NPG

Nonlinear Processes in Geophysics

NPG

Nonlin. Processes Geophys.

1607-7946

Copernicus Publications

Göttingen, Germany

10.5194/npg-10-131-2003

Resonant-to-nonresonant transition in electrostatic ion-cyclotron wave phase velocity

Carroll III

J. J.

¹ ² Koepke

M. E.

¹ Zintl

M. W.

¹ ³ Gavrishchaka

⁴

Department of Physics, West Virginia University, Morgantown, WV 26506-6315, USA

present address: Eastern Michigan University, Ypsilanti, MI 48197, USA

present address: SARA, Inc., Huntington Beach, CA 92649, USA

Science Applications International Corp., McLean, VA 22102, USA

30 04 2003

10 1/2 131 138

2003

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Because of the implications for plasmas in the laboratory and in space, attention has been drawn to inhomogeneous energy-density driven (IEDD) waves that are sustained by velocity-shear-induced inhomogeneity in cross-field plasma flow. These waves have a frequency vr in the lab frame within an order of magnitude of the ion gyrofrequency vci, propagate nearly perpendicular to the magnetic field (kz /k^ << 1), and can be Landau resonant (0 < v1/kz < nd) with a parallel drifting electron population (drift speed nd), where subscripts 1 and r indicate frequency in the frame of flowing ions and in the lab frame, respectively, and kz is the parallel component of the wavevector. A transition in phase velocity from 0 < v1/kz < nd to 0 > v1/kz > nd for a pair of IEDD eigenmodes is observed as the degree of in-homogeneity in the transverse E × B flow is increased in a magnetized plasma column. For weaker velocity shear, both eigenmodes are dissipative, i.e. in Landau resonance, with kz nd > 0. For stronger shear, both eigenmodes become reactive, with one's wavevector component kz remaining parallel, but with v1/kz > nd , and the other's wavevector component kz becoming anti-parallel, so that 0 > v1/kz . For both eigenmodes, the transition (1) involves a small frequency shift and (2) does not involve a sign change in the wave energy density, which is proportional to vr v1, both of which are previously unrecognized aspects of inhomogeneous energy-density driven waves.