Frequency dependence of tokamak plasma response to the externally applied rotating helical field

The frequency dependence of the tokamak plasma response to the externally a pplied rotating helical field was investigated by measuring the radial prof ile of the perturbation field with small magnetic probes which were inserte d in the plasma. The experimental results are discussed, directly comparing with the generally accepted linear theory, and taking into account the ExB drift and diamagnetic effect of the plasma. It was found that the experime ntal results are in good agreement with the simple linear analysis based on the single helicity approximation in a cylindrical geometry, except for th e ergodic region, which comes from the overlapping of several sideband comp onents of the perturbation. It is also found that the radial component of t he perturbation field is still amplified inside the resonance surface (r < r(s)), even when a partial shielding takes place at r approximate to r(s). (C) 2000 American Institute of Physics. [S1070-664X(00)01408-7].