Breaking the poloidal symmetry of the magnetic shear induced tilt of turbulent structures, by either divertor X-point resistivity or limiter positions, can lead to a finite (residual) contribution to the flux-surface averaged radial-binormal Reynolds stress. This residual stress supports or works against the radial electric field at the plasma edge of a tokamak. The impact of divertor geometry on the poloidal pattern of the Reynolds stress is studied by flux-coordinate-independent fluid simulations. Clear modifications of the Reynolds stress are found due to the magnetic shear in the confined region. The impact of different poloidal limiter positions on the radial electric field and the Reynolds stress is studied by means of magnetic field aligned gyrofluid simulations. Only if the limiter is close to the outer midplane can its position have a substantial effect on the radial electric field.

The link between plasma collisionality and the intermittency of edge drift-wave turbulence is investigated experimentally in the stellarator TJ-K and compared to results obtained from slab Hasegawa-Wakatani (HW) simulations. The kurtosis of experimental time series of density and potential fluctuations was analysed at different frequency scales. Using this method on data from a range of discharges, it was found that the intermittency level increases with increasing collisionality for density fluctuations, whereas potential fluctuations are generally self-similar. In addition, a high-order structure function analysis of density time-series data also shows a trend towards higher intermittency levels as collisionality is increased. HW simulations are found to produce a qualitatively similar trend in the intermittency level compared to experimental analyses. The transition to intermittent fluctuations at higher collisionalities can be understood in the framework of the HW model as the decoupling of the density field from the self-similar potential field when moving from the adiabatic to the hydrodynamic limit, where the density behaves like a passive scalar, resulting in the intermittency levels observed in the vorticity.

We present a new open-source software package, FIT-MART, that allows non-experts to quickly get started simulating quantum magnetism. FIT-MART can be downloaded as a platformidependent executable Java (JAR) file. It allows the user to define (Heisenberg) Hamiltonians by electronically drawing pictures that represent quantum spins and operators. Sliders are automatically generated to control the values of the parameters in the model, and when the values change, several plots are updated in real time to display both the resulting energy spectra and the equilibruim magnetic properties. Several experimental data sets for real magnetic molecules are included in FIT-MART to allow easy comparison between simulated and experimental data, and FIT-MART users can also import their own data for analysis and compare the goodness of fit for different models. * lengelhardt@fmarion.edu;

Relatively dense, field-aligned, filament-like structures (blobs) have been observed to propagate radially and poloidally through the SOL in magnetically confined fusion plasmas, and contribute significantly to SOL transport. A detailed understanding of blob structure and dynamics, and their dependence on magnetic field geometry, is of high importance in magnetic confinement physics for the prediction of heat loads on reactor wall facing components, as well as for understanding plasma confinement and neutral particle recycling. Experimentally deduced centre of mass poloidal blob velocity components, obtained using the conditional averaging technique, have been compared to an analytical blob model which has been simplified to express blob velocity in terms of the magnetic field curvature vector. Background flows are not incorporated into the analytical model, and must be added in to obtain good agreement with the experimental data. In addition, the 3D structure of blobs in TJ-K has been investigated using the conditional average of density fluctuations in two toroidally separated poloidal planes. Blobs are observed to be aligned to a flux tube near to the last closed flux surface, in the blob birth region. However at positions further along the blob trajectory, the structures do not deform according to the magnetic shear, rather they remain rigid, and retain their original form.Submitted to: Plasma Phys. Control. Fusion

The influence of magnetic field curvature on the intermittency in density and potential fluctuations in driftwave turbulence has been investigated in the stellarator TJ-K in the framework of an extended Hasegawa-Wakatani model. A structure function analysis was used to estimate the intermittency level of poloidally resolved drift-wave turbulence measurements of a deuterium plasma in TJ-K. Potential fluctuations were found to be broadly self-similar, whereas density fluctuations were found to be more intermittent in the region with negative normal and positive geodesic curvature. This behaviour could be understood by comparing the data to two-dimensional extended Hasegawa-Wakatani simulations which retain gradients in the magnetic field strength, giving rise to curvature effects. The model is able to reproduce the trends in the experimental data if both normal and geodesic curvature effects are accounted for, as well as the local anisotropy of turbulent length scales. The analysis indicates the importance of local magnetic geometry as a factor in the decoupling of density and potential fluctuations, leading to intermittency in drift-wave turbulence.