Thesis supervisor: Prof. Palumbo, Prof. Morvillo (Dipartimento di Scienze di base ed applicate per l'Ingegneria)
Thesis title: Study the beam-cavity interaction in the PS 10 MHz cavities in detail and investigate on new possible hardware solutions finalized to reach higher circulating beam intensities and to reduce beam loading.
In the framework of the LHC Injector Upgrade (LIU) project, the present 10 MHz RF system of the PS accelerator requires an upgrade, in order to reach higher beam intensities and to reduce beam loading. Each PS 10 MHz accelerating cavity consists of two ferrite-loaded lambda/4 resonators. Both resonators oscillate in phase, as their gaps are electrically connected by short bars. They are in addiction magnetically coupled via the bias loop for cavity tuning. However, measurements of beam induced voltage in the two half-cavities indicate that the coupling as seen by the beam is not as tight as expected. The thesis work should study the beam-cavity interaction in the PS 10 MHz cavities in detail, by numerical simulations and by measurements with the high-intensity proton beam. The beam loading reduction requires lowering the cavity impedance seen by the beam, by increasing the feedback of the power amplifiers chain driving the cavities. Ideally the feedback gain may be increased by at least 6 dB. The study will cover new possible hardware solutions based on circuit simulation models, which may require the modification of the present vacuum tube configuration, the characterization of a prototype amplifier and its validation with beam in the accelerator. These investigations should result in a consistent beam loading model, capable of predicting the effective cavity impedance. Moreover, alternatives to the present scheme of powering the cavities, e.g. a separate power amplifier with local feedback per resonator or re-arrangement for a single accelerating gap per cavity, could be evaluated. A preliminary evaluation of a system based on modern Finemet technology, as implemented in other synchrotrons, will be also performed, if possible, in the perspective of the possible replacement of the entire main RF system of the PS.