We returned to WEB and performed tappings in different locations. Each tapping consists of 2 minute long sequence of fast hits with the hammer tool. Accelerometers on the cryotrap vacuum chamber (ENV_WE_CT_ACC_Z), on the 1200 flange AR side (ENV_WE_ACC_Z) and on the symmetric flange on HR side (ENV_WE_HRSIDE_ACC_Z) are used as calibrated monitors of how much vibration propagates to the different parts.

We tapped in the previously tested locations excluding those that did not produce effects, plus locations under the tower that were not tested before. This time we have the accelerometer monitor on the 1200-flange HR side.

We then went to NEB and repeated a similar (reduced) set of tappings.

The WEB tapping locations are:

• near VAT flange
• structure around cryo-trap holding points (4 of them) both in horizontal and vertical direction (PICTURES)
•  cryotrap chamber in correspondence of the cryo-baffle (south side (near CT_ACC) and north side (opposite of CT_ACC))
• near bellow (tower side)
• 1200-flange HR side
• cylindric vacuum pipe (two locations)
• under tower: HR side, HR side gap, AR side (PICTURES)

The NEB tapping locations are:

• near VAT flange
• structure around cryo-trap holding points (only 1) both in horizontal and vertical direction
•  cryotrap chamber in correspondence of the cryo-baffle (east side (near CT_ACC))
• near bellow (tower side)
• 1200-flange HR side
• under tower: HR side, HR side gap, AR side

Some preliminary concluding notes:

• Tappings at NE did not produce effects in Hrec (apart from a little structure at 128Hz when tapping under the tower, to be confirmed if correlated to our actions) 
• Tappings at WE:
  • the lagest effects in hrec is seen when tapping on the cryotrap chamber (cryo-baffle position and "holding point structure")
  • in some locations (holding points, FIGURES) the CT ACC seems a good witness of the frequency of the scattering bump in hrec.
  • sometimes also harmonic peaks are seen in hrec (FIGURES)
  • on the tower side and under the tower the hrec is excited less, and mainly in the region below 60-100Hz  and around 100Hz