High gradient issues in S-band RF acceleration structure for hadrontherapy and radio frequency quadrupoles
- Autores: Anna Vnuchenko
- Directores de la Tesis: Benito Gimeno Martínez (dir. tes.), Angeles Faus Golfe (codir. tes.)
- Lectura: En la Universitat de València ( España ) en 2020
- Idioma: inglés
- Tribunal Calificador de la Tesis: Alessandra Lombardi (presid.), José Luis Cruz (secret.), Concepción Celia Oliver Amorós (voc.)
- Programa de doctorado: Programa de Doctorado en Física por la Universitat de València (Estudi General)
- Materias:
- Enlaces
- Tesis en acceso abierto en: RODERIC
- Resumen
The achievement of high-gradient in the linac structures is a key issue in design facility for the high energy physics and other applications. This thesis is focused on the study of the high-gradient limitations in the normal-conducting radio-frequency accelerating structures. One of the effects that could appear during high power operation of the accelerating structures is the RF vacuum arcs or breakdowns. This occurs due to the high electromagnetic fields in the structure. Such events have an impact on the structure performance and the quality of the accelerated beam. Therefore, this phenomenon requires a detailed study on the dedicated developed systems.
A general introduction of the RF theory and the basic concepts related to linear accelerators are given in this thesis. The main limiting quantities and the issues related to RF breakdown phenomena are discussed in detail. The advantages, that HG technology offers for medical application, and a summary of the current activities in the development of HG hadron therapy linacs are also described. Afterwards, the results of the breakdown experiments are presented together with the instruments and facilities used. The high power tests on a 3 GHz prototype of accelerating structure for hadron therapy have been successfully performed at the CERN Sbox, and the maximum operation limit of a linac in terms of maximum achievable fields and breakdown probability have been determined. Apart from the conditioning, another measurements have been performed. The data analysis techniques used for the breakdowns localization in this structure are presented in detail in comparison with post-processing results. A statistical investigation of the breakdown occurrences is also made to understand the underlying processes of these events. The data collected have been compared with CLIC X-band RF prototypes results in order to estimate the structure performance.
A first systematic study of breakdown events in RFQs is presented. Two RFQs designed for different frequencies and applications are considered. The design features and the relative merits of these structures are discussed. The long term behaviour of the RFQs is also presented. The main changes observed during breakdown events are discussed and a technique of identification of breakdown location is proposed based on these observations.
The experimental work presented in this thesis is carried out in order to compare the physics of breakdowns occurring in the high-gradient accelerating structures and RFQs. These studies have been served to determine the breakdown limitations and to predict the structure performances. The final goal of the overall breakdown research is to understand the phenomenon to maximize the structure performance and to confirm the ability of using high-gradient technologies for various applications.
