Resonant excitation of radial modes in a nonuniform cylindrical plasma waveguide
A nonuniform waveguide in the form of a double magnetic tube is studied in a cylindrical coordinate system. In the inner (\(r<b\)) and outer (\(r>a\)) parts of the cylindical plasma system (\(r\): radial parameter), the plasma densities are constant and a constant magnetic field is axially directed. In the intermediated part of the system (\(b<r<a\)), there exists an azimuthal magnetic field the amplitude of which is proportional to the inverse of the distance \(r\) from the cylinder axis and a plasma density decreasing proportional to \(r^{-2}\). It is shown that in the system axially symmetric torsion modes and radial magnetoacoustic modes may be excited. Investigating the resonant interaction of two torsion waves and one radial mode it is found that the amplitude of the radial mode grows with decreasing torsion mode amplitudes. Further, mathematical expressions for the wave-interaction coefficients are derived in the case of long wavelengths \(ka\ll1\) (\(k\): wave number). Applying the derived waveguide model to solar coronal loops, it is pointed out that the described radial waves can lead to the initiation of a loop flare.
scientific article; zbMATH DE number 6122481