Multi-field Characteristics and Eigenmode Spatial Structure of Geodesic Acoustic Modes (GAMs) in DIII-D*

Understanding GAMs is important since they are thought to regulate turbulence and transport levels in the outer regions of fusion plasmas. For the first time, two simultaneous, radially-overlapping eigenmode GAMs (constant frequency vs radius) have been observed in the poloidal $E\times B$ flow in L-mode \mbox{DIII-D} plasmas. Intermediate-k density fluctuations ($k_\theta^\ast \rho_s \sim 1$) are modified by these GAMs. Multi-field oscillations at the GAM frequency are also clearly observed in $n_e$, $T_e$, and $B_\theta$. Magnetic GAM activity is much stronger on the high-field side of the tokamak. This unique information provides a new perspective on GAM activity. Direct comparison with global gyrokinetic simulations (GYRO) will be presented to improve understanding.