Andrei Seryi (SLAC)
Investigations of slow transverse motion of the linac tunnel of the Stanford Linear Collider have been performed over period of about one month in December 1999 -- January 2000. The linac laser alignment system, equipped with a quadrant photodetector, allowed to measure motion of the center of the linac tunnel with respect to its ends with submicron resolution. Measurements revealed two major sources responsible for the observed relative motion. Variation of the external atmospheric pressure were found to be the most significant cause of the short wavelength transverse motion of the tunnel. Large contribution of tidal effects to the long wavelength component of the motion has been also observed. The measured data are essential for determination of parameters of the Next Linear Collider.
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