The ion beam shepherd is an innovative contactless technique for space debris removal, in which an impulse transfer thruster pushes the debris object through the action of a plasma plume and an impulse compensation thruster maintains formation ying. The optimal operational point of both thrusters strongly depends on their characteristics and on the physics of the plasma plume expansion into vacuum. With the use of dedicated thruster performance models, complemented with simplied plume expansion and plasma-debris interaction models, a system-level optimization study of the impulse transfer thruster alone and of the overall electric propulsion subsystem is presented for an ion beam shepherd mission example. An optimum design point is found for minimum overall power consumption in both cases.
Abstract. The lithium problem in Ap-CP stars has been, for a long time, a subject of debate. Individual characteristics of CP stars, such as high abundance of the rare-earth elements presence of magnetic fields, complicate structure of the surface distribution of chemical elements, rapid oscillations of some CP-stars, make the detection of the lithium lines and the determination of the lithium abundance, a difficult task. During the International Meeting in Slovakia in 1996, the lithium problem in Ap-CP stars was discussed. The results of the Li study carried out in CrAO Polosukhina (1973)(1974)(1975)(1976), the works of Hack & Faraggiana (1963), Wallerstein & Hack (1964), Faraggiana et al. (1992Faraggiana et al. ( -1996 formed the basis of the International project 'Lithium in the cool CP-stars with magnetic fields'. The main goal of the project was, using systematical observations of Ap-CP stars with phase rotation in the spectral regions of the resonance doublet Li I 6708Å and subordinate 6104Å lithium lines with different telescopes, to create a database, which will permit to explain the physical origin of anomalous Li abundance in the atmospheres of these stars.
The process of microrelief formation on Si (100) surface under 30 keV Ga+ ion beam bombardment with doses 2⋅1017 - 4⋅1018 ion/cm2 at incident angles θ = 0 - 50° was studied. It was found that wave-like structures form on the surface at θ = 25° - 35° and doses 6⋅1017 - 2⋅1018 ion/cm2. The nice ripple formed at θ = 30±2° incident angles and irradiation dose 1018 ion/cm2.
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