Studies of vacuum discharges in the CLIC accelerating structure

Sammanfattning: The Compact Linear Collider (CLIC), is one of the proposed successors to the Large Hadron Collider (LHC) accelerator at the European Organization for Nuclear Research. (CERN). In CLIC, particles are accelerated by very strong electric fields. Unfortunately, large electric fields may lead to vacuum discharges, which in turn can affect the particle beam by disrupting the flow of energy inside the accelerating structure and deteriorate the performance of the accelerator. Studies of the physics of vacuum discharges and its effect on the beam are crucial for the realization of the CLIC accelerator. The objective of this master thesis is to improve the knowledge of how vacuum discharges occur and what can be done to prevent them. The project was done together with the CLIC group at Uppsala University. They have their diagnostic equipment, Uppsala/CLIC X-band spectrometer (UCXS), at the High Gradient Test Stand for research on RF-structures X-Box2, where also the accelerating structure is located. The spectrometer consists of a collimator, a dipole and a fluorescent screen, which receives images from electrons that come from discharges. These images have been analysed, together with Radio Frequency (RF)-signal data from X-Box2, to find discharge positions inside the accelerating structure. The achieved results are consistent with previous analyses used with the help of the RF signals. We see that there is a possibility to use images to study the geometrical shape of the discharges. Longitudinal positioning of the discharges with the help of images, cannot be done. While longitudinal positioning cannot be done, transversal have had success and can be found. Images have also been seen with multiple features. It is hard to accredit one image to a single breakdown and a hypothesis is that there are more than one breakdown during a pulse, creating multiple features.