[en] Applying the model of Molodensky et al. we have investigated the fibril directions (H-alpha level) for the penumbran and superpenumbran region of a sunspot, namely the main, but following spot of the small, simple active region SD 135/1984 on June 24. To reduce the number of free parameters of the model we used vector magnetograms. Comparing structures of H-alpha filtergrams and heliograms with the theoretical field model we got the following information: The chromospheric structure of the sunspot magnetic field was essentially a result of two subsstems. The two sources had nearly the same magnetic flux densities, a very small distance relative to the sunspot areal, and the resulting magnetic field topolog had nearly a current-free configuration. These results are in good agreement with earlier investigations of this active region. (author). 7 refs

[en] The magnetic surfaces and rotational transform of a stellarator with low poloidal-field wave number and elliptical minor cross-section have been computed numerically by utilizing a predictor-corrector code. The surfaces exhibit stagnation points the positions of which are related to the aspect ratio of the ellipse and the l-number of the configuration. The rotational transform is less than in an equivalent stellarator with circular cross-section for the same toroidal and helical currents in the magnet coils. (author)

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[en] We have developed two strong focusing field configurations that provide high midplane accessibility and therefore are compatible with presently contemplated extraction schemes for high-current, toroidal accelerators. When these windings are attached to a modified betatron accelerator, the bandwidth of the device is slightly smaller than the bandwidth of a modified betatron with unsplit stellarator windings. However, the bandwidth of the two new configurations is more than sufficient even for modest (20--30 kA) winding currents

[en] The concept of magnetic field line merging is defined as the process whereby plasma flows across a surface that separates regions containing topologically different magnetic field lines, and is illustrated by reference to various possible structures of magnetic topology in the magnetosphere. A key element is the electric field tangent to the magnetic separatrix surfaces; its role and its relation to the MHD approximation can be viewed both in a global and a local context. (Auth.)

[en] The return-flux sunspot model is generalized by including azimuthal magnetic field Bsub(PHI). The basic equation is obtained and numerical solutions are compared with the analogous solutions for the Schlueter-Temesvary sunspot theory for two cases: Bsub(PHI)proportionalBsub(r) and Bsub(PHI)proportionalrBsub(r). The solutions demonstrate that the twisting of the sunspot magnetic field decreases with height. Our models confirm Yun's early statement: the azimuthal field only slightly influences sunspot structure. (orig.)

No abstract available

[en] Experimental investigations into the effects of the magnetic field configuration near the channel exit on the plume of Hall thrusters were conducted. The magnetic field configuration near the channel exit is characterized by the inclination angle between the magnetic field lines and the thruster radial direction. Different inclination angles were obtained by varying the current ratio in the coils. The plume divergence angles were measured by a dual-directed probe. The results showed that the plume divergence angle increased obviously with the increase in the magnitude of the inclination angle near the channel exit. Therefore, in order to optimize the magnetic field for reducing plume divergence, the magnitude of the inclination angle should be reduced as much as possible. It suggests that the magnetic field configuration near the channel exit is another important factor that affects plume divergence.

[en] This lecture deals with the nonlinear properties of individual tearing modes. First the purely resistive case is considered. The nonlinear island growth is a slow diffusion process on the resistive skin time scale. The different effects determining the saturation are outlined. Tearing modes in a high temperature plasma are then discussed, where, in addition to resistivity, diamagnetic and viscous effects are important. Nonlinearly, these so-called drift tearing modes may behave quite similarly to purely resistive modes, since diamagnetic effects are quenched at a certain island size depending on the rate of cross-field plasma diffusion. (orig.) 891 GG/orig. 892 HIS