Kinetic Alfven wave instability driven by field-aligned currents in a low-β plasma

Kinetic Alfven 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 omega < omega(ci) (the ion cyclotron frequency), KAW instability driven by a field-aligned current, which is carried by the field-aligned drift of electrons at velocity V-D, is investigated in a low-beta plasma of beta < Q << 1, where beta is the kinetic-to-magnetic pressure ratio and Q (equivalent to m(e)/m(i) << 1) is the mass ratio of electrons to ions. An instability condition and the corresponding growth rate are obtained, which depends on the plasma beta parameter as well as the drift velocity V-D. The results show that the KAW instability occurs in the perpendicular wave number range of k(perpendicular to)(-) < k(perpendicular to) < k(perpendicular to)(+), in which the growth rate reaches its maximum at k(perpendicular to)(m) for fixed V-D and beta. As V-D increases, this growing wave number range widens and the growth rate increases, but the maximal-growing wave number k(perpendicular to)(m) decreases. On the other hand, as the plasma beta parameter 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.