Phase Control at CLIC
In a two-beam system, the RF power is provided by the drive beam to the main beam accelerating structure. Drive Beam timing errors must be avoided to maximize the acceleration gradient uniformity in the accelerating structures, and consequently to stabilize the Main Beam energy and optimize the collider luminosity. Image credit: CERN.
Extremely precise beam phase control is required for CLICtwo-beam acceleration technology as well as in Free Electron Lasers (FELs). The development of beam arrival time measurement systems has been carried out within Task 5 of the EuCARD Work Package 9, in collaboration with CERN, INFN/LNF and PSI.
In CLIC the Main Beam must be precisely synchronized with respect to the RF power produced by the Drive Beam. Timing errors would have an impact on the collider performance. The Drive Beam phase errors should be controlled, by means of a feed forward system, within 0.1Рat 12 GHz, corresponding to a timing stability below 23 fs, to avoid a luminosity reduction larger than 2%. A prototype of such a system is being installed in the CLIC Test Facility CTF3 and the performances of the beam phase arrival monitor have been already successfully tested.
FELs also require a tight synchronization of the beam with respect to photo injector lasers, RF and other systems. The beam phase measurement has been pursued at PSI with a different approach based on electro optical modulators. It has the advantage of very high band width, allowing the measurement of individual bunches arrival time with a potential resolution below 10 fs. The system was tested and the performance with beam validated at the PSI FEL test injector.
