Heat pinches in electron-heated Tokamak plasmas: theoretical turbulence models versus experiments

Two fluid turbulence models, the drift wave based quasilinear 1.5D Weiland model and the electromagnetic global 3D nonlinear model CUTIE, have been used to account for heat pinch evidence in off-axis modulated electron cyclotron heating experiments in the Rijnhuizen Tokamak Project. Both models reproduce the main features indicating inward heat convection in mildly off-axis cases. In far-off-axis cases with hollow electron temperature profiles, the existence of outward convection was reproduced only by CUTIE. Turbulence mechanisms driving heat convection in the two models are discussed.     

Highly birefringent photonic crystal fibers

We report a strongly anisotropic photonic crystal fiber. Twofold rotational symmetry was introduced into a single-mode fiber structure by creation of a regular array of airholes of two sizes disposed about a pure-silica core. Based on spectral measurements of the polarization mode beating, we estimate that the fiber has a beat length of approximately 0.4 mm at a wavelength of 1540 nm, in good agreement with the results of modeling.     

The origin of quantum beats in photoionization

The origin of quantum beats in photoionization of a coherent superposition of excited states is examined. Two types of beat are distinguished; one in the production of polarized final states, and the other a higher-order Raman-induced multiphoton beat in the total photoionization signal.     

The covariant derivative in the affine approach to general relativity

The affine presentation of general relativity is considered and a possible generalisation of the definition of covariant derivative is proposed. Under certain weak symmetry conditions it is shown that the only theories resulting from this generalisation are general relativity and Weyl's theory, of which general relativity arises in the most natural way.