Universität Stuttgart
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Item Open Access Self-consistent modelling of pulsar magnetospheres(1989) Herold, Heinz; Ertl, Thomas; Finkbeiner, Bernd; Ruder, HannsThe magnetosphere of a rapidly rotating, strongly magnetized neutron star with aligned magnetic and rotational axes (parallel rotator) is modelled numerically. Including the radiation of the particles accelerated to relativistic energies as an efficient damping mechanism, we obtain a quasi-stationary selfconsistent solution to this classical problem. The numerical simulation, which was started from the well-known vacuum solution, yields a global magnetospheric structure that can be characterized by two regions of oppositely charged particles, which eventually produce a relativistic pulsar wind, separated by a vacuum gap of considerable extent.Item Open Access Particle motion in pulsar magnetospheres(1987) Finkbeiner, Bernd; Ertl, Thomas; Herold, Heinz; Ruder, HannsThis report discusses some new results we found in studying the trajectories of single charged particles in the vacuum magnetosphere of a pulsar using the oblique rotator model. We believe that investigations of individual particles in the vicinity of the star can be useful for a better understanding of some fundamental problems of pulsar physics, e.g. the global structure of the magnetosphere or the pulsar radiation.Item Open Access Rydberg atoms in uniform magnetic fields: uncovering the transition from regularity to irregularity in a quantum system(1986) Wunner, Günter; Woelk, Ulrich; Zech, Ingrid; Zeller, Gudrun; Ertl, Thomas; Geyer, Florian; Schweizer, Wolfgang; Ruder, HannsWe investigate the eigenvalue spectra of hydrogen Rydberg atoms in strong magnetic fields for manifestations of quantum stochasticity and find (i) a smooth transition from a Poisson-type to a Wigner-type distribution of level spacings in the range of energy where classical motion becomes increasingly chaotic, (ii) the occurrence of multiple avoided crossings, and (iii) connected with this, an extreme sensitivity of oscillator strengths, and thus of observable spectra, with respect to small variations of an external parameter, viz., the magnetic field strength.Item Open Access Generation of relativistic particles in pulsar magnetospheres(1985) Herold, Heinz; Ertl, Thomas; Ruder, HannsThe problem - fundamental for the physics of pulsars - of determining the global structure of the magnetosphere in a self-consistent way has not yet been solved satisfactorily. We report on some progress in this direction, which we have achieved by studying the trajectories of individual charged particles in the electromagnetic vacuum fields of an aligned rotator.Item Open Access Effects of radiation damping on particle motion in pulsar vacuum fields(1989) Finkbeiner, Bernd; Herold, Heinz; Ertl, Thomas; Ruder, HannsThe effects of radiation reaction on the motion of charged particles are studied in strong electric and magnetic fields with special attention to the vacuum near-field region of an oblique rotator. For strong radiation damping a local velocity field is derived from the Lorentz-Dirac equation, which efficiently describes the motion of electrons and positrons in the whole range of typical pulsar parameters. The velocity field makes it possible to define regions in the inner magnetosphere, where particle trapping occurs due to the radiation losses. By numerical integration of particle trajectories from the pulsar surface, regions around the magnetic poles are found which are defined by particle emission into the wave zone. The shapes of the escape regions on the pulsar surface are determined to a considerable extent by the presence of the accumulation regions.Item Open Access Towards a self-consistent modelling of pulsar magnetospheres(1986) Herold, Heinz; Ertl, Thomas; Ruder, HannsThe numerical modelling of the general case of an obligue rotator is a very complicated time-dependent three-dimensional problem and in its full extent probably outside the capacity of present-day computers. A considerable simplification occurs if one can assume that the essential effects may be understood by modelling the magnetosphere of an aligned rotator (where the rotation axis is parallel to the magnetic axis of the neutron star). This assumption is only reasonable for small obliguenses, since by this approach all electromagnetic wave effects are not taken into account. An advantage, however, is that unipolar induction, which should be responsible for populsting the magnetosphere with charged particles pulled out from the neutron star surface via field emission, can be studied purity.Item Open Access Hydrogenic Rydberg atoms in strong magnetic fields: theoretical and experimental spectra in the transition region from regularity to irregularity(1987) Holle, Armin; Wiebusch, Gerd; Main, Jörg; Welge, Karl H.; Zeller, Gudrun; Wunner, Günter; Ertl, Thomas; Ruder, HannsFor deuterium Rydberg atoms in a magnetic field of sim6~T we compare the complete experimental spectrum in the range -190 cm-1 to -20 cm-1 with the positions and oscillator strengths of the corresponding quantum theoretically calculated photoabsorption lines. The agreement is excellent. The range of energy covered extends from the end of thel-mixing regime up to the regions where the approximate integrability of the problem is completely lost, and the corresponding classical system undergoes a transition to chaos.Item Open Access Analysis of hydrogen Rydberg spectra in a uniform magnetic field: uncovering the transition from regularity to irregularity in a real quantum system(1986) Wunner, Günter; Woelk, Ulrich; Zech, Ingrid; Zeller, Gudrun; Ertl, Thomas; Geyer, Florian; Steitz, Arno; Schweizer, Wolfgang; Ruder, HannsStudies of the behaviour of quantum systems in a range of energy where their classical counterparts undergo transitions from regularity to irregularity, as manifested in phase space by the gradual destruction of invariant tori, to date have largely been confined to model Hamiltonian systems such as harmonic oscillators with cubic, quartic, or higher-degree polynomial corrections, or the stadium problem. We show that phenomena which have turned out characteristic of the onset of "quantum stochasticity" in these model systems can in fact be recovered in the quantal energy spectra of a "real" physical system, viz. spectra of hydrogen Rydberg atoms in strong magnetic fields. This implies that one has a simple prototype system at hand in which to study - not only in theory but also in experiment, quantitatively and in detail, and as a function of a continuously tunable external parameter - phenomena that are expected to be typical of the quantum properties of nonintegrable systems in general.Item Open Access Line-of-sight integration: a powerful tool for visualization of three-dimensional scalar fields(1989) Ruder, Hanns; Ertl, Thomas; Geyer, Florian; Herold, Heinz; Kraus, UteAn easy conceivable but very powerful method for the visualization of three-dimensional scalar fields is described. The way this method works is illustrated by some examples and the computed pictures are compared with the results of other methods of representation.Item Open Access Visualization in astrophysics(1989) Ertl, Thomas; Geyer, Florian; Herold, Heinz; Kraus, Ute; Niemeier, Roland; Nollert, Hans-Peter; Rebetzky, Andreas; Ruder, Hanns; Zeller, GudrunThis paper reports on progress we have made in modelling cosmic X·ray sources on supercomputers. The results we present are meant to serve as an example for the fact that sophisticated visualization techniques play a crucial role in scientific computing. Among the graphical methods we demonstrate, raytracing in curved space-time and a physically motivated 3D-volume rendering algorithm might be of interest to the graphics community in general.