High Resolution Probe for filament transport and current density study at the edge region of W7-X

For the study of electrostatic and magnetic properties of filaments characterizingthe edge region of the stellarator experiment W7-X, a specifically designedinsertable probe head was constructed within the framework of EUROfusion WP.S1 work package in collaboration between Consorzio RFX, IPP Greifswald and FZJJulich. The probe head, named High Resolution Probe (HRP), was conceived to beinstalled on the mid-plane multi-purpose fast reciprocating manipulator on W7-X. Electromagnetic filamentary turbulent structures are found to characterize theedge region of different magnetic configurations [M. Spolaore et al., PoP 2015] including Reversed Field Pinch, stellarator and tokamak, where strong currents areassociated also to ELM filamentary structures. The study of those phenomena inW7-X stellarator is of particular interest as the electromagnetic features offilaments are expected to become more relevant with the increase of the localplasma beta. In particular the aim is to provide information about the presenceand the features of parallel current density associated to filamentary turbulent or ELM-like structures. Furthermore, the possibility to measure the time evolution ofthe flow radial profiles using the Mach probe array was considered as a further interesting part of the study, given the strong interplay expected between theturbulent fluctuation and the average flows. Further important information provided is the radial propagation of turbulent flux. The contribution will present the design development, the R&D studies and theapplied solutions for the sensors embedded in the probe head. In particular, the presence of 140 GHz ECRH plasma environment represents one of the main challenges for reliable magnetic fluctuation measurements. First measurements were performed during the W7-X experimental campaign OP1.2b, where in particular the probe was exploring different magnetic configurations. The respective features of the electromagnetic turbulence will be compared.