Complete multi-field characterization of the geodesic acoustic mode in the TCV tokamak

Abstract

The geodesic acoustic mode (GAM) is a coherently oscillating zonal flow that may regulate turbulence in toroidal plasmas. Uniquely, the complete poloidal and toroidal structure of the magnetic component of the turbulence-driven GAM has been mapped in the TCV tokamak. Radially localized measurements of the fluctuating density, ECE radiative temperature and poloidal flow show that the GAM is a fully coherent, radially propagating wave. These observations are consistent with electrostatic, gyrokinetic simulations.

Turbulence and zonal flow structures in the core and L-mode pedestal of tokamak plasmas

“…In physical units and for TCV parameters this is a frequency of f = 28.2kHz, which corresponds very well to the experimentally measured frequency, see Fig.3(a) of Ref. [21]. In our parameter scans, we found that avalanches do not always repeat with a well-defined frequency.…”

Experimental turbulence studies for gyro-kinetic code validation using advanced microwave diagnostics

“…In earlier studies, simulations with the global gyrokinetic PIC code ORB5 described fairly well data from the PCI diagnostic where the GAM frequency assumed constant values over a wide radial area, i.e. the outer 30 % of the plasma cross section [50]. Later on, however, a transition from eigenmode to continuum GAMs was observed as the safety factor was systematically increased [42].…”

Geodesic acoustic modes in tokamak plasmas with a radial equilibrium electric field

“…21 Many other eigenmode characteristics, such as the global structure with constant frequency, 23 radial plateaus in the GAM frequency, 24 and the radial propagation of kinetic GAMs, 25,26 have also been observed in experiments. To have a comparison with these observed features, we need to have an extension of the theory in the present work.…”