On the Applicability of GAM Theory to Real Tokamaks with Rippled Magnetic Fields

The influence of the toroidal magnetic field ripples on the spatial structure and frequency of the geodesic acoustic mode (GAM) in tokamak plasma has been investigated. It is shown that the toroidal asymmetry of the magnetic configuration leads to coupling of oscillations of the GAM electric potential with toroidal and poloidal inhomogeneous perturbations of the plasma pressure. For tokamaks with a large aspect ratio, the GAM dispersion law is derived, taking the non-uniformity of the ripple in the tokamak cross-section into account. Increasing the number of coils $$n$$ of the toroidal field reduces the effect of ripple as $$ {\sim} {\text{1/}}{{n}^{2}}$$ . The applicability of the standard theory to finding the frequency and spatial structure of GAM in large tokamaks is shown.