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Titel |
Numerical simulation of auroral magnetospheric cyclotron emission processes |
VerfasserIn |
D. C. Speirs, R. Bingham, R. A. Cairns, B. J. Kellett, S. L. McConville, K. M. Gillespie, I. Vorgul, A. D. R. Phelps, A. W. Cross, K. Ronald |
Konferenz |
EGU General Assembly 2012
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Medientyp |
Artikel
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Sprache |
Englisch
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 14 (2012) |
Datensatznummer |
250069665
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Zusammenfassung |
A variety of astrophysical radio emissions have been identified to date in association with
non-uniform magnetic fields and accelerated particle streams. Numerous such sources,
including planetary and stellar auroral radio emission are spectrally well defined with a high
degree of extraordinary (X-mode) polarisation [1]. In particular, for the terrestrial auroral case
it is now widely accepted that such emissions are generated by an electron cyclotron-maser
instability driven by a horseshoe shaped electron velocity distribution [2,3]. Such
distributions are formed when particles descend into the increasing magnetic field of
planetary / stellar auroral magnetospheres, where conservation of the magnetic
moment results in conversion of axial momentum into rotational momentum forming
an electron velocity distribution having a large spread in pitch factor. Theory has
shown that such distributions are unstable to cyclotron emission in the X-mode
[4].
Experiments and simulations have been conducted at the University of Strathclyde
investigating the electrodynamics of an electron beam subject to significant magnetic
compression [5]. More recently, a background plasma of variable density has been introduced
to the interaction region of the laboratory experiment and the resultant stability of the
cyclotron-maser instability investigated [6]. Corroboratory simulations have been conducted
using the PiC code VORPAL to investigate the cyclotron emission process in the presence of
a background plasma and in the absence of radiation boundaries [7]. Simulations have
investigated the spatial growth of the instability in a sheet electron beam in the
presence of a background plasma whose density increases along the path of beam
propagation. These simulations demonstrate a significant enhancement in spatial growth
over the larger cross-sectional dimension of the sheet beam, and can simulate the
upward refraction of the generated radiation – consistent with theoretical predictions
and geophysical observations of enhanced emission / growth of terrestrial AKR
tangential to the auroral cavity boundary and upward refraction of the resultant
radiation due to the increasing background plasma density with decreasing altitude
[8].
[1] R. Bingham, R.A. Cairns and B.J. Kellett, Astron. Astrophys., 370, 1000
(2001).
[2] R.E. Ergun, C.W. Carlson, C.W. McFadden et al., Astrophys. J., 538, 456
(2000).
[3] I. Vorgul, R.A. Cairns and R. Bingham, Phys. Plasmas 12, 122903 (2005).
[4] R.A. Cairns, I. Vorgul, R. Bingham et al., Phys. Plasmas 18, 022902 (2011).
[5] K. Ronald, D.C. Speirs, S.L. McConville, et al., Phys. Plasmas, 15, 056503
(2008).
[6] S.L. McConville, M.E. Koepke, K.M. Gillespie et al., Plasma Phys. Control. Fusion,
53, 124020 (2011).
[7] D.C. Speirs, K. Ronald, S.L. McConville, Phys. Plasmas, 17, 056501 (2010).
[8] J.D. Menietti, R.L. Mutel, I.W. Christopher et al., J. Geophys. Res., 116, A12219
(2011). |
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