1. Aperture measurements during LHC commissioning 2017
C. Hessler, W. Bartmann, C. Bracco, J. Mertens

2. Injection aperture measurement
16/05/2017
Beam setup: Circulating pilot bunch LHC Trim: 4 magnet closed orbit bump in horizontal and vertical plane Collimator settings: TDI injection settings
Measurement flow: Apply bumps using LHC trim application until significant losses are shown on BLM display. Note down the corresponding trajectory offset and which element saw the biggest losses.
Beam IR
Horizontal aperture
Vertical aperture B1
IR2
+16/-17
+15/-16
IR8
+10/-11
+12/-14 B2
+20/-18
+11/-8
+15/-15
+16/-15.5

3. Transfer line aperture
16/05/2017
Beam setup: Inject & Dump pilot bunch (0 turns) LHC Trim: Phase knobs in horizontal and vertical plane. Collimator settings: To avoid losses in LHCb, TDI, TCTH and TCTV have been closed. TCDIs completely open.
Measurement flow: Apply various phase oscillations on extracted beam using LHC trim application until significant losses are shown on BLM display. Note down the corresponding number of sigmas and phases.
Bottleneck found as expected at the MSI in the vertical plane: → -/+6 sigma for B1, -7/+6 sigma for B2 On 60 degree phase advance vert. plane B2, at 11 sigma losses in the line around BPM were created: → Only seen if the TCDIs are completely open → No show stopper for higher intensity beams.

4. Phase scan results
TI 8

5. LBDS aperture measurement
12/05/2017
Aim: Verify available aperture in extraction region in both directions for three cases:
Circulating beam aperture in Point 6
14/15 MKD: extraction aperture for different numbers of kickers firing
Aperture along dump line using oscillations at various phases

6. Circulating beam aperture in Point 6
Beam setup: Circulating pilot bunch LHC Trim: 4 magnet closed orbit bump in horizontal and vertical plane Collimator settings: TCDQ and TCSP retracted.
Measurement flow: Apply bumps using LHC trim application until significant losses are shown on BLM display. Note down the corresponding trajectory offset and which element saw the biggest losses.
Plane
Beam
Aperture
Horizontal
Beam 1
+15 mm (TCDS)/ -20 mm (TCSP)
Beam 2
+15 mm (TCSP)/ -16 mm (TCDS)
Vertical
+16 mm (TCSP)/ -19 mm (TCSP)
+17 mm (Q5)/ -18 mm (Q5)

7. 14/15 MKD: extraction aperture for different numbers of kickers firing
Beam setup: Inject & Dump pilot bunch (0 turns) LHC Trim: One MKD knob in horizontal plane Collimator settings: TCDQ and TCSP not needed. TCDS is fixed anyway.
Measurement flow: Apply kicks in units of 1/15 MKD strengths using LHC trim application until significant losses are shown on BLM display. Note down the corresponding number of MKDs (lower and upper limit).
Beam
Losses
Beam 1
Start seeing losses on TCDS at 13 MKD and no losses for 16 MKD
Beam 2
Start seeing losses on TCDS at 12 MKD and 17 MKD

8. Aperture along dump line using oscillations at various phases
Beam setup: Inject & Dump pilot bunch (0 turns) LHC Trim: Phase knobs in horizontal and vertical plane. Collimator settings: TCDQ and TCSP not needed. TCDS is fixed anyway.
Measurement flow: Apply various phase oscillations on extracted beam using LHC trim application until significant losses are shown on BLM display. Note down the corresponding number of sigmas and phases.
Beam
Phase
Aperture
Beam 1
0 deg
+9 sigma/ -9 sigma loss onset
90 deg
+15 sigma/ -18 sigma loss onset
Beam 2
+10 sigma/ -10 sigma already shows clear losses

9. Conclusion Injection aperture OK
Transfer line aperture OK → Bottleneck at MSI as expected. Losses near BPM.86904, only seen if TCDIs completely open
LBDS: Circulating beam aperture in both planes OK
LBDS: 14/15 MKD OK
LBDS: Phase oscillation for 90 deg B2 starts already to create losses at +/- 10 sigma → smaller than for B1 and for B2 after LS1 (15/-16)
Lessons learned:
Problem with inject&dump 0 turn: Made obviously 1 turn and created losses around the machine. → Has to be tested beforehand the next time → Workaround: Changed I&D to 5 turns and extracted with MKD knob.
Closing TDI, TCTH and TCTV solved problem with showers in LHCb during TL aperture measurement