Proton temperature anisotropy upper bound
- Los Alamos National Laboratory, Los Alamos, New Mexico (United States)
- Jet Propulsion Laboratory, Pasadena, California (United States)
- Lockheed Martin Palo Alto Research Laboratory, Palo Alto, California (United States)
The electromagnetic proton cyclotron instability and the mirror instability are driven by the proton temperature anisotropy T{sub {perpendicular}p}/T{sub {parallel}p}{gt}1, where {perpendicular} and {parallel} denote directions relative to the background magnetic field. Linear theory and one-dimensional hybrid simulations imply that the former mode grows more rapidly over 0.05{le}{beta}{sub {parallel}p}{le}5 and that wave-particle scattering by its enhanced fluctuations imposes an upper bound on the temperature anisotropy of the form T{sub {perpendicular}p}/T{sub {parallel}p}{minus}1=S{sub p}/{beta}{sub {parallel}p}{sup {alpha}{sub p}} where {beta}{sub {parallel}p}{equivalent_to}8{pi}n{sub p}T{sub {parallel}p}/B{sub o}{sup 2} and B{sub o} is the background magnetic field. Here S{sub p} and {alpha}{sub p} are fitting parameters, and 0.4{approx_lt}{alpha}{sub p}{approx_lt}0.5. This paper describes results from more general two-dimensional hybrid simulations, which permit both instabilities to grow simultaneously. These simulations confirm the one-dimensional results on the initial domain 0.05{le}{beta}{sub {parallel}p}{approx_lt}5; enhanced fluctuations display the properties of the proton cyclotron instability and {alpha}{sub p}{approx_equal}0.4. On this domain the two-dimensional simulations also yield an upper bound for the fluctuating field energy density of the form {vert_bar}{delta}B{vert_bar}{sup 2}/B{sub o}{sup 2}{equivalent_to}{summation}{sub k}{vert_bar}{delta}B{sub k}{vert_bar}{sup 2}/B{sub o}{sup 2}=S{sub B}{beta}{sub {parallel}p}{sup {alpha}{sub B}} with fitting parameter 0.5{approx_lt}{alpha}{sub B}{approx_lt}1. The simulations on the initial domain 10{le}{beta}{sub {parallel}p}{le}100 show spectral characteristics of both instabilities and exhibit a more stringent bound on the proton anisotropy, in agreement with observations in the terrestrial magnetosheath. {copyright} 1997 American Geophysical Union
- OSTI ID:
- 610120
- Journal Information:
- Journal of Geophysical Research, Vol. 102, Issue A12; Other Information: PBD: Dec 1997
- Country of Publication:
- United States
- Language:
- English
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