We study the radio emission from young supernova remnants by means of 3Dnumerical MHD simulations of the Rayleigh-Taylor instability in the shell ofthe remnant. The computation is carried out in spherical polar coordinates ($r,\theta, \phi$) by using a moving grid technique which allows us to finelyresolve the shell. Three-dimensional result shows more turbulent (complex)structures in the mixing region than the two-dimensional result, and theinstability is found to deform the reverse shock front. Stokes parameters (I,Q,and U) are computed to study the radio properties of the remnant. The totalintensity map shows two distinctive regions (inner and outer shells). The innershell appears to be complex and turbulent exhibiting loop structures and plumesas a result of the Rayleigh-Taylor instability, while the outer shell is faintand laminar due to the shocked uniform ambient magnetic fields. The inner shellresembles the observed radio structure in the main shell of young SNRs, whichis evidence that the Rayleigh-Taylor instability is an ongoing process in youngSNRs. When only the peculiar components of the magnetic fields generated by theinstability are considered, the polarization B-vector in the inner radio shellis preferentially radial with about $20 \sim 50\%$ of fractional polarizationwhich is higher than the observed value. The fractional polarization is lowestin the turbulent inner shell and increases outward, which is attributed to thegeometric effect. The polarized intensity is found to be correlated with thetotal intensity. We demonstrate that the polarized intensity from the turbulentregion can dominate over the polarized intensity from the shocked uniformfields if the amplified field is sufficiently strong. Therefore, we concludethat the Rayleigh-Taylor instability can explain the dominant radial magnetic
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