Influence of magnetic perturbation fields on the heat transport in the boundary of tokamaks  

In order to control edge-localized instabilities in future fusion devices, the use of three-dimensional (3D) magnetic perturbation (MP) fields is currently discussed. How these perturbation fields affect the particle and heat transport in the boundary layer of the plasma has now been investigated in a doctoral thesis carried out at IPP.

Simulated and experimentally measured heat flux onto the outer divertor plate in ASDEX Upgrade with magnetic perturbations. The large viewing angle is achieved by rotating the perturbation field.

For this the heat flux onto the divertor target plates was measured by thermography in experiments with perturbation fields at ASDEX Upgrade and compared with numerical predictions of a 3D transport simulation code (EMC3-EIRENE). In particular, it was investigated whether the heat flow is more beneficially distributed on the target plates with perturbation fields. Experimentally, however, contrary to the expectations no effect of the MP field on the toroidally averaged heat flux was measured in ASDEX Upgrade. In the course of this work, these results have now been better understood and their significance for ITER was discussed. Even if a prediction for ITER remains difficult and is associated with large uncertainties, one can hope for a bigger effect there.

Furthermore, it was investigated whether the MP fields lead to the negative effect of a strongly toroidally asymmetric heat flux distribution on the target plates. However, for ITER such an event seems unlikely, since diffusive processes in the divertor region counteract the asymmetry of the heat flux under typical plasma conditions.

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