It is shown that compressional magnetohydrodynamic (MHD) wave modes ex
cited in the macroscopic vicinity of a magnetic field null in an other
wise 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 r
elevant diffusion coefficient, such as the resistivity, and by Q we me
an the ratio real frequency/damping rate. This result is shown to be v
alid for two-dimensional nulls, where the field is zero on some line,
as well as for three-dimensional nulls, i.e., for cusp-like configurat
ions. Thus field nulls are extremely efficient convertors of compressi
onal MHD wave energy to thermal energy. (C) 1995 American Institute of
Physics.