3 research outputs found
Geodesic acoustic modes in a fluid model of tokamak plasma : the effects of finite beta and collisionality
Starting from the Braginskii equations, relevant for the tokamak edge region,
a complete set of nonlinear equations for the geodesic acoustic modes (GAM) has
been derived which includes collisionality, plasma beta and external sources of
particle, momentum and heat. Local linear analysis shows that the GAM frequency
increases with collisionality at low radial wave number and decreases
at high . GAM frequency also decreases with plasma beta. Radial profiles
of GAM frequency for two Tore Supra shots, which were part of a collisionality
scan, are compared with these calculations. Discrepency between experiment and
theory is observed, which seems to be explained by a finite for the GAM
when flux surface averaged density and temperature are assumed to vanish. It is shown that this agreement is incidental
and self-consistent inclusion of and
responses enhances the disagreement more with at high . So the
discrepancy between the linear GAM calculation, (which persist also for more
"complete" linear models such as gyrokinetics) can probably not be resolved by
simply adding a finite