A Kinetic Alfvén Wave Cascade Subject to Collisionless Damping Cannot Reach Electron Scales in the Solar Wind at 1 AU

• Published in: The Astrophysical journal Vol. 712; no. 1; pp. 685 - 691
• Main Authors: Podesta, J. J, Borovsky, J. E, Gary, S. P
• Format: Journal Article
• Language: English
• Published: Bristol IOP Publishing 20.03.2010; IOP
• Subjects: ALFVEN WAVES; Astronomy; ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; DAMPING; Earth, ocean, space; ELECTRONS; ELEMENTARY PARTICLES; Exact sciences and technology; FERMIONS; FLUCTUATIONS; FLUID MECHANICS; HYDRODYNAMICS; HYDROMAGNETIC WAVES; LANDAU DAMPING; LEPTONS; MAGNETIC FIELDS; MAGNETOHYDRODYNAMICS; MECHANICS; PLASMA; SOLAR ACTIVITY; SOLAR WIND; STELLAR ACTIVITY; STELLAR WINDS; TURBULENCE; VARIATIONS; Alfven waves; waves; Kinetic Alfven wave; Plasma; Fluctuations; Turbulence; Power spectra; Linear damping; Landau damping; Models; Solar magnetic field; Power law; Solar wind
• ISSN: 0004-637X; 1538-4357
• DOI: 10.1088/0004-637X/712/1/685

Turbulence in the solar wind is believed to generate an energy cascade that is supported primarily by Alfven waves or Alfvenic fluctuations at MHD scales and by kinetic Alfven waves (KAWs) at kinetic scales k{sub perpendicular}rho{sub i} {approx}> 1. Linear Landau damping of KAWs increases with increasing wavenumber and at some point the damping becomes so strong that the energy cascade is completely dissipated. A model of the energy cascade process that includes the effects of linear collisionless damping of KAWs and the associated compounding of this damping throughout the cascade process is used to determine the wavenumber where the energy cascade terminates. It is found that this wavenumber occurs approximately when |gamma/omega| {approx_equal} 0.25, where omega(k) and gamma(k) are, respectively, the real frequency and damping rate of KAWs and the ratio gamma/omega is evaluated in the limit as k{sub perpendicular} >> k{sub ||}. For plasma parameters typical of high-speed solar wind streams at 1 AU, the model suggests that the KAW cascade in the solar wind is almost completely dissipated before reaching the wavenumber k{sub perpendicular}rho{sub i} {approx_equal} 25. Consequently, an energy cascade consisting solely of KAWs cannot reach scales on the order of the electron gyro-radius, k{sub perpendicular}rho{sub e} {approx} 1. This conclusion has important ramifications for the interpretation of solar wind magnetic field measurements. It implies that power-law spectra in the regime of electron scales must be supported by wave modes other than the KAW.