Radiation From Instabilities In Space Plasmas

Melrose, D. B.

doi:10.1007/978-94-011-4203-8_30

Cited by 2 publications

(1 citation statement)

References 19 publications

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“…The electron loss-cone distribution [Wu and Lee 1979; Winglee and Pritchett 1986] was suggested as the population inversion required for maser emission. However there is little or no evidence [Delory et al 1998;Ergun et al 2000] of the loss -cone distribution in the satellite data to support this assertion and as pointed out by Melrose (Melrose 1998), for the emission to be explained by a loss-cone instability it has to be supposed that all observations are of a saturated state after the loss -cone has filled by pitch angle diffusion. The loss-cone instability was also questioned as the source of terrestrial auroral kilometric radiation (AKR) by the results of particle-in-cell simulations conducted by Pritchett [Pritchett, 1986;Pritchett et al 1999], based on observed electron distribution functions.…”

Section: Introductionmentioning

confidence: 92%

Laboratory astrophysics: Investigation of planetary and astrophysical maser emission

et al. 2013

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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 polarization 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.

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Section: Introductionmentioning

confidence: 92%

Laboratory astrophysics: Investigation of planetary and astrophysical maser emission

et al. 2013

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Propagation and escape of astrophysical cyclotron-maser radiation

Speirs

Gillespie

Ronald

et al. 2013

2013 19th IEEE Pulsed Power Conference (PPC)

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A multitude of astrophysical plasma environments exist where a combination of particle acceleration, convergent magnetic fields and a sufficiently large ratio of electron cyclotron frequency to plasma frequency are present to support electron cyclotron-maser emission [1-6]. The resultant radiation signatures typically comprise of well-defined spectral components (around the relativistic electron cyclotron frequency) with near 100% left or right handed circular polarization when viewed out-with the source region. Although the generation mechanism has been well documented [7-25], there are numerous potential hindrances to the propagation and escape of the radiation from the source region, including issues of geometry/mode conversion [26] and coupling onto the dispersion branch connecting with vacuum propagation [12]. In the current context we consider the results of numerical Particle-in-cell (PiC) simulations conducted at the University of Strathclyde to study the spatial growth rate and emission topology of the cyclotron-maser emission process. The results have significant bearing on the radiation propagation characteristics and highly debated question of propagation/escape, with particular relevance to the planetary/stellar auroral magnetospheric case

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Radiation From Instabilities In Space Plasmas

Cited by 2 publications

References 19 publications

Laboratory astrophysics: Investigation of planetary and astrophysical maser emission

Laboratory astrophysics: Investigation of planetary and astrophysical maser emission

Propagation and escape of astrophysical cyclotron-maser radiation

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