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IR1 and IR5 aperture at 3.5 TeVPreliminary results

S. Redaelli, C. Alabau Pons, R. Assmann, R. Bruce, M. Giovannozzi, G. Müller, F. Schmidt, R.

Tomas, J. Wenninger, D. Wollmann

•Introduction•Method for 3.5TeV •Measurement results•What we had at 450 GeV•Preliminary conclusions

Acknowledgements: S. Fartoukh, M. Lamont

LHC Studies WG - MG13/09/2011

Proposal for 3.5 TeV measurements

Unlike at injection, we cannot lose the full beam! We have to be very careful with damage and quenches, even with pilot beam! Idea: local bumps in the triplet with safe, blown-up pilot bunch and tertiary

collimators to protect the tripletEven if we planned to work with safe beam, a detailed planning was submitted to rMPP for approval.Selective emittance blow-up tested in the MD with the ADT: looks very promising and opens the path for efficient measurements at top energy.

TCTH.4L1

IP56 sigma envelope

Thanks to ATLAS, CMS: special BCM settingsLHC Studies WG - MG13/09/2011

Example of 3.5 TeV measurementProcedure for “gentle” measurements:

1. Open TCT by 0.5 sigma (250-320μm in H-V)2. Increase bump by 0.25 sigma3. Check relative height of BLM spikes: TCT vs MQX (Q2)

Start from initial settings: TCTs at 11.8 sigmas.

Orbit at TCT and Q2

TCT positions [mm] 18.8 σ

18.3 σ17.8 σ

TCT losses [Gy/s]

Q2 losses [Gy/s]

Loss spikes while the orbit is increased, touching TCT or MQX

LHC Studies WG - MG13/09/2011

Overall measurement timeline

BCT

TCT gaps

Measurements completed in ~ 4h (H+V in IR1+IR5)LHC Studies WG - MG13/09/2011

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Summary of IR1/5 scans (preliminary)Figures quoted in the eLog, from online estimate:http://elogbook/eLogbook/eLogbook.jsp?lgbk=60&date=20110826&shift=1

IR1 - H (Sep) -> 19.8 - 20.3 sigmas IR1 - V (Xing) -> 18.3 - 18.8 sigmas IR5 - H (Xing) -> 19.8 - 20.3 sigmas IR5 - V (Sep) -> > 20.3 sigmas Resolution:

0.5 sigmas from TCT step size

This means that we had to open the TCT by 6.0-7.5 sigmas to “see” the triplet aperture. Present assumptions: 2 sigma retraction.Effect of bump shape (RBCX contribution) under investigation.

What could we do if these good aperture was confirmed?Squeeze below 1m with tight collimator settings

or

Run at 1m with present relaxed collimator settings and 120 μrad crossingIn operation!

LHC Studies WG - MG13/09/2011

2011 injection measurementsMeasurements performed at the end of Feb. 2011.

- Essentially, the same geometry as 3.5 TeV was used: additional crossing angles added on top of reference orbit.

- Used a different method to “touch” the aperture: (emittance blow-up + local bump at the triplet).

- Measured absolute aperture and not retraction to TCT.

R. Bruce

LHC Studies WG - MG13/09/2011

Comparison (IP5, crossing plane)

3.5TeV, squeezed, Aug.2011

This is where we saw losses!

450 GeV, injection optics, Feb. 2011

LHC Studies WG - MG13/09/2011

Comparison: a few numbers in mm

Model BPM (COXing+ ΔCObump)450 GeV IP5-H (crossing) COXing = 8.0 mm

(170 μrad) ΔCObump = 8.3 mm 14. mmnσ x σ = 16.0 mm 16. mmAmm = 32.3 mm 30 mm

Model BPM (COXing+ ΔCObump)3.5 TeV IP5-H (crossing) COXing = 5.8 mm

(120 μrad) ΔCObump = 17.7 mm 24.4 mmnσ x σ = 4.8 mm 4.8 mm

(nσ = 4) Amm = 28.3 mm 29.2 mm

PRELIMINARY ANALYSIS. Error analysis under preparation.Comparison table will be extended to all other available IRs / planes

Mechanical aperture: 28.9 mm (30 mm without tolerance)

LHC Studies WG - MG13/09/2011

3.5 TeV loss maps at 1m,Xing = 120μrad, relaxed collimator settings

Loss maps cannot easily be used to determine the margin TCT to triplet (MP relevant) but clearly the MQX were not exposed to beam halo. Cleaning looks good. Seen some leakage TCT → MQX for B2, IR1-L.

Betatron

Off-momentum Dump

TCTs TCTs

Beam 2

TCTs

Loss maps done with remaining intensity of ~ e9p

LHC Studies WG - MG13/09/2011

Conclusions• We measured gently the aperture in the triplet region at

3.5 TeV.– Triplets in the shade of the TCT– 4 planes in 2 IPs: 1 fill, < 5h at top energy

• Preliminary analysis: indicated a triplet aperture of ~ 18-20 sigmas. – Inferred from the retraction of the TCTs that sit at ~ 12

sigmas.• Comparison with previous injection measurements show

that these figures are consistent with a few millimeters.• Triplet aperture compatible with a well-aligned machine, a

well centred orbit and a ~ design mechanical aperture (small tolerance).

• Parasitically tune and coupling were measured during the scans: they might provide information on triplet FQ.

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