Demonstration of auroral radio emission mechanisms by laboratory experiment

S L McConville, D C Speirs, K Ronald, A D R Phelps, A W Cross, R Bingham, C W Robertson, C G Whyte, W He, K Gillespie, I Vorgul, R A Cairns, B J Kellett

Research output: Contribution to journalArticle

Abstract

Auroral kilometric radiation occurs in regions of depleted plasma density in the polar magnetosphere. These emissions are close to the electron cyclotron frequency and appear to be connected to the formation of high pitch angle electron populations due to the conservation of the magnetic moment. This results in a horseshoe type distribution function being formed in velocity space where electrons are magnetically compressed as they descend towards the Earth's atmosphere. Satellites have observed that radio emissions occur in conjunction with the formation of this distribution and show the radiation to have propagation and polarization characteristics of the extraordinary (X-mode) plasma mode with emission efficiency observed at ~1–2%. To investigate this phenomenon a laboratory experiment, scaled to microwave frequencies and lab dimensions by increasing the cyclotron frequency, was constructed whereby an electron beam propagated through a region of increasing magnetic field created by five independently variable solenoids. Results are presented for two experimental regimes of resonant coupling, 11.7 and 4.42 GHz, achieved by varying the peak magnetic field. Measurements of the experimental radiation frequency, power and efficiency were undertaken as a function of the magnetic compression. Results showed the radiation to be polarized in the near cut-off transverse electric radiation modes, with efficiency of emission ~1–2%, peak power outputs of ~19–30 kW and frequency close to the cyclotron frequency. This represented close correlation between the laboratory radiation efficiency, spectra, polarization and propagation with that of numerical predictions and the magnetospheric observations.
LanguageEnglish
Article number074010
Number of pages13
JournalPlasma Physics and Controlled Fusion
Volume50
Issue number7
Early online date3 Jun 2008
DOIs
Publication statusPublished - 31 Jul 2008

Fingerprint

radio emission
Demonstrations
Radiation
cyclotron frequency
Cyclotrons
radiation
Experiments
Electrons
magnetic compression
Polarization
Magnetic fields
Magnetosphere
Earth atmosphere
electrons
polarization characteristics
propagation
Plasma density
Solenoids
pitch (inclination)
Microwave frequencies

Keywords

  • plasma density
  • polar magnetosphere
  • electron cyclotron frequency
  • microwave

Cite this

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title = "Demonstration of auroral radio emission mechanisms by laboratory experiment",
abstract = "Auroral kilometric radiation occurs in regions of depleted plasma density in the polar magnetosphere. These emissions are close to the electron cyclotron frequency and appear to be connected to the formation of high pitch angle electron populations due to the conservation of the magnetic moment. This results in a horseshoe type distribution function being formed in velocity space where electrons are magnetically compressed as they descend towards the Earth's atmosphere. Satellites have observed that radio emissions occur in conjunction with the formation of this distribution and show the radiation to have propagation and polarization characteristics of the extraordinary (X-mode) plasma mode with emission efficiency observed at ~1–2{\%}. To investigate this phenomenon a laboratory experiment, scaled to microwave frequencies and lab dimensions by increasing the cyclotron frequency, was constructed whereby an electron beam propagated through a region of increasing magnetic field created by five independently variable solenoids. Results are presented for two experimental regimes of resonant coupling, 11.7 and 4.42 GHz, achieved by varying the peak magnetic field. Measurements of the experimental radiation frequency, power and efficiency were undertaken as a function of the magnetic compression. Results showed the radiation to be polarized in the near cut-off transverse electric radiation modes, with efficiency of emission ~1–2{\%}, peak power outputs of ~19–30 kW and frequency close to the cyclotron frequency. This represented close correlation between the laboratory radiation efficiency, spectra, polarization and propagation with that of numerical predictions and the magnetospheric observations.",
keywords = "plasma density, polar magnetosphere, electron cyclotron frequency, microwave",
author = "McConville, {S L} and Speirs, {D C} and K Ronald and Phelps, {A D R} and Cross, {A W} and R Bingham and Robertson, {C W} and Whyte, {C G} and W He and K Gillespie and I Vorgul and Cairns, {R A} and Kellett, {B J}",
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Demonstration of auroral radio emission mechanisms by laboratory experiment. / McConville, S L; Speirs, D C; Ronald, K; Phelps, A D R; Cross, A W; Bingham, R; Robertson, C W; Whyte, C G; He, W; Gillespie, K; Vorgul, I; Cairns, R A; Kellett, B J.

In: Plasma Physics and Controlled Fusion, Vol. 50, No. 7, 074010, 31.07.2008.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Demonstration of auroral radio emission mechanisms by laboratory experiment

AU - McConville, S L

AU - Speirs, D C

AU - Ronald, K

AU - Phelps, A D R

AU - Cross, A W

AU - Bingham, R

AU - Robertson, C W

AU - Whyte, C G

AU - He, W

AU - Gillespie, K

AU - Vorgul, I

AU - Cairns, R A

AU - Kellett, B J

PY - 2008/7/31

Y1 - 2008/7/31

N2 - Auroral kilometric radiation occurs in regions of depleted plasma density in the polar magnetosphere. These emissions are close to the electron cyclotron frequency and appear to be connected to the formation of high pitch angle electron populations due to the conservation of the magnetic moment. This results in a horseshoe type distribution function being formed in velocity space where electrons are magnetically compressed as they descend towards the Earth's atmosphere. Satellites have observed that radio emissions occur in conjunction with the formation of this distribution and show the radiation to have propagation and polarization characteristics of the extraordinary (X-mode) plasma mode with emission efficiency observed at ~1–2%. To investigate this phenomenon a laboratory experiment, scaled to microwave frequencies and lab dimensions by increasing the cyclotron frequency, was constructed whereby an electron beam propagated through a region of increasing magnetic field created by five independently variable solenoids. Results are presented for two experimental regimes of resonant coupling, 11.7 and 4.42 GHz, achieved by varying the peak magnetic field. Measurements of the experimental radiation frequency, power and efficiency were undertaken as a function of the magnetic compression. Results showed the radiation to be polarized in the near cut-off transverse electric radiation modes, with efficiency of emission ~1–2%, peak power outputs of ~19–30 kW and frequency close to the cyclotron frequency. This represented close correlation between the laboratory radiation efficiency, spectra, polarization and propagation with that of numerical predictions and the magnetospheric observations.

AB - Auroral kilometric radiation occurs in regions of depleted plasma density in the polar magnetosphere. These emissions are close to the electron cyclotron frequency and appear to be connected to the formation of high pitch angle electron populations due to the conservation of the magnetic moment. This results in a horseshoe type distribution function being formed in velocity space where electrons are magnetically compressed as they descend towards the Earth's atmosphere. Satellites have observed that radio emissions occur in conjunction with the formation of this distribution and show the radiation to have propagation and polarization characteristics of the extraordinary (X-mode) plasma mode with emission efficiency observed at ~1–2%. To investigate this phenomenon a laboratory experiment, scaled to microwave frequencies and lab dimensions by increasing the cyclotron frequency, was constructed whereby an electron beam propagated through a region of increasing magnetic field created by five independently variable solenoids. Results are presented for two experimental regimes of resonant coupling, 11.7 and 4.42 GHz, achieved by varying the peak magnetic field. Measurements of the experimental radiation frequency, power and efficiency were undertaken as a function of the magnetic compression. Results showed the radiation to be polarized in the near cut-off transverse electric radiation modes, with efficiency of emission ~1–2%, peak power outputs of ~19–30 kW and frequency close to the cyclotron frequency. This represented close correlation between the laboratory radiation efficiency, spectra, polarization and propagation with that of numerical predictions and the magnetospheric observations.

KW - plasma density

KW - polar magnetosphere

KW - electron cyclotron frequency

KW - microwave

UR - http://iopscience.iop.org/journal/0741-3335

U2 - 10.1088/0741-3335/50/7/074010

DO - 10.1088/0741-3335/50/7/074010

M3 - Article

VL - 50

JO - Plasma Physics and Controlled Fusion

T2 - Plasma Physics and Controlled Fusion

JF - Plasma Physics and Controlled Fusion

SN - 0741-3335

IS - 7

M1 - 074010

ER -