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Im Rahmen einer bayerisch-tschechischen Kooperation entstanden zwei mechanisch baugleiche Röntgenteleskope, bestückt mit Gold- und Iridium-beschichteten Planspiegeln. Die Charakterisierung der nach dem ägyptischen Gott HORUS benannten Teleskope erfolgte an der Röntgentestanlage PANTER des Max-Plack-Instituts für extraterrestrische Physik. Diese Vakuum-Testanlage simuliert parallel auf die Teleskope einfallendes Sternenlicht, wobei hier die Strahlung aus einer Röntgenquelle in 120 Metern Abstand stammt. Die Messungen selbst fanden in einer daran angebauten 12 Meter langen Testkammer von 3,5 Metern Durchmesser statt. Im März 2021 sahen die HORUS-Teleskope zum erstem Mal Röntgenlicht. Während der Testkampagne von ca. 54 Stunden Dauer wurden 536 Einzelmessungen an den beiden Teleskopen durchgeführt, bei denen Photonenenergien und Einfallswinkel variiert wurden. Von einer empfindlichen CCD-Kamera, einem Prototyp der eROSITA-Satellitenkamera, wurden hierbei insgesamt 11.153.574 Röntgenphotonen individuell detektiert, analysiert und digital verarbeitet. Die beiden Weitwinkel-Röntgenteleskope haben eine Winkelauflösung von circa 4 Bogenminuten und eine Brennweite von rund zwei Metern.
X-ray telescopes usually operate in space and are quite different from astronomical telescopes for visible light. For normal angles of incidence, optical light is reflected on the mirror surface, whereas X-rays are either transmitted or absorbed. However, also high reflectivity X-rays mirrors are possible, when the incident rays direction is almost parallel to the mirror surface. Such grazing incidence mirrors are usually coated with thin layers of precious metals like iridium, gold or platinum, as this result in high X-ray reflectivity. These noble metals offer a wide range of reflection up to high photon energies, but, due to a series of absorption edges, have low reflectivity in the 2 - 4 keV band and below. This contribution presents the development of innovative material combinations based on thin layers of iridium and chromium, followed by an additional layer of carbon-based materials. We also discuss corresponding production methods (like dip coating) for enhanced reflectivity mirror coatings of future X-ray telescopes.
Poster
We report on a comprehensive micromachining study of rotationally symmetric parts using femtosecond laser. A
laser turning process with tangential impingement of the laser radiation complemented by a trepanning optics is
implemented as to accomplish a true laser lathe micromachining approach. With the objective of optimized
ablation rate and reduced surface roughness, the influence of pulse energy, feed rate, trepanning diameter and
angular beam incidence, respectively, is investigated for processing stellite rods. We find the smallest feasible
feature sizes of 8.5 μm in diameter and smoothest surfaces with an arithmetic average of the roughness profile as
low as 0.18 μm. The surface roughness, however, appears to be limited by the occurrence of laser induced periodic
surface structures provoked by the femtosecond laser radiation. Furthermore, the variation of the fluence
in accordance to the incidence on a curved surface is discussed and the heat input into the material is examined
through a longitudinal cross section.
Laser turning with ultra-short laser pulses provides the possibility of manufacturing rotationally symmetric geometries, even of hard to machine materials as fused silica, down to a micrometer scale. In this laser micro machining approach, the laser beam is oriented perpendicularly to the rotational axis and tangentially to the material, whereas the target geometry is realized by moving the constantly rotating specimen according to the specified geometry under the focused laser spot. Due to the fric-tion-less laser ablation it is possible to realize a turning process in fused silica without the use of a contacting tool and therefore without causing mechanical tensions in the work piece. The processing head focuses the laser to a calculated spot size of 18 μm in diameter and the applied processing gas pressure assists in removing the ablated material. In this study, femto-second laser turning of fused silica with a diameter of 3.7 mm is investigated. The influence of the applied pulse energy is stated and the use of a trepanning optic during the turning process is characterized. Furthermore, compre-hensive parameter studies in order to optimize roughness and to find the maximum achievable abla-tion rate are shown. Limited by the mechanical speed of the rotational axis, the highest feasible abla-tion rate is 19.5 mm³/min. A roughness of Ra 0.65 μm are demonstrated.
Im vorliegenden Beitrag wird die Topologie des Doppelzweipunktwechselrichters für die Anwendung in Elektrofahrzeugen vorgestellt. Dazu werden zunächst der Schaltungsaufbau und die spezifischen Schaltungseigenschaften näher erläutert. Anschließend werden relevante Vorteile dieser Topologie für die Anwendung in Elektrofahrzeugen dargestellt. Für die Kombination unterschiedlicher Energiequellen mit Hilfe des Doppelzweipunktwechselrichters werden geeignete Steuerungsstrategien präsentiert und anhand von realen Messungen am Systemprüfstand verifiziert. Mit dem Vorgestellten Verfahren kann die Leistungsaufteilung auf die beiden Energiespeicher und deren Energieaustausch untereinander mit hohem Freiheitsgrad gesteuert werden.
Electric drives in road vehicles with a battery as energy storage are about to be introduced to the mass market. In order to guarantee the quality and operational safety of battery-powered vehicles, considerable efforts must be made by car manufacturers and their suppliers. Since the properties of the batteries significantly determine the performance of the vehicles, special test benches with precise measuring systems are required for the accurate determination of the battery properties. The safety devices of the traction batteries must also be tested on high-performance test benches. In this paper the necessary test benches and the corresponding measuring systems are presented. Estimations of the measurement uncertainty and possibilities to increase measurement accuracy are presented.
High Dynamic Power Balancing for Dual Two-Level Inverters during High-Speed Machine Operation
(2020)
This paper aims to present optimized square-wave modulation strategies for the dual two-level inverter, fed by two separate and galvanically isolated energy sources, to balance and control the energy distribution of both inverter systems. Especially for high-speed operation, the methods keep the machine in the required state while decreasing the switching operations to a minimum. Method one aims to compensate voltage fluctuations of variable DC-link voltages, while the second method ensures a symmetrical power distribution for the two inverter systems. In addition, both methods offer the possibility of adapting the amplitude of the usually fixed fundamental load voltage during square-wave modulation.
This paper aims to present an optimized inverter topology, based on the dual two-level inverter, for feeding an open-end winding electrical machine with superconductive stator windings and a superconductive rotor. In order to achieve a high torque density, the stator windings are built of several superconducting tapes being in parallel. One inverter of the dual two-level inverter is equipped with powerful IGBT semiconductors and supplies the machine with energy. The second inverter is a low voltage MOSFET inverter that monitors the superconductor resistance (quench detection) and balances the current on the parallel superconductive tapes for guaranteeing an optimum operation with respect to the superconductive losses.
In this contribution, a highly dynamic calculation method of power quantities and additional electrical quantities, such as RMS values and fundamental waveforms, is presented. Typically, these quantities are calculated periodically based on the fundamental cycle of the electrical voltages and currents. Hence, they are well defined during steady state conditions for ideal periodical waveforms. During dynamic balancing processes, electrical signals are non-periodic. In a strict sense, the fundamental cycle-based definitions, which are well known from the literature, are not valid for these transient signals. However, this paper presents a novel definition for the calculation of cycle-based quantities based on the switching cycle of the inverter output voltages. This definition delivers instantaneous results during transient balancing processes, whereby it approximates the conventional fundamental cycle-based definitions during the steady state.