16L2 aperture measurements D. Mirarchi

Measurement procedure 4 correctors bump in H plane 3 correctors bump in V plane Q16 Q16 Q17 Q15 Local aperture measurements (beam 1) carried out the 29th November: Beam screen Beam gently blown up with ADT to fill 5.7s (TCP aperture) No losses at Q16 Local orbit bump with 0.5 mm steps (1s ~ 1mm) Bump reverted and gentle blow up each time aperture touched 1st losses at Q16

Overview Arrows show the orbit movements performed (the blue star is the starting orbit) Local orbit bumps are increased until losses are observed Displacement in the horizontal plane limited by shift at Q17 and Q15

BLM layout All BLMs installed on internal/external side BLMMI.16L2.B1E50_MC BLMMI.16L2.B2I50_MC All BLMs installed on internal/external side Symmetric in the vertical plane Same response if source of hadronic showers top/bottom of the beam screen

Measured orbit bump UP DOWN Example of measured vertical orbit plus beam envelope when touching the aperture Q16 MCB Q16 MCB UP DOWN Main considerations: Bump well matched and symmetric when scanning up/down directions Maximum orbit shift in the middle of MQ.16L2, 2% less amplitude at MCB.16L2 Aperture reached in agreement with aperture model (i.e. orbit + envelope ~ 17 mm)

Example of local beam loss pattern when touching up/down Background subtracted and losses normalized to the highest peak for an easier visual comparison Q16 MCB Q16 MCB UP DOWN Beam 1 Beam 1 Clear difference observed: When touching UP source of hadronic shower at the beginning of MQ.16L2 When touching DOWN source of hadronic shower moved toward MCB.16L2

Beam loss pattern (2) Possible explanations: Internal misalignment? Are we really touching something different on the top/bottom? Loss pattern observed when touching UP, with horizontal shift of -10 mm UP, H=-10mm Beam 1 It seems that we are touching something different as a function of H orbit and V direction!

Based on different loss pattern observed we can extrapolate: Measured aperture Based on different loss pattern observed we can extrapolate: Compatible with pumping direction

Conclusions Local aperture measurements show no evident aperture restriction (as opposed to the ULO) Different beam loss pattern as a function of H displacement and V direction Possible indication of something “sticking” on the beam screen close to MCB.16L2 Compatible with pumping direction Possible further investigations: Energy deposition simulations to evaluate change of source of hadronic shower based of the different loss pattern observed

Measurements 29th of May UP DOWN Re-checked previous measurements: similar features in the loss pattern (even though less BLMs were present) Probably we were in the same situation: UP Beam 1 DOWN