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Pulsed Poloidal Current Drive (PPCD)

Top: Electron temperature profiles during standard operation (open circles) and during PPCD (full circles).  Bottom: Density profiles during standard operation (dashed line) and during PPCD (solid line).The PPCD is a technique for transiently inducing a poloidal current in the edge plasma. This is accomplished by driving one or more current pulses in the toroidal field winding. The aim of the procedure is to drive from the outside part of the poloidal current required to sustain the toroidal field reversal against resistive diffusion. This current is normally produced by the plasma itself through the dynamo mechanism, which requires a substantial level of magnetic turbulence, leading to magnetic chaos in the core plasma.

By driving a fraction of the current from the outside a less intense dynamo is required, and thus a lower level of magnetic fluctuations, leading to a partial recovery of the magnetic surfaces and to an improvement in the core energy confinement. Indeed, a peaking of the electron temperature profile is observed during the PPCD. A detailed transport analysis shows that the core thermal diffusivity, which in normal conditions is much higher than at the edge, is brought down to the edge values. As a consequence, an increase in the energy confinement time is observed.

Thermal conductivity during standard operation (blue line) and during PPCD (red line). The shaded regions give the 25%-75% confidence interval

EUROPEAN DOCTORATE IN FUSION

A European Doctoral initiative on Fusion Science and Engineering has been undertaken among the Universities of Padova, Lisbon and Munich aiming at combining two formal participation modalities in the same Doctoral programme course.

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