations of L-I-H and H-I-L transitions with the X-point reciprocating probe in ASDEX Upgrade

Müller¹,

Conway

Birkenmeier

et al. 2014

Physics of Plasmas

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A reciprocating Langmuir probe was used to directly measure the behavior of turbulence and flows in the X -point region during transitions between low-(L) and high-confinement (H ) mode in ASDEX Upgrade. The probe traverses the divertor horizontally in 140 ms, typically 2-5 cm below the X -point. Toroidal Mach number, density, floating potential (φ f ) and electron temperature (T e ) are measured. In the regime accessible to the probe (P inj < 1.5 MW, line-integrated core density < 4 × 10 19 m −2 ), the L-H transition features an intermediate phase (I -phase), characterized by limit-cycle oscillations (LCO) at 0.5-3 kHz [G.D. Conway et al., PRL 106, 065001 (2011)]. The probe measurements reveal that this pulsing affects both the density and the toroidal Mach number. It is present in both the low-(LFS) and high-field sides (HFS) of the scrape-off layer, while high-amplitude broadband turbulence usually dominates the private-flux region. Profile comparisons between L-mode and I -phase show lower density in pulsing regions and small shifts in T e , directed oppositely on LFS and HFS, which are compensated by shifts in φ f to yield a surprisingly unchanged plasma potential profile. Directly observed L-I -phase transitions reveal that the onset of the pulsing is preceded by a fast 50% density drop in the HFS X -point region. Back transitions to L-mode occur essentially symmetrically, with the pulsing stopping first, followed by a fast recovery to L-mode density levels in the divertor.

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Section: Discussionsupporting

confidence: 91%

Section: Introductionmentioning

confidence: 99%

Direct observations of L-I-H and H-I-L transitions with the X-point reciprocating probe in ASDEX Upgrade

Müller¹,

Conway

Birkenmeier

et al. 2014

Physics of Plasmas

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“…Since T v at the GAM frequency converges faster than T v for the ZF, not all GAM measurement points have a corresponding ZF evaluation. The trend measured in this regime corroborates previous observations [26] of a monotonic, increasing trend of ZF drive with GAM drive shown to peak and decrease against heating. In contrast to Ref.…”

supporting

confidence: 90%

“…In contrast to Ref. [26], no evidence points to a competition between ZF and GAM en route to direct L-H transitions, with favorable plasmas not even exciting any measurable GAM in C-Mod. Thus GAMs do not appear to be necessary for producing the H mode, which instead relies on the ZF drive.…”

contrasting

confidence: 77%

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Turbulence Nonlinearities Shed Light on Geometric Asymmetry in Tokamak Confinement Transitions

et al. 2017

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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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MHD Stability

Kikuchi¹,

Azumi²

2015

Frontiers in Fusion Research II

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Ideal, resistive and kinetic MHD instabilities are described. Since the birth of steady state tokamak research in 1990, there are number of important understandings of MHD modes related to steady state tokamak. In Sect. 8.1, we introduce the spectral property of MHD operator such as continuous spectrum and spectral gap, in brief. Marginal stability is discussed using the Newcomb equation in Sect. 8.2. Section 8.3 deals with flow effect on ideal MHD based on the Frieman-Rotenberg equation briefly. Localized MHD instabilities such as ELM, peeling/ballooning modes, infernal and barrier localized modes are discussed in Sect. 8.4. In Sect. 8.5, we introduce progress of resistive MHD such as the classical tearing mode (TM), the neoclassical tearing mode (NTM), the double tearing mode (DTM). Kinetic MHD equation is introduced in Sect. 8.6. In Sect. 8.7, Alfven eigenmode (AE) is introduced extensively. An important resistive/kinetic instability called the resistive wall mode (RWM) is introduced in Sect. 8.8. Control of ideal, resistive and kinetic MHD is essential element of fusion research. For three types of advanced tokamak operation (WS, NS, CH) to realize efficient steady state operation, ideal MHD modes such as peeling/ballooning modes for edge plasma, infernal modes for core plasma and BLM for ITB, resistive MHD modes such as NTM, DTM, RWM, kinetic MHD modes such as TAE, RSAE are understood well including control knob, while some kinetic MHD are still in progress in understanding. Key issue is that plasma profile does not match optimum profile for high beta advanced tokamak operation since profile is determined by the turbulent transport. Hence, combined understanding of MHD and turbulent transport is essential to optimize operation scenario for steady state tokamak operation.

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Frequency-Resolved Nonlinear Turbulent Energy Transfer into Zonal Flows in Strongly HeatedL-Mode Plasmas in the HL-2A Tokamak

Cited by 81 publications

References 36 publications

Direct observations of L-I-H and H-I-L transitions with the X-point reciprocating probe in ASDEX Upgrade

Direct observations of L-I-H and H-I-L transitions with the X-point reciprocating probe in ASDEX Upgrade

Turbulence Nonlinearities Shed Light on Geometric Asymmetry in Tokamak Confinement Transitions

MHD Stability

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