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Electron-Radio-Frequency Quadrupole (ERFQ) Linear Accelerator: Theory, Design and Measurements for the GHz Region

Gueye, Serigne Bira

Es geht in dieser Doktorarbeit um das Design von Laufwellenroehren, welche die Eigenschaft haben, Elektronstrahlen zu beschleunigen, zu bunchen und zu fokussieren. Ihr Entwurf ist sowohl durch die Hochfrequenztechnik als auch durch die Strahldynamik bestimmt. Diese Strukturen koennen z.B. in Kliniken bei der Strahlentherapie eingesetzt werden. Bis jetzt wurden sie fuer schwere Ionen bei 400 MHz aufgebaut und es gab Versuche fuer Elektronen bei 3 GHz . Die Dissertation behandelt die Theorie, den Entwurf und die Messung von ERFQs fuer relativistische Elektronen bei 90 GHz.
When traversing RF cavities, particle beams experience in the majority of cases defocusing forces during their acceleration. The resonator field and the beam self field are acting on the particles. With the RF Quadrupole (RFQ), invented by Kapchinskii and Tepliakov in 1970, a resulting focusing force is produced and at the same time an acceleration. This structure has been first manufactured at the Los Alamos Scientific Laboratory (LASL) for proton beams at 425 MHz. Nowadays, it is used in some hospitals for tumor therapy. The first essay to design RFQ for electrons in the GHz region is done at Frascati for 3 GHz in 1990. In this work, the electromagnetic fields are approximated with good accuracy by solving the wave equation. Then, the transverse and longitudinal particle dynamics are treated. Thus, a 10 GHz scaled model is designed, manufactured and measured. Lastly, an Electron Radio-Frequency Quadrupole (ERFQ) at 91 GHz is designed and beam computations are performed with the Particle-in-Cell (PIC) method.