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Laboratory astrophysics: Investigation of planetary and astrophysical maser emission

  • R. Bingham
  • D. C. Speirs
  • B. J. Kellett
  • I. Vorgul
  • S. L. McConville
  • R. A. Cairns
  • A. W. Cross
  • A. D. R. Phelps
  • K. Ronald
Part of the Space Sciences Series of ISSI book series (SSSI, volume 47)

Abstract

This paper describes a model for cyclotron maser emission applicable to planetary auroral radio emission, the stars UV Ceti and CU Virginus, blazar jets and astrophysical shocks. These emissions may be attributed to energetic electrons moving into convergent magnetic fields that are typically found in association with dipole like planetary magnetospheres or shocks. It is found that magnetic compression leads to the formation of a velocity distribution having a horseshoe shape as a result of conservation of the electron magnetic moment. Under certain plasma conditions where the local electron plasma frequency ω pe is much less than the cyclotron frequency ω ce the distribution is found to be unstable to maser type radiation emission. We have established a laboratory-based facility that has verified many of the details of our original theoretical description and agrees well with numerical simulations. The experiment has demonstrated that the horseshoe distribution produces cyclotron emission at a frequency just below the local electron cyclotron frequency, with polarisation close to X-mode and propagating nearly perpendicularly to the electron beam motion. We discuss recent developments in the theory and simulation of the instability including addressing radiation escape problems, and relate these to the laboratory, space, and astrophysical observations. The experiments showed strong narrow band EM emissions at frequencies just below the cold-plasma cyclotron frequency as predicted by the theory. Measurements of the conversion efficiency, mode and spectral content were in close agreement with the predictions of numerical simulations undertaken using a particle-in-cell code and also with satellite observations confirming the horseshoe maser as an important emission mechanism in geophysical/astrophysical plasmas. In each case we address how the radiation can escape the plasma without suffering strong absorption at the second harmonic layer.

Keywords

Auroral kilometric radiation Cyclotron maser radiation Plasma instabilities Blazar jets 

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Copyright information

© Springer Science+Business Media Dordrecht 2013

Authors and Affiliations

  • R. Bingham
    • 1
    • 2
  • D. C. Speirs
    • 2
  • B. J. Kellett
    • 1
  • I. Vorgul
    • 3
  • S. L. McConville
    • 2
  • R. A. Cairns
    • 3
  • A. W. Cross
    • 2
  • A. D. R. Phelps
    • 2
  • K. Ronald
    • 2
  1. 1.Central Laser FacilitySTFC Rutherford Appleton LaboratoryChiltonUK
  2. 2.Department of Physics, SUPAUniversity of StrathclydeGlasgowUK
  3. 3.School of Mathematics and StatisticsUniversity of St. AndrewsSt. AndrewsUK

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