A new proposal for damping the resonances in CERN accelerators, using HOM couplers

Parasitic resonances are a fundamental problem in the world of accelerators (there are also resonating cavities, but in this case the resonance is designed and is used to accelerate the beam). These parasitic resonances must be reduced, and cut them down have multiple benefits. The resonances studied in this thesis are the unwanted ones. Two enormous problems in accelerator physics are caused by these resonances: instability and overheating. These problems will be explained in more details in the thesis. Nowadays generally resonances in accelerator equipment are damped with ferrites. It can also be done by completely redesigning the equipment, but this is expensive and takes a long time and therefore damping with ferrites is preferred. However, when ferrites absorbs the energy from the resonance, they become hot and start to outgas, which is detrimental to the vacuum. Also if the ferrite gets too hot and reaches the Curie temperature, it will no longer absorb the resonance and the beam will again be exposed to the resonance. In addition ferrites are fragile and easily break when attached to the equipment. In order to avoid the problems of the ferrites, we are now proposing a new method of damping the resonances. It uses a well-know technique from RF-cavities, where higher order modes (HOM) are removed with HOM-couplers. This technique have never been used before for other equipment than RF cavities, but we have now tested it with excellent results for the QUATTRO-TANK (QT) in SPS. The coupler for the QT is a coil, that couples to the magnetic fields in the resonance. The design is experimental, and in a later paper we will give a derivation of the theory for the coupling.