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We performed 3D MHD calculations of stream accretion in cataclysmic variablestars for which the white dwarf primary star possesses a strong and complexmagnetic field. These calculations are motivated by observations of polars;cataclysmic variables containing white dwarfs with magnetic fields sufficientlystrong to prevent the formation of an accretion disk. So an accretion streamflows from the L1 point and impacts directly onto one or more spots on thesurface of the white dwarf. Observations indicate that the white dwarf, in somebinaries, possesses a complex (non-dipolar) magnetic field. We performsimulations of 10 polars or equivalently one asynchronous polar at 10 differentbeat phases. Our models have an aligned dipole plus quadrupole magnetic fieldcentered on the white dwarf primary. We find that for a sufficiently strongquadrupole component an accretion spot occurs near the magnetic equator forslightly less than half of our simulations while a polar accretion zone isactive for most of the rest of the simulations. For one or two configurations;accretion at the dominant polar region and at an equatorial zone occurssimultaneously. These are the first 3D MHD calculations to confirm theexistence of complex magnetic fields in magnetic CVs. We conclude, that itmight be difficult observationally determine if the field is a pure dipole orif it is complex for polars, but there will be indications for some systems.Specifically, a complex magnetic field should be considered if the there is anaccretion zone near the white dwarf's spin equator (orbital plane) or if thereare two or more accretion regions that cannot be fit by a dipole magneticfield. For asynchronous polars, magnetic field constraints are expected to besubstantially stronger, with clearer indicators of complex field geometry dueto changes in accretion flow structure as a function of spin-orbit beat phase.

Full 3-D MHD calculations of accretion flow Structure in magnetic cataclysmic variable stars with strong and complex magnetic fields