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Using the assumption of a weak normalized turbulent viscosity, usually valid in practice, the modulated-transport model (Stoltzfus-Dueck 2012 Phys. Plasmas 19 055908) is generalized to allow the turbulent transport coefficient to vary in an arbitrary way on radial and poloidal position. The new approach clarifies the physical interpretation of the earlier results and significantly simplifies the calculation, via a boundary-layer asymptotic method. Rigorous detailed appendices verify the result of the simple boundary-layer calculation, also demonstrating that it achieves the claimed order of accuracy and providing a concrete prediction for the strong plasma flows in the immediate vicinity of the last closed flux surface. The new formulas are used to predict plasma rotation at the core-edge boundary, in cases with and without externally applied torque. Dimensional formulas and extensive discussion are provided, to support experimental application of the new model.

Using a global gyrofluid code, we conduct comprehensive flux-driven simulations incorporating external heat and momentum sources/sinks. They involve an external torque ramp while keeping a heating power constant. Simulations show the formation of internal transport barriers (ITBs) in ion heat and parallel momentum in weak magnetic shear configuration. The ITB formation is attributed to the reduction of turbulent transport accompanied by strong $\boldsymbol{E} \times \boldsymbol{B}$ flow shear generation, where the majority of $\boldsymbol{E} \times \boldsymbol{B}$ shear arises from plasma rotation shear. In contrast, only a minor confinement improvement is observed in strong magnetic shear configuration. There exists a substantial difference in the rotation shear between the weak and strong magnetic shear cases at the same amount of external torque. Transport analysis implies that the difference comes from intrinsic rotation generated by residual stress. Global linear simulations demonstrate that the effect of $\boldsymbol{E} \times \boldsymbol{B}$ shear on $k_\parallel$ symmetry breaking is enhanced in weak magnetic shear configuration, explaining the origin of the difference in intrinsic rotation. The ITB is not achieved when the external torque is injected in counter-direction to intrinsic rotation. It is also shown that threshold torque for the ITB formation depends on power and the ratio of external torque to heating power should exceed a critical value to attain an ITB.

The isotope effect on intrinsic rotation was studied at the Joint European Torus (JET) tokamak. With the unique capability of JET to operate with tritium (T), for the first time, experiments in hydrogen (H), deuterium (D) and T in Ohmic plasmas were compared. Two rotation reversals per isotope type are observed in plasma density scans spanning the linear and the saturated Ohmic confinement regimes. A clear isotope mass dependence is observed at the higher densities. The magnitude of the core rotation was found to depend on isotope mass, with stronger co-current rotation observed in H. Change on intrinsic rotation characteristics coexist with a stronger thermal energy confinement in T.

The effects of different working gases on the transition from linear ohmic confinement (LOC) regime to saturated ohmic confinement (SOC) regime and its relation to the intrinsic toroidal rotation reversal phenomenon were explored in the TCV tokamak. The energy confinement saturation was studied across D, H and He density ramps, and a range of ECRH injection power and through variations of ohmic plasma current. The occurrence of rotation reversal, concomitantly with the LOC–SOC transition, was observed only for certain cases, making us formally exclude a causal relation between the two phenomena. A strong correlation between the evolution of toroidal rotation profiles and electron density gradients was, however, observed, in agreement with previous works (Lebschy et al 2017 Nucl. Fusion 58 026013; Hornsby et al 2018 Nucl. Fusion 58 056008). Linear gyrokinetic simulations were performed to probe the turbulent regime of these discharges, showing a dominance of trapped electron mode (TEM) during the LOC phase and a mixture of TEM and ion temperature gradient (ITG) following the transition to SOC regime in D. Such a TEM/ITG bifurcation was less pronounced in H and He. MHD activity was monitored throughout the discharges and possible correlations between sawteeth instability activity, energy confinement time saturation and rotation reversal are highlighted.

Changes in rotation have been observed in LHCD experiments. From these observations, reversals in intrinsic torque have been inferred. This paper identifies the mechanism for intrinsic torque reversal linked to magnetic shear (͉). Gyrokinetic simulations demonstrate that as compared to the normal ͉ case, the intrinsic torque reverses, for ͉ < ͉crit. Analysis shows that the reversal occurs due to the dominance of the symmetry breaking mechanism in residual stress due to the synergy of toroidal coupling and the intensity gradient. This mechanism is a consequence of ballooning structure at weak ͉. Gyrokinetic simulation gives ͉crit ≈ 0.3 for trapped electron modes (TEM) and ͉crit ≈ 1.1 for ion temperature gradient (ITG) modes. The value of ͉crit is consistent with results from the Alcator C-Mod LHCD experiments, for which ͉ > 0 in the whole plasma column and ͉crit ≈ 0.2 ∼ 0.3 exp (Rice et al Phys. Rev. Lett. 111 125003).

The ion orbit loss (IOL) can drive the bulk ions co-current rotation at the edge of the tokamak plasmas. The effect of triangularity on the IOL is investigated by using an analytical tokamak equilibrium model for the shaped plasmas. The peaking speed of the bulk ions co-current rotation at the tokamak edge will be increased greatly with the negative triangularity.

• A custom-built 532 nm polarimeter was used to measure the intrinsic rotation of (+)-camphor dissolved in polar and nonpolar organic solvents at room temperature. • The solvent dipolarity, acidity, and the solvent relative permittivity show a weak correlation with the intrinsic rotation of (+)-camphor. • The solvent polarizability, basicity, and the solubility of (+)-camphor in the solvents show little correlation with the intrinsic rotation of the solute. Optical activity, or the ability of a chiral molecule to rotate the plane of linearly polarized light, varies with the solvent for chiral molecules in solution. In an attempt to derive relationships between solvent properties and solute optical activity, the intrinsic rotations of (+)-camphor were measured in organic solvents at ambient temperature using a laser-based polarimeter with a wavelength of 532 nm. The intrinsic rotation values were analyzed using various solvent properties as independent parameters. Our results suggest that solvent dipolarity, solvent acidity, and solvent relative permittivity are weakly correlated with (+)-camphor intrinsic rotation, while solvent polarizability, solvent basicity, and (+)-camphor solubility show no significant correlation with the optical activity. A clear chemical underpinning of the solvent effect on optical activity remains elusive. [ABSTRACT FROM AUTHOR]

Recent developments in electromagnetic particle pinch, ion orbit loss, intrinsic rotation, rotation theory and radial electric field theory in the tokamak plasma edge are described. (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]