Evidence for a Toroidal-Momentum-Transport Nondiffusive Term from the JFT-2M Tokamak

Ida, K.; Miura, Y.; Matsuda, Toshiaki; Itoh, K.; Hidekuma, S.; Itoh, Susumu

doi:10.1103/physrevlett.74.1990

Cited by 92 publications

(126 citation statements)

References 18 publications

(12 reference statements)

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“…1͒ and intrinsic rotation in toroidal direction, 2,3 play an important role in achieving better confinement and improving stability. The reduction of turbulent transport by radially sheared E ϫ B flow 4,5 is a widely accepted concept in the fusion community.…”

Section: Introductionmentioning

confidence: 99%

“…The system is characterized by no external momentum input, while energy is injected into a system using methods such as radio-frequency heating. To explain the generation of flows, the concept of a wave driven residual stress was developed and extensive experimental 2,7,8 and theoretical 9,10 research on this topic is ongoing. The residual stress is a component of momentum flux which is not proportional to either flow or flow shear as ͗Ṽ r Ṽ ʈ ͘ = − ͗V ʈ ͘Ј + U r ͗V ʈ ͘ + ⌸ rʈ res .…”

Section: Introductionmentioning

confidence: 99%

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On the efficiency of intrinsic rotation generation in tokamaks

2010

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A theory of the efficiency of the plasma flow generation process is presented. A measure of the efficiency of plasma self-acceleration of mesoscale and mean flows from the heat flux is introduced by analogy with engines, using the entropy budget defined by thermal relaxation and flow generation. The efficiency is defined as the ratio of the entropy destruction rate due to flow generation to the entropy production rate due to ٌT relaxation ͑i.e., related to turbulent heat flux͒. The efficiencies for two different cases, i.e., for the generation of turbulent driven E ϫ B shear flow ͑zonal flow͒ and for toroidal intrinsic rotation, are considered for a stationary state, achieved by balancing entropy production rate and destruction rate order by order in O͑k ʈ / k Ќ ͒, where k is the wave number. The efficiency of intrinsic toroidal rotation is derived and shown to be e IR ϳ͑Mach͒ th 2 ϳ 0.01. The scaling of the efficiency of intrinsic rotation generation is also derived and shown to bewhich suggests a machine size scaling and an unfavorable plasma current scaling which enters through the shear length.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

On the efficiency of intrinsic rotation generation in tokamaks

2010

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“…The toroidal flow has been considered to be determined by the radial transport of momentum driven by neutral beam injection (NBI) with anomalous shear viscosity [8,9]. Although the E 3 B velocity shear due to the toroidal flow can be important in the plasma core [10], there have been few experiments that demonstrate a spontaneous toroidal flow not driven by NBI in tokamaks [11][12][13][14]. It is generally the case in tokamaks that the plasma rotates parallel (antiparallel) to the plasma current for the coinjected (counterinjected) NBI, which corresponds to a positive (negative) radial electric field ͑E r ͒ in L-mode plasmas [15].…”

mentioning

confidence: 99%

Observation of Toroidal Flow Antiparallel to the〈Er×Bθ〉Drift Direction in the Hot Electron Mode Plasmas in the Compact

et al. 2001

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A toroidal flow antiparallel to the ͗E r 3 B u ͘ drift direction is observed in the hot electron mode plasmas when a large positive electric field and a sharp electron temperature gradient are sustained inside the internal transport barrier in the Compact Helical System. This toroidal flow reaches up to 5 3 10 4 m͞s at the plasma center, and it is large enough to reverse the toroidal flow driven by a tangentially injected neutral beam. These observations clearly show the plasma favors flow in the minimum =B direction at the transport barrier. DOI: 10.1103/PhysRevLett.86.3040 PACS numbers: 52.55.HcA spontaneous poloidal flow has been recognized to be important in the confinement of toroidal plasmas, since poloidal flow velocity and radial electric field shear were found to contribute an improvement of plasma confinement in H-mode plasmas [1,2]. The turbulence in the plasma is predicted to be suppressed by a E 3 B velocity shear through the mechanism of a nonlinear decorrelation [3,4]. It has been confirmed experimentally that the E 3 B shearing rate exceeds the growth rate of the turbulence at the transport barrier [5][6][7]. The toroidal flow has been considered to be determined by the radial transport of momentum driven by neutral beam injection (NBI) with anomalous shear viscosity [8,9]. Although the E 3 B velocity shear due to the toroidal flow can be important in the plasma core [10], there have been few experiments that demonstrate a spontaneous toroidal flow not driven by NBI in tokamaks [11][12][13][14]. It is generally the case in tokamaks that the plasma rotates parallel (antiparallel) to the plasma current for the coinjected (counterinjected) NBI, which corresponds to a positive (negative) radial electric field ͑E r ͒ in L-mode plasmas [15]. However, when a negative E r is produced at the transport barrier, both localized toroidal flow in the counterdirection and localized poloidal flow in the electron diamagnetic direction are observed even for plasmas with coinjected NBI [5,16,17]. These results show the need for detailed measurements of both toroidal and poloidal flow at the transport barrier, where the toroidal flow profile is not determined by the transport of momentum driven by NBI alone. Yet, despite the importance of the coupling between toroidal and poloidal flow, no studies until now have discussed the toroidal flow at the internal transport, where there is a large radial electric field.In a Heliotron/Torsatron device, there is no toroidal symmetry, and the minimum =B trace has a helical structure and helical flow along the minimum =B can be expected. The significant difference between tokamaks and Heliotron devices is the relationship between the poloidal field direction and the direction of dominant symmetry.The pitch angle of dominant symmetry is even larger than that of the averaged poloidal field in a Heliotron device, while it is zero due to the toroidal symmetry in tokamaks. This helical flow should change sign depending on the sign of E r or on the direction of the magnetic field. H...

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“…(2) and (3) are diagonal terms representing MHD effects, while the others are off-diagonal, purely kinetic terms. The existence of off-diagonal terms in the momentum transport matrix has been predicted theoretically and confirmed experimentally [20]. The drive in the off-diagonal terms is related to ion and electron density and temperature gradients, as well as the gradient of the safety factor q saf .…”

Section: Theoretical Modelmentioning

confidence: 81%

Turbulent contributions to Ohm's law in axisymmetric magnetized plasmas

Chavdarovski

Gatto

2017

Physics of Plasmas

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Abstract.The effect of magnetic turbulence in shaping the current density in axisymmetric magnetized plasma is analyzed using a turbulent extension of Ohm's law derived from the self-consistent action-angle transport theory. Besides the well-known hyperresistive (helicity-conserving) contribution, the generalized Ohm's law contains an anomalous resistivity term, and a turbulent bootstrap-like term proportional to the current density derivative. The numerical solution of the equation for equilibrium and turbulence profiles characteristic of conventional and advanced scenarios shows that, trough "turbulent bootstrap" effect and anomalous resistivity turbulence can generate power and parallel current which are a sizable portion (about 20 − 25 %) of the corresponding effects associated with the neoclassical bootstrap effect. The degree of alignment of the turbulence peak and the pressure gradient plays an important role in defining the steady-state regime. In fully bootstrapped tokamak, the hyper-resistivity is essential in overcoming the intrinsic limitation of the hollow current profile.

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Evidence for a Toroidal-Momentum-Transport Nondiffusive Term from the JFT-2M Tokamak

Cited by 92 publications

References 18 publications

On the efficiency of intrinsic rotation generation in tokamaks

On the efficiency of intrinsic rotation generation in tokamaks

Observation of Toroidal Flow Antiparallel to the〈Er×Bθ〉Drift Direction in the Hot Electron Mode Plasmas in the Compact

Turbulent contributions to Ohm's law in axisymmetric magnetized plasmas

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