Asian Research Thesis Index

Abstract

Present work aimed to study a thin film of amorphous carbon (a-C) produced by DC magnetron sputtering on stainless steel (SS) and aluminum (Al) to investigate the proposed solution for elimination of e-cloud arising in the beam pipes of high energy accelerators. Large Hadron Collider (LHC) at CERN is under upgradation to achieve high luminosity (HL-LHC). To achieve this goal some integral developments in the injection chain of LHC have been planned. Suppression of electron cloud effect in beam pipe is one of the activities to improve the beam performance of HL-LHC. To mitigate the electron cloud effect, the beam pipe should have low secondary electron yield (SEY). The a-C coatings were prepared at CERN and PINSTECH with different process parameters. In the primary part of the study coatings produced at CERN under different coating parameters, were investigated for UHV properties. In this study outgassing rate of coated SS samples were measured in comparison with uncoated SS sample for both unbaked and baked conditions. Furthermore, electron stimulated desorption yields for these coatings were also measured. The coating produced on SS and Al by DC magnetron sputtering were compared with those of commercially available standard samples of other allotropes of carbon such as highly oriented pyrolytic graphite and glassy carbon. The samples were characterized with Atomic Force Microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy and SEY measurements by electron irradiation. A theoretical model based on Cs+ irradiation effect on single-walled carbon nanotubes (SWCNTs) has been proposed to explain the interaction and energy dissipation mechanisms. Mono-layered nature of sp2 hybridized SWCNTs makes them perfect to be taken as monolayer graphene folded cylindrically. Information theoretic parameters identify, distinguish and characterize the existence and the relative operational efficiency of the linear cascades and nonlinear thermal spikes on the surface of the irradiated SWCNTs. The study proved to be helpful to comprehend the characteristics of a-C coatings prepared by DC magnetron sputtering and its role in electron cloud mitigation. On the basis of findings, the a-C coatings have been confirmed to be applicable in UHV systems with minimum required SEY ~ 1 for high energy accelerators like HL-LHC. Minimization of SEY is attributed to the disorder in the aC due to reasonably selected coating parameters.

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