1. 16L2 aperture measurements
D. Mirarchi

2. 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

3. 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

4. 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

5. 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)

6. 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

7. 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!

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

9. 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

10. 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