Recent high-resolution (see, e.g., [13]) observations of astrophysical jets reveal complex structures apparently caused by ejecta from the central engine as the ejecta interact with the surrounding interstellar material. These observations include time-lapsed “movies” of both AGN and microquasars jets which also show that the jet phenomena are highly time-dependent. Such observations can be used to inform models of the jet–ambient-medium interactions. Based on an analysis of these data, we posit that a significant part of the observed phenomena come from the interaction of the ejecta with prior ejecta as well as interstellar material. In this view, astrophysical jets interact with the ambient medium through which they propagate, entraining and accelerating it. We show some elements of the modeling of these jets in this paper, including energy loss and heating via plasma processes, and large scale hydrodynamic and relativistic hydrodynamic simulations.
Summary form only given, as follows. A dimensionless stability model that tracks the growth and predation of various wave populations is compared with one-dimensional particle-in-cell (PIC) simulations. The stability model uses rate equations to evaluate the coupling of longitudinal waves created by beam-plasma instabilities in order to estimate beam propagation distances. These wave energies and beam propagation distance estimates are compared with bounded one-dimensional PIC simulations. The onset and saturation of the beam-plasma instabilities are evaluated in the simulations. The simulations enable the stability model to be benchmarked and to explore the temporal evolution of background plasma energy distribution, a capability not presently included in the stability model. The scaleable, dimensionless stability model can be used in laboratory and astrophysical parameter regimes while numerical constraints limit the parameter regimes treatable in the PIC simulations.
A convection instability characteristic of plasmas in an inhomogeneous azimuthal magnetic field is treated in the linear stage and in nonlinear saturation. The analysis is done in such a way that collisional and collisionless limits can be taken, and these limits are displayed along with the more general intermediate result. The instability, known previously in the literature in its collision-dominated form, is shown to be a ’’flute’’ instability with collisional modifications to the growth rate. The nonlinear saturation is analyzed by examining a finite amplitude restoring-force term in the differential equation that describes the instability. This term is due to the fact that the instability convects plasma into striations of the plasma column surface, modifying the density gradient driving force. The effects of finite ion gyroradius are displayed, and applications of this study to convection cells in a thermal plasma and to exploding wire plasmas are discussed.
A fully electromagnetic linear stability analysis is used to investigate beam-plasma interactions in a filled cylindrical conducting waveguide. The system is immersed in a finite applied axial magnetic field, and it assumed that the electron gyroradius is small compared with the waveguide radius. The effects on stability of a small spread in the perpendicular and parallel beam momentum are considered. Particular attention is focused on the two-stream and beam cyclotron instabilities, and it is shown that the cyclotron instability can grow faster than the two-stream instability for ωce≳ωpe when the beam is sufficiently relativistic.
This program has as its primary objective the quantitative exploration and generalization of the core-corona model of imploding plasma load dynamics in close collaboration with radiation physics and modeling work. As a qualitative summary, one may say that the core-corona model arises from four physical considerations, all interrelated. The first assumption is that of a sharp density falloff in the outer regions of the annular plasma load. The transition region between the dense core plasma and the halo of corona plasma surrounding it is associated with a change from classical to anomalous resistivity, due to the onset of marginally stable microturbulence in the low density corona plasma. The second assumption is that the high-density annular wire/plasma core stops a penetrating coronal electron in distances short compared to the core dimensions, so that the coronal heating can couple to the core and soften the implosion. However, it is important to note that coronal electrons will not tend to execute straight orbits into the core, due to the large magnetic fields in the current carrying zone on the core surface. A third ingredient in the core/corona equation is an isothermal corona, and for this one must assume the corona to be sufficientlymore » limited in space that equilibration to an isothermal pressure balance can be established rapidly as the core annulus implodes. The corona continuously re-established its pressure balance as the transition interface moves inward. The final constraint in the original core-corona model equations was that of quasi-static heat balance between ohmic heating in the corona, net deposition of hot electron energy into the core, and coronal radiative losses.« less
Abstract : When astrophysical jets interact with the ambient medium through which they propagate, they lose energy and entrain (and accelerate) that medium. Recent observations of such interactions, including time-lapsed movies of both AGN and microquasar jets, can be used to inform models of the jet-ambient-medium interactions. In this paper, we discuss some aspects of these jets, including the mechanisms of their propagation, their constitution and the non-linear character of their energy loss via plasma processes. We also present for the first time PIC code simulations to show momentum transfer via caviton formation as a result of plasma processes. An illustration of the microphysics of the interaction of a proton-electron beam with an ambient magnetic field is also presented.
Abstract : Virtual cathode formation in vacuum-propagating beams may be more widespread than previously recognized. The spin death of parallel beam energy by E sub r x B sub z rotation in front of a density pileup, may assist or steepen the axial density gradient, since the rotation speed tends toward Brillouin flow, omega = omega sub c/2. It may be that the propagation limit (on the beam density) is not omega-squared sub p approx. equal omega-squared sub c in the applied or total magnetic field, but rather omega-squared sub p max (in the presence of self-field pileup) small enough that cE sub r/B sub z V sub 0 (V sub 0 = beam electron speed), with E sub r given self-consistently from the charge distribution. In what follows, self-consistent BGK-like axially dependent equilibria will be described, in which the space charge effects determine the axial extent and profile of the beam. Generalization to axially nonuniform magnetic fields is relatively straightforward. Sections III and IV treat the problem in a purely one-dimensional way, keeping the electrostatic effects of E sub z electric fields but not the effects of beam rotation caused by E sub r. Section V generalizes these results to include E sub r.
'%3e%3cpath fill='%23012169' d='M0 0v30h60V0z'/%3e%3cpath stroke='%23fff' stroke-width='6' d='m0 0 60 30m0-30L0 30'/%3e%3cpath stroke='%23C8102E' stroke-width='4' d='m0 0 60 30m0-30L0 30' clip-path='url(%23b)'/%3e%3cpath stroke='%23fff' stroke-width='10' d='M30 0v30M0 15h60'/%3e%3cpath stroke='%23C8102E' stroke-width='6' d='M30 0v30M0 15h60'/%3e%3c/g%3e%3c/svg%3e)