Fabrication and study of thallium based high-temperature superconductors for the beam screen of Future Circular Collider (FCC-hh)
Creators: name: SABA, AISHA
Publisher: name: Universit� degli studi di Genova
Year: 2021

description: Research and study on the Future Circle Collider (FCC, 100 km in circumference) have been initiated to create new possibilities for the science world. The conceptual design emphasises achieving centre-of-mass collision energy of 100 TeV by counter-rotating beams. The construction of such a massive accelerator comes with several complications to deal with, and beam stability is one of the essential tasks in an accelerator. It has been theoretically estimated that copper, the current conducting beam screen material, could not offer low surface resistance to cope with the instabilities in the suggested temperature scale (40-60 K) for the beam screen of FCC-hh. Moreover, the beam screen is subjected to a magnetic field of 16 T generated by the magnets that bend the beam. Only a few superconducting materials survive in these conditions.
This thesis discusses the detailed fabrication procedures and measurements carried out on thallium-based high-temperature superconductors to verify the possibility to use this material as screen for the beam. This thesis discusses the detailed fabrication procedures and measurements carried out on thallium-based high-temperature superconductors to verify the possibility to use this material as a screen for the beam.
Bulk superconductors were synthesised and optimised by a planetary ball milling system to obtain the pure and preferential phase Tl-1223 having the highest critical temperature among the thallium superconducting system. For the coatings, rapid and cost-effective electrodeposition technique was used to deposit the highly reactive precursor. The morphology and substrate coverage with superconducting material and grains? formation has improved by depositing precursor coatings at pulsed potential and annealing with unreacted bulk pellet in an oxygen atmosphere. Moreover, safety precautions have always been the priority while working with thallium. 
The superconducting grains of bulk and thin-film superconductors were identified using X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) studies. The critical temperature was determined using a four-probe resistivity and scanning superconductivity quantum interference device, and the field profile was mapped using Scanning Hall Probe Microscopy (SHPM) measurements.
For the vacuum analysis, the outgassing rate, the residual gas analysis (RGA), secondary electron yield (SEY), and X-ray Photoelectron Spectroscopy (XPS) measurements. All the obtained results: 5�10-8 mbar. l/s per cm2 outgassing rate after 10 hours, no detection of heavy metals in RGA, and especially least obtained SEY values of 0.77 and 0.97 for amorphous carbon deposited bulk and coatings, respectively, make thallium superconductors acceptable in a vacuum.
In conclusion, the current study on Tl-based superconductors has helped to develop techniques to produce improved superconducting bulk and superconducting thin films. The results obtained from characterisation and vacuum analysis strongly believe in Tl-based superconducting coatings as a potential solution for improving the beam stability in high-energy h-h particle accelerators