Purely growing electromagnetic modes in high-β plasmas

Electromagnetic waves propagating transverse to an external magnetic field in a high-β (β being the ratio of the kinetic pressure to the magnetic pressure) plasma become unstable through purely growing modes when β∥ e , (electron β parallel to the magnetic field) exceeds a certain minimum value β∥ * . For J ≦ 2 ( J being the distribution index), the region of instability consists of a single band of unstable wavenumbers k , whereas for J ≥ 3 more than one unstable wave number band may exist. The growth rates are largest for J = 0, and tend to decrease as J increases. The presence of hot ions increases the instability region by exciting a low-frequency instability. This instability gets excited at considerably lowered values of β ‖e , and has growth rates of the order of ion cyclotron frequency. The effect of T ‖i /T ‖e and T ‖e /T ⊥e is destabilizing, whereas that of T ⊥i /T ⊥e is stabilizing.