Regions of kinetic geodesic acoustic modes and streamers in JIPPT-IIU tokamak plasmas

The radial extent of kinetic geodesic acoustic modes (KGAMs) and streamers is measured using a heavy ion beam probe. Intense KGAM oscillations are observed in the core region of a low-density ohmic (OH) plasma where Te ≫ Ti and outside this region, streamers characterized by steepening fronts are observed. The radial profile of plasma density stays flat in the region of the streamers, showing a rise in the plasma density in two regions, one at the scrape-off layer and the other in the core region during the radial scan of sample volumes. Intense (up to eΦ/kTe ∼ 0.1) and broad GAM oscillations (δf/f ∼ 0.5) are observed in the r < ap/2 region of tokamak plasmas. GAM oscillations and streamers are strongly reduced in the heated phase. In addition, the radial profile of the spectra of GAM in the heated phase is very different from that of a low-density OH plasma. The streamers and the two-step rise in the density radial profile disappear in the heated phase.