Modeling Alfven and Whistler Waves Generation by Rotating Magnetic Field Source

Details Modeling Alfven and Whistler Waves Generation by Rotating Magnetic Field Source Modeling Alfven and Whistler Waves Generation by Rotating Magnetic Field Source

Dec 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufmsm21a1664g&link_type=abstract

American Geophysical Union, Fall Meeting 2008, abstract #SM21A-1664

Statistics

Computation

2471 Plasma Waves And Instabilities (2772), 2483 Wave/Particle Interactions (7867), 2487 Wave Propagation (0689, 3285, 4275, 4455, 6934), 2753 Numerical Modeling

Scientific paper

Recent experiments by Gigliotti et all., 2008 and Karavaev et al., 2008 (two posters in this meeting) demonstrated excitation of shear Alfven wave and whistler wave, respectively, by Rotating Magnetic Fields (RMF) created by a phased orthogonal loop antenna. This paper presents a combination of computational results along with experiments that emphasize the RMF properties for generating MHD and whistler waves. For RMF rotating frequencies in the whistler wave frequency range, the electrons quickly come to a co- rotation with the RMF, generating a differential azimuthal current. For rotating frequencies below the ion cyclotron frequency wave, the electrons and ion motion decouple within the ion skin-depth near the antenna and co-rotates with the RMF outside the ion skin depth, generating a JxB force. In order to understand the RMF and plasma interaction and the resultant radiation in different frequency regimes, we developed a 3D code that simulate the process. The code solves the linearized Maxwell equations coupled to the two-fluid description of the plasma motion in the frequency-domain. The antenna excitation is modeled as a set ofexternal current sources. The magnetized plasma response to the wave excitation at different frequencies,i.e. in the MHD and whistler frequency regime, are described by elements of the dielectric tensor. An iterative sparse matrix-solver is used to solve for the near field antenna-plasma coupling and the far-field wave propagation. The code is able to determine the radiation from antennas with complex geometry. The experimental configurations used in Gigliotti et all., 2008 and Karavaev et al., 2008 were simulated. The simulation results help us understand the general characteristics of impedance matching, energy coupling and far field radiation pattern from an RMF antenna in plasmas. The scaling of the induced magnetic field as a function of the RMF frequency, the plasma parameters and the spatial decay rate of magnetic field, as well as the use of RMFs as efficient radiation sources of MHD and whistler waves in space plasmas are also discussed. This work was sponsored by ONR MURI Grant 5-28828

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