CWG 02.04.2012

Overview and alignment results of the BPM button

collimator mock-up

D. Wollmann, on behalf of

O. Aberle, R.W. Assmann A. Bertarelli, C. Boccard, F. Burkart, R. Bruce, M. Cauchi, A. Dallochio, D.

Deboy, M. Gasior, R. Jones, V. Kain, L. Lari, A. Masi, A. Nosych, A. Rossi, S. Redaelli, B.

Salvachua, G. Valentino, E. Veyrunes

Outline

• Introduction

• Why Collimators with Beam Diagnostics Functionality?

• Design overview

• Results from Beam Measurement

• ConclusionDaniel Wollmann 2

PRESENT: Beam based setup and qualification of collimation

system• Centre collimator jaws around beam (by touching

the beam halo create losses BLM based method)

• Determine local beam size at collimators• Set up system with agreed collimator settings

~7 mins per collimator & state (two beams in parallel)

Destructive in halo. Overhead: special fills and ramps!• Qualify system by measuring the cleaning efficiency

– β-tron losses– Momentum lossesDaniel Wollmann 3

History of Collimator Jaws with BPM Buttons

• First discussions early on in 2004 during design of the phase 1 collimators: F. Caspers and R. Assmann.

• Due to time pressure: Decision to delay this improvement to the phase 2 collimator design.

• Given as design requirement for any new LHC collimators:– Concerns on impact of shower initially strong. However:

• Phase 1 collimator tests in SPS were not able to generate shower-induced changes in BPM’s in SPS good news that showers do not impact performance.

• Also no shower effects so far reported in LHC for LHC BPM’s in IR3/7.

– EN/MME detailed design work to integrate BPM buttons ongoing. – SLAC pursuing design with buttons in flanges.– BE/BI designing BPM button solution and electronics.

• First phase 2 mockup collimator with buttons installed in SPS early 2010. 4Daniel Wollmann

Conceptual Strengths of Design with Buttons in Movable Jaws

• Advantages:– Centering of beam done by minimizing difference signal

(L-R), down to zero independent of absolute calibration of BPM signals, electronics offsets, … for same cable length.

– The now movable buttons are placed much closer to the circulating beam much better resolution than achievable with standard LHC BPM’s.

– No intercepting of beam halo, so fully non-destructive. No special fills and intensity constraints!

• Disadvantages:– If buttons are inside loss-induced showers then signals

could be disturbed? Setup with buttons might only be possible during low-loss periods (e.g. just before colliding, during stable beams, …). Look at difference up- (no shower) and downstream (max shower).

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Operational Gains with in-jaw BPM buttons?

• Drastic reduction of setup time of collimation system (gain time for physics). For example 7 min 1 second Factor > 100!

• Continuous monitoring of beam offsets at collimators. Measurement of jaw angle w.r.t. the closed orbit. Increased passive machine protection as orbit drifts are quickly detected (watch dog).

• Collimators can follow without overhead long-term orbit drifts.

• More flexibility for local orbit changes in the experimental IPs (crossing angle, separation for luminosity leveling, etc.). Relaxed restrictions for luminosity optimization in the experimental IPs.

• Allows reduction of margins between collimator families, as collimators can follow orbit drifts tighter collimator settings possible better cleaning and lower beta* possible.

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First CERN mock-up collimator with integrated BPM buttons

(Jan 2010)• BPM mock-up produced at CERN

(EN-MMI, BE-BI, Collimation Team)• Installed into SPS in 2010

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BPM buttons

Distance from jaw face (Up-, Downstream buttons): 10mm

Courtesy A. Bertarelli, A. Dallocchio, O. Aberle, et. al

First CERN mock-up collimator with integrated BPM buttons

(Jan 2010)• BPM mock-up produced at CERN

(EN-MMI, BE-BI, Collimation Team)• Installed into SPS in 2010

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BPM buttons

Distance from jaw face (Up-, Downstream buttons): 10mm

Courtesy A. Bertarelli, A. Dallocchio, O. Aberle, et. al

Buttons at extremities proved most useful (no shower effects seen). Therefore here focus on results of these buttons. No beam results from central two buttons!

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8th January 2010

From the lab into the SPS tunnel

First CERN mock-up collimator with integrated BPM buttons

(Jan 2010)

Tank

Jaws

Courtesy A. Bertarelli, A. Dallocchio, O. Aberle et. al

Measurements in the SPS 2011:4 MDs (Mai/June,

September/October)• Test new BPM electronics (details see talk by M.

Gasior).• Test new BPM based alignment method.• Compare to classic BLM based alignment method.• Measure non-linearity of BPM buttons (see talk by

A. Nosych)• Vacuum: measure out-gazing during movement and

beam impacts (not discussed here).• Test BPMs with standard LHC electronics to

measure beam offsets in single pass / turn by turn application of button collimators in transfer line collimators?Daniel Wollmann 10

SPS Beam Tests: Compare present BLM and new BPM method for jaw alignment

• Create a four corrector orbit bump at collimator (steps of 500 mm).

• New method: Align collimator jaws around beam with in-jaw BPM buttons (~few seconds).

• Present method: Align collimator jaws around beam with BLM based method (~7min per collimator).

Accuracy:• BLM-method: max. error ± 50mm due to used step

size of 50mm.• BPM-method: assumed max. error ± 50mm as

electronic channels were not yet calibrated for gain and cable length.Daniel Wollmann 11

Measurements: Beam offsets with 2 methods

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NEW (few seconds)

OLD(~7mins)

Good agreement between orbit bump, BLM and BPM centers.

Correlation: Bump versus BPM-method,

BLM-method

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Correlation: BPM-method versus BLM-

method

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Correlation: BPM-method versus BLM-

method

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Takes 7 min per collimator setup. Requires special low intensity fills.

Correlation: BPM-method versus BLM-

method

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Takes a few s per collimator setup. Can be done all the time: no overhead.

Correlation: BPM-method versus BLM-

method

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Excellent correlation between the two methods.

Measured deviation between: bump & BLM / BPM

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Maximum deviation to bump :

[-50mm, +140mm]

HIGHLIGHT summary result

Measured deviation between: BLM & BPM

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Maximum deviation between BLM and BPM :

[-50mm, +63mm]

HIGHLIGHT summary result

Measured deviation to bump: BLM & BPM

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Orbit drifted

Deviation to bump:

≤ ±40mm

HIGHLIGHT summary result

Measured deviation between: BLM & BPM

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Orbit drifted

Deviation between BLM and BPM :

≤ ±25mm

HIGHLIGHT summary result

Measurement: Influence of radiation on BPM signals

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• Variation of BPM signal (<35mm)

• Drift of signal due to non-linearities in the BPM electronics at low beam intensities

Collimator gap: 21mm

Measurement with secondary halo created by an upstream SPS collimator

Low intensity point

SPS beam tests with standard LHC electronics: Measure turn

by turn accuracy

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• Measurement performed over 10mins.

• Move jaw around beam at constant gap (0.5mm steps).

• Average beam position measured by BPMs.

• Calibrating slope and offset to bump settings.

SPS Beam Tests with standard LHC electronics: Measure turn

by turn accuracy

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Agreement between bump and BPM measurement not as good as with other

electronics.

SPS Beam Tests with standard LHC electronics: Measure turn

by turn accuracy

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• RMS of variation: ~82mm.• b-tron oscillations to bet

taken into account.

Conclusion• Collimators with integrated BPMs have been shown

to:– Decrease setup time: ~ factor > 100 per collimator

without overheads.– Continuous monitoring of beam in collimator: Passive

machine protection.• Measurements show:

– Excellent agreement between the two methods.– Average discrepancy between BPM and BLM method

better than 25mm, limited by the step size used. Present LHC setup accuracy shown with BPM’s.

– No disturbance in BPM signal due to primary protons or secondary showers seen so far.

– RMS variation for turn by turn measurements ~82mm. Further measurements for single pass application needed.

• Better cleaning and lower beta* possible.Daniel Wollmann 26

END

Thank you for your attention!

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Backup slides

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Design: BPM Mockup

• Simplified jaw design: only to support BPM buttons• Almost no cooling• Thin jaw material

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Cross section of Mockup jaw

Cross section of phase 1 secondary collimator jaw