Experimental Evidence of Momentum Transport Induced by an Up-Down Asymmetric Magnetic Equilibrium in Toroidal Plasmas

Camenen, Y.; Bortolon, A.; Duval, B. P.; Federspiel, L.; Peeters, A. G.; Casson, F. J.; Hornsby, W. A.; Karpushov, A.; Piras, Francesco; Sauter, O.; Snodin, A. P.; Szepesi, G.

doi:10.1103/physrevlett.105.135003

Cited by 37 publications

(74 citation statements)

References 31 publications

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“…6 In TCV L-modes, the location of the sawtooth inversion radius was found to play a major role for the rotation profile, 7,9 and an effect of the plasma up-down asymmetry on toroidal rotation was theoretically predicted 11 and experimentally verified. 12 Investigating intrinsic rotation inevitably leads to the problem of toroidal angular momentum transport in the plasma. Historically, momentum transport has generally played a secondary role in tokamak transport theory, since only the even moments of the distribution function, density, and temperature enter the Lawson criterion that must be satisfied for a self-sustained burning plasma.…”

Section: Introductionmentioning

confidence: 99%

Intrinsic rotation generation in ELM-free H-mode plasmas in the DIII-D tokamak—Experimental observations

et al. 2011

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A detailed description is presented of the experiment reported in [S. H. Müller et al., Phys. Rev. Lett. 106, 115001 (2011)], which reported the first measurements of fluid turbulent stresses in a tokamak H-mode pedestal. Mach probe measurements disclosed a narrow co-current rotation layer at the separatrix, which is also seen in some L-modes [J. A. Boedo et al., Phys. Plasmas 18, 032510 (2011)]. Independent evidence for the existence of the edge co-rotation layer is presented from mainion rotation measurements by charge-exchange-recombination spectroscopy in comparable helium plasmas. The probe measurements are validated against density and electron temperature profiles from Thomson scattering and in terms of the measured turbulent particle transport, which is consistent with the global density rise. Non-diffusive non-convective angular momentum transport is required by two independent experimental observations: (1) A persistent dip in the rotation profile separates the edge layer from the evolving core region during intrinsic rotation development. (2) The rotation profiles with co-and counter-current neutral beam injection appear well described as the simple sum of a constant intrinsic part and the beam-driven part, also demonstrating the profileindependence of the intrinsic torque. Characteristics of the turbulent fluctuations composing the fluid turbulent stresses are discussed: Up to 0.5 cm inside the separatrix, the low amplitude of the Reynolds stress (<0.05 Nm of torque) is due to both a reduction of the fluctuation amplitudes at the peak of the edge co-rotation layer and weak correlations between the toroidal and radial velocity fluctuations. Further into the core, the correlations increase significantly up to a value of þ0.75, resulting in an almost unidirectional character of the turbulent Reynolds stress, generating substantial counter-current torques up to À2 Nm. Additional mechanisms must be present to balance these torques and explain the co-current core-plasma spin-up at a rate of þ0.3 Nm.

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Section: Introductionmentioning

confidence: 99%

Intrinsic rotation generation in ELM-free H-mode plasmas in the DIII-D tokamak—Experimental observations

et al. 2011

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“…21 An up-down asymmetric magnetic equilibrium can also result in momentum transport. This effect can in principle be larger than other symmetry breaking mechanisms, but the intrinsic rotation observed in an extremely up-down asymmetric tokamak was found to be insignificant (Mach number < 0.05) 22 and up-down asymmetry driven momentum transport is also found to be small in numerical analysis. 23 This paper focuses on the diamagnetic flow effects, showing that they can explain some experimental observations using the three examples in Sec.…”

Section: Introductionmentioning

confidence: 85%

The effect of diamagnetic flows on turbulent driven ion toroidal rotation

et al. 2014

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Turbulent momentum redistribution determines the radial profile of rotation in a tokamak. The momentum transport driven by diamagnetic flow effects is an important piece of the radial momentum transport for sub-sonic rotation, which is often observed in experiments. In a nonrotating state, the diamagnetic flow and the E Â B flow must cancel. The diamagnetic flow and the E Â B flow have different effects on the turbulent momentum flux, and this difference in behavior induces intrinsic rotation. The momentum flux is evaluated using gyrokinetic equations that are corrected to higher order in the ratio of the poloidal Larmor radius to the minor radius, which requires evaluation of the diamagnetic corrections to Maxwellian equilibria. To study the momentum transport due to diamagnetic flow effects, three experimental observations of ion rotation are examined. First, a strong pressure gradient at the plasma edge is shown to result in a significant inward momentum transport due to the diamagnetic effect, which may explain the observed peaking of rotation in a high confinement mode. Second, the direction of momentum transport is shown to change as collisionality increases, which is qualitatively consistent with the observed reversal of intrinsic rotation by varying plasma density and current. Last, the dependence of the intrinsic momentum flux on the magnetic shear is found, and it may explain the observed rotation changes in the presence of lower hybrid current drive. V C 2014 AIP Publishing LLC.

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“…The existence of the momentum flux generated through an up-down asymmetric magnetic equilibrium has been demonstrated through a dedicated experiment on the TCV tokamak [110,111]. The unique plasma shaping capabilities of TCV allow for the generation of an equilibrium which has a large up-down asymmetry even in the confinement region.…”

Section: Experimental Observationsmentioning

confidence: 99%

Overview of toroidal momentum transport

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et al. 2011

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Toroidal momentum transport mechanisms are reviewed and put in a broader perspective. The generation of a finite momentum flux is closely related to the breaking of symmetry (parity) along the field. The symmetry argument allows for the systematic identification of possible transport mechanisms. Those that appear to lowest order in the normalized Larmor radius (the diagonal part, Coriolis pinch, E ×B shearing, particle flux, and up-down asymmetric equilibria) are reasonably well understood. At higher order, expected to be of importance in the plasma edge, the theory is still under development.

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Experimental Evidence of Momentum Transport Induced by an Up-Down Asymmetric Magnetic Equilibrium in Toroidal Plasmas

Cited by 37 publications

References 31 publications

Intrinsic rotation generation in ELM-free H-mode plasmas in the DIII-D tokamak—Experimental observations

Intrinsic rotation generation in ELM-free H-mode plasmas in the DIII-D tokamak—Experimental observations

The effect of diamagnetic flows on turbulent driven ion toroidal rotation

Overview of toroidal momentum transport

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