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 Tavian Kicker team: Chiara Bracco, Mike Barnes, Brennan Goddard, Jan Uythoven RF team: Philippe Baudrenghien, Themistoklis Mastoridis, Juan Esteban Mueller, 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).link 1

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 2

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 3

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 Uythoven 15/07/2011 Mini Cham Jan Uythoven at Mini-Chamonix 2011

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 5

Example of fill 2216 (Oct. 15 th 2011): dynamics of temperature and pressure increase Temp TCTVB Intensity Pressure TDI Temp TCP Temp MKI Energy - 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 6 60 °C 20 °C

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 7

MKIs: steady temperature increase over April 1st 2011October 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 …but MKI-8D and MKI-8B are a factor ~2 off

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 9 M. Barnes et al Reduction of rise time Above 60 degrees

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? 10

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

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) 12 Re[Zlong] Power Spectrum (dB) frequency Re[Zlong] Power Spectrum (dB) frequency Broadband impedanceNarrow band impedance

Measured 50ns power spectra during fill 2261 by P. Baudrenghien and T. Mastoridis 13  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

Measured 50ns power spectra during fill 2261 by P. Baudrenghien and T. Mastoridis 14  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)

Measured 50ns power spectra during fill 2261 by P. Baudrenghien and T. Mastoridis 15  Amplitude decreases in stable beams (begininng of physics)  Spectrum is most critical during the ramp, but the ramp does not last very long

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

Effect of bunch length on simulated power loss (50 ns) very preliminary… more at Chamonix! 17 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 Semi-empirical model to predict temperature in 2012 (Brennan Goddard) 50 ns, 1.6e11 per bunch Brennan Goddard 61 degrees 65 degrees

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 19

20 - Dump in Sept 17 th  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

TCP.B6L7.B1 temperature as a function of total injected intensity 21 ? 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)

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 22

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 downstream 60 °C 20 °C 40 °C 60 °C 20 °C 40 °C

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 24

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 spectrum Injection (dB) Power spectrum Stable beams (dB) Sharp narrow band resonances

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 27

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 c b Spring was broken between May and November 2011 d Vincent Baglin

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 impedance shielding and spring thermal resistance (Bernard Henrist et al) 29 Bernard Henrist

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 30

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. 31

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 % 100 %

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 33

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? 34

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 35

observableCooling?Limits operation?better if bunch length increased improves with time? Is it happening to all similar devices TCP_B6L7_B1temperaturewaterYes, dump in Sept 17 th interlock increase from 55 to 70 degrees yesnoNo (1/6) TCTVB.4R2temperaturewaterYes, dump in October 9 th interlock increase from 50 to 70 degrees YesNot obviousNo (1/4) TDIVacuum Temperature (outside tank) noNot anymore, should be put in parking position ?noYes (2/2) MKITemperature and Rise time and delay (soon) noYes (kick strength), and temp interlock increased from 50 deg to 62 deg. Needed to wait 4h in Oct 2011 YesnoAll are heating but MKI-8D seems to be heating more No (1/8) Beam screenHeat load computed from regulation response yesNo, except in one cell Q6R5 YesnoNo (only one) ALFATemperature on the roman pots noNot yet (18deg increase in temperature in 2011, with margin of 40 degrees) ?Cooling was needed in TOTEM VMTSAVacuum Spring broken after May noYes (spring broken and dangling fingers) ?Yes BSRT MirrorJitter in BSRT measurement mirror is deforming and RF heating is suspected N/A BGIVacuumProbably not a heating issue No dataN/A 36

Thank you 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 Nothing seen this year. 40

TCTVB Increase from 22 to 35 degrees 41

TCTVB 4R2 up and down 42

TCTVB 4R8 Got better after bunch length increase Max 35 degrees 43

TCTVB.4L2 44

TCTVB.4L8 45

TCTVB.4R2 temperature 46

TCP B6L7.B1 47

Other TCPs 48

TDI 49

Pressure history 50 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 mbar range Opened

TDI8R – Pressure and Temperature 51 No change in temperature (at measured positions)

MKI8 temperature 52

Fill 1836: Inner triplets with nominal bunch population & 1092 bunches Scaling to nominal beam (2808 bunches i.e. factor 2.6): 130 W ! (Just OK with local limitation) 53

Serge Claudet 54

Cryo in Q6R5 25 ns  domine actuellement par scrubbing. Converge towards predictions, ce qui serait manageable par la cryo 55