Current-driven Alfvén instability

The current-driven Alfvén instability is discussed analytically. The instability is driven by the resonant Landau and transit-time terms for propagation not parallel to B₀. The critical current for instability is slightly less than the corresponding one for the ‘k-like’instability thus, the instability discussed in this paper may be the more important for the parameter range in which our approximations are valid. The effect of current flow on the magnetosonic mode is also discussed, but no instability is found.