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Physics 777 Plasma Physics and Magnetohydrodynamics (MHD)

Physics 777 Plasma Physics and Magnetohydrodynamics (MHD). Instructor: Gregory Fleishman Lecture 8. Weak Turbulence and Magnetic Reconnection. 21 October 200 8. Plan of the Lecture. MHD turbulence, general ideas and approaches Plasma Nonlinearity and Wave-Wave Interactions

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Physics 777 Plasma Physics and Magnetohydrodynamics (MHD)

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  1. Physics 777Plasma Physics and Magnetohydrodynamics (MHD) Instructor: Gregory Fleishman Lecture 8. Weak Turbulence and Magnetic Reconnection 21 October 2008

  2. Plan of the Lecture • MHD turbulence, general ideas and approaches • Plasma Nonlinearity and Wave-Wave Interactions • Spectral Description of the Turbulence; Random Phase Approximation, • Magnetic Reconnection in the Plasma

  3. + = - l b Section 1. MHD turbulence, general ideas and approaches What is the turbulence? • Reynolds number: Re=VL/n (V2/L) / (nV/L2) • V2/L nV/L2 • When Re << Recritical, flow = laminar When Re >> Recritical, flow = turbulent Credit: J.Cho

  4. Example: wake behind a sphere critical Re = 40~50 Re~15,000 Credit: J.Cho

  5. Example: cylinder in water nwater ~ 0.01 (cgs) If v=10cm/sec & D=1 cm, Re~1000. ==> turbulence! Credit: J.Cho

  6. Orion nebula Interstellar gas Astrophysical fluids areturbulentandmagnetized (Re > 1010) Credit: J.Cho

  7. |B| B0 Spectra: Cho & Vishniac (2000) See also Muller & Biskamp (2000); Maron & Goldreich (2001) Credit: J.Cho

  8. Credit: J. M. Stone B Anisotropy • Smaller eddies are more elongated • Relation between parallel size and perp size? • Critically balanced turbulence l|| ~l^2/3 Credit: J.Cho

  9. Section 2. Plasma Nonlinearity and Wave-Wave Interactions Credit: E.Kontar

  10. Section 3. Spectral Description of the Turbulence • Structural functions of the turbulence • Spectral description • Random phase approximation • Statistically uniform turbulence • Isotropic and anisotropic turbulence

  11. Section 4. Magnetic Reconnection in the Plasma

  12. Section 7. Homework • See the web page

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