PhD Defence Nis Christian Gellert

Principal supervisor

• Senior researcher Desiree D. M. Ferreira, DTU Space

Examiners

• Senior researcher Irfan Kuvvetli, DTU Space
• Senior scientist Suzanne Romaine, Harvard & Smithsonian, USA
• Associate Professor Heloisa Bordallo, University of Copenhagen, Denmark

Chairperson at defence

• Head of division, Allan Hornstrup

Summary

The main application of this PhD research is to contribute to the development of new optic technologies for the next generation of high-energy astrophysical space missions, specifically for the NASA probe-class mission concept: The High Energy X-ray Probe (HEX-P).

The research aims to enable the development of X-ray reflecting multilayer coatings to significantly increase the X-ray flux density, with focus on expanding the telescopes focusing performance to 200 keV and above. The project has strong interdisciplinary aspects and brings together the fields of X-ray physics, material science, data science and astronomy, and involves the design, development and characterization of nanometer-thin multilayer coatings. The research will help enable HEX-P and other future space missions to observe some of the most extreme environments of the universe, i.e. shocks in supernovae explosions and merging galaxies, hot plasma around black holes, and the strong magnetic fields of neutron stars.

This thesis presents a systematic method for optimizing the design of depth-graded multilayers, where a Python-based optimization tool has been developed that utilizes a Differential Evolution algorithm, to effectively explore the vast parameter space of a multilayer structure, to find the optimum multilayer structure which enables the highest performance.

The simulated performances show that nickel (Ni) based multilayer coatings enable higher performance of focusing X-ray telescopes, compared to platinum (Pt). However, the current fabricated Ni-based coatings contain high interfacial roughnesses, which will affect the predicted performance of the telescope. To evaluate the roughness in the Ni coatings, the DC magnetron sputtering facility at DTU Space is used to coat and test Ni thin films. The roughness in the Ni thin films are evaluated, and different techniques are presented which reduce the roughness.

The last part of this PhD dissertation presents the challenge of coating long X-ray reflective mirrors, as part of the thin film coating development for the 456 mm long parabolic mirror used in the Beam Expander Testing X-ray (BEaTriX) facility.