Active stabilization of mechanical quadrupole vibrations for linear colliders

To achieve luminosities of some 1033 cm−2 s−1, all linear collider schemes currently under study require extremely low beam emittances to achieve spot sizes of some 10 nm height and some 100 nm width at the interaction point. Therefore, high beam position stability is required in order to provide central collisions of the opposing bunches. Since ground motion amplitudes are likely to be larger than the required tolerances of 85 nm rms for the 500 GeV and 43 nm rms for the 1 TeV S-band linear collider SBLC, some means of active stabilization is necessary to damp quadrupole motion to the desired value. Therefore, an inexpensive active stabilization system to be installed in the S-band test accelerator at DESY has been developed and successfully tested. It damps quadrupole motion in the frequency range 2–30 Hz by up to 14 dB, thus leading to rms values of approximately 25 nm even in very noisy environments. Since the system is based on geophone type motion sensors with an internal noise level corresponding to 1.1 nm at 2 Hz, it is likely that this system allows stabilization below the 10 nm level.