Experimental study of small ELMs on the spherical Globus-M2 tokamak

On the spherical Globus-M2 tokamak, small edge localized modes (ELMs) that develop in regimes with high toroidal magnetic field and plasma current values were studied using a multi-diagnostics approach. A systematic increase in Te and ne values by almost 50% in the scrape-off layer (SOL) was observed during ELM bursts. Direct measurements of divertor heat fluxes made in the form of floating potential were interpreted based on the analysis of the structure of the SOL and private flux region currents. The perpendicular plasma rotation velocity V⊥ values increased by about 50% during ELM bursts up to 7 cm inside the last closed field surface. Experimental observations indicate transport of fast ions with energies up to 52 keV (6 keV above the injection energy) and suprathermal electrons to the plasma periphery. Filamentary structures moving in a downward direction toward the divertor region at a velocity ranging from 3 to 10 km/s during the ELM cycle were estimated to be around 3 cm in diameter with a distance within a series of filaments of about 10 cm.