X-ray1,2,3 and radio4,5,6 observations of the supernova remnant Cassiopeia A reveal the presence of magnetic fields about 100 times stronger than those in the surrounding interstellar medium. Field coincident with the outer shock probably arises through a nonlinear feedback process involving cosmic rays2,7,8. The origin of the large magnetic field in the interior of the remnant is less clear but it is presumably stretched and amplified by turbulent motions. Turbulence may be generated by hydrodynamic instability at the contact discontinuity between the supernova ejecta and the circumstellar gas9. However, optical observations of Cassiopeia A indicate that the ejecta are interacting with a highly inhomogeneous, dense circumstellar cloud bank formed before the supernova explosion10,11,12. Here we investigate the possibility that turbulent amplification is induced when the outer shock overtakes dense clumps in the ambient medium13,14,15. We report laboratory experiments that indicate the magnetic field is amplified when the shock interacts with a plastic grid. We show that our experimental results can explain the observed synchrotron emission in the interior of the remnant. The experiment also provides a laboratory example of magnetic field amplification by turbulence in plasmas, a physical process thought to occur in many astrophysical phenomena.
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We thank the Vulcan technical team at the Central Laser Facility of the Rutherford Appleton Laboratory for their support during the experiments; in particular, R. Clarke, M. Notley and R. Heathcote. A.R.B. acknowledges valuable discussions with H. Li (Los Alamos National Laboratory). The research leading to these results has received financial support from the European Research Council under the European Community’s Seventh Framework Programme (FP7/2007-2013)/ERC grant agreements no. 256973 and 247039, LASERLAB-EUROPE grant agreement No. 284464, the US Department of Energy under Contract No. B591485 to Lawrence Livermore National Laboratory, and Field Work Proposal No. 57789 to Argonne National Laboratory. Partial support from the Science and Technology Facilities Council and the Engineering and Physical Sciences Research Council of the United Kingdom (Grant No. EP/G007187/1) is also acknowledged. The work of R.P.D., C.C.K., M.J.M. and W.C.W. was supported by the USDOE under grant DE-NA0001840.
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The International Journal of High Performance Computing Applications (2019)