Characterization of Higher Order Modes in the MAX IV Active 100 MHz Cavities

University essay from Lunds universitet/Institutionen för elektro- och informationsteknik

Abstract: In circular accelerators, and in storage rings in particular, charged particles are kept in a closed orbit for a very long time by means of a magnet lattice. When the particle beam is bent by the magnetic field it emits light, which decreases the particle beam energy by an amount equal to the radiated energy. Over many bends in the magnets and many turns in the machine, these relatively small energy losses amount to significant values, and so it is crucial to replenish this energy to keep the beam orbiting. In storage rings, such as the MAX IV rings, this is done with radio frequency (RF) cavities containing an oscillating electromagnetic field which, on average, restores the correct amount of energy each turn. However, the beam itself can excite so-called higher order modes (HOMs) in the cavities which can ruin the beam stability if these HOMs happen to resonate well and have certain resonating frequencies. The aim of this thesis is to determine the different HOMs of the active 100 MHz cavities of the MAX IV storage rings, as well as the impact these have on the beam stability.

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