Kinetic Alfvén wave instability driven by field‐aligned currents in a low‐β plasma

Abstract

Kinetic Alfvén waves (KAWs) can play an important role in the energization of plasma particles and the formation of filamentous structures, which commonly are encountered and frequently accompanied by field‐aligned currents in various magneto‐plasmas, such as laboratory, auroral, and coronal plasmas. Based on a low‐frequency kinetic dispersion equation in frequency ω<ωci (the ion cyclotron frequency), KAW instability driven by a field‐aligned current, which is carried by the field‐aligned drift of electrons at velocity VD, is investigated in a low‐β plasma of β<Q≪1, where β is the kinetic‐to‐magnetic pressure ratio and Q (≡me/mi≪1) is the mass ratio of electrons to ions. An instability condition and the corresponding growth rate are obtained, which depends on the plasma β parameter as well as the drift velocity VD. The results show that the KAW instability occurs in the perpendicular wave number range of , in which the growth rate reaches its maximum at for fixed VD and β. As VD increases, this growing wave number range widens and the growth rate increases, but the maximal‐growing wave number decreases. On the other hand, as the plasma βparameter decreases, the growing wave number range also widens, and the maximal‐growing wave number and growth rate both increase. These results have potential importance in understanding the physics of the electric current dissipation and plasma active phenomena since the field‐aligned current is one of the most active factors in space and astrophysical plasmas.