DYNAMICS AND DISSIPATION OF COMPRESSIONAL ALFVEN WAVES NEAR MAGNETIC NULLS

It is shown that compressional magnetohydrodynamic (MHD) wave modes excited in the macroscopic vicinity of a magnetic field null in an otherwise strongly magnetized plasma damp at a rate consistent with a Q of order ln[LV(A)/eta], where L is the characteristic length scale of the magnetic configuration, V-A is the typical Alfven speed, eta is the relevant diffusion coefficient, such as the resistivity, and by Q we mean the ratio real frequency/damping rate. This result is shown to be valid for two-dimensional nulls, where the field is zero on some line, as well as for three-dimensional nulls, i.e., for cusp-like configurations. Thus field nulls are extremely efficient convertors of compressional MHD wave energy to thermal energy. (C) 1995 American Institute of Physics.