Density fluctuations induced by MARFE on FTU

Abstract

High density operations on FTU (Frascati Tokamak Upgade) are affected by strong density oscillations due to the so-called MARFE (Multifaceted Asymmetric Radiation From the Edge). An analysis of these oscillations is reported here. The MARFE on FTU occurs at the value of ρ = 0.48 (ρ is ratio between line-averaged density with averaged current density in the plasma); at the MARFE onset, the volume averaged density versus central density is almost constant, corresponding to the value of 0.8. The MARFE is observed to move up and down along the poloidal circumference on FTU. The MARFE movement causes continuous density fluctuations. Amplitude of density fluctuations decreases with edge safety factor and with electron density. The mechanism to cause MARFE movement is discussed. If amplitude exceeds a certain threshold, it may cause poloidal heat flux asymmetry between the edges of the MARFE, which will make the MARFE moving along the poloidal circumference.