Peaked density profiles and MHD activity on FTU in lithium dominated discharges

Abstract: Density profiles become broader, as the line averaged density is increased. At higher density, change of the trend is associated with the appearance of the MARFE. Lithium coated wall extends the maximum density accessible at low current (well above the Greenwald density limit) and can produce profiles with very high density gradient. At higher current the effect on the density limit can be exceeded only if the magnetic field is raised too. A comparison of successive similar discharges before and after wall conditioning with lithium showed a reduction of the MHD activity. [ABSTRACT FROM AUTHOR]