Ultra-relativistic electrostatic Bernstein waves

Laing, E. W.; Diver, D. A.

doi:10.1088/0741-3335/55/6/065006

Cited by 17 publications

(12 citation statements)

References 24 publications

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“…It has been widely observed that Ohmic energy confinement in tokamaks increases linearly with electron density, and then saturates at a critical density [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15]. An example of this behavior is shown in Fig.1 was obtained from a shot by shot scan of the electron density in 5.2 T, 0.81 MA (q 95 = 4.3) plasmas from Alcator C-Mod [13].…”

Section: Introductionmentioning

confidence: 91%

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Ohmic energy confinement saturation and core toroidal rotation reversal in Alcator C-Mod plasmas

et al. 2012

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Ohmic energy confinement saturation is found to be closely related to core toroidal rotation reversals in Alcator C-Mod tokamak plasmas. Rotation reversals occur at a critical density, depending on the plasma current and toroidal magnetic field, which coincides with the density separating the linear Ohmic confinement regime from the saturated Ohmic confinement regime. The rotation is directed co-current at low density and abruptly changes direction to counter-current when the energy confinement saturates as the density is increased. Since there is a bifurcation in the direction of the rotation at this critical density, toroidal rotation reversal is a very sensitive indicator in the determination of the regime change. The reversal and confinement saturation results can be unified since these processes occur at a particular value of the collisionality.

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Section: Introductionmentioning

confidence: 91%

“…An example of this behavior is shown in Fig.1 was obtained from a shot by shot scan of the electron density in 5.2 T, 0.81 MA (q 95 = 4.3) plasmas from Alcator C-Mod [13]. The energy confinement time was determined from the kinetic profiles during the steady state portion of each discharge.…”

Section: Introductionmentioning

confidence: 99%

Ohmic energy confinement saturation and core toroidal rotation reversal in Alcator C-Mod plasmas

et al. 2012

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“…One example would be a change of wave propagation from the electron diamagnetic drift direction (electron drift waves) to the ion direction (ion drift waves or ITG modes) as the density exceeds a critical threshold [22]. Such a change from TEM (or ETG) to ITG turbulence domination has been invoked to explain the transition in global energy confinement from the linear (neo-Alcator) to saturated Ohmic confinement regimes [23]. In fact, the reversal density of ∼0.8×10 20 /m 3 for 5.4 T, 0.8 MA discharges (Fig.10) is very close to the density separating the linear energy confinement regime from the saturated confinement regime for Ohmic discharges (Fig.1 of [23]).…”

Section: Turbulence Changes During Reversalsmentioning

confidence: 99%

Observations of core toroidal rotation reversals in Alcator C-Mod ohmic L-mode plasmas

Rice¹,

Duval

Reinke³

et al. 2011

Nucl. Fusion

171

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Direction reversals of intrinsic toroidal rotation have been observed in Alcator CMod Ohmic L-mode plasmas following modest electron density or toroidal magnetic field ramps. The reversal process occurs in the plasma interior, inside of the q = 3/2 surface. For low density plasmas, the rotation is in the co-current direction, and can reverse to the counter-current direction following an increase in the electron density above a certain threshold. Reversals from the co-to counter-current direction are correlated with a sharp decrease in density fluctuations with k R ≥2 cm −1 and with frequencies above 70 kHz. The density at which the rotation reverses increases linearly with plasma current, and decreases with increasing magnetic field. There is a strong correlation between the reversal density and the density at which the global Ohmic L-mode energy confinement changes from the linear to the saturated regime.

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“…There are several longstanding mysteries in tokamak research: explanation of the observed edge up/down impurity density asymmetries [1,2,3,4], the mechanism governing the linear Ohmic confinement (LOC, also known as neo-Alcator scaling) regime and the transition to saturated Ohmic confinement (SOC, L-mode) [5,6,7,8,9,10,11,12,13,14,15,16,17], and the underlying cause of 'non-local electron heat transport' following cold pulses [18,19,20,21,22,23,24,25,26,27]. A recent mystery to add to this list is the rotation reversal or inversion process [28,29,30,31,32,33], in which the core toroidal rotation abruptly switches direction, with negligible effect on other macroscopic plasma parameters.…”

Section: Introductionmentioning

confidence: 99%

Non-local heat transport, rotation reversals and up/down impurity density asymmetries in Alcator C-Mod ohmic L-mode plasmas

Rice¹,

Gao²,

Reinke³

et al. 2013

Nucl. Fusion

155

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Several seemingly unrelated effects in Alcator C-Mod Ohmic L-mode plasmas are shown to be closely connected: non-local heat transport, core toroidal rotation reversals, energy confinement saturation and up/down impurity density asymmetries. These phenomena all abruptly transform at a critical value of the collisionality. At low densities in the linear Ohmic confinement regime, with collisionality ν * ≤ 0.35 (evaluated inside of the q=3/2 surface), heat transport exhibits non-local behavior, core toroidal rotation is directed co-current, edge impurity density profiles are up/down symmetric and a turbulent feature in core density fluctuations with k θ up to 15 cm −1 (k θ ρ s ∼ 1) is present. At high density/collisionality with saturated Ohmic confinement, electron thermal transport is diffusive, core rotation is in the counter-current direction, edge impurity density profiles are up/down asymmetric and the high k θ turbulent feature is absent. The rotation reversal stagnation point (just inside of the q=3/2 surface) coincides with the non-local electron temperature profile inversion radius. All of these observations can be unified in a model with trapped electron mode prevalence at low collisionality and ion temperature gradient mode domination at high collisionality.

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Ultra-relativistic electrostatic Bernstein waves

Cited by 17 publications

References 24 publications

Ohmic energy confinement saturation and core toroidal rotation reversal in Alcator C-Mod plasmas

Ohmic energy confinement saturation and core toroidal rotation reversal in Alcator C-Mod plasmas

Observations of core toroidal rotation reversals in Alcator C-Mod ohmic L-mode plasmas

Non-local heat transport, rotation reversals and up/down impurity density asymmetries in Alcator C-Mod ohmic L-mode plasmas

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