Engineering topics

Contopoulos, J.

Publications and source records attributed to Contopoulos, J..

5 records

NASA NTRS2000

The Axisymmetric Pulsar Magnetosphere

We present the structure of the axisymmetric force-free magnetosphere of an aligned rotating magnetic dipole, in the case in which there exists a sufficiently large charge density (whose origin we do not question) to satisfy the ideal MHD condition, E (raised dot) B = 0, everywhere. The unique distribution of electric current along the open magnetic field lines which is required for the solution to be continuous and smooth is obtained numerically. We expect that our solution will be useful as the starting point for detailed studies of pulsar magnetospheres under more general conditions, namely when either the force-free and/or the ideal MHD condition E (raised dot) B = 0 are not valid in the entire magnetosphere. Based on our solution, we consider that the most likely positions of such an occurrence are the polar cap, the crossings of the zero space charge surface by open field lines, and the return current boundary, but not the light cylinder.

Contopoulos, J.↗

NASA NTRS1994

Magnetically driven relativistic jets and winds: Exact solutions

We present self-consistent solutions of the full set of ideal MHD equations which describe steady-state relativistic cold outflows from thin accretion disks. The magnetic field forms a spiral which is anchored in the disk, rotates with it, and accelerates the flow out of the disk plane. The collimation at large distances depends on the total amount of electric current that flows along the jet. We considered various distributions of electric current and derived the result that in straight jets which extend to infinite distances, a strong electric current flows along their axis of symmetry. The asymptotic flow velocities are of the order of the initial rotational velocity at the base of the flow (a few tenths of the speed of light). The solutions are applied to both galactic (small-scale) and extragalactic (large-scale) jets.

Contopoulos, J.↗

NASA NTRS1994

Magnetically driven jets and winds: Exact solutions

We present a general class of self-similar solutions of the full set of MHD equations that include matter flow, electromagnetic fields, pressure, and gravity. The solutions represent axisymmetric, time-independent, nonrelativistic, ideal, magnetohydrodynamic, collimated outflows (jet and winds) from magnetized accretion disks around compact objects. The magnetic field extracts angular momentum from the disk, accelerates the outflows perpedicular to the disk, and provides collimation at large distances. The terminal outflow velocities are of the order of or greater than the rotational velocity of the disk at the base of the flow. When a nonzero electric current flows along the jet, the outflow radius oscillates with axial distance, whereas when the total electric current is zero (with the return current flowing across the jet's cross section), the outflow radius increase to a maximum and then decreases. The method can also be applied to relativistic outflows.

Contopoulos, J.↗

NASA NTRS1993

Theory of jets from young stars

Simple equations are derived for the long-distance propagation of magnetohydrodynamic (MHD) jets. Solutions of these equations are fitted to two observed jets providing estimates of the fast magnetosonic speeds (V(f)) and the distances of the fast magnetosonic points. The relation of the jet properties at large distances to a complete family of MHD jet solutions is discussed, and it is shown that there is one key dimensionless parameter, B. The dependences of the fast magnetosonic speed and of the fluxes of mass, energy, momentum, and angular momentum of the jet on B are discussed. For B larger than a critical value (about 0.45), the central star spins down, while for smaller values it spins up. For increasing from the critical value, V(f) increases while the mass and momentum fluxes of the jet decrease.

Lovelace, R. V. E.↗

NASA NTRS1991

Magnetically driven jets and winds

Four equations for the origin and propagation of nonrelativistic jets and winds are derived from the basic conservation laws of ideal MHD. The axial current density is negative in the vicinity of the axis and positive at larger radii; there is no net current because this is energetically favored. The magnetic field is essential for the jet solutions in that the zz-component of the magnetic stress acts, in opposition to gravity, to drive matter through the slow magnetosonic critical point. For a representative self-consistent disk/jet solution relevant to a protostellar system, the reaction of the accreted mass expelled in the jets is 0.1, the ratio of the power carried by the jets to the disk luminosity is 0.66, and the ratio of the boundary layer to disk luminosities is less than about 0.13. The star's rotation rate decreases with time even for rotation rates much less than the breakup rate.

Lovelace, R. V. E.↗