GROUND MOTION IN LEP AND LHC

The subject of ground motion has been introduced in the field of accel erator physics by G. Fischer(1,2) of SLAG about 10 years ago. At that moment several colliders, linear and circular, are at various stages i n the design phase. Their common characteristics are large machine dim ensions and extremely small beam sizes. The extreme dimensions make th ese colliders more prone to ground motion effects while the minute bea m size increases their sensitivity. The object of this paper is to rep ort on the results obtained with a dedicated beam position monitor, co ncerning ground motion effects on the LEP beams. It starts with some p roperties of ground vibrations which are relevant to the observation o f the phenomenon in LEP. The results of the observations will be prese nted both at the betatron frequencies and at very low frequencies. The y are compared with published data to check the plausibility of the hy pothesis that ground motion is indeed the primary cause of the observe d signals. Finally, a discussion on the influence of the effect on the LHC beams is presented.