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Beam induced heating

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 ,

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Beam induced heating

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  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, LuisellaLari, Stefano Redaelli, Marc Timmins, Daniel Wollman, Cryogenics team: Serge Claudet, Laurent Tavian Kicker team:Chiara Bracco , Mike Barnes, Brennan Goddard, Jan Uythoven RF team: Philippe Baudrenghien, ThemistoklisMastoridis, Juan EstebanMueller, Elena Shaposhnikova Impedance team: Gianluigi Arduini, Fritz Caspers, Hugo Day, Alexey Grudiev, Elias Métral, Nicolas Mounet, Jean-Luc Nougaret, Giovanni Rumolo, Instrumentation team: Rhodri Jones, Mariusz, Federico Roncarolo Operators and OP team Vacuum 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-8Dandmaybe 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

  4. Conclusions Jan Uythoven at Mini-Chamonix 2011 • 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 Uythoven

  5. 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 60 °C Intensity Temp MKI Energy Temp TCP Pressure TDI Temp TCTVB 20 °C 13h • MKI-8D.B2: slow steadyincrease of temperaturewhichstartswith the ramp • TCP.B6L7.B1: slow steadyincrease of temperaturewhichstartswith the ramp and saturates • TCTVB: veryodd non reproduciblebehaviour, withveryfasttemperatureincrease • TDI: only pressure available, slow increasefollowed by decrease.

  7. Agenda • Main messages • Conclusions from mini-Chamonix • Observations and limitations in 2011 • Fill example • MKI kicker (cfChiara’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: steadytemperatureincrease over 2011 60 °C All MKIs are getting hotter… MKI in point 2 40 °C 20 °C MKI8-D …but MKI-8D and MKI-8B are a factor ~2 off 60 °C MKI8-B MKI in point 8 40 °C 20 °C April 1st 2011 October 31st 2011

  9. 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 MKIsseem ok • MKI8D reached 68 degrees, MKI8B 57 degrees, all the otherMKIs are below 45 degrees Reduction of rise time Above 60 degrees M. Barnes et al

  10. Whatcanwe 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?

  11. “Short” digression on longitudinal impedance and power spectramotivation effect of bunch length on heat deposition

  12. Heating due to beamcouplingimpedance (from E. Métral et al.) • Power lost by the beam in itssurrounding: • Case 1: one sharpnarrowbandimpedance (e.g. cavity) • Case 2: broadbandimpedance(e.g.ferritekicker) Broadband impedance Narrow band impedance Power Spectrum (dB) Power Spectrum (dB) Re[Zlong] Re[Zlong] frequency frequency

  13. Measured 50ns power spectraduringfill 2261 by P. Baudrenghien and T. Mastoridis Factor 2000 in power • power spectrumis made of peaksseparated by 20 MHz (50 ns) • power spectrumat injection extends to 2.5 GHz with a notcharound 1.3 GHz

  14. Measured 50ns power spectraduringfill 2261 by P. Baudrenghien and T. Mastoridis Cannot be trusted above 2.8 GHz(cable specs) • spectrumextends to largerfrequencies due to smallerbunchlength and modified distribution • notch in the spectrum shifts to 1.6 GHz

  15. Measured 50ns power spectraduringfill 2261 by P. Baudrenghien and T. Mastoridis • Amplitude decreases in stable beams (begininng of physics) • Spectrum ismostcriticalduring the ramp, but the rampdoes not last very long

  16. Simulations and bench measurements of MKI Power spectrum Stable beams (dB) 3D simulations Bench measurements Power spectrum Injection (dB) Low frequencies contribute much more than high frequencies for a broadband impedance • Very complicated 3D model!!! • Simulations seem to grasp the physics Hugo Day et al

  17. Effect of bunch length on simulated power loss (50 ns)very preliminary… more at Chamonix! Cos^2 distribution  To be checked with measurements Hugo Day et al 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! Without conductors, the power loss shoots to 20 kW

  18. Semi-empirical model to predict temperature in 2012(Brennan Goddard) • 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 50 ns, 1.6e11 per bunch Brennan Goddard 65 degrees 61 degrees

  19. 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

  20. 60 °C TCP B6L7.B1 temperature in 2011 40 °C 20 °C 60 °C All other TCPs in IR7 in 2011 40 °C 20 °C - Dump in Sept 17th had interlock increased from 55°C to 70°C - Onlycollimator in IR7 thatisheatingsomuch.  misalignment? non conformity? EN/STI and EN/MME are aware

  21. TCP.B6L7.B1 temperature as a function of total injected intensity ? 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. TCTVB 4R2 upstream 60 °C 40 °C 20 °C TCTVB 4R2 downstream 60 °C 40 °C 20 °C - No obviouscorrelation of temperaturewithbunchlength or beamintensity. - TCTVB_4R2_LU gotbetterafterincreasing the bunchlength in beginning of June. - Gotsuddenlybetter in September and worse in October. - 4R2 is the only TCTVB thatheatsbeyond 35°C. Somecorrelationwithlosses are investigated.

  24. 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

  25. TDI pressure and temperature • Pressure and temperature increase in both TDIs during physics fills TDI8 temperature TDI2 gap TDI8 pressure TDI8 gap TDI2 pressure TDI8 pressure Vincent Baglin and TE/VSC colleagues 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 Sharp narrow band resonances Estimated power loss is divided by 10 when putting the TDI half gap from 20 mm gap to 55 mm 4 mm 20 mm Power spectrum Stable beams (dB) Power spectrum Injection (dB) 55 mm

  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

  28. VMTSA double bellows typical default Left 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 b d Spring was broken between May and November 2011 c Vincent Baglin

  29. 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. Beamscreentemperatureregulation • OK for 2011 (seeSerge’s talk) • Operation iseasiersince the bunchlength has been slightlylenghtened. • Main worry: Q6R5 has no margin for more cooling. • 25 ns heatloadiscurrentlydominated by electroncloud, but itisnowconvergingtowardspredictions, whichwouldbemanageable. • There isalso the worrythat the nominal beammightbejust ok for the triplets if scalingisapplied. However Serge mentionedthat more cooling power couldbeappliedwithin a few days if needed.

  32. No margin left for the cooling in Q6R5 100 % 70 % 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.

  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. Thankyou for your attention!

  37. All MKIs

  38. MKIA5L2

  39. collimators Why was the level of TCP_B6R5_B2 (?) increased TCLIB.6R2.B1 dumped beam in August 2010. Nothing seen this year.

  40. TCTVB Increase from 22 to 35 degrees

  41. TCTVB 4R2 up and down

  42. TCTVB 4R8 Gotbetterafterbunchlengthincrease Max 35 degrees

  43. TCTVB.4L2

  44. TCTVB.4L8

  45. TCTVB.4R2 temperature

  46. TCP B6L7.B1

  47. OtherTCPs

  48. TDI

  49. 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

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