Injector linac optimizations for FCC-ee and applications for PRAE

In the last years there has been intense linear electron-accelerator development driven by different communities as the X-FEL community, the High Energy Physics (HEP) linear-collider community: ILC and CLIC as well as HEP circular-collider community: FCC-ee and CEPC. Furthermore, there are also many other applications from medical science to industry that will use such a linac as main accelerators. In all these studies, a high-efficient e-linac with energies from 10 to 1000 MeV is needed as driver or injector. Even if the linac technology to cope with the performances needed is very well known, an important R&D effort on more compact, simpler, cost-effective, efficient, robust and reliable is in progress. In this frame, this thesis will optimize the linac and its associated transfer lines in two cases: (1) The injector linac for FCC-ee (Future electron-positron Circular Collider), in particular the positron one. (2) The linac for applications known as PRAE project (Platform for Research and Application with Electrons). The Future Circular Collider (FCC) hosted by CERN, is an international collaboration to explore the feasibility of different particle collider scenarios with the aim of significantly increasing the energy and luminosity compared to existing colliders, in the search for new physics. In the case of the Future Circular electron-positron Collider (FCC-ee), 2.13*10^10 (3.5 nC) electron and positron particles per bunch are needed for the most demanding full filling of Z running mode in the conceptual design report (CDR). The baseline selection for FCC-ee injector linac is based on the SuperKEKB one, which gives us a positron yield of 0.2 e+/e- against 0.4 e+/e- design in recent experiment. The main objective of this thesis is to perform the start-to-end design and optimization for beam production, acceleration and transport from the feeding electron source to the positron damping ring as well as to increase the efficiency and the flexibility of the positron production (the positron yield needs to be larger than 0.7) for FCC-ee injector linac. A complementary study for positron target optimisation using conventional target or hybrid target is also shortly summarized. Considered the drawbacks of the current SuperKEKB injector scheme, three new different bypass scheme designs have been finished to transfer electron and positron particles separately for a better transmission and improved flexibility of the whole system, which finally could gives us a positron yield of around 1.2 e+/e- at the e+ damping ring in theoretical simulations. In conclusion, this work is a first step in the optimization of the FCC-ee injector system from the point of view of the efficiency of the transport and optics design. The various schemes proposed are based on established technologies and different paths for electrons and positrons are used in order to improve the efficiency of the transport from the point of view of losses and cost. In the second part of this thesis, the design for a radiobiology and nuclear physics application linac platform PRAE(Platform for Research and Application with Electrons) based on a high-quality pulsed electron beam of energy up to 70 MeV in phase 1 and 140 MeV in phase 2 has been realized. 2 nC electron bunches in the PRAE accelerator phase 1 are produced in a RF gun at 50 Hz frequency, post-accelerated by a S-band linac to 50-70 MeV and injected into the direct beam line plus a deviated line. The optics design of the beam lines has to be as flexible as possible to cope with different kinds of beam characteristics (beam size, energy, dispersion, current…) and operation modes depending on the application. The study of the different optics options and the implementation of these two beam lines as well as the beam-water interaction for pre-clinical studies for the case of the radiobiology experiments has also been done and presented in this thesis.