Search

Poloidal E×B shear flows are widely accepted as a trigger mechanism of transport barriers in the edge of fusion plasmas. Strong E×B flows can act on turbulence and turbulent transport through the shear decorrelation mechanism, which can reduce the radial size of turbulent structures or change the phase relation between density and potential fluctuations. In this contribution the influence of E×B shear flows on the microscopic structure of turbulence is investigated. The experiments have been carried out on the toroidally confined low-temperature plasma of the torsatron TJ-K. The plasma is dimensionally similar to fusion edge plasmas and accessible throughout for Langmuir probes. Multi-probe arrays are used to resolve the turbulent dynamics perpendicular to the confining magnetic field in high detail.Strong E×B flows are externally generated by core plasma biasing. It is shown that the fluctuations are dominated by large-scale coherent structures even though strong flow shear is present. These structures r...

In the torsatron TJ-K, low-temperature plasmas are created by means of microwaves at 2.45 GHz and 8.25 GHz. The plasmas are characterized as overdense which means that densities higher than the cut-off density are achieved. Studies in a wide parameter space show that the power deposition occurs predominantly at the upper-hybrid resonance. This can be seen in the electron-energy distribution function and the measured wave electric field. Full wave simulations support these measurements. An array antenna is presented which allows to scan the angle of incidence by variation of the microwave frequency.