The magnetic field amplification downstream of supernova blast wave

We study the interaction between a supernova blast wave and a turbulent interstellar medium and its effect on the downstream magnetic field. We report on two-dimensional ideal MHD simulations with high-order accuracy for supernova shocks propagating through a plasma which contains turbulent density and magnetic field. We show that a population of initial weak magnetic field can be amplified downstream by a factor much larger than that expected from the shock jump condition as a consequence of the irregular shock front interacting with the density fluctuations. The downstream vorticity produced at the rippling shock front can stretch and distort the field lines of force, which leads to a turbulent dynamo process. These results confirm the mechanism previously found for 2-D planar shocks (Giacalone & Jokipii 2007). We find that the magnetic field amplification depends on numerical resolutions. For high resolution simulations the maximum magnetic field and magnetic energy increase are larger than the cases with low resolutions since the process is more rapid at small scales. This provides an explanation for the discrepancy with the previous work. However, in our simulation we did not observe a systematic strong magnetic field within a thin region downstream of the supernova shock. This indicates if the thin X-ray rims seen in young supernova remnants are indeed caused by electron losing energy in synchrotron emission, some other physics such as the effect of cosmic rays is needed to explain the peripheral thin X-ray rims.