Gyrokinetic analysis of inter-edge localized mode transport mechanisms in a DIII-D pedestal

Halfmoon, Michael; Hatch, D. R.; Kotschenreuther, M.; Mahajan, S. M.; Nelson, A.; Kolemen, Egemen; Curie, M.; Diallo, A.; Groebner, R. J.; Hassan, Ehab; Belli, E. A.; Candy, J.

doi:10.1063/5.0102152

Cited by 11 publications

(13 citation statements)

References 65 publications

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“…On JET, detailed comparisons with gyrokinetic simulations showed that experimentally-observed frequency bands in magnetic fluctuations were consistent with expectations from MTMs and that MTM fluctuations produce experimentally-relevant transport [25]. Additional ongoing work at DIII-D [27,28] and elsewhere is continuing to support the notion that MTMs are present in the H-mode pedestal, perhaps alongside additional instabilities.…”

Section: Introductionsupporting

confidence: 52%

“…In particular, models based off of KBM constraints have been extensively developed and are able to reproduce observed pedestal heights and widths to within ∼ 20% on many machines [6,7]. However, ongoing gyrokinetic work has suggested that other modes, especially the MTM [9][10][11][12], may also contribute to transport mechanisms in the pedestal region, potentially having large effects on energy regulation [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28].…”

Section: Introductionmentioning

confidence: 99%

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Time-dependent experimental identification of inter-ELM microtearing modes in the tokamak edge on DIII-D

et al. 2021

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In a series of discharges on the DIII-D tokamak, fast vertical plasma jogs are used to induce current perturbations in the steep gradient region of the H-mode edge. These current perturbations directly influence the edge q profile, decoupling the resonant location and instability drive of pedestal-localized microtearing modes (MTMs). By exploiting this effect, we develop and apply a new experimental technique to track the dynamical frequency evolution of MTMs in the pedestal region, providing a compelling validation of the MTM model. The frequency of potential MTMs is calculated as the Doppler-shifted electron diamagnetic frequency at rational q = m/n surfaces, showing remarkable agreement with chirped frequency behavior of n = 3, 4 and 5 modes detected with fast magnetics. Data is collected throughout multiple ELM cycles in order to build robust statistics describing the time-dependent frequency evolution of MTMs, which can be explained by examining the recovery of pedestal gradients after an ELM event. MTMs have a dominant transport contribution in the electron thermal channel, so the presented results indicate that reduced models of pedestal transport must be electromagnetic in nature and constructed with accurate calculations of MTM stability; inclusion of this physics is essential for accurate predictions of the electron temperature pedestal profile. Supporting measurements of mode saturation, propagation direction and transport fingerprints are made to support the dynamic frequency determination, unambiguously and experimentally identifying MTMs in the pedestal region of DIII-D.

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Section: Introductionsupporting

confidence: 52%

Section: Introductionmentioning

confidence: 99%

Time-dependent experimental identification of inter-ELM microtearing modes in the tokamak edge on DIII-D

et al. 2021

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“…Recently, Hatch et al [13] demonstrated quantitative agreement between gyrokinetic simulations and magnetic spectrograms from JET and explained the distinctive frequency bands by the alignment of certain rational surfaces with the peak in the profile of the diamagnetic frequency ω * . More generally, the recent DOE-FES theory performance target (of which this work was a part), surveyed a broad range of discharges spanning several devices and modes of operation and identified MTM in nearly all ELMy H-modes examined as shown in [14,15]. In addition to the pedestal observations, Jian et al [16] identifies MTM in an internal transport barrier on DIII-D, suggesting that MTM are not limited solely to edge transport barriers, but, rather, may be a common feature of transport barriers in general.…”

Section: Introductionmentioning

confidence: 99%

Identifying the microtearing modes in the pedestal of DIII-D H-modes using gyrokinetic simulations

Hassan¹,

Hatch²,

Halfmoon³

et al. 2021

Nucl. Fusion

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Recent evidence points toward the microtearing mode (MTM) as an important fluctuation in the H-mode pedestal for anomalous electron heat transport. A study of the instabilities in the pedestal region carried out using gyrokinetic simulations to model an ELMy H-mode DIII-D discharge (USN configuration, 1.4 MA plasma current, and 3 MW heating power) is presented. The simulations produce MTMs, identified by predominantly electromagnetic heat flux, small particle flux, and a substantial degree of tearing parity. The magnetic spectrogram from Mirnov coils exhibits three distinct frequency bands---two narrow bands at lower frequency ($\sim$35-55 kHz and $\sim$70-105 kHz) and a broader band at higher frequency ($\sim$300-500 kHz). Global linear GENE simulations produce MTMs that are centered at the peak of the $\omega_*$ profile and correspond closely with the bands in the spectrogram. The three distinctive frequency bands can be understood from the basic physical mechanisms underlying the instabilities. For example (i) instability of certain toroidal mode numbers (n) is controlled by the alignment of their rational surfaces with the peak in the $\omega^*$ profile, and (ii) MTM instabilities in the lower n bands are the conventional collisional slab MTM, whereas the higher n band depends on curvature drive. While many features of the modes can be captured with the local approximation, a global treatment is necessary to quantitatively reproduce the detailed band gaps of the low-n fluctuations. Notably, the transport signatures of the MTM are consistent with careful edge modeling by SOLPS.

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“…It is possible that other electrostatic instabilities are also present but not captured in the scale ranges of our simulations. Another possibility is that KBM fluctuations are present in the discharge but not captured in the simulations (reference [48] investigates such possibilities for another DIII-D discharge). Such fluctuations would produce relatively stronger density fluctuations while the MTM is the primary contributor to the magnetic fluctuations.…”

Section: Fluctuation Ratiomentioning

confidence: 99%

Gyrokinetic simulations compared with magnetic fluctuations diagnosed with a Faraday-effect radial interferometer-polarimeter in the DIII-D pedestal

et al. 2022

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Experimental data on electromagnetic fluctuations in DIII-D, made available by the Faraday-effect Radial Interferometer-Polarimeter (RIP) diagnostic\cite{rip}, is examined in comparison with detailed gyrokinetic simulations using Gyrokinetic Electromagnetic Numerical Experiment (GENE). The diagnostic has the unique capability of making internal measurements of fluctuating magnetic fields $\frac{\int n_e \delta B_r dR}{\int n_e dR}$. Local linear simulations identify microtearing modes (MTMs) over a substantial range of toroidal mode numbers (peaking at $n=15$) with frequencies in good agreement with the experimental data. Local nonlinear simulations reinforce this result by producing a magnetic frequency spectrum in good agreement with that diagnosed by RIP. Simulated heat fluxes are in the range of experimental expectations. However, magnetic fluctuation amplitudes are substantially lower than the experimental expectations. Possible sources of this discrepancy are discussed, notably the fact that the diagnostics are localized at the mid-plane---the poloidal location where the simulations predict the fluctuation amplitudes to be smallest. Despite some discrepancies, several connections between simulations and experiments, combined with general criteria discriminating between potential pedestal instabilities, strongly point to MTMs as the source of the observed magnetic fluctuations.

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Gyrokinetic analysis of inter-edge localized mode transport mechanisms in a DIII-D pedestal

Cited by 11 publications

References 65 publications

Time-dependent experimental identification of inter-ELM microtearing modes in the tokamak edge on DIII-D

Time-dependent experimental identification of inter-ELM microtearing modes in the tokamak edge on DIII-D

Identifying the microtearing modes in the pedestal of DIII-D H-modes using gyrokinetic simulations

Gyrokinetic simulations compared with magnetic fluctuations diagnosed with a Faraday-effect radial interferometer-polarimeter in the DIII-D pedestal

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