Physics – Plasma Physics
Scientific paper
Nov 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004aps..dpphi1005c&link_type=abstract
American Physical Society, 46th Annual Meeting of the Division of Plasma Physics, 15-19 November, 2004, Savannah, GA. MEETING I
Physics
Plasma Physics
Scientific paper
A large variety of objects and phenomena in the Universe depend on the excitation of collective modes which can redistribute angular momentum at a rate that cannot be accounted for by classical viscosity. Accretion disks formed around a massive object, star formation and relevant self-gravitating disks are significant examples. Many of the theoretical tools to study these problems have a basis related to the fundamental stability investigations initiated by Marshall Rosenbluth. The emission of jets from plasma accretion disks support the argument that magnetic fields are important and that their energy density should be significant relative to the thermal energy density. This, and the fact that disks are thin, rule out the possibility that axisymmetric modes, driven by the rotation frequency gradient and contained within the disk[1], may provide the required rate of angular momentum transport. For this, the most promising modes are tridimensional, co-rotate with the disk at a given radius, and exhibit two sets of singularities when treated by the linearized MHD approximation. The most important of these occurs at the radii where the mode Doppler shifted frequency equals the slow magnetosonic frequency and the compressibility becomes infinite[1]. The singularity cannot be removed by classical dissipation, as in the case of theories on magnetic reconnection, but by non linear effects. At the laboratory scale, the explanation for the speed up of millisecond pulsars has inspired the ``accretion theory''[2] of the spontaneous rotation phenomenon observed in well confined toroidal plasmas without an external source of angular momentum. The explanation for the relevant ``negative viscosity'' involves the ejection of angular momentum to the material wall surrounding the plasma column and the transport of opposite angular momentum toward the center related to the outward flux of thermal energy due to electrostatic modes. Thus rotation and energy confinement are intrinsically connected. [1] B.Coppi and P.S.Coppi,Phys.Rev.Lett.,87,051101(2001) [2]B.Coppi,Nucl.Fus.,41,12,1(2001).
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