Observation of Spontaneous Toroidal Rotation Inversion in Ohmically Heated Tokamak Plasmas

Abstract

Bulk plasma toroidal rotation is observed to invert spontaneously from counter to cocurrent direction in TCV (Tokamak à Configuration Variable) Ohmically heated discharges, in low confinement mode, without momentum input. The inversion occurs in high current discharges, when the plasma electron density exceeds a well-defined threshold. The transition between the two rotational regimes has been studied by means of density ramps. The results provide evidence of a change of the balance of nondiffusive momentum fluxes in the core of a plasma without an external drive.

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

“…It covers a region from well outside the sawtooth inversion radius to just inside the last CXRS measurement points. While the core of TCV L-mode plasmas usually rotates in the countercurrent direction, it can also rotate in the cocurrent direction [19,21,22]. Such a reversed rotation state is, quite interestingly, sometimes observed in the present experiments.…”

Neoclassical physics in full distribution function gyrokinetics

“…(9) to its sub-class associated with a vanishing mean toroidal velocity therefore allows to relax this degeneracy and unambiguously relate the radial electric field to the poloidal rotation and the thermodynamic forces whilst accurately modeling the exact cross-field transport and flow generation mechanisms in the radial-poloidal plane as a more general Galilean-invariant Fokker-Planck operator would. On the other hand, this sim- [76][77][78] In that case, the Galilean-invariant versions Eqs. (3) and (18) are required; a dedicated study of intrinsic rotation with both GYSELA and XGC1 is to be reported elsewhere.…”

Residual parallel Reynolds stress due to turbulence intensity gradient in tokamak plasmas

“…In terms of its direction and scaling trends, L-mode rotation seems to be a complex phenomenon with various competing effects, which may frequently involve sign flips. 7,9,10 In contrast, H mode rotation is usually in the co-current direction, and the on-axis plasma velocity appears to increase with stored energy W p and decrease with total plasma current I p . 11 This empirical scaling, which has come to be called the Rice scaling, particularly manifests itself strongly in Alcator C-Mod and D-IIID, 1,2 and if taken at face value gives rather optimistic predictions for ITER's rotation speed.…”