Drift Compressional Modes in Magnetospheric Plasmas

Details Drift Compressional Modes in Magnetospheric Plasmas Drift Compressional Modes in Magnetospheric Plasmas

Dec 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agufmsm23a0494c&link_type=abstract

American Geophysical Union, Fall Meeting 2004, abstract #SM23A-0494

Other

7827 Kinetic And Mhd Theory, 7867 Wave/Particle Interactions, 7871 Waves And Instabilities, 2720 Energetic Particles, Trapped, 2772 Plasma Waves And Instabilities

Scientific paper

The global eigenmode structure of drift compressional modes (DCM) is examined using gyrokinetic formalism along with a radial WKB procedure. DCM are ultralow frequency trapped-ion modes that occur in high beta plasmas, whose underlying instability mechanism is a kinetic wave-particle resonance between the perturbed magnetic field compression δ B&|slash; and the magnetic gradient-curvature drifts of ions; tapping the free energy associated with plasma nonuniformities. The coupling of DCM to other polarizations is mitigated by two parameters: 1) cold electrons that decouple the electrostatic mode from the DCM, and 2) small mode localization width along the field line that decouples the DCM from the shear Alfvén mode. Exploiting the fact that the most unstable modes typically have azimuthal wavenumbers comparable to the ion gyroradii, the general two-dimensional gryokinetic eigenvalue problem for DCM can be reduced to an integral equation along the field line with the radial structure determined by a WKB procedure. Using realistic equilibria appropriate for magnetospheric plasmas, numerical solutions for the two dimensional mode structure of DCM are presented. Implications of the wave excitation mechanisms and the global radial structures to the nonlinear saturation process will also be discussed. \footnote{ C.C. is supported in part by the U.S. D.O.E. Fusion Energy Postdoctoral Research Program administered by the Oak Ridge Institute for Science and Education. L.C. is supported by NSF Grant ATM-0335279 and U.S. D.O.E. grant DE-FG-94ER54736.}

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