Study of the Dynamic Response of CLIC Accelerating Structures

CLIC is a linear electron-positron collider, 48 km long, consisting of more than 20000 repetitive modules. The target beam size of 1 nm dictates very tight alignment tolerances for the accelerating structures (AS). In order to assess the effect of short-term RF power interruptions (breakdowns or failure modes) on the alignment, the dynamic behaviour of the AS was investigated on the prototype two-beam module. On a dedicated experimental setup, the thermal and mechanical time constant (TC) was monitored as a function of ambient temperature, water flow and power. The experimental results showed that the thermal TC ranged between 4 and 11 minutes and presented strong correlation with the cooling water flow. These results were in very good agreement with the theoretical expectations. The displacement dynamics were found to be comparable with the thermal ones. The study indicates that temperature measurement, which is a fast and easy process, can be used as an indicator of the AS displacement. Moreover, it is shown than the transient response can be efficiently controlled through appropriate regulation of the cooling water flow.