RWA LTC 27.10.04 Preliminary results from SPS collimator MDs LTC 27.10.04 R. Assmann for the collimation team

RWA LTC 27.10.04

Preliminary results from SPS collimator MDs

LTC 27.10.04

R. Assmann for the collimation team

RWA LTC 27.10.04

People involved in collimator design/construction/testing

• This has been an outstanding team effortteam effort over the last 12 months!

• Work by:

O. Aberle, G. Arduini, R. Assmann, A. Bertarelli, T. Bohl, L. Bruno, H. Burkhardt, S. Calatroni, F. Caspers, E. Chiaveri, B. Dehning, A. Ferrari, E.B. Holzer, J.B. Jeanneret, L. Jensen, M. Jimenez, R. Jones, M. Jonker, T. Kroyer, M. Lamont, M. Mayer, E. Metral, R. Perret, L. Ponce, S. Redaelli, G. Robert-Demolaize, S. Roesler, F. Ruggiero, D. Schulte, H. Tsutsui, P. Sievers, R. Steinhagen, V. Vlachoudis, L. Vos, J. Wenninger, F. Zimmermann, ...

• Not including work on LHC collimation design!

Goals of SPS TestsGoals of SPS Tests1. SPS ring:

Show that the LHC prototype collimator has the required functionality and properties (mechanical Show that the LHC prototype collimator has the required functionality and properties (mechanical movements, tolerances, impedance, vacuum, loss maps, …).movements, tolerances, impedance, vacuum, loss maps, …).

2. TT40 extraction:Show that an LHC collimator jaw survives its expected maximum beam load without damage to jaw Show that an LHC collimator jaw survives its expected maximum beam load without damage to jaw material nor metallic support nor cooling circuit (leak).material nor metallic support nor cooling circuit (leak).

Crucial project milestone Mechanical engineering(installation 18Aug04) Tolerances

Prototype productionControl and motorizationSet-up of a single LHC collimator

with beam

(APC April 04)

RWA LTC 27.10.04

Beam conditions• Beams prepared by G. Arduini, J. Wenninger and OP team

• Low intensity MD: Monday Oct 11th Bunch population 1.1e11 pNumber of bunches 1-16Beam energy 270 GeVEmittance ~ 1 mH beam size at collimator ~ 0.4 mmBeam orbit stability ~ 10 m

• High intensity MD: Monday Oct 18th Bunch population 1.1e11 pNumber of bunches 288Beam energy 270 GeVEmittance ~ 3.75 mH beam size at collimator ~ 0.7 mm

• Robustness test: Monday Oct 25th

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Configuration

Collimation team: Collimator in P5 of SPS

BLM team: 8 downstream BLMs

Together: 1 Hz DAQ and plotting in

control room

BLM team

RWA LTC 27.10.04

Different issues1. Functionality and basic collimator control

2. Set-up and beam-based alignment of jaw (includes BLM diagnostics)

3. Halo dynamics

4. Impedance and trapped modes

5. Heating of collimator

6. Vacuum and e-cloud (outgassing)

7. Effects on BPM’s and orbit feedback

RWA LTC 27.10.04

1. Functionality: Mechanical movement and tolerances

• Collimators moved in a FULLY operational wayFULLY operational way: no limits or unexpected

difficulties encountered!

• Closest gap of ~ 1 mm~ 1 mm achieved with circulating beam! Mechanical tolerances

and angular alignment at the ~ 100 m level!

Much smaller gaps than required in the 7 TeV LHC have been Much smaller gaps than required in the 7 TeV LHC have been

achieved with the LHC collimator prototype and circulating beam!achieved with the LHC collimator prototype and circulating beam!

• Knowledge of full collimator gap (excluding human math errors):

Absolute ± 100 ± 100 mm

Reproducibility ± 20 ± 20 mm

Anti-collision settings 1.188/1.146/1.160 mm

Gap known to 100 Gap known to 100 m with excellent reproducibility (20 m with excellent reproducibility (20 m) over 16 m) over 16

h h (motor setting reproducibility)!(motor setting reproducibility)!

Some sensors useful others less useful: Reduce numberReduce number of sensors!

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2a. Set-up and beam-based alignment of jaw

-10

0

10

20

30

40

50

6013

:22:

15

13:2

4:43

13:2

6:47

13:2

9:55

13:3

2:14

13:3

3:36

13:3

5:03

13:3

6:26

13:3

8:44

13:4

0:09

13:4

2:08

13:4

3:34

13:4

5:11

13:4

6:41

13:4

8:45

13:5

1:16

13:5

2:37

13:5

4:18

13:5

5:28

13:5

6:48

13:5

8:17

13:5

9:16

14:0

0:42

14:0

1:57

14:0

7:25

14:0

8:39

14:0

9:45

Day time

Ga

p w

idth

an

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[mm

]

Gap width

Gap center

First basic set-up (100 m accuracy) within 50 min!

RWA LTC 27.10.04

2b. Set-up and BBA: Typical BLM signal for move of jaw

Observation of BLM signal tails: Up to 10-20 seconds10-20 seconds in length

BLM teamBLM team: Many measurements Beam related true signalBeam related true signal!

RWA LTC 27.10.04

2c. Studies of BLM systematics

Time

L. Ponce et al

RWA LTC 27.10.04

2d. Set-up and BBA: High precision set-up

• LHC requirement: Center gap around beam with ~ 25 m accuracy for

nominal * (beam-based alignment).

• SPS beam: 120 h beam lifetime (de-bunched beam?)

orbit stable to 5 m ideal tuning conditions

• Observation:Beam-based alignment ... ... to 100 ... to 100 m is OK!m is OK!

... to 50 ... to 50 m is difficult!m is difficult!

... to 10-20 ... to 10-20 m is impossible?m is impossible?

• Understand effect to improve beam-based set-up!

RWA LTC 27.10.04

3a. Halo dynamics: Re-shaping

After 10-20 seconds: New stable shape

•Problem: Re-shaping of beam with collimator in!?

–Edge 1 jaw 1 creates sharp edge and stays in!

–Rectangular distribution close to edge unstable!

–Particles in sharp edge diffuse and are lost!

–No sharp edge for precise alignment of edge 2 jaw 1 or jaw 2!

–Similar effects observed in ISR, SPS, ...

No sharp edges!

Collimator jaw

Beam distribution

RWA LTC 27.10.04

3b. Measurement of repopulation rate – jaw positions

2.7 mm ≈ 6.5

• Move from 7.7 mm (~ 19) back and forth to 2.7 mm (~ 6.5).• Wait different times in between.• Observe beam loss.

Left jaw

Right jaw

Dump beam on collimator

G. Robert-Demolaize et al

RWA LTC 27.10.04

3c. Measurement of repopulation rate - BLM signals


DC coll at 19

DC coll at 6.5


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3d. Measurement of repopulation rate – low intensity analysis

Shows how much beam diffuses out of sharp edge versus time!


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3e. Measurement of repopulation rate – high intensity analysis


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3f. Beam distribution close to the edge after 30 seconds


50 m 1 mm

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3g. DC beam loss versus collimation depth

~ 10 ~ 20

More beam losses with collimator jaws further in: Enhanced diffusion rate?

S. Redaelli et al

RWA LTC 27.10.04

4a. Impedance and trapped modes

• Impedance is a limitation for the LHC collimators.

• Impedance depends on collimator gap.

• Measurement is simplified as impedance can controlled through

gap.

• Different measurements tried:

Tune shifts, orbit kicks, trapped modes, growth rates, ...

Direct Diode Detection Base-Band Q-MeasurementM.Gasior, R.Jones, CERN-AB-BDI

Collimator MDs #2 – (some) BBQ results

Collimator cycled between

51 mm and 3.86 mm (5h04) 51 mm and 2.86 mm (5h35) 51 mm and 2.46 mm (5h43) 51 mm and 2.06 mm (5h50) 51 mm and 1.86 mm (5h58)

LARGE gap

SMALL gap



Collimator cycled (at ca 4h33) between the gap of 51 mm and 2 mm. Tune frequency was changing by 10 Hz, i.e. 2.310-4

( frev)

BBQ system 245 MHz system

245 MHz system confirms data (F. Caspers/T. Kroyer)

Also: Standard tune measurments (H. Burkhardt)



2 .02 .53 .03 .54 .0C o llim a to r g ap [m m ]

0

5

1 0

1 5

2 0

Tun

e ch

ange

[H

z]

0

0 .5

1

Inte

nsit

y / 1

e11T u n e freq u en cy

In te n s ity

C o rrec te d tu n e

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4b: Trapped modes

• Collimators were equipped with RF pickups to measure trapped modes.

• Measurement with and without beam by F. Caspers and T. Kroyer.

Observation:

• There are trapped modes.

• They are excited by beam.

• No effect on collimator

temperature or beam stability

observed.

• Detailed analysis required.

• Fritz has won a bottle of

Champaign and 20 straws...

F. Caspers & T. Kroyer

RWA LTC 27.10.04

5. Heating of collimator (high intensity)

No sign of problematic heating... Maximum increase 10 deg for closing gaps quickly!?No over- or under-design of collimator cooling...

RWA LTC 27.10.04

6. Vacuum and e-cloud

• No sign of vacuum pressure increase.• No sign of local e-cloud at the collimator.

RWA LTC 27.10.04

7. Effects on BPM’s and orbit feedback

• Scraping of up to 5e12 protons at 270 GeV.

• No effect observed on downstream BPMs and overall orbit feedback (R. Steinhagen & J. Wenninger).

• Orbit feedback stabilized to 10 m orbit drifts. However, increased noise observed on BLM (equivalent to 10 m jaw steps and consistent with BPM noise).

FB

ON

FB

ON

RWA LTC 27.10.04

Robustness test in TT40• Beam accidentBeam accident just before sending first beam to collimator.

• Septum/power supply problem ( Jan). Safe extraction of nominal LHC beam for another trial?

• Collimator in TT40 saw no beamCollimator in TT40 saw no beam (except showers from accident).

• Concerns about collimator safetycollimator safety:

– Lot’s of calculations and lab measurements We are convinced it will survive without damage (both jaw and water cooling circuit)!

– We had vacuum/radiation protection/cooling water experts on stand-by in the control room for an eventually needed emergency intervention.

– Was not needed for the collimator but was helpful for fast recovery of the SPS.

• Try again the robustness testTry again the robustness test:We are convinced there will be no problem. However, there can always be a bad surprise

Test now with SPS beam so we can still correct problems!

If there is an unexpected problem it would be a real mess to only find real mess to only find it in the LHCit in the LHC!

RWA LTC 27.10.04

Preliminary conclusionsCollimator design has been validated successfullyCollimator design has been validated successfully in beam operation:

• Fully functional deviceFully functional device with no significant hardware problems.

• Real world performance provides knowledge base for possible savings: Reduce number of sensorsReduce number of sensors to required minimal level (save budget).

• Small gapsSmall gaps (smaller than in LHC) established with good accuracy and tolerancesgood accuracy and tolerances (circulating beam for 1 mm gap).

• Impedance measurements confirm predictionsImpedance measurements confirm predictions: Phase 2 collimators are required for above 50% of nominal

intensity (resources???).

• Set-up and beam-based jaw alignmentbeam-based jaw alignment worked at intermediate precisionintermediate precision: Need to advance quantitative understanding of halo dynamics for *

below ~ 1m with high precision jaw set-up (resources???).

• Collimator design does not require any modificationsCollimator design does not require any modifications (except maybe some material for absorbing trapped modes, if found dangerous).

• Collimators will now be producednow be produced and we are convinced that phase 1 collimators will be robust and powerful tools for the LHCrobust and powerful tools for the LHC (robustness test should still be done)!

RWA LTC 27.10.04

Gap center and width versus time

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13:2

9:39

14:3

1:36

15:3

4:30

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5:35

16:4

1:08

17:1

0:19

18:1

0:05

19:0

3:05

20:0

0:02

20:5

0:39

21:4

2:41

22:3

7:09

23:2

8:42

0:15

:47

0:52

:40

1:38

:20

2:23

:17

3:02

:57

3:55

:43

4:31

:36

5:10

:20

5:47

:04

6:30

:13

7:45

:27

Day time

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cen

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siti

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m]

0

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12:2

1:07

13:2

2:16

14:0

0:44

15:2

4:04

15:4

9:57

16:2

4:39

16:4

9:09

17:2

2:35

18:1

2:01

18:4

9:37

19:4

0:58

20:4

2:51

21:2

3:48

22:0

9:35

22:5

6:18

23:4

3:24

0:19

:32

0:53

:01

1:34

:46

2:12

:16

2:50

:13

3:39

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4:11

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5:16

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6:29

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7:35

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Day time

Ga

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[m

m]

RWA LTC 27.10.04

Documents

RWA LTC 27.10.04 Preliminary results from SPS collimator MDs LTC 27.10.04 R. Assmann for the collimation team