1

Beam induced heating

Benoit Salvant, with the invaluable input and help of many colleagues:

Collimation team: Oliver Aberle, Ralph Assmann , Roderik Bruce, Alessandro Bertarelli, Federico Carra, Luca Gentini, Luisella Lari, Stefano Redaelli, Marc Timmins, Daniel Wollman,

Cryogenics team: Serge Claudet, Laurent TavianKicker team: Chiara Bracco , Mike Barnes, Brennan Goddard, Jan Uythoven RF team: Philippe Baudrenghien, Themistoklis Mastoridis, Juan Esteban Mueller, Elena ShaposhnikovaImpedance team: Gianluigi Arduini, Fritz Caspers, Hugo Day, Alexey Grudiev, Elias Métral, Nicolas Mounet, Jean-Luc Nougaret, Giovanni Rumolo, Instrumentation team: Rhodri Jones, Mariusz, Federico RoncaroloOperators and OP teamVacuum team: Vincent Baglin, Alexis Vidal, Giulia Lanza, Bernard Henrist, Gregory And the TIMBER team!

With reference to the talk by Jan Uythoven in mini-Chamonix on 15 July 2011 (link).

2

Main messages• Pressure and temperature:

indirect diagnostics: not everything is clear and understood. please let us know if we forgot equipements! Electron cloud and scrubbing aspects are reported in Giovanni’s talk

• Suspected beam induced heating limitations in 2011 have been:– MKI injection kicker (1/8, delays injection, interlock increased) – double bellow module VMTSA (6/8, broken spring, dangling fingers, vacuum spikes

consolidation during Winter stop)

– TCP collimator in IR7 (1/6, 1 dump, interlock increased OK)– TCTVB collimator (1/4, 1 dump, interlock increased OK)– TDI collimators (2/2, vacuum, background for ALICE, gap to parking OK)– Beam screens (all, longer bunch length eased operation + scrubbing OK)

• Main expected beam induced heating limitations in 2012:– MKI-8D and maybe MKI-8B will need to wait for cooldown before injection– Beam screen in stand alone Q6R5 not much cooling margin left– double bellow module VMTSA

• To be kept under monitoring during 2012– Triplets, TCP and TCTVB collimators for outgasing– ALFA roman pot temperature– Mirror of the BSRT

3

Agenda

• Main messages

• Conclusions from mini-Chamonix in June

• Observations and limitations in 2011

• Would we want to do something during the winter stop?

• Outlook

Conclusions

MKI Measured temperature rise is in agreement with present models

Seems enough margin to operate with nominal parameters However, if bunch current significantly above nominal might become an issue

Count on further increasing the actual temp. interlock limit (60 C to 100 C) Cautious because of large damage potential

Increase temperature interlock in small steps! Development of thermal models and effect of different beam screens

Can gain a factor two in screening by increasing the number of screen conductors from 15 to 24 (24 = original design)

Cryogenics No hard operational limit, but ‘easier’ when temperatures more stable Suspicion on some RF fingers – non conformity

Collimators Suspicion on temperature measurement Possibly Higher Order Modes due to reduced damping by ferrites Can increase temperature interlock limit when required

RF Heating, Jan Uythoven15/07/2011 Mini Cham

Jan Uythoven at Mini-Chamonix 2011

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Agenda

• Main messages

• Conclusions from mini-Chamonix

• Observations and limitations in 2011– Fill example– MKI kicker– TCP.B6L7.B1 collimator– TCTVB.4R2 collimator– TDI collimator– VMTSA bellow module– Beam screen

• Would we want to do something during the winter stop?

• Outlook

6

Example of fill 2216 (Oct. 15th 2011): dynamics of temperature and pressure increase

Temp TCTVB

Intensity

Pressure TDI

Temp TCP

Temp MKIEnergy

- MKI-8D.B2: slow steady increase of temperature which starts with the ramp- TCP.B6L7.B1: slow steady increase of temperature which starts with the ramp and saturates- TCTVB: very odd non reproducible behaviour, with very fast temperature increase- TDI: only pressure available, slow increase followed by decrease.

13h

60 °C

20 °C

7

Agenda

• Main messages

• Conclusions from mini-Chamonix

• Observations and limitations in 2011– Fill example– MKI kicker (cf Chiara’s talk)– TCP.B6L7.B1 collimator– TCTVB.4R2 collimator– TDI collimator– VMTSA bellow module– Beam screen

• Would we want to do something during the winter stop?

• Outlook

8

MKIs: steady temperature increase over 2011

April 1st 2011 October 31st 2011

MKI in point 8

MKI in point 2

60 °C

20 °C

60 °C

20 °C

MKI8-D

MKI8-B

All MKIs are getting hotter…

40 °C

40 °C

…but MKI-8D and MKI-8B are a factor ~2 off

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MKIs interlock level see Chiara’s talk• Interlock had to be raised from 50 degrees to 62 degrees for MKI-8. No obvious issue so

far with the current heating rate. • However, the probe is far from the ferrite and there is no guarantee that this interlock

level will be ok with higher heating rate.• For MKI-8D, already noted significant reduction in current rise time during SoftStart at

68 deg, which would correlate to a reduction in kick strength.• From the rise time, all other 7 MKIs seem ok• MKI8D reached 68 degrees, MKI8B 57 degrees, all the other MKIs are below 45 degrees

y = -1.325E-05x + 7.069E-01

R² = 1.501E-02

y = -7.324E-05x + 7.041E-01R² = 7.792E-01

y = -2.065E-05x + 6.970E-01R² = 3.514E-01

y = -3.563E-05x + 7.004E-01R² = 8.375E-01

y = -2.828E-04x + 7.153E-01R² = 6.809E-01

0.695

0.696

0.697

0.698

0.699

0.7

0.701

0.702

0.703

0.704

0.705

0.706

0.707

0.708

0.709

20.00 25.00 30.00 35.00 40.00 45.00 50.00 55.00 60.00 65.00 70.00

Rise

Tim

e (µ

s)

MKI8 Measured Temperature (˚C)

MKI.UA87.IPOC.?B2:T_RISETIME (October 2011)

MKI.UA87.IPOC.AB2:T_RISETIME

MKI.UA87.IPOC.BB2:T_RISETIME

MKI.UA87.IPOC.CB2:T_RISETIME

MKI.UA87.IPOC.DB2:T_RISETIME

M. Barnes et al

Reduction of rise timeAbove 60 degrees

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What can we do?• Recommendations from Mike Barnes (TE/ABT) :

– Analyze systematically SoftStart data to check that the kicker is in a good state before injection if the temperature approaches SIS level automated system to be developed

– Analyze carefully potential miskicks on the probe beam

• Longer term actions– Work on the impedance reduction of the full kicker assembly – Impedance measurements on MKI8D to understand higher heating on this kicker– Building spares (1 already available) following ongoing studies

• Questions:– Assess the RF fingers state of MKI-8D during winter stop using X-rays? (old design of RF fingers

for this kicker)– Can we replace MKI8D by a spare now ? Difficult decision…– Can we find a way to put 24 conductors instead of currently 15 conductors? Potential

solutions are being investigated.– Would larger bunch length effectively reduce the heat load?

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“Short” digression on longitudinal impedance and power spectra

motivation effect of bunch length on heat deposition

12

Heating due to beam coupling impedance (from E. Métral et al.)

• Power lost by the beam in its surrounding:

• Case 1: one sharp narrowband impedance (e.g. cavity)

• Case 2: broadband impedance (e.g.ferrite kicker)

1

2 22Re2p

revrevlongrevbloss pMfrumPowerspectpMfZfeMNP

resonatorresonatorlongrevbloss pMfrumPowerspectMfZfeMNP 22Re2 2

2

0

2 22Re1

2 blosslongrev

revbloss MNPdffrumPowerspectfZMf

feMNP

22bloss NMP

Re[Zlong]

Power Spectrum (dB)

frequency

Re[Zlong]

Power Spectrum (dB)

frequency

Broadband impedance Narrow band impedance

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Measured 50ns power spectra during fill 2261 by P. Baudrenghien and T. Mastoridis

power spectrum is made of peaks separated by 20 MHz (50 ns) power spectrum at injection extends to 2.5 GHz with a notch around 1.3 GHz

Factor 2000 in power

14

Measured 50ns power spectra during fill 2261 by P. Baudrenghien and T. Mastoridis

spectrum extends to larger frequencies due to smaller bunch length and modified distribution notch in the spectrum shifts to 1.6 GHz

Cannot be trusted above 2.8 GHz(cable specs)

15

Measured 50ns power spectra during fill 2261 by P. Baudrenghien and T. Mastoridis

Amplitude decreases in stable beams (begininng of physics) Spectrum is most critical during the ramp, but the ramp does not last very long

16

Hugo Day et al

- Very complicated 3D model!!!- Simulations seem to grasp the physics

Simulations and bench measurements of MKI

3D simulations

Bench measurementsPower spectrumInjection (dB)

Power spectrumStable beams (dB)

Low frequencies contribute much more than high frequencies for a broadband impedance

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0.9 1 1.1 1.2 1.3 1.4 1.50

10

20

30

40

50

60

70

80

90

100

MKI power loss as a function of bunch length

MKI 24 conductorsMKI 15 conductors

4 sigma bunch length (ns)

pow

er lo

ss in

WEffect of bunch length on simulated power loss (50 ns)

very preliminary… more at Chamonix!

Without conductors, the power loss shoots to 20 kW

Increasing bunch length could help!But using 1.4 ns instead of 1.2 ns gives a 12 W reduction

not drastic

Nice to try in the beginning in 2012!

Cos^2 distribution To be checked with measurements

Hugo Day et al

• Cooling at about 3 deg per hour Cool to 334 K (61 C) after 2 h after dump

• Operation at 2e11 per bunch in 2012 significantly affected (4h after dump)

• 25 ns seems to have more margin – looks OK for 1.1e11 per bunch and 2600 b

0.00E+00

1.00E+14

2.00E+14

3.00E+14

4.00E+14

5.00E+14

6.00E+14

7.00E+14

8.00E+14

9.00E+14

1.00E+15

330

332

334

336

338

340

342

344

346

348

70 71 72 73 74 75 76 77 78 79 80

Inte

nsit

y [p

+]

Tem

p [K

]

Time [h]

Semi-empirical model to predict temperature in 2012(Brennan Goddard)

50 ns, 1.6e11 per bunchBrennan Goddard

61 degrees

65 degrees

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Agenda

• Main messages

• Conclusions from mini-Chamonix

• Observations and limitations in 2011– Fill example– MKI kicker– TCP.B6L7.B1 collimator– TCTVB.4R2 collimator– TDI collimator– VMTSA bellow module– Beam screen

• Would we want to do something during the winter stop?

• Outlook

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- Dump in Sept 17th had interlock increased from 55°C to 70°C- Only collimator in IR7 that is heating so much.

misalignment? non conformity? EN/STI and EN/MME are aware

60 °C

20 °C

40 °C

60 °C

20 °C

40 °C

TCP B6L7.B1 temperature in 2011

All other TCPs in IR7 in 2011

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TCP.B6L7.B1 temperature as a function of total injected intensity

0 100000000000000 2000000000000000

10

20

30

40

50

60

70

injected beam intensity

TCP

tem

pera

ture

at s

atur

ation

?

1380 bunches at 1.6e11p/b

- Linear behaviour with increasing number of bunches until end of June - followed by quadratic with bunch intensity increase after the end of June- Consistent with a large broadband impedance (M*Nb^2)

22

Agenda

• Main messages

• Conclusions from mini-Chamonix

• Observations and limitations in 2011– Fill example– MKI kicker– TCP.B6L7.B1 collimator– TCTVB.4R2 collimator– TDI collimator– VMTSA bellow module– Beam screen

• Would we want to do something during the winter stop?

• Outlook

23

- No obvious correlation of temperature with bunch length or beam intensity.- TCTVB_4R2_LU got better after increasing the bunch length in beginning of June.- Got suddenly better in September and worse in October.- 4R2 is the only TCTVB that heats beyond 35°C. Some correlation with losses are investigated.

TCTVB 4R2 upstream

TCTVB 4R2 downstream60 °C

20 °C

40 °C

60 °C

20 °C

40 °C

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Agenda

• Main messages

• Conclusions from mini-Chamonix

• Observations and limitations in 2011– Fill example– MKI kicker– TCP.B6L7.B1 collimator– TCTVB.4R2 collimator– TDI collimator– VMTSA bellow module– Beam screen

• Would we want to do something during the winter stop?

• Outlook

TDI pressure and temperature• Pressure and temperature increase in both TDIs during physics fills

Vincent Baglin and TE/VSC colleagues

TDI8 temperature

TDI8 pressure

TDI2 gap

TDI2 pressure

TDI8 gap

TDI8 pressure

Increasing the gap of the TDI from +/-20mm to +/-55mm from fill 2219 damped the pressure increase, but not the temperature increase.

Decreasing the gap on B2 back to +/-20mm for fill 2261 generated pressure again. Clear correlation with the gap.

• For the last fills, TDI gap was put to +/-37.5mm for B2 but no significant difference with +/-55mm was observed • problem seems solved for now!

26

Impedance simulations for the TDI

55 mm

20 mm4 mm

Estimated power loss is divided by 10 when putting the TDI half gap from 20 mm gap to 55 mm

Power spectrumInjection (dB)

Power spectrumStable beams (dB)

Sharp narrow band resonances

27

Agenda

• Main messages

• Conclusions from mini-Chamonix

• Observations and limitations in 2011– Fill example– MKI kicker– TCP.B6L7.B1 collimator– TCTVB.4R2 collimator– TDI collimator– VMTSA bellow module– Beam screen

• Would we want to do something during the winter stop?

• Outlook

VMTSA double bellows typical defaultLeft side

Side view (xray from corridor to QRL)

b) Metallic noise due to loose spring when hitting vacuum chamber

c) RF fingers falling due to broken spring

d) aperture reduced ?

Non Conform

c

b

Spring was broken between May and November 2011

d

Vincent Baglin

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VMTSA double bellows• Spring failed.• These bellows are very special (only 10 modules in the LHC):

– Very long RF fingers (28 cm instead of 17 cm)– Very small contact force between fingers and beam screen (fingers preconstrained to open as

a flower)– Large cylindrical surrounding cavity

• Electro-Magnetico-Thermo-mechanical fatigue of the spring?

• Impedance measurements and simulations were performed (Jean-Luc Nougaret et al)

• Consolidation planned during winter stop to improve both impedanceshielding and spring thermal resistance(Bernard Henrist et al)

Bernard Henrist

30

Agenda

• Main messages

• Conclusions from mini-Chamonix

• Observations and limitations in 2011– Fill example– MKI kicker– TCP.B6L7.B1 collimator– TCTVB.4R2 collimator– TDI collimator– VMTSA bellow module– Beam screen

• Would we want to do something during the winter stop?

• Outlook

31

Beam screen temperature regulation

• OK for 2011 (see Serge’s talk)

• Operation is easier since the bunch length has been slightly lenghtened.

• Main worry: Q6R5 has no margin for more cooling.

• 25 ns heat load is currently dominated by electron cloud, but it is now converging towards predictions, which would be manageable.

• There is also the worry that the nominal beam might be just ok for the triplets if scaling is applied. However Serge mentioned that more cooling power could be applied within a few days if needed.

32

No margin left for the cooling in Q6R5

Valve at Q6R5 is open at almost 100% and the baseline can not be lowered anymore.Temperature would then increase above 17K potential issue for Vacuum.

70 %

100 %

33

Agenda

• Main messages

• Conclusions from mini-Chamonix

• Observations and limitations in 2011– Fill example– MKI kicker– TCP.B6L7.B1 collimator– TCTVB.4R2 collimator– TDI collimator– VMTSA bellow module– Beam screen

• Would we want to do something during the winter stop?

• Outlook

34

Would we want to do something during the winter stop?

• Consolidation of the double bellow is being done• Check for non conformities

– TCP.B6L7.B1 (fiducialization already checked. Cooling?)– TCTVB.4R2– MKI-8D (RF fingers)– Q6R5 (Xray already done)Possibly with Xray or tomoscope?

• Possibility to add cooling for ALFA?

• Check TDI metalization?

• Add additional diagnostics:– Temperature closer to the TDI jaw– Temperature closer to the kicker ferrite for MKI– More diagnostics in Q6R5?

35

Outlook• In 2011, a few beam induced heating problems were quickly overcome

• For 2012, the most limiting equipment for operation appears to be the MKI

• Suggestion of checking the effect of bunch length with few fills Philippe: change settings during the ramp, as little margin with voltage

• Heavy effort on impedance simulations to understand if impedance can be the origin of the observed heat load for– MKI– TCTVB– Bellow module– TCTVB– TDI– ALFA

36

observable Cooling? Limits operation? better if bunch length increased

improves with time?

Is it happening to all similar devices

TCP_B6L7_B1 temperature water Yes, dump in Sept 17th interlock increase from 55 to 70 degrees

yes no No (1/6)

TCTVB.4R2 temperature water Yes, dump in October 9th interlock increase from 50 to 70 degrees

Yes Not obvious No (1/4)

TDI VacuumTemperature (outside tank)

no Not anymore, should be put in parking position

? no Yes (2/2)

MKI Temperature and Rise time and delay (soon)

no Yes (kick strength), and temp interlock increased from 50 deg to 62 deg. Needed to wait 4h in Oct 2011

Yes no All are heating but MKI-8D seems to be heating more No (1/8)

Beam screen Heat load computed from regulation response

yes No, except in one cell Q6R5

Yes no No (only one)

ALFA Temperature on the roman pots

no Not yet (18deg increase in temperature in 2011, with margin of 40 degrees)

? Cooling was needed in TOTEM

VMTSA VacuumSpring broken after May

no Yes (spring broken and dangling fingers)

? Yes

BSRT Mirror Jitter in BSRT measurement

mirror is deforming and RF heating is suspected

N/A

BGI Vacuum Probably not a heating issue

No data N/A

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Thank you for your attention!

38

All MKIs

39

MKIA5L2

40

collimators

Why was the level of TCP_B6R5_B2 (?) increased

TCLIB.6R2.B1 dumped beam in August 2010. Nothing seen this year.

41

TCTVB

Increase from 22 to 35 degrees

42

TCTVB 4R2 up and down

43

TCTVB 4R8

Got better after bunch length increaseMax 35 degrees

44

TCTVB.4L2

45

TCTVB.4L8

46

TCTVB.4R2 temperature

47

TCP B6L7.B1

48

Other TCPs

49

TDI

50

Pressure history• The pressure at TDI exhibit a pressure increase characteristic of heating• Since fill 2219 (16/10, PM), the TDI gap was increased in parking position from 22 mm to 55 mm• As a result, the pressure stays in the few 10-8 mbar range

Opened

51

TDI8R – Pressure and Temperature• No change in temperature (at measured positions)

2219 2222

MKI8 temperature

52

2022242628303234363840424446485052545658606264666870

0.695

0.696

0.697

0.698

0.699

0.7

0.701

0.702

0.703

0.704

0.705

0.706

0.707

0.708

0.709

0.71

Tem

per

atu

re [˚C

]

TMR

5%

to

95%

Ris

eTim

e (µ

s)

Date & Time

MKI8 SoftStart (Average RiseTimes 7.0us + (7points), 53.3kV)

MKI.UA87.IPOC.AB2:T_RISETIMEMKI.UA87.IPOC.BB2:T_RISETIMEMKI.UA87.IPOC.CB2:T_RISETIMEMKI.UA87.IPOC.DB2:T_RISETIMEMKI8 SS: Average RiseTimeMKI.D5R8.B2:TEMP_MAGNET_DOWN

y = -1.325E-05x + 7.069E-01R² = 1.501E-02

y = -7.324E-05x + 7.041E-01R² = 7.792E-01

y = -2.065E-05x + 6.970E-01R² = 3.514E-01

y = -3.563E-05x + 7.004E-01R² = 8.375E-01

y = -2.828E-04x + 7.153E-01R² = 6.809E-01

0.695

0.696

0.697

0.698

0.699

0.7

0.701

0.702

0.703

0.704

0.705

0.706

0.707

0.708

0.709

20.00 25.00 30.00 35.00 40.00 45.00 50.00 55.00 60.00 65.00 70.00

Rise

Tim

e (µ

s)

MKI8 Measured Temperature (˚C)

MKI.UA87.IPOC.?B2:T_RISETIME (October 2011)

MKI.UA87.IPOC.AB2:T_RISETIME

MKI.UA87.IPOC.BB2:T_RISETIME

MKI.UA87.IPOC.CB2:T_RISETIME

MKI.UA87.IPOC.DB2:T_RISETIME

53

Fill 1836: Inner triplets withnominal bunch population & 1092 bunches

-10

0

10

20

30

40

50

60

2/6/11 0:00 2/6/11 6:00 2/6/11 12:00 2/6/11 18:00

IT b

eam

indu

ced

heati

ng [

W],

Ibea

m [1

0^13

p], E

[TeV

]

ITL1

ITR1

ITL2

ITR2

ITL5

ITR5

ITL8

ITR8

Ibeam 1

Ibeam 2

Beam energy

Scaling w/r to DR

Scaling to nominal beam (2808 bunches i.e. factor 2.6):130 W ! (Just OK with local limitation)

54

Serge Claudet

Serge Claudet

55

Cryo in Q6R5

25 ns domine actuellement par scrubbing. Converge towards predictions, ce qui serait manageable par la cryo