Electrostatic turbulence in the low-density plasma column

Electron plasma density fluctuations are observed in plasma when a radial pressure gradient excites drift waves. The linear machine GyM (R=0.125 m, L= 2.11 m, B$<$0.1T), operating at IFP-CNR since 2008, has started experiments aimed at characterizing drift waves excited in its non-uniform magnetized plasma. Two different plasma sources (magnetron 2.45 GHz or hot filament) have been used to sustain plasma with adjustable sections (1.5 cm$<$r$<$10 cm). The diagnostic system is composed by different sets of movable electrostatic probes and by optical emission spectroscopy, dedicated to the electron temperature measurement. Fluctuations in plasma density have been observed and characterized as a function of the injected RF power. The dynamic (frequency and amplitude) of such fluctuations has been related to the spontaneous radial electric field consequence of different electron density profiles. The results from the new probe array, recently implemented in GyM to provide a deeper study of the spatial distribution of turbulence, are shown.