Resumo

TREMOLA, C; SIGALOTTI, L. Di G  e  SIRA, E. Propagation of linear MHD waves in a hydrogen plasma: the mode crossing problem. Rev. mex. fis. [online]. 2006, vol.52, suppl.3, pp.233-235. ISSN 0035-001X.

Here we use linear analysis to investigate the propagation of small thermal and magnetohydrodynamic (MHD) disturbances in a heat-conducting, ionizing-recombining, hydrogen plasma threaded by an external uniform magnetic field. Linearization of the governing MHD equations for this model leads to a dispersion equation for the wavenumber k as a function of the frequency ω which may be either quadratic or cubic in k², depending on the orientation of the magnetic field. In either case, the solution of the dispersion equation is such that crossing of the roots may happen at some frequencies, implying that they may not always correspond to the same particular physical wave. The crossing of modes is merely a mathematical property of the solution and must not be interpreted as an interchange of the thermal and MHD waves' physical nature at the crossing frequency. Here we find that mode crossing is a function of the wave frequency, plasma temperature, magnetic field strength and orientation.

Palavras-chave : Magnetohydrodynamics and plasmas; magnetohydrodynamic waves; sound waves; wave propagation.

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