Experiments

The ultimate goal of our Theory and Simulation activities is to understand what is observed in experiments, specifically in the TJ-II stellarator device. Some of the measurements we would like to improve our understanding of are

  • Decay of Zonal flow-like structures detected with double Langmuir probe systems. These turbulence-generated, global ExB¬†rotation patterns are thought to be beneficial for confinement and have been proposed to trigger Low-to-High confinement transitions. The figure shows a clear anti-correlation between an H-alpha signal (blue, related to the outward flux of particles) and the amplitude of the Zonal flow (green) measured in TJ-II.

Has-minimal

  • Radiation asymmetries caused by impurity density re-distribution within flux surfaces. Impurities with a high charge are prone to develop density inhomogeneities on flux surfaces, which should be manifest in radiation signals. The re-distribution of impurities is mainly caused by ion-impurity friction which is also a main drive of radial impurity transport. Therefore, understanding those asymmetries is a way to test our understanding of impurity radial transport, which is one of the most important issues in future reactor viability and performance.

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