A mechanical feedback system for linear colliders to compensate fast magnet motion

For high luminosity, all linear collider schemes under study require very low emittance beams. When transverse beam dimensions of the opposing linacs become very small, high beam position stability is necessary to maintain high luminosity. For the 500 GeV c.m. S-band collider SBLC uncorrelated rms quadrupole vibrations must be smaller than some 70 nm and have to be reduced to 20 nm for the 1 TeV upgrade. An inexpensive mechanical stabilization scheme based on geophones, piezocrystals and a digital feedback system has been successfully tested. It damps quadrupole motions in a frequency range of 2-30 Hz by factors up to 4, such that remaining magnet motions may be within tolerance limits. Based on a geophone with noise level below 1 nm, it is likely that this system may allow stabilization below the 10 nm level