1 Ground Motion Measurements at ESA M. Albrecht (Notre Dame) F. Gournaris (UCL)

2 Why ?  Energy Spectrometry ILC test beam experiments T474 and T475 will test concepts for incident beam energy monitoring at the ILC Upstream spectrometer uses a 4 magnet chicane with microwave BPMs before, in the middle, and after the chicane. In order to get the best possible measurement, we need accurate knowledge of B*dl and position of the beam  ground motion can limit the precision of the chicane !! 3 concrete blocks on which the chicane will sit.. Motion of interest is the relative motion of the concrete blocks!

3 Geophone measurements I Calibration measurements (side by side) Only vertical motion ! Freq. range 1 to ~20 Hz (i.e. mostly fast motion) 30sec 400Hz sampling rate x30 amplification (with possible problems!!) 20nm relative motion ? Freq HZ

4 Ch0 Geophone measurements II Ch1 Relative vertical ‘fast’ motion between the two ends of the chicane ~50nm Similar for other arrangements along the chicane.. Freq HZ

5 STS-2 Seismometers Low noise broadband (0.01 – 50 Hz) feedback seismographs (‘Very sensitive’) Can get to 100sec measurements (0.01Hz) ~ calibration cycle of spectrometer! x,y,z differential signals Usual measurement setup includes covering the STS-2’s with styrofoam boxes for thermal and air current insulation… After movement, the seismometers were let to settle for ~2hours In NLC 0 th Order Rep. measurements, seismometers were let to settle for 1 day, and usually movement cycle was 2-3 days.. Due to time restrictions, this was not possible in our case…

6 Seismometers I Calibration measurement:  4kHz sampling rate, 30 sec sample Relative motion: 3nm Freq HZ Other configurations give similar signals in the 30 – 50 nm range. But only valid for ‘fast’ motion (>0.1Hz) due to 30sec sample x signal

7 Seismometers II 400 sec 1kHz sampling rate Which means we can get to 100sec timescales x signal y signal  On the floor at the two ends of the chicane On the concrete blocks

8 Comments Data give 50 – 100nm relative motion between girders at frequencies 0.5 Hz. Noise sources (water cooling, cultural noise) exist in ESA.. Need more STS-2 long timescale measurements (400+ sec samples) Need to determine amount of noise introduced by short settling period for the seismometers… Do we need to follow the long settling strategy? Very time consuming.. Suggestions for improvement… Data still ‘preliminary’  Need to better understand seismometer behavior