1,721,116 research outputs found
Plasma Component of Self-gravitating Disks and Relevant Magnetic Configurations
No full textAstrophysical disks in which the disk self-gravity is more important than the gravity force associated with the central object can have significant plasma components where appreciable toroidal current densities are produced. When the vertical confinement of the plasma rotating structures that can form is kept by the Lorentz force rather than by the vertical component of the gravity force, the disk self-gravity remains important only in the radial equilibrium condition, modifying the rotation curve from the commonly considered Keplerian rotation. The equilibrium equations that are solved involve the vertical and the horizontal components of the total momentum conservation equations, coupled with the lowest order form of the gravitational Poisson's equation. The resulting poloidal field configuration can be visualized as a sequence [1] of Field Reverse Configurations, in the radial direction, consisting of pairs of oppositely directed current channels. The plasma density thus acquires a significant radial modulation that may grow to the point where plasma rings can form [2]. [1] B. Coppi, Phys. Plasmas, 12, 057302 (2005) [2] B. Coppi and F. Rousseau, to be published in Astrophys. J. (April 2006
Self-gravitating Disks and Plasma Structures Immersed in Them
No full textWhen considering axisymmetric differentially rotating plasma structures in the prevalent gravity of a central object these are found to be characterized by a sequence of current filaments and to develop a corresponding ring sequence configuration for the plasma. The same type of structure can be found when the self-gravity of a differentially rotating plasma component is no less important than the gravity of the central object. Then in addition to the vertical and horizontal equilibrium equations to be solved, Poisson's equation for the gravitational potential has to be dealt with. The fact that the vertical equilibrium is ensured by the vertical component of the Lorentz force due to the internal plasma currents (``Lorentz compression'') simplifies the problem considerably.
*Sponsored in part by the Universita' di Milano and by the U.S. DOE B. Coppi and F. Rousseau, Ap. J. 641 (1), 458 (2006)
Importance and Unpredictability of Self-organization Processes in Fusion Burning Plasmas
No full textSelf-organization processes are considered to have an important role in well confined plasmas produced by present day experiments where the heating source is externally applied. The observation of ``Profile Consistency'' [1] is viewed as a manifestation of the presence of these processes. In the case of fusion burning plasmas close to self-sustainment (ignition) most of the heating due to fusion products is strongly dependent on the evolution of both the plasma temperature and density profiles. Therefore, self-organization is expected to be of considerably greater importance than in the case of non-reacting plasmas. This fact involves a significant degree of unpredictability on the outcome of envisioned experiments on burning plasmas that has to be added to the complexity of the collective modes that are expected to emerge. Thus, one of the motivations for the Ignitor program is to shed light on these issues and minimize the uncertainties for the design of more ambitious undertakings such as a Compact Pilot Plant. *Sponsored in part by CNR of Italy. [1] B. Coppi, Comm. Plasma Phys. Cont. Fusion extbf{5}, 261 (1980)
Axisymmetric Equilibria of Thin Plasma Accretion Disks
No full textThe equilibrium axisymmetric configurations that thin plasma accretions disks immersed in force-free external magnetic fields can sustain are identified. In the case where the plasma pressure exceeds the magnetic pressure (β ≫ 1) the fields produced by toroidal currents localized within the disk are shown to correspond to the marginally stable axisymmetric ballooning modes identified in Refs. [1] and [2]. These fields are periodic radially with a period of the order of the height of the disk. When β ̃ 1, the radial periodicity of the magnetic field has a significant influence on the radial dependence of the plasma pressure as well. Then the radial equilibrium equation can no longer be treated separately from the vertical equilibrium equation as in the case where β ≫ 1. The relevant non-linear problem has been posed but not solved yet
Physical regimes available to the Ignitor experiment and relevant theoretical developments
No full textFormation of Magnetic Fields on Grand Scale Distances
Full text linkThe emergence of significant magnetic fields in cosmic plasmas over large scale distances is an important issue to deal with as known and potentially applicable theories, such as those based on the Weibel instability, suffers from the difficulty of involving unrealistically small distances (e.g. ). The presently proposed theory, to avoid this difficulty, starts from considering the electron density and temperature fluctuations [1] which can be excited in circumbinary disks sustained by pairs of black holes. These low frequency fluctuations can drive a ``magneto-thermal alternator’’ of the kind introduced in Ref. [2] which can produce a slowly varyingly and sheared magnetic field structure. The shearing component of this field can then be amplified by a magneto-thermal reconnection process [2] up to more significant amplitudes. This however requires an event that would produce a strong local electron pressure gradient. An important feature of magneto-thermal reconnection is that the width of the layer where reconnection takes place can grow with the involved macroscopic distances [2] unlike the case of the collisionless tearing mode whose analysis was given in Ref. [3]. *Sponsored by the Kavli Foundation and CNR.
[1] B. Coppi, Fundamental Pl. Phys., 100007 (2023).
[2] B. Coppi, and B. Basu, Phys. Lett. A, 397, 127265 (2021).
[3] B. Coppi, L. Sugiyama, J. Mark and G. Bertin, Ann. Phys. 119, 2 (1979)
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