Physics of Plasma Accreting Structures$^*$

Plasma accretion is considered to take place within thin differentially rotating structures, (sequence of density rings\footnote {B. Coppi and F. Rousseau, \textit{Ap. J.}, \textbf{641}, 458 (2006)}) in the prevalent gravity of a central object where the vertical confinement is provided by the Lorentz force associated with internal toroidal currents. The factors that are needed to complete the solution of the equations$^1$ that describe ``ring configurations'' are identified and included in the relevant analysis. The relationship between poloidal flows and ``seed'' magnetic fields is uncovered and analyzed\footnote {B. Coppi and F. Rousseau, Paper O4.034, {Proceedings of the 2007 E.P.S. Conference on Plasma Physics} and MIT-LNS Report 07/06}. The significance of the symmetries of the poloidal currents that are found to be associated with the presence of an effective viscosity is pointed out. The problem of having a radial inflow velocity in a two-dimensional configuration with internal currents has been dealt with in the limit of very small ``seed'' magnetic fields by finding a narrow family ``open'' magnetic surfaces on which the plasma can spiral toward the central object$^2$. $^*$Sponsored in part by the US D.O.E.