Speaker
Dr
Monica Spolaore
(Consorzio RFX, Padova)
Description
The presence of filamentary structures widely characterizes the edge region of fusion devices,
independently from their magnetic configuration. These structures are generally revealed by
pressure peak locally emerging on the cross-field plane from the plasma background and the name
filaments is due to their extended size along the magnetic field line.
Filaments emerging from turbulence background share these general features with Edge Localized
Modes (ELMs), which are responsible of a large fraction of transport towards the plasma wall and
divertor plates. The filament electromagnetic features were experimentally studied in the recent
years due to the relevance of this aspect on the transport, considering as an example the transition
between closed and open magnetic field line topology, i.e X-points and advanced divertor magnetic
configurations, up to the possible magnetic field line bending effect in case of enough high current
associated to ELM filaments, which could enhance their interaction with the first wall. A further
aspect to be considered is the enhancement of the electromagnetic effect is expected at high beta
plasmas, in particular an increasing current density characterizing turbulent structures was
experimentally observed to characterize turbulent filaments as the beta increases.
Local magnetic fluctuations were experimentally detected in presence of ELMs in different tokamaks
such as MAST, ASDEX-U and EAST and DII-D and JET. In this contribution a direct measurement of
current density associated to ELM will be presented in the two tokamak experiments COMPASS and
RFX-mod. Measurements were performed with specifically designed insertable probe heads,
properly equipped with 2D arrays of electrostatic and magnetic sensors. The diagnostic set is
completed in both experiments with arrays of probes located on the divertor or first wall. The
plasmas analyzed are based on SN shaped tokamak discharges where the H-mode was achieved in
ohmic or NBI heated plasmas, in COMPASS, or edge biasing stimulated in RFX-mod. The latter
representing a newly explored scenario with this technique, where ELM electromagnetic composite
filamentary structures are observed. They are characterized by clear vorticity and parallel current
density patterns. On the other side, recent preliminary analysis revealed the presence of parallel
current associated to the COMPASS ELMs and evidenced their fragmented structure within the
Scrape-Off Layer (SOL) region. The comparative analysis of the experimental results will be based on
the same method applied on the two devices, aiming to the identification of insight on possible
common physics.
Primary author
Dr
Monica Spolaore
(Consorzio RFX, Padova)
