Breaking tidal bore: comparison between field data and laboratory experiments

A tidal bore is a surge of waters propagating upstream as the tidal flow turns to rising and the flood tide rushes into a funnel shaped river mouth with shallow waters. The present study focused on the unsteady turbulence induced by a breaking tidal bore through some physical modelling. The laboratory data were compared systematically with some field measurements conducted in the breaking bore of the Sélune River (France) by Mouazé et al. [12]. A key finding was the close agreement in terms of dimensionless free-surface and velocity data between laboratory and field observations. The results supported the implementation of the Froude dynamic similarity

Extension of geodesic acoustic mode theory to helical systems

The present paper extends the theory of geodesic acoustic mode (GAM) oscillation, which so far has been applied to tokamaks, to helical systems. By using drift kinetic equations for three-dimensional equilibriums, a generalized dispersion relation is obtained including Landau damping. The oscillation frequency is obtained in terms of the squared sum of Fourier components of the magnetic field intensity expressed by means of magnetic flux coordinates. An analytic form of the collisionless damping rate of GAM is obtained by solving the dispersion relation perturbatively. It is found that the GAM frequency is higher in helical systems than in tokamaks and that damping rate is enhanced in multi-helicity magnetic configurations. However, damping rates are predicted to be small if the temperature of electrons is higher than that of ions