Discussion on Machine Protection requirements for the first LHCb velo insertion (19.08.2022)

Participants: V. Coco, P. Collins, C. Hernalsteens, F. Moortgat, S. Ravat, S. Redaelli, M. Solfaroli, J. Uythoven, J. Wenninger, C. Wiesner, D. Wollmann

Excused: G. Pigny, B. Salvant

Goal of the meeting: 

Agree on machine protection requirements for the first insertion(s) of the LHCb velo. The proposal will be presented in the LMC on 24.08.

Indico page: https://indico.cern.ch/event/1192017/

Summary:

• The commissioning of the LHCb Velo is advancing. The interlocking via the velo safety systems has been fully tested and validated. The details of the status of the commissioning can be found in Victor’s slides on the Indico page above.
• LHCb is requesting to do a first insertion of the velo to a minimum aperture of 10 mm, moving the velo in steps of 1 mm from its current position of 27 mm. The nominal in position is leading to a distance of the pixel detector of 5.1 mm and the foil of 3.5 mm from the beam. Following the insertion to 10 mm, the data will be carefully analysed and the aperture and position of the velo in respect to the beam will be validated. This validation will take 1-2 months. If the analysis does not reveal any issues and the commissioning of the velo is successfully finished, LHCb will request the routine insertion of the velo during physics fills to its nominal closed position.
• Before the meeting, the vacuum group confirmed that the vacuum system is ready for the insertion of the velo. The vacuum experts will closely follow and observe the first insertions of the velo.
• Based on the available aperture, simulation results and experience from LS2, it was concluded that no loss-maps or asynchronous beam dump tests have to be performed with the LHCb velo in its nominal position before routine insertion. It has been noted, that with the current interlocking strategy (velo only allowed if stable beams flag is TRUE), the performing of loss maps is practically impossible. This  implementation will be reviewed offline between LHCb and OP and it will be evaluated if this needs to be modified to velo allowed in when movable devices flag is TRUE.

• For the insertion to 10 mm the following approach concerning machine protection was agreed:
  • 1) Fill with 12 bunches with step-wise manual insertion of the velo to 10mm, keeping the fill for minimum 10 mins after the successful insertion. This fill is meant to ensure that the mechanics of the insertion is working as expected, without any surprises.
  • 2) Fill with 300b with step-wise manual insertion of the velo to 10mm. The fill should be kept for a minimum of 1 hour after the velo insertion. This time should be sufficient to identify issues to due RF heating and for LHCb to take sufficient data to validate the correct position and aperture of the velo.
• Daniel will verify with Benoit S. if the 10 mm position is potentially more critical from an RF heating point of view than the nominal closed position and validate with him that the 300b intensity and the proposed time in stable beams is sufficient to identify potential RF heating issues.

• Following the finalisation of the LHCb velo commissioning, the velo will be inserted routinely to its nominal position. Pending the outcome of the velo insertion of the LHCb velo and the commissioning the following approach for machine protection has been agreed, which is similar to an intensity ramp-up after a technical stop:
  • 1) Fill with 12 bunches to SB and insertion of the velo and keeping the fill for some tens of minutes.
  • 2) Fill with 300b and keeping stable beams for a minimum of 2 hours.
  • 3) Fill with half full intensity (~1200 b) keeping the fill for minimum of 2 hours in stable beams.
  • 4) Back to full intensity
• The above proposal will be confirmed at a later stage when the LHCb velo commissioning is further advanced.