The Drive Beam Phase Stability in CTF3 and its Relation to the Bunch Compression Factor

The proposed Compact Linear Collider (CLIC) is based on a two-beam acceleration scheme. The energy needed to accelerate a low intensity “main” beam is provided by a high intensity, low energy “drive” beam. The precision and stability of the phase relation between two beams is crucial for the performance of the scheme. The tolerable phase jitter is 0.2 deg rms at 12 GHz. For this reason it is fundamental to understand the main possible causes of the drive beam timing jitter. Experimental work aimed at such understanding was done in the CLIC Test Facility (CTF3) where a drive beam with characteristics similar to the CLIC one is produced. Several phase measurements allowed us to conclude that the main source of phase jitter is energy jitter of the beam transformed and amplified into phase jitter when passing through a magnetic chicane. This conclusion is supported by measurements done with different momentum compaction values in the chicane. In this paper the results of these several phase measurements will be presented and compared with expectations.