Collisionless microtearing modes in hot tokamaks: Effect of trapped electrons

Swamy, Aditya Krishna; Ganesh, R.; Brunner, S.; Václavík, J.; Villard, L.

doi:10.1063/1.4927579

Cited by 7 publications

(10 citation statements)

References 26 publications

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“…These MTMs are fundamentally different to the low k y MTMs as they will be shown to be unstable in the collisionless regime, which have been found previously [35,43,44], though the driving mechanisms are not completely understood.…”

Section: Low K Y Kbmmentioning

confidence: 57%

Linear gyrokinetic stability of a high β non-inductive spherical tokamak

et al. 2021

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Spherical tokamaks (STs) have been shown to possess properties desirable for a fusion power plant such as achieving high plasma β and having increased vertical stability. To understand the confinement properties that might be expected in the conceptual design for a high β ST fusion reactor, a 1 GW ST plasma equilibrium was analysed using local linear gyrokinetics to determine the type of micro-instabilities that arise. Kinetic ballooning modes and micro-tearing modes are found to be the dominant instabilities. The parametric dependence of these linear modes was determined and, from the insights gained, the equilibrium was tuned to find a regime marginally stable to all micro-instabilities at θ 0 = 0.0. This work identifies the most important micro-instabilities expected to generate turbulent transport in high β STs. The impact of such modes must be faithfully captured in first-principles-based reduced models of anomalous transport that are needed for predictive simulations.

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Section: Low K Y Kbmmentioning

confidence: 57%

Linear gyrokinetic stability of a high β non-inductive spherical tokamak

et al. 2021

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“…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%

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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“…Examining the impact of collisions on the high k y MTM, it can be seen from Figure 14c that these are collisionless MTMs, highlighting the completely different nature of these modes compared to the longer wavelength MTMs. Collisionless MTMs have been seen before [35,43,44,52], but their mechanism is not fully understood. These are weakly stabilised by collisions over the range of the scan, but it appears that the impact is not significant.…”

Section: Collision Frequencymentioning

confidence: 99%

Linear gyrokinetic stability of a high $β$ non-inductive spherical tokamak

Patel,

Dickinson,

Roach

et al. 2021

Preprint

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Spherical tokamaks (STs) have been shown to possess properties desirable for a fusion power plant such as achieving high plasma β and having increased vertical stability. To understand the confinement properties that might be expected in the conceptual design for a high β ST fusion reactor, a 1GW ST plasma equilibrium was analysed using local linear gyrokinetics to determine the type of micro-instabilities that arise. Kinetic ballooning modes (KBMs) and micro-tearing modes (MTMs) are found to be the dominant instabilities. The parametric dependence of these linear modes was determined and from the insights gained, the equilibrium was tuned to find a regime marginally stable to all micro-instabilities at θ 0 = 0.0. This work identifies the most important micro-instabilities expected to generate turbulent transport in high β STs. The impact of such modes must be faithfully captured in first principles based reduced models of anomalous transport that are needed for predictive simulations.

show abstract

Collisionless microtearing modes in hot tokamaks: Effect of trapped electrons

Cited by 7 publications

References 26 publications

Linear gyrokinetic stability of a high β non-inductive spherical tokamak

Linear gyrokinetic stability of a high β non-inductive spherical tokamak

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

Linear gyrokinetic stability of a high $β$ non-inductive spherical tokamak

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