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.

Access optionsAccess options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.


  1. 1.

    , & Mapping the x-ray-emitting ejecta in Cassiopeia A with Chandra. Astrophys. J. 537, 119–122 (2000).

  2. 2.

    & Proper motions and brightness variations of nonthermal x-ray filaments in the Cassiopeia A supernova remnant. Astrophys. J. 697, 535–543 (2009).

  3. 3.

    , , & Cosmic-ray diffusion near the Bohm limit in the Cassiopeia A supernova remnant. Nature Phys. 2, 614–619 (2006).

  4. 4.

    & The deceleration powering of synchrotron emission from ejecta components in supernova remnant Cassiopeia A. Astrophys. J. 441, 307–333 (1995).

  5. 5.

    , & The polarization and depolarization of radio emission from supernova remnant Cassiopeia A. Astrophys. J. 441, 300–306 (1995).

  6. 6.

    Proper motions and temporal flux changes of compact features in Cassiopeia A at 5 GHz. Mon. Not. R. Astron. Soc. 179, 537–585 (1977).

  7. 7.

    & On the magnetic fields and particle acceleration in Cassiopeia A. Astrophys. J. 584, 758–769 (2003).

  8. 8.

    Turbulent amplification of magnetic field and diffusive shock acceleration of cosmic rays. Mon. Not. R. Astron. Soc. 353, 550–558 (2004).

  9. 9.

    The X-ray, optical and radio properties of young supernova remnants. Mon. Not. R. Astron. Soc. 171, 263–278 (1975).

  10. 10.

    & Optical studies of Cassiopeia A. I. Proper motions in the optical remnant. Astrophys. J. 162, 485–493 (1970).

  11. 11.

    & Cassiopeia A and its clumpy presupernova wind. Astrophys. J. 593, L23–L26 (2003).

  12. 12.

    , , & A circumstellar shell model for the Cassiopeia A supernova remnant. Astrophys. J. 466, 866–870 ( 1996).

  13. 13.

    , , & Enhanced cloud disruption by magnetic field interaction. Astrophys. J. 441, L113–L116 (1999).

  14. 14.

    & Magnetic field amplification by shocks in turbulent fluids. Astrophys. J. 663, L41–L44 (2007).

  15. 15.

    et al. On the amplification of magnetic fields by a supernova blast shock wave in a turbulent medium. Astrophys. J. 747, 98 (2012).

  16. 16.

    & A detailed kinematic map of Cassiopeia A’s optical main shell and outer high-velocity ejecta. Astrophys. J. 772, 134 (2013).

  17. 17.

    et al. Similarity criteria for the laboratory simulation of supernova hydrodynamics. Astrophys. J. 518, 821–832 (1999).

  18. 18.

    , , & Modeling astrophysical phenomena in the laboratory with intense lasers. Science 284, 1488–1493 (1999).

  19. 19.

    & The use of a contraction to improve the isotropy of grid-generated turbulence. J. Fluid Mech. 25, 657–682 (1966).

  20. 20.

    & Astrophysical blastwaves. Rev. Mod. Phys. 60, 1–68 (1988).

  21. 21.

    & The effect of porosity on shock interaction with a rigid porous barrier. Shock Waves 16, 321–337 (2007).

  22. 22.

    et al. Generation of scaled protogalactic seed magnetic fields in laser-produced shock waves. Nature 481, 480–483 (2012).

  23. 23.

    Über den Ursprung der Magnetfelder auf Sternen und im interstellaren Raum. Z. Naturforsch. A 5, 65–71 (1950).

  24. 24.

    Fluctuations of the magnetic field and current density in a turbulent flow of a weakly conducting fluid. Sov. Phys. Dokl. 5, 536–539 (1960).

  25. 25.

    et al. Fluctuation dynamo and turbulent induction at low magnetic Prandtl numbers. New J. Phys. 9, 300 (2007).

  26. 26.

    The amplification of a weak applied magnetic field by turbulence in fluids of moderate conductivity. J. Fluid Mech. 11, 625–635 (1961).

  27. 27.

    , & Advection of a magnetic field by a turbulent swirling flow. Phys. Rev. E 58, 7397–7401 (1998).

  28. 28.

    & Characterizing the nonthermal emission of Cassiopeia A. Astrophys. J. 686, 1094–1102 (2008).

  29. 29.

    et al. Design, construction, and calibration of a three-axis, high-frequency magnetic probe (B-dot probe) as a diagnostic for exploding plasmas. Rev. Sci. Instrum. 80, 113505 (2009).

  30. 30.

    , , , & Spect3d—a multi-dimensional collisional-radiative code for generating diagnostic signatures based on hydrodynamics and PIC simulation output. High Energy Dens. Phys. 3, 181–190 (2007).

Download references


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.

Author information


  1. Department of Physics, University of Oxford, Parks Road Oxford OX1 3PU, UK

    • J. Meinecke
    • , H. W. Doyle
    • , A. R. Bell
    • , M. Fatenejad
    • , A. A. Schekochihin
    • , P. Tzeferacos
    • , B. Reville
    •  & G. Gregori
  2. Department of Physics, ETH Zürich, Wolfgang-Pauli-Strasse 27, CH-8093 Zürich, Switzerland

    • F. Miniati
  3. Rutherford Appleton Laboratory, Chilton, Didcot OX11 0QX, UK

    • R. Bingham
  4. Department of Physics, University of Strathclyde, Glasgow G4 0NG, UK

    • R. Bingham
  5. Department of Physics, University of York, Heslington, York YO10 5D, UK

    • R. Crowston
    •  & N. C. Woolsey
  6. Atmospheric, Oceanic, Space Science, University of Michigan, 2455 Hayward Street Ann Arbor, Michigan 48103, USA

    • R. P. Drake
    • , C. C. Kuranz
    • , M. J. MacDonald
    •  & W. C. Wan
  7. Department of Astronomy and Astrophysics, University of Chicago, 5640 South Ellis Avenue Chicago, Illinois 60637, USA

    • M. Fatenejad
    • , D. Q. Lamb
    • , D. Lee
    • , A. Scopatz
    • , P. Tzeferacos
    •  & G. Gregori
  8. Laboratoire pour l’Utilisation de Lasers Intenses, UMR7605, CNRS CEA, Université Paris VI Ecole Polytechnique, 91128 Palaiseau Cedex, France

    • M. Koenig
    • , A. Pelka
    • , A. Ravasio
    •  & R. Yurchak
  9. Institute of Laser Engineering, Osaka University, 2-6 Yamadaoka, Suita, Osaka 565-0871, Japan

    • Y. Kuramitsu
    •  & Y. Sakawa
  10. School of Physics and Astronomy, University of Edinburgh, Edinburgh EH8 9YL, UK

    • C. D. Murphy
  11. Lawrence Livermore National Laboratory, Livermore, California 94550, USA

    • H-S. Park
  12. School of Mathematics and Physics, Queens University of Belfast, Belfast BT7 1NN, UK

    • B. Reville


  1. Search for J. Meinecke in:

  2. Search for H. W. Doyle in:

  3. Search for F. Miniati in:

  4. Search for A. R. Bell in:

  5. Search for R. Bingham in:

  6. Search for R. Crowston in:

  7. Search for R. P. Drake in:

  8. Search for M. Fatenejad in:

  9. Search for M. Koenig in:

  10. Search for Y. Kuramitsu in:

  11. Search for C. C. Kuranz in:

  12. Search for D. Q. Lamb in:

  13. Search for D. Lee in:

  14. Search for M. J. MacDonald in:

  15. Search for C. D. Murphy in:

  16. Search for H-S. Park in:

  17. Search for A. Pelka in:

  18. Search for A. Ravasio in:

  19. Search for Y. Sakawa in:

  20. Search for A. A. Schekochihin in:

  21. Search for A. Scopatz in:

  22. Search for P. Tzeferacos in:

  23. Search for W. C. Wan in:

  24. Search for N. C. Woolsey in:

  25. Search for R. Yurchak in:

  26. Search for B. Reville in:

  27. Search for G. Gregori in:


G.G., D.Q.L, B.R. and F.M. conceived this project, and it was designed by G.G., J.M., B.R., C.D.M., R.B., A.A.S., N.C.W. and R.P.D. The Vulcan experiment was carried out by J.M., H.W.D., M.J.M., R.C., C.C.K., C.D.M., A.P. and W.C.W. The paper was written by J.M., G.G., H.W.D., A.A.S., A.R.B., D.Q.L., P.T. and B.R. The data were analysed by J.M. and H.W.D. Numerical simulations were performed by P.T. Further experimental and theoretical support was provided by R.B., R.P.D., M.F., M.K., Y.K., D.L., H-S.P., A.R., Y.S., A.S., P.T., N.C.W. and R.Y.

Competing interests

The authors declare no competing financial interests.

Corresponding authors

Correspondence to J. Meinecke or G. Gregori.

Supplementary information

PDF files

  1. 1.

    Supplementary Information

    Supplementary Information


  1. 1.

    Supplementary Movie

    Supplementary Movie 1

  2. 2.

    Supplementary Movie

    Supplementary Movie 2

About this article

Publication history






Further reading

Newsletter Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing