Design realization and commissioning of RF Power system and accelerating structures for a Gamma Source

Thanks to the recent technological progress in the fields of high power lasers and high brightness linac accelerators, new Gamma and X ray sources based on electron-photon interaction are under development in several laboratory world-wide. These kind of sources uses Inverse Compton scattering in the collision between a relativistic high quality electron beam and high power optical laser pulses to generate secondary photon beams of unique performances. These photon beams are suitable for a wide range of applications and open new perspectives in many research fields. In particular gamma rays in the energy interval between 1-20~MeV are of great interest for basic research and application studies in the fields of nuclear physics and photonics. In this framework, a very innovative Compton source is under construction in Magurele (RO), by the EuroGammaS association, with the aim to generate photon beams in that energy range, characterized by unprecedented performances in terms of mono-chromaticity, brilliance, spectral density, tunability and polarization. The realization of this source called ELI-NP-GBS is in the framework of the European Extreme Light infrastructure (ELI) project that pursues the creation of an international laser research infrastructure. The challenging parameters of this source rely on the performances of the Linac and in particular of his radiofrequency (RF) system. The electron accelerator is a high brightness normal conducting RF Linac consisting of two S-band (2856 MHz) and twelve C-band (5712 MHz) RF structures. The main advantages of using a Linac accelerator are the energy "tunability" and the excellent electron beam quality that is possible to obtain. The accelerator will be operated at a repetition rate of 100 Hz. For every RF pulse up to 32 electron bunches, each one carrying 250 pC of charge, separated by 16 ns, will be accelerated. The Linac is required to achieve a normalized emittance in both planes better than 0.5 mm mrad and energy spread below 0.1\%. To guarantee these performances in a reliable and stable way, innovative and advance RF components have been developed. The aim of this thesis is the study, design and commissioning of the main components of RF system used for the realization of a state of the art gamma source such as the ELI-NP-GBS. High power RF sources driven by solid state modulators have to feed the accelerating structures with high pulse to pulse amplitude stability and RF pulse uniformity in order to minimize the electron beam energy spread. An innovative C-band High Order Mode (HOM) damped RF cavity has been conceived and designed in order to avoid beam emittance and energy spread degradation due to the Beam Break-Up instability along the Linac. In addition the S-band RF Gun has been realized with an innovative technique called "Gasket-clamping technique'' and implements new radiofrequency features to sustain the 100 Hz repetition rate operation. All these devices have been realized and tested and the results obtained are reported in this work. Taking into account the extremely good results obtained by RF Gun realized with the gasket-clamping technique, in the last part of this dissertation, it has been explored the possibility to extend this fabrication procedure to the realization of an entire travelling wave Linac structure. This technique, thanks to the use of RF/vacuum special gaskets, allows avoiding the brazing process thus reducing the fabrication costs, the risk of failure and improving the performances of the device in terms of reachable peak electric field. To demonstrate the feasibility of the implementation of such technique an accurate electromagnetic and mechanical design of an S-band travelling wave structure has been performed.