Universität Stuttgart
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Item Open Access Science planning for the DESTINY+ Dust Analyzer : leveraging the potential of a space exploration instrument(2024) Sommer, Maximilian; Srama, Ralf (Apl. Prof. Dr.-Ing.)The DESTINY+ Dust Analyzer (DDA) is a highly sophisticated planetary science instrument to provide cutting-edge in-situ characterization of individual cosmic dust grains, with respect to their composition, as well as their physical and dynamical properties. As such, it constitutes a critical component of the upcoming JAXA mission DESTINY+, which is scheduled to launch in 2025. After a three-year cruise phase, the spacecraft will perform a flyby of the target asteroid 3200 Phaethon, with the goal of observing the enigmatic Geminids parent body with two camera instruments, and sampling particles released from its surface with the DDA. Until that flyby, DESTINY+ will execute a highly diverse, ion-engine-driven flight plan that allows DDA to extensively study the dust environments of the Earth, Moon, and interplanetary space - a breadth of science opportunities that is unique to this mission and instrument. This dissertation provides a comprehensive study of the dust types and phenomena possibly encountered by DDA during its journey to Phaethon and applies the principles and methods of science planning to prepare for the operational phase of the mission. The work synthesizes technical considerations and scientific analyses of relevant cosmic dust populations, aiming to optimize DDA’s scientific potential. Detailed examinations of spacecraft and instrument factors, such as the dynamic spacecraft attitude during the near-Earth phase or the instrument’s two-axis pointing mechanism, lay the groundwork for the scientific planning. The thorough analysis of known (and lesser known) dust populations in the inner solar system and of previous relevant measurements by other dust instruments form the core of the study. Finally, the findings are consolidated into a draft science activity plan for the entire mission, as well as exemplary pointing timelines to be executed by the instrument for optimal scientific return. The latter is accomplished with the DOPE tool, which aids in intuitive and efficient planning of DDA observations, having been developed in the scope of this project. The presented work builds the foundation for the scientific operations of DDA, setting it up for a successful and scientifically impactful mission. The findings of this study also provide a valuable perspective for other ventures of in-situ dust astronomy to the inner solar system and contribute to the field of cosmic dust as a whole.Item Open Access Spectroscopic characterization of extrasolar planets from ground-, space- and airborne-based observatories(2010) Angerhausen, Daniel; Krabbe, Alfred (Prof. Dr. rer. nat.)This thesis deals with techniques and results of observations of exoplanets from several platforms. In this work I present and then attempt solutions to particular issues and problems connected to ground- and space-based approaches to spectroscopic characterization of extrasolar planets. Furthermore, I present the future prospects of the airborne observatory, SOFIA, in this field of astronomy. The first part of this thesis covers results of an exploratory study to use near-infrared integral-field-spectroscopy to observe transiting extrasolar planets. I demonstrate how adaptive-optics assisted integral field spectroscopy compares with other spectroscopic techniques currently applied, foremost being slit spectroscopy. An advanced reduction method using elements of a spectral-differential decorrelation and optimized observation strategies is discussed. This concept was tested with K-Band time series observations of secondary eclipses of HD 209458b and HD 189733b obtained with the SINFONI at the Very Large Telescope (VLT), at spectral resolution of R~3000. In ground-based near infrared (NIR) observations, there is considerable likelihood of confusion between telluric absorption features and spectral features in the targeted object. I describe a detailed method that can cope with such confusion by a forward modelling approach employing Earth transmission models. In space-based transit spectroscopy with Hubble's NICMOS instrument, the main source of systematic noise is the perturbation in the instrument's configuration due to the near Earth orbital motion of the spacecraft. I present an extension to a pre-existing data analysis sequence that has allowed me to extract a NIR transmission spectrum of the hot-Neptune class planet GJ 436b from a data set that was highly corrupted by the above mentioned effects. Satisfyingly, I was able to obtain statistical consistency in spectra (acquired over a broad wavelength grid) over two distinct observing visits by HST. Earlier reductions were unable to achieve this feat. This work shows that systematic effecting the spectrophotometric light-curves in HST can be removed to levels needed to observe features in the relatively small scale-height atmospheres of hot Neptune class planets orbiting nearby stars. In the third and final part of this thesis, I develop and discuss possible science cases for the airborne Stratospheric Observatory for Infrared Astronomy (SOFIA) in the field of detection and characterization of extrasolar planets. The principle advantages of SOFIA and its suite of instrumentation is illustrated and possible targets are introduced. Possible next generation instrumentation (dedicated to exoplanetary science) is discussed.Item Open Access Machine learning and Monte Carlo based data analysis methods in cosmic dust research(2019) Albin, Thomas; Srama, Ralf (Priv.-Doz. Dr.-Ing.)This work applies miscellaneous algorithms from the fields Machine Learning and Computational Numerics on the research field Cosmic Dust. The task is to determine the scientific and technical potential of using different methods. Here, the methods are applied on two different projects: the meteor camera system Canary Island Long-Baseline Observatory (CILBO) and the Cassini in-situ dust telescope Cosmic-Dust-Analyzer (CDA).Item Open Access Ion beam lithographic and multilayer fresnel zone plates for soft and hard X-rays: nanofabrication and characterization(2015) Keskinbora, Kahraman; Schütz, Gisela (Prof. Dr.)X-ray microscopy has become an important analytical characterization method for a plethora of applications in materials science, physics, chemistry and biology, thanks to the emergence of modern synchrotron radiation facilities. These facilities enable high brilliance, energy tunable, variable polarization X-rays which gives access to mass density, elemental, chemical, electronic and magnetic properties of materials. In the soft X-ray energies nearly all elements can be probed by spectromicroscopic methods. Another important property of synchrotron radiation is the time structure in the ns to ps range, which can be utilized for sophisticated time resolution studies. These opportunities can be combined with high spatial resolution which is determined by the focusing method and the optic. Focusing of X-rays has historically been a difficult task due to strong absorption and weak phase shift of X-rays within matter. The required phase shift of X-rays, which depends on the real part of the complex refractive index, differs from 1 (the vacuum refractive index) only on the order of 10^-2 to 10^-6 and conventional lenses do not work. One very successful X-ray optic is the Fresnel Zone Plate (FZP), a diffractive optic that act as a lens under certain conditions and can focus X-rays to nanometer sized spots. The resolution of the FZP depends on the width of the outermost zone and is highly correlated with the smallest feature that can be fabricated. Conventionally, the e-beam lithography (EBL) is used for production FZPs which could resolve up to 10 nm structures with serious limitations. One difficulty of EBL is its ever increasing complexity for many-step fabrication of smaller features or intricate geometries. Therefore, EBL is mostly constrained to planar, binary geometries with moderate efficiencies strongly decreasing with energy and not effective for hard X-rays. Special 3D geometries in the form of kinoform lenses can theoretically have 100 % focusing efficiencies. Attempts to approximate these geometries via EBL increased the number of process steps even further. The smallest FZP feature size even for low aspect ratios achievable via EBL is fundamentally limited due to the proximity effect which is the interaction and spread of electrons within the resist material. We addressed these issues by focusing our research on alternative FZP fabrication techniques as high-speed ion beam lithography (IBL), and gray scale ion lithography to realize efficient kinoforms. Another approach towards full-material multilayer FZPs with infinite aspect ratio was based on atomic layer deposition (ALD) with subsequent ion beam slicing. Each of these three methods targets specific challenges faced by the e-beam lithography based FZP fabrication techniques. All the fabricated FZPs were tested for their resolution and efficiency performances at a state of the art scanning transmission X-ray microscope at BESSY for soft X-rays and/or at optical test stations at ESRF and PETRA III for hard X-rays. Using IBL the rapid preparation of a 110 nm thick Au FZP with 50 µm diameter and 50 nm ∆r in less than 13 minutes is demonstrated. Employed for X-ray microscopy, the FZP clearly resolved 28.5 nm features with a cut-off of 24.3 nm at ~1120 eV. Additional process improvements were made towards smaller zones with higher zone quality. They allowed the preparation of a FZP with 30 nm outermost half-period remarkably, in about 8 min. This FZP was shown to clearly resolve 21 nm features on a multilayer test object with large room for improvement. This high through-put FZP production route is of special interest not only concerning the low cost and easy availability. A large array of these optical components is attractive, for experiments such as one-shot ultra-high brilliance FEL investigations due to the radiation damage or for instance for coded-aperture arrays for high-angle resolving X-ray astronomy. Towards fabrication of kinoforms for high efficiency X-ray focusing, we have performed various materials optimization studies in order to achieve a high surface quality optic. After various trials the materials were finally optimized and the fabricated lenses achieved more than 14 % absolute diffraction efficiency that is almost 90 % compared to the theoretical prediction. This confirms how closely we were able to replicate the ideal three dimensional surface relief structure for the first time. It was possible to carry out imaging with these lenses with half-pitch resolutions down to 60 nm. The kinoform lenses were tested at the soft X-ray range where a significant absorption is present in materials. These results also potentially pave the way for very high efficiency hard X-ray focusing which can in principle be utilized in laboratory based X-ray sources, X-ray astronomy and the new rising field of X-ray ptychography. To fabricate high resolution ML-FZPs, Al2O3/Ta2O5multilayers, deposited on a smooth glass optical fiber via atomic layer deposition using non-dedicated instruments were carefully cut-out, sliced and polished to a high quality surface finish using focused ion beams. Following the transfer of the slice to a TEM grid as holder the slices were polished to a high surface finish quality, also via a focused ion beam. Fabricated ML-FZPs were synchrotron tested using an in-house constructed 2-axis tilt stage specially designed for aligning ML-FZP with respect to the X-ray optical axis. The results showed that it was possible to resolve 21 nm features in direct imaging at 1200 eV and sub-30 nm focusing at 8 keV. This is the highest demonstrated resolving power for a multilayer type FZP, to date to the best of our knowledge. Results exhibit the potential for high-resolution hard X-ray focusing where this type of optics are especially efficient. For ultra-high resolution hard and soft X-ray imaging, with potentially achievable ∆r of a few nm is well below what can be achieved through any lithography method available today.Item Open Access Instrument study of the Lunar Dust eXplorer (LDX) for a lunar lander mission(2016) Li, Yanwei; Srama, Ralf (Priv.-Doz. Dr.-Ing.)One of the highest-priority issues for a future human or robotic lunar exploration is the fine lunar dust created by meteoroid bombardment on the lunar surface with an average speed of 17 km/s. This problem should be studied in depth in order to develop an environment model for future lunar explorations. The proposed ESA lunar lander mission requires the measurement of dust transport phenomena above the lunar surface. In response to the mission requirements, an instrument design concept was developed, simulated, manufactured and tested at the Heidelberg dust accelerator facility. In contrast to former detectors, the sensor is capable to measure charged particles in a broader speed window, ranging from as low as meter per second to several kilometers per second. Furthermore, the new instrument approach is optimized for the instrument requirements of the lunar lander concept investigated by ESA. The Lunar Dust eXplorer (LDX) has a low mass of 1.2 kg and consumes a power of 1.1 W (digital electronics). The sensitive area of LDX is approximately 400 cm2. It measures the charge, speed and trajectory of individual dust particles. Meanwhile, LDX has an impact ionization target to monitor the mass of interplanetary dust and high speed ejecta. In the beginning of this study, the charge induction signals of the detector were simulated using the COULOMB software package in order to constrain the sensor accuracies. Simulations reveal trajectory uncertainties of better than 2° with an absolute position accuracy of better than 2 mm. Following simulations, a laboratory model of the LDX sensor was designed, manufactured and tested using the 2 MV Van-de-Graaff accelerator located at the Max-Planck Institute for Nuclear Physics in Heidelberg. This accelerator is a world wide unique facility to simulate hyper-velocity impacts of micron and sub-micron particles. It is currently operated by the Institute of Space System of the University of Stuttgart (IRS, Stuttgart). The experimental results additionally reveal particle primary charge uncertainties of better than ±5% and particle speed uncertainties of better than ±7%. What are the dust populations a sensor like LDX can detect on the lunar surface? How large is the contribution by secondary ejecta falling back to the surface and what is their angular distribution and speed range? To answer these questions, Autodyn 14.0/2D software was used to simulate hyper-velocity impacts of micrometeoroids bombarding the lunar surface. The initial projectiles were selected as 10 mm spheres in diameter with an average speed of 17 km/s. Furthermore, we used impact angles of 15°, 30°, 45°, 60°, 75° and 90°. In the early stage of the impact process, the projectile is coupling its energy and momentum to the target. A part of the ejecta grains created during this early stage can be captured by a sensor located on the lunar surface like e.g. the Lunar Ejecta and Meteorites (LEAM) experiment or mounted on a lander (e.g. LDX). The simulations show, that most of the detectable ejecta have low speeds (< 100 m/s1), and there are also a few grains with high speeds (> 1 km/s). The observation geometry of the sensor was investigated. Here we discuss a trade-off between a lander-mounted sensor and a surface located system. Although the LEAM data are not fully understood until today, our recent re-analysis of the data consider impact ejecta as one of the most likely sources to explain the observed event rates. Meanwhile, our studies show that a sensor mounted on the lander instead of standing on the lunar surface has more chances to measure the high-speed component of the ejecta population. The newly developed LDX sensor system is a powerful tool to study the lunar dust environment. In addition to lunar landers, smaller rover systems are also very interesting in future missions. A dust detector onboard a lunar rover would have several advantages: the measurements by the sensor can be taken at different regions of the lunar surface. Furthermore, the sensor will monitor the interaction of the rover with the lunar dust environment (plasma, electric fields, and dust). On the other hand, there are also disadvantages. The instruments onboard a rover have to maintain severe mass and data volume restrictions. Therefore we developed two further simplified designs with a lower number of electrodes and an even lower instrument mass with respect to the original LDX design. The fundamental difference between the two versions is their housing geometries. One design uses a cylindrical housing (LDX-c), and the second design has a square cross section (LDX-s). The measurement accuracies of these two detector designs are similar to LDX, but the trajectory accuracy decreases slightly by up to 2 degrees. Nevertheless, such an instrument promises, for the first time, reliable data for the properties of the lunar dust environment.Item Open Access The numerous phases of the interstellar medium in the starburst galaxy NGC 253 : a multi-wavelength study(2024) Beck, André; Krabbe, Alfred (Prof. Dr.)The physical properties of the nuclear region of the starburst galaxy NGC 253 are analysed using observations from various mid- to far-infrared telescopes. The data of these telescopes are homogeneously reduced and combined. Afterwards, the data are used in a complex Monte-Carlo to determine the physical conditions in the observed region.Item Open Access Theoretical investigations of atom tunneling in the interstellar medium(2018) Meisner, Jan; Kästner, Johannes (Prof. Dr.)