Doctor's Theses (authored and supervised):

A. Moros:
"Microstructural Characterization of Advanced Superconducting Materials for Di erent Components of the CERN hadron-hadron Future Circular Collider";
Supervisor, Reviewer: M. Stöger-Pollach, Z. Zhang, F. Hofer; Ustem E057-02, 2021; oral examination: 2021-09-07.

English abstract:
How far can the curiosity push our capabilities? Is our thirst of knowledge stronger than
the fear of our human limits? This is not the incipit of a philosophy manual, but the
beginning of a magni cent idea. This idea led the great scientists at the European Organization
for Nuclear Research (CERN) to start the huge project of the Future Circular
Collider (FCC). We have been asking for ages about the evolution of our Universe and
the nature of the matter, antimatter and particles describing it. The Large Hadron Collider
(LHC) is the rst great machine built at CERN with the aim of satisfying all the
open questions related to the origin of the Universe. The discoveries it led to, together
with the breakthrough represented by the observation of the Higgs boson, can be considered
the starting point transforming the need of exploring new physics into a worldwide
collaboration for the realization of a new extraordinary machine. In fact, the FCC aims
at pushing the energy and intensity frontiers of particle colliders towards reaching collision
energies of 100 TeV: the discovery of a new physics, possible when such energies
are at stake, can lead to an extension of the known
Standard Model\ and a better understanding
of the Higgs boson. Within this study, scenarios for three di erent types of
particle collisions are examined: hadron (proton-proton and heavy ion) collisions, like in
the LHC, electron-positron collisions, as in the former LEP, and proton-electron collisions
[1], [2], [3], [4]. This magni cent collider of the future will be the next large research
facility after the LHC and its High-Luminosity upgrade (HL-LHC), whose realization is
ongoing, once they approach the limits of their discovery potential [5].
According to CERN recently published conceptual design study for a future hadron collider
(FCC-hh), this extraordinary machine with its center-of-mass energy target of 100
TeV would be located in a 100 km circumference ring close to Geneva (Switzerland).
A key requirement for such a machine is the development of high- eld superconducting
accelerator magnets, capable of satisfying the requirements given by a non-copper critical
current density (Jc) of at least 1500 A/mm2 at 16 T and 4.2 K [1]. Nb3Sn, a low
temperature superconductor with a critical temperature Tc up to 18.3 K, is currently
the best candidate for such magnets, since it is the only a ordable material able to meet
the afore mentioned requirements. To feed the FCC-hh magnets, new superconducting
lines will be developed. Similarly to the LHC electrical layout, also for the FCC case the
transfer of the current from the surface to the tunnel, where the magnets are located,
would be possible via superconducting links containing tens of cables feeding di erent
circuits [6]. The work related to the realization of such links focuses on the development
of novel types of cables made out of MgB2. Furthermore, since the FCC-hh is expected
to produce unprecedented amounts of synchrotron radiation, a superconducting beam
screen is necessary in order to protect its sensitive components. Two suitable candidates
for the beam screen coating are the high temperature superconductors YBCO and the technologically still unexploited thallium-based cuprate Tl-1223. Since YBCO is expensive
and has a complex preparation on large scale, Tl-1223 could represent the proper
choice for the material addressed to the beam screen coating. The introduced materials
(Nb3Sn, MgB2 and Tl-1223), which represent the best candidates for some of the FCChh
fundamental components, are the
main characters\ of my PhD thesis. In particular,
I investigated their structure on a micro- and nanoscale level, and a greater emphasis
was given to the study of Nb3Sn for the FCC-hh bending magnets.
The microstructural investigation is an essential tool for understanding how the material
superconducting properties can be enhanced, in order to exploit them for future
applications. The electron microscopy, the science allowing the material microstructural
analysis, plays a very important role in terms of studying the material intrinsic and
extrinsic attributes for understanding its superconducting behavior. The manufacturing
processes the superconducting materials come from are crucial in de ning their characteristics:
a key point in my work is to understand how the parameters involved in
such processes in
uence the material microstructural features, strictly connected to its
superconducting properties. In this way, it would be possible to give the manufactures
an e ective contribution in terms of producing wires and thin lms with enhanced superconducting
performance. For the material microstructural characterization electron
microscopes were employed: these instruments use accelerated electrons under vacuum
conditions in order to generate highly magni ed images of specimens. In particular, both
a scanning electron microscope (SEM) and a transmission electron microscope (TEM)
were used. The rst one provides information from the surface of a sample: in fact, electrons
scattered by or emitted from its surface are used for image generation. TEM uses
instead the electrons transmitted from a very thin specimen (approx. 100 nm) to build
images. Since these microscopes are equipped with several attachments such as X-ray
detectors (both SEM and TEM) or energy lters (TEM), they provide element-speci c
information from the sample, e.g. chemical composition, elemental distributions, grain
size and shape, doping agents size and density.
This work is part of the Marie Sk lodowska-Curie Action EASITrain, funded by the
European Union's H2020 Framework Programme under grant agreement no. 764879.

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