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Waveparticle interaction around the lower hybrid resonance Horita, Robert Eiji
Abstract
Waveparticle interaction in the ionosphere is studied theoretically for wave frequencies around the lower hybrid resonance (LHR) frequency. Expressions are derived by two methods for the growth rate of whistlermode waves propagating in a magnetoactive plasma penetrated by a tenuous beam of nonthermal particles. The first method employs the electrostatic dispersion equation; the second uses the fullwave dispersion equation which reduces to the electrostatic one for large values of refractive index. The equilibrium distribution function for the plasma is Maxwellian, and that for the diffuse streaming particles is also Maxwellian, but is shifted by a streaming velocity parallel to the background magnetic field. The first method assumes that the temperatures are isotropic, while the second assumes that the distributions are characterized by the perpendicular and parallel temperatures, T[subscript: I] and T[subscript: II] . The growthrate expressions are fairly general, but numerical calculations are performed for the case of a cold plasma consisting of electrons, H⁺ , He⁺ , and 0⁺ ions and a beam of nonthermal electrons. The growthrate expression obtained using the electrostatic dispersion equation shows that waves propagating slightly off the direction perpendicular to the background magnetic field can grow due to the Landau instability process which is excited by high energy (∼ 10 keV) electrons streaming along the direction of the magnetic field of the earth. The growing wave thus triggered is shown to have a frequency band with a sharp lower cutoff at the LHR frequency and an upper limit at the electron cyclotron frequency or electron plasma frequency, whichever is lower. The previous growthrate expression is generalized by making use of the fullwave dispersion equation. It is shown that there are two regions in propagation angle 6 where the Landau instability may occur. The "electrostatic" region lies just below the resonant angle and, separated by a region of damping, the "lowθ" region lies above θ = 0 . The growthrate values calculated in the "electrostatic" region correspond to the values obtained in the previous calculation. Generally, the maximum growth rate is larger in the "electrostatic" than in the "lowθ" region. It is also seen that with increasing frequency the "electrostatic" maximum growth rate increases monotonically and the cyclotron instabilities become important at frequencies above about ten times the LHR frequency. The influence of the following parameters on the growth rate is also examined: temperature ratio T[subscript: II]/T[subscript: I], streaming velocity of the nonthermal particles, and the ratio of the kinetic energy in the streaming motion to the thermal energy of the streaming electrons. The theory presented is applied to LHR noise bands discovered by the Canadian Alouette I satellite. It is shown that many features are in good agreement. Other observations, such as auroral hiss, also have features which suggest that the theoretical work may be relevant to these types of ionospheric noise.
Item Metadata
Title 
Waveparticle interaction around the lower hybrid resonance

Creator  
Publisher 
University of British Columbia

Date Issued 
1968

Description 
Waveparticle interaction in the ionosphere is studied theoretically for wave frequencies around the lower hybrid resonance
(LHR) frequency. Expressions are derived by two methods for the growth rate of whistlermode waves propagating in a magnetoactive plasma penetrated by a tenuous beam of nonthermal particles. The first method employs the electrostatic dispersion
equation; the second uses the fullwave dispersion equation
which reduces to the electrostatic one for large values of refractive index. The equilibrium distribution function for the plasma is Maxwellian, and that for the diffuse streaming
particles is also Maxwellian, but is shifted by a streaming velocity parallel to the background magnetic field. The first method assumes that the temperatures are isotropic, while the second assumes that the distributions are characterized by the perpendicular and parallel temperatures, T[subscript: I] and T[subscript: II] . The growthrate expressions are fairly general, but numerical calculations
are performed for the case of a cold plasma consisting
of electrons, H⁺ , He⁺ , and 0⁺ ions and a beam of nonthermal electrons.
The growthrate expression obtained using the electrostatic
dispersion equation shows that waves propagating slightly off the direction perpendicular to the background magnetic field can grow due to the Landau instability process which is excited by high energy (∼ 10 keV) electrons streaming along the direction of the magnetic field of the earth. The growing wave thus triggered is shown to have a frequency band with a sharp lower cutoff at the LHR frequency and an upper limit at the electron cyclotron frequency or electron plasma frequency, whichever is lower.
The previous growthrate expression is generalized by making use of the fullwave dispersion equation. It is shown that there are two regions in propagation angle 6 where the Landau instability may occur. The "electrostatic" region lies just below the resonant angle and, separated by a region of damping, the "lowθ" region lies above θ = 0 . The growthrate values calculated in the "electrostatic" region correspond to the values obtained in the previous calculation. Generally, the maximum growth rate is larger in the "electrostatic" than in the "lowθ" region. It is also seen that with increasing frequency the "electrostatic" maximum growth rate increases monotonically and the cyclotron instabilities become important at frequencies above about ten times the LHR frequency. The influence of the following parameters on the growth rate is also examined: temperature ratio T[subscript: II]/T[subscript: I], streaming velocity of the nonthermal particles, and the ratio of the kinetic energy in the streaming motion to the thermal energy of the streaming electrons.
The theory presented is applied to LHR noise bands discovered
by the Canadian Alouette I satellite. It is shown that many features are in good agreement. Other observations, such as auroral hiss, also have features which suggest that the theoretical work may be relevant to these types of ionospheric noise.

Subject  
Genre  
Type  
Language 
eng

Date Available 
20110719

Provider 
Vancouver : University of British Columbia Library

Rights 
For noncommercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.

DOI 
10.14288/1.0053387

URI  
Degree  
Program  
Affiliation  
Degree Grantor 
University of British Columbia

Campus  
Scholarly Level 
Graduate

Aggregated Source Repository 
DSpace

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Rights
For noncommercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.