Electron temperature anisotropy instabilities: Whistler, electrostatic and z mode
- Los Alamos National Laboratory, Los Alamos, New Mexico (United States)
- School of Physics, University of Sydney, New South Wales (Australia)
An electron temperature anisotropy T{sub {perpendicular}e}/T{sub {parallel}e}{gt}1 leads to excitation of three distinct instabilities in collisionless plasmas at frequencies below the electron cyclotron frequency {vert_bar}{Omega}{sub e}{vert_bar} (Here {perpendicular} and {parallel} denote directions relative to the background magnetic field {bold B}{sub o}.). Linear Vlasov theory is used to study these growing modes, with emphasis on the scaling of the temperature anisotropy at instability threshold. If the electron plasma frequency {omega}{sub e} is greater than {vert_bar}{Omega}{sub e}{vert_bar} and electrons are sufficiently hot, the whistler is the unstable mode with smallest anisotropy threshold; this electromagnetic mode has maximum growth rate at propagation parallel to {bold B}{sub o}. At {omega}{sub e}{gt}0.5{vert_bar}{Omega}{sub e}{vert_bar}, an electrostatic electron anisotropy instability can arise propagation oblique to {bold B}{sub o}; this mode may have the smallest threshold for sufficiently cool electrons and {omega}{sub e}{approximately}{vert_bar}{Omega}{sub e}{vert_bar}. And T{sub {perpendicular}e}/T{sub {parallel}e}{gt}1 drives the {ital z} mode unstable at {omega}{sub e}{lt}{vert_bar}{Omega}{sub e}{vert_bar}; this electromagnetic mode also has maximum growth rate at parallel propagation and is the persistent instability at {omega}{sub e}{approx_lt}0.5{vert_bar}{Omega}{sub e}{vert_bar}. The results are discussed in connection with observations from the polar and auroral regions of the terrestrial magnetosphere. {copyright} 1999 American Geophysical Union
- OSTI ID:
- 688000
- Journal Information:
- Journal of Geophysical Research, Journal Name: Journal of Geophysical Research Journal Issue: A9 Vol. 104; ISSN 0148-0227; ISSN JGREA2
- Country of Publication:
- United States
- Language:
- English
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