THE DISPERSION RELATIONS AND INSTABILITY THRESHOLDS OF OBLIQUE PLASMA MODES IN THE PRESENCE OF AN ION BEAM

Journal Article · Sun Feb 10 00:00:00 EST 2013 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/764/1/88· OSTI ID:22167780

Verscharen, Daniel ^[1]; Chandran, Benjamin D. G., ^[2]

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1. Space Science Center, University of New Hampshire, Durham, NH 03824 (United States)
2. Also at Department of Physics, University of New Hampshire, Durham, NH 03824, USA. (United States)

An ion beam can destabilize Alfven/ion-cyclotron waves and magnetosonic/whistler waves if the beam speed is sufficiently large. Numerical solutions of the hot-plasma dispersion relation have previously shown that the minimum beam speed required to excite such instabilities is significantly smaller for oblique modes with k Multiplication-Sign B {sub 0} {ne} 0 than for parallel-propagating modes with k Multiplication-Sign B {sub 0} = 0, where k is the wavevector and B {sub 0} is the background magnetic field. In this paper, we explain this difference within the framework of quasilinear theory, focusing on low-{beta} plasmas. We begin by deriving, in the cold-plasma approximation, the dispersion relation and polarization properties of both oblique and parallel-propagating waves in the presence of an ion beam. We then show how the instability thresholds of the different wave branches can be deduced from the wave-particle resonance condition, the conservation of particle energy in the wave frame, the sign (positive or negative) of the wave energy, and the wave polarization. We also provide a graphical description of the different conditions under which Landau resonance and cyclotron resonance destabilize Alfven/ion-cyclotron waves in the presence of an ion beam. We draw upon our results to discuss the types of instabilities that may limit the differential flow of alpha particles in the solar wind.

• OSTI ID: 22167780
• Journal Information: Astrophysical Journal, Vol. 764, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
ALPHA PARTICLES
APPROXIMATIONS
BEAMS
COLD PLASMA
CYCLOTRON RESONANCE
CYCLOTRONS
DISPERSION RELATIONS
HOT PLASMA
MAGNETIC FIELDS
MAGNETOHYDRODYNAMICS
NUMERICAL SOLUTION
PARTICLES
PLASMA INSTABILITY
POLARIZATION
QUASILINEAR PROBLEMS
SOLAR WIND
SUN
TURBULENCE
WHISTLERS