LHC CRYOGENICS – PERSPECTIVES FOR RUN2 OPERATION K. Brodzinski, S. Claudet, G. Ferlin and L. Tavian, CERN, Geneva, Switzerland

Abstract The first period of LHC cryogenic operation between

2008 and 2013 allowed gaining practical knowledge about the machine operational behaviour. The cryogenic system operation scenario for Run1 was defined and set regarding minimization of potential failures and energy consumption. Tuning of the cooling power in local cooling loops was adjusted according to the requirements for the heat extraction.

The Long Shutdown 1 (LS1), started on the beginning of 2013, allowed for maintenance, upgrade and necessary repairs on the LHC cryogenic installation focusing on preparation for post LS1 accelerator run.

In order to provide required cooling power, configuration of the cryoplants for Run2 will be set differently than for Run1, the available margins will change. The constraints imposed by beam-induced heating during scrubbing run or normal Run2 have been analyzed.

In case of installation failures, the critical spare components management will allow for direct replacement of faulty elements of the installation in most adapted time. The mitigation of failures can be also done by cryogenic plants reconfiguration, in some cases with impact on LHC beam operation scenarios.

INTRODUCTION The cryogenic infrastructure built around LHC ring

is composed of 8 cryogenic plants supplying 8 related LHC sectors. Four of the plants were upgraded from LEP cryogenic system and are supplying low load sectors, and four of them have been installed as new for LHC and are supplying high load sectors [1] (see Fig 1).

Figure 1: LHC cryogenic infrastructure.

The helium refrigeration process is ensured by considerable number of rotary machines (64 screw compressors, 74 expansion turbines and 28 cold compressors). The system provides cooling power for the magnets, RF cavities and DFBs with their 1258 current leads. The related control system drives ~4000 PID loops and consists of nearly 60000 I/O signals.

LHC RUN1 SUMMARY The LHC Run1 allowed gaining operational knowledge

about performance and requirements related to the cryogenic system. The Run1, with beam parameters lower than nominal, allowed for LHC operation with disabled cryoplants A at P6 and P8 (see Fig.1). The cooling power for both related sectors was provided by plants B. This configuration allowed for electrical power savings over all 3 years of operation between 10 and 20% with relation to the installed power (see Fig.2). The negative aspect of the configuration was longer recovery time at P6 and P8 after the failures. Such configuration was not applied nor at P4 because of additional heat load coming from RF modules neither at P18 because of non-standard configuration of the plants.

Figure 2: Power consumption and savings during Run1.

Thanks to collective effort in the cryogenic team the helium loses were reduced by factor of ~2 during 3 years of operation (see Fig. 3).

Figure 3: Helium losses reduction during Run1.

135

LHC CRYOGENICS – PERSPECTIVES FOR RUN2 OPERATION K. Brodzinski, S. Claudet, G. Ferlin and L. Tavian, CERN, Geneva, Switzerland

Abstract The first period of LHC cryogenic operation between

2008 and 2013 allowed gaining practical knowledge about the machine operational behaviour. The cryogenic system operation scenario for Run1 was defined and set regarding minimization of potential failures and energy consumption. Tuning of the cooling power in local cooling loops was adjusted according to the requirements for the heat extraction.

The Long Shutdown 1 (LS1), started on the beginning of 2013, allowed for maintenance, upgrade and necessary repairs on the LHC cryogenic installation focusing on preparation for post LS1 accelerator run.

In order to provide required cooling power, configuration of the cryoplants for Run2 will be set differently than for Run1, the available margins will change. The constraints imposed by beam-induced heating during scrubbing run or normal Run2 have been analyzed.

In case of installation failures, the critical spare components management will allow for direct replacement of faulty elements of the installation in most adapted time. The mitigation of failures can be also done by cryogenic plants reconfiguration, in some cases with impact on LHC beam operation scenarios.

INTRODUCTION The cryogenic infrastructure built around LHC ring

is composed of 8 cryogenic plants supplying 8 related LHC sectors. Four of the plants were upgraded from LEP cryogenic system and are supplying low load sectors, and four of them have been installed as new for LHC and are supplying high load sectors [1] (see Fig 1).

Figure 1: LHC cryogenic infrastructure.

The helium refrigeration process is ensured by considerable number of rotary machines (64 screw compressors, 74 expansion turbines and 28 cold compressors). The system provides cooling power for the magnets, RF cavities and DFBs with their 1258 current leads. The related control system drives ~4000 PID loops and consists of nearly 60000 I/O signals.

LHC RUN1 SUMMARY The LHC Run1 allowed gaining operational knowledge

about performance and requirements related to the cryogenic system. The Run1, with beam parameters lower than nominal, allowed for LHC operation with disabled cryoplants A at P6 and P8 (see Fig.1). The cooling power for both related sectors was provided by plants B. This configuration allowed for electrical power savings over all 3 years of operation between 10 and 20% with relation to the installed power (see Fig.2). The negative aspect of the configuration was longer recovery time at P6 and P8 after the failures. Such configuration was not applied nor at P4 because of additional heat load coming from RF modules neither at P18 because of non-standard configuration of the plants.

Figure 2: Power consumption and savings during Run1.

Thanks to collective effort in the cryogenic team the helium loses were reduced by factor of ~2 during 3 years of operation (see Fig. 3).

Figure 3: Helium losses reduction during Run1.

135

LHC CRYOGENICS — PERSPECTIVES FOR RUNZ OPERATION

K. Brodzinski, S. Claudet, G. Ferlin and L. Tavian, CERN, Geneva, Switzerland

AbstractThe first period of LHC cryogenic operation between

2008 and 2013 allowed gaining practical knowledgeabout the machine operational behaviour. The cryogenicsystem operation scenario for Runl was defined and setregarding minimization of potential failures and energyconsumption. Tuning of the cooling power in localcooling loops was adjusted according to the requirementsfor the heat extraction.

The Long Shutdown 1 (L81), started on the beginningof 2013, allowed for maintenance, upgrade and necessaryrepairs on the LHC cryogenic installation focusingon preparation for post LSl accelerator run.

In order to provide required cooling power,configuration of the cryoplants for Run2 will be setdifferently than for Runl, the available margins willchange. The constraints imposed by beam-inducedheating during scrubbing run or normal Run2 have beenanalyzed.

In case of installation failures, the critical sparecomponents management will allow for directreplacement of faulty elements of the installation in mostadapted time. The mitigation of failures can be also doneby cryogenic plants reconfiguration, in some cases withimpact on LHC beam operation scenarios.

INTRODUCTIONThe cryogenic infrastructure built around LHC ring

is composed of 8 cryogenic plants supplying 8 relatedLHC sectors. Four of the plants were upgraded from LEPcryogenic system and are supplying 10w load sectors, andfour of them have been installed as new for LHC and aresupplying high load sectors [1] (see Fig 1).

[P5P4 Runl P60 Compressor station LLD 4.5 K relrlgeratorI= Interconnention box

O 1.8 K pumping unit (cold compressor]

A — upgraded exLEP cryo plantB — new LHC cryogenic plantLL LL

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x HL

Figure 1: LHC cryogenic infrastructure.

The helium refrigeration process is ensured byconsiderable number of rotary machines (64 screwcompressors, 74 expansion turbines and 28 coldcompressors). The system provides cooling power for themagnets, RF cavities and DFBs with their 1258 currentleads. The related control system drives ~4000 PID loopsand consists of nearly 60000 I/O signals.

LHC RUNl SUMMARYThe LHC Runl allowed gaining operational knowledge

about performance and requirements related tothe cryogenic system. The Runl, with beam parameterslower than nominal, allowed for LHC operation withdisabled cryoplants A at P6 and P8 (see Fig.1).The cooling power for both related sectors was providedby plants B. This configuration allowed for electricalpower savings over all 3 years of operation between 10and 20% with relation to the installed power (see Fig.2).The negative aspect of the configuration was longerrecovery time at P6 and P8 after the failures. Suchconfiguration was not applied nor at P4 because ofadditional heat load coming from RF modules neither atP18 because of non-standard configuration of the plants.

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Figure 2: Power consumption and savings during Runl.

Thanks to collective effort in the cryogenic teamthe helium loses were reduced by factor of ~2 during 3years of operation (see Fig. 3).

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Figure 3: Helium losses reduction during Runl.

The cryogenic global availability for first 2 years of Run1 was equal to about 90% (see Fig 4). The significant impact of single event upset (SEU) was noted during increase of beam parameters in 2011. The problem of SEU and utilitiy failures were treated for last year of Run1 alowing to raise up the global availability to ~95%.

Figure 4: Cryogenic availability – Run1 summary.

MAIN LS1 ACTIVITIES During LS1 multiple activities were performed on

the cryogenic system. The main of them are listed below (see Fig. 5): • The maintenance work was done on all helium

compressor stations (major overhaul of the compressors and electrical motors),

• 4 leaks were repaired on 4.5 K refrigerators,the leaks have been declared during Run1 and warm up before LS1,

• 16 leaky QRL bellows were replaced, the leaks havebeen declared during the warm up before LS1,

• 2 DFB’s gimbal bellows were replaced, the bellowswere found deformed during the LS1 inspection,

• R2E campaign was performed in 4 LHC places toavoid excessive radiation to electronics during future LHC runs.

Also many other smaller activities, not visible on the large scale, were performed during LS1 with aim to higher the machine reliability.

Figure 5: Main activities on cryogenic system during LS1.

RUN2 OPERATION SCENARIOS AND POSSIBLE REDUNDANCY

In order to guarantee required heat extraction from LHC during Run2 the baseline for cryogenic system operation scenario is to run all cryogenic plants (see Fig. 6).

Figure 6: Baseline for LHC Run2 operation scenario.

Compressor station possible redundancy Thanks to installed inter-piping connections between

the cryogenic plants, the compressor stations A and B at P4, 6 and 8 can be linked together to profit from the existing helium flow global margin in case of any compressor failure (see P8 on Fig. 6 and Fig 7).

Figure 7: Configuration of linked compressor stations.

More difficult situation is at P18 and P2 where replacement of the faulty compressor has to be considered (except P2 low pressure stage). The available flow margins on low pressure stage (LP) and high pressure stage (HP), considering the biggest compressor lost, are presented in Fig. 8 (the analysis is done for the case of nominal cold box refrigeration capacity). The spares for each type of the compressors and related electrical motors are available at CERN storage and are ready to replace the faulty machines when needed.

136

The cryogenic global availability for first 2 years of Run1 was equal to about 90% (see Fig 4). The significant impact of single event upset (SEU) was noted during increase of beam parameters in 2011. The problem of SEU and utilitiy failures were treated for last year of Run1 alowing to raise up the global availability to ~95%.

Figure 4: Cryogenic availability – Run1 summary.

MAIN LS1 ACTIVITIES During LS1 multiple activities were performed on

the cryogenic system. The main of them are listed below (see Fig. 5): • The maintenance work was done on all helium

compressor stations (major overhaul of the compressors and electrical motors),

• 4 leaks were repaired on 4.5 K refrigerators,the leaks have been declared during Run1 and warm up before LS1,

• 16 leaky QRL bellows were replaced, the leaks havebeen declared during the warm up before LS1,

• 2 DFB’s gimbal bellows were replaced, the bellowswere found deformed during the LS1 inspection,

• R2E campaign was performed in 4 LHC places toavoid excessive radiation to electronics during future LHC runs.

Also many other smaller activities, not visible on the large scale, were performed during LS1 with aim to higher the machine reliability.

Figure 5: Main activities on cryogenic system during LS1.

RUN2 OPERATION SCENARIOS AND POSSIBLE REDUNDANCY

In order to guarantee required heat extraction from LHC during Run2 the baseline for cryogenic system operation scenario is to run all cryogenic plants (see Fig. 6).

Figure 6: Baseline for LHC Run2 operation scenario.

Compressor station possible redundancy Thanks to installed inter-piping connections between

the cryogenic plants, the compressor stations A and B at P4, 6 and 8 can be linked together to profit from the existing helium flow global margin in case of any compressor failure (see P8 on Fig. 6 and Fig 7).

Figure 7: Configuration of linked compressor stations.

More difficult situation is at P18 and P2 where replacement of the faulty compressor has to be considered (except P2 low pressure stage). The available flow margins on low pressure stage (LP) and high pressure stage (HP), considering the biggest compressor lost, are presented in Fig. 8 (the analysis is done for the case of nominal cold box refrigeration capacity). The spares for each type of the compressors and related electrical motors are available at CERN storage and are ready to replace the faulty machines when needed.

136

The cryogenic global availability for first 2 years ofRunl was equal to about 90% (see Fig 4). The significantimpact of single event upset (SEU) was noted duringincrease of beam parameters in 2011. The problemof SEU and utilitiy failures were treated for last year ofRunl alowing to raise up the global availability to ~95%.

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Figure 4: Cryogenic availability , Runl summary.

MAIN LS1 ACTIVITIESDuring LSl multiple activities were performed on

the cryogenic system. The main of them are listed below(see Fig. 5):

The maintenance work was done on all heliumcompressor stations (major overhaul of thecompressors and electrical motors),4 leaks were repaired on 4.5 K refrigerators,the leaks have been declared during Runl and warmup before LSl,16 leaky QRL bellows were replaced, the leaks havebeen declared during the warm up before LS1,2 DFB’s gimbal bellows were replaced, the bellowswere found deformed during the LSl inspection,R2E campaign was performed in 4 LHC places toavoid excessive radiation to electronics during futureLHC runs.

Also many other smaller activities, not Visible onthe large scale, were performed during LS1 with aimto higher the machine reliability.

M e maintenance 01‘52 compressors

R — Repairs of 4 refrigerators

D~ QRL compensators replacement3;} — DFBAs SM repairs{R — R2E campaign

Figure 5: Main activities on cryogenic system during LSl.

RUN2 OPERATION SCENARIOS ANDPOSSIBLE REDUNDANCY

In order to guarantee required heat extraction fromLHC during Run2 the baseline for cryogenic systemoperation scenario is to run all cryogenic plants(see Fig. 6).

Figure 6: Baseline for LHC Run2 operation scenario.

Compressor station possible redundancyThanks to installed inter-piping connections between

the cryogenic plants, the compressor stations A and B atP4, 6 and 8 can be linked together to profit from theexisting helium flow global margin in case of anycompressor failure (see P8 on Fig. 6 and Fig 7).

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Figure 7: Configuration of linked compressor stations.

More difficult situation is at P18 and P2 wherereplacement of the faulty compressor has to be considered(except P2 low pressure stage). The available flowmargins on low pressure stage (LP) and high pressurestage (HP), considering the biggest compressor lost,are presented in Fig. 8 (the analysis is done for the caseof nominal cold box refrigeration capacity). The sparesfor each type of the compressors and related electricalmotors are available at CERN storage and are readyto replace the faulty machines when needed.

136

Figure 8: Helium flow margins for compressor stations.

Main LHC 4.5K refrigerators The most fragile parts in the main LHC cryogenic

refrigerators are the rotary machines – turbines. The analysis of possible redundancy and spare parts management lead to identify 3 categories of the turbines regarding associated criticality in case of failure. An example of the analysis for AirLiquide refrigerator is presented in Fig. 9.

Figure 9: Air Liquide QSRB – turbines criticality.

• Category 1 (high criticality): Operation withoutthe turbine results in a considerable loss in refrigeration power. All types of this turbinescategory are covered with available spares in CERNstorage.

• Category 2 (moderate criticality): Operation withoutthe turbine is possible with a moderate lossin refrigeration power. All types of this turbinecategory are covered with available spares in CERNstorage.

• Category 3 (low criticality): Operation without thisturbine is possible with nearly no loss in refrigerationpower as the refrigeration power loss can becompensated with LN2. The special contracts signedwith the suppliers allow for this turbine categoryrepairs within 4 weeks while normal repair delay cantake up to a few months.

Cold compressors – 1.8K pumping units There are two types of 1.8 K pumping units installed

on LHC. One of them is equipped with 3 and other with 4 cold compressors. The cold compressor is the most fragile part of the unit. The run of the unit without even one compressor is not possible, so in case of failure the faulty compressor has to be replaced to allow further operation.

All types of the compressors are covered by a spare available in CERN storage.

However, behaviour of the LHC machine shows lower than expected thermal load at 1.8 K. This fact let to presume that operation of two sectors with one pumping unit running together with two 4.5 K refrigerators should be possible during Run2 (see Fig. 10). The proposed scenario was never set up for operation and is to be tested before Run2. The operation in such configuration will require longer recovery times in case of failures but could be considered as a redundancy if needed.

Figure 10: Run2 optional scenario with one pumping unit for 2 sectors.

Cryogenic plant major failure In case of the major failure of a cryogenic plant at P6 or

P8 the operation of the LHC will be possible with reduced beam parameters setting configuration from Run1 (see Fig. 11). Loss of cryoplant A has less impact on the cryogenic power than loss of cryoplant B.

Figure 11: Example of operation scenario in case of cryoplant A loss at P6.

NON CONFORMITIES There are currently two known non conformities

present in the cryogenic system. Both concerns helium leaks specified below: • Sector 8-1, internal leak on QRL header D, rate of

1.6 E-6 mbarl/s @ 10 bar, 1.4 E-7 mbarl/s @ 1 bar,localization at Q24R8 at dcum 24455 m,

• Sector 1-2, internal leak on QRL header C, rate of1.7 E-5 mbarl/s @ 10 bara, pre-localized at ~Q13L2

137

Figure 8: Helium flow margins for compressor stations.

Main LHC 4.5K refrigerators The most fragile parts in the main LHC cryogenic

refrigerators are the rotary machines – turbines. The analysis of possible redundancy and spare parts management lead to identify 3 categories of the turbines regarding associated criticality in case of failure. An example of the analysis for AirLiquide refrigerator is presented in Fig. 9.

Figure 9: Air Liquide QSRB – turbines criticality.

• Category 1 (high criticality): Operation withoutthe turbine results in a considerable loss in refrigeration power. All types of this turbinescategory are covered with available spares in CERNstorage.

• Category 2 (moderate criticality): Operation withoutthe turbine is possible with a moderate lossin refrigeration power. All types of this turbinecategory are covered with available spares in CERNstorage.

• Category 3 (low criticality): Operation without thisturbine is possible with nearly no loss in refrigerationpower as the refrigeration power loss can becompensated with LN2. The special contracts signedwith the suppliers allow for this turbine categoryrepairs within 4 weeks while normal repair delay cantake up to a few months.

Cold compressors – 1.8K pumping units There are two types of 1.8 K pumping units installed

on LHC. One of them is equipped with 3 and other with 4 cold compressors. The cold compressor is the most fragile part of the unit. The run of the unit without even one compressor is not possible, so in case of failure the faulty compressor has to be replaced to allow further operation.

All types of the compressors are covered by a spare available in CERN storage.

However, behaviour of the LHC machine shows lower than expected thermal load at 1.8 K. This fact let to presume that operation of two sectors with one pumping unit running together with two 4.5 K refrigerators should be possible during Run2 (see Fig. 10). The proposed scenario was never set up for operation and is to be tested before Run2. The operation in such configuration will require longer recovery times in case of failures but could be considered as a redundancy if needed.

Figure 10: Run2 optional scenario with one pumping unit for 2 sectors.

Cryogenic plant major failure In case of the major failure of a cryogenic plant at P6 or

P8 the operation of the LHC will be possible with reduced beam parameters setting configuration from Run1 (see Fig. 11). Loss of cryoplant A has less impact on the cryogenic power than loss of cryoplant B.

Figure 11: Example of operation scenario in case of cryoplant A loss at P6.

NON CONFORMITIES There are currently two known non conformities

present in the cryogenic system. Both concerns helium leaks specified below: • Sector 8-1, internal leak on QRL header D, rate of

1.6 E-6 mbarl/s @ 10 bar, 1.4 E-7 mbarl/s @ 1 bar,localization at Q24R8 at dcum 24455 m,

• Sector 1-2, internal leak on QRL header C, rate of1.7 E-5 mbarl/s @ 10 bara, pre-localized at ~Q13L2

137

Margin on QSCx for CB nominal case with precooler andwithout the biggest compressor

L I l I LP margin

I I HP marginPl P4 P6 P8

Figure 8: Helium flow margins for compressor stations.

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Main LHC 4.5K refrigeratorsThe most fragile parts in the main LHC cryogenic

refrigerators are the rotary machines turbines.The analysis of possible redundancy and spare partsmanagement lead to identify 3 categories of the turbinesregarding associated criticality in case of failure.An example of the analysis for AirLiquide refrigeratoris presented in Fig. 9.

300K 75K 50K 20K

Figure 9: Air Liquide QSRB , turbines criticality.

0 Category 1 (high criticality): Operation withoutthe turbine results in a considerable lossin refrigeration power. All types of this turbinescategory are covered with available spares in CERNstorage.Category 2 (moderate criticality): Operation withoutthe turbine is possible with a moderate lossin refrigeration power. All types of this turbinecategory are covered with available spares in CERNstorage.Category 3 (low criticality): Operation without thisturbine is possible with nearly no loss in refrigerationpower as the refrigeration power loss can becompensated with LN2. The special contracts signedwith the suppliers allow for this turbine categoryrepairs within 4 weeks while normal repair delay cantake up to a few months.

Cold compressors — I .8Kpumping unitsThere are two types of 1.8 K pumping units installed

on LHC. One of them is equipped with 3 and other with 4cold compressors. The cold compressor is the most fragilepart of the unit. The run of the unit without even onecompressor is not possible, so in case of failure the faultycompressor has to be replaced to allow further operation.

137

All types of the compressors are covered by a spareavailable in CERN storage.

However, behaviour of the LHC machine shows lowerthan expected thermal load at 1.8 K. This fact let topresume that operation of two sectors with one pumpingunit running together with two 4.5 K refrigerators shouldbe possible during Run2 (see Fig. 10). The proposedscenario was never set up for operation and is to be testedbefore Run2. The operation in such configuration willrequire longer recovery times in case of failures but couldbe considered as a redundancy if needed.

Figure 10: Run2 optional scenario with one pumping unitfor 2 sectors.

Cryogenic plant majorfailureIn case of the major failure of a cryogenic plant at P6 or

P8 the operation of the LHC will be possible with reducedbeam parameters setting configuration from Runl (seeFig. 11). Loss of cryoplant A has less impact onthe cryogenic power than loss of cryoplant B.

Figure 11: Example of operation scenario in caseof cryoplant A loss at P6.

NON CONFORMITIESThere are currently two known non conformities

present in the cryogenic system. Both concerns heliumleaks specified below:

0 Sector 8-1, internal leak on QRL header D, rate of1.6 E-6 mbarl/s @ 10 bar, 1.4 E-7 mbarl/s @ 1 bar,localization at Q24R8 at dcum 24455 m,

0 Sector 1-2, internal leak on QRL header C, rate of1.7 E-5 mbarl/s @ 10 bara, pre-localized at ~Q13L2

QUENCHES AND RECOVERY Until now experience for quenches recovery with

current above 6.5 kA comes from before Run1 quench training campaign (already 5-6 years ago). The LHC Run1 experienced some “easy quenches” without opening of the quench valves (QV), with pressure rise in the cold mass below 15 bars. The analysis of the recovery after quenches was presented during Chamonix Workshop in 2009. The updated analysis combined with presented in Chamonix graph is shown in Fig. 12.

Figure 12: Recovery after quenches

Any quench occurred up to now on the LHC installation did not cause helium loss from the cryogenic installation. In case of opening of the QVs (quenches above 6.5 kA) the helium lost from the cold mass volume was recovered as foreseen in the system. New learning with quenches and recovery will be the subject of future experience for Run2 during the magnets training.

RUN2 BEAM PARAMETERS – CRYOGENIC MARGINS AND LIMITS

The detailed analysis of the beam induced heating was presented during Evian Workshop in December 2012 [2]. This chapter will summarize the work done during LS1 to upgrade the system and will present key values for margins and limits for the refrigeration power.

ARC, SAMs and ITs beam screen circuit The analysis of scrubbing runs (December 2012) shown

e-cloud heat deposition measured on beam screen circuits (BS). The curves in Fig. 13 show topology of the heat deposition with existed before LS1 limitations on specific BS cooling loops.

Figure 13: Scrubbing run heat deposition.

The hydraulic limitations on local cooling loops of the beam screen had to be upgraded on SAM and semi-SAM magnets over the accelerator length (38 valve poppets were replaced during LS1). The upgrade was applied also on arc section in sector 3-4 where the cryogenic valve poppets were replaced to go back to the level of cooling capacity equal to the other sectors. The present local limitation for beam scrubbing on all BS cooling loops is about 2 W/m per aperture (see Table 1).

Table 1: Old and new local limitation on BS circuits.

The upgrade allows for full distribution of available refrigeration power moving the limits from local cooling loops to the limit on global refrigeration power. Taking into account equal distribution of the available refrigeration power the new limitation for beam scrubbing will be 1.6 W/m per aperture (see Table 2).

Table 2: Old and new local limitation on BS circuits.

The distribution of the heat load on the BS and available cooling power for all sectors is presented in Fig. 14 (Qs – static heat load, Qsr – synchrotron radiation, Qic – image current, Qec – electron cloud).

Figure 14: BS heat load and available cooling power.

138

QUENCHES AND RECOVERY Until now experience for quenches recovery with

current above 6.5 kA comes from before Run1 quench training campaign (already 5-6 years ago). The LHC Run1 experienced some “easy quenches” without opening of the quench valves (QV), with pressure rise in the cold mass below 15 bars. The analysis of the recovery after quenches was presented during Chamonix Workshop in 2009. The updated analysis combined with presented in Chamonix graph is shown in Fig. 12.

Figure 12: Recovery after quenches

Any quench occurred up to now on the LHC installation did not cause helium loss from the cryogenic installation. In case of opening of the QVs (quenches above 6.5 kA) the helium lost from the cold mass volume was recovered as foreseen in the system. New learning with quenches and recovery will be the subject of future experience for Run2 during the magnets training.

RUN2 BEAM PARAMETERS – CRYOGENIC MARGINS AND LIMITS

The detailed analysis of the beam induced heating was presented during Evian Workshop in December 2012 [2]. This chapter will summarize the work done during LS1 to upgrade the system and will present key values for margins and limits for the refrigeration power.

ARC, SAMs and ITs beam screen circuit The analysis of scrubbing runs (December 2012) shown

e-cloud heat deposition measured on beam screen circuits (BS). The curves in Fig. 13 show topology of the heat deposition with existed before LS1 limitations on specific BS cooling loops.

Figure 13: Scrubbing run heat deposition.

The hydraulic limitations on local cooling loops of the beam screen had to be upgraded on SAM and semi-SAM magnets over the accelerator length (38 valve poppets were replaced during LS1). The upgrade was applied also on arc section in sector 3-4 where the cryogenic valve poppets were replaced to go back to the level of cooling capacity equal to the other sectors. The present local limitation for beam scrubbing on all BS cooling loops is about 2 W/m per aperture (see Table 1).

Table 1: Old and new local limitation on BS circuits.

The upgrade allows for full distribution of available refrigeration power moving the limits from local cooling loops to the limit on global refrigeration power. Taking into account equal distribution of the available refrigeration power the new limitation for beam scrubbing will be 1.6 W/m per aperture (see Table 2).

Table 2: Old and new local limitation on BS circuits.

The distribution of the heat load on the BS and available cooling power for all sectors is presented in Fig. 14 (Qs – static heat load, Qsr – synchrotron radiation, Qic – image current, Qec – electron cloud).

Figure 14: BS heat load and available cooling power.

138

QUENCHES AND RECOVERYUntil now experience for quenches recovery with

current above 6.5 kA comes from before Runl quenchtraining campaign (already 5-6 years ago). The LHCRunl experienced some “easy quenches” without openingof the quench valves (QV), with pressure rise in the coldmass below 15 bars. The analysis of the recovery afterquenches was presented during Chamonix Workshopin 2009. The updated analysis combined with presentedin Chamonix graph is shown in Fig. 12.

Recovery Time after Limited Resistive Transitions(Predictions at design stage)

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Figure 12: Recovery after quenches

Any quench occurred up to now on the LHC installationdid not cause helium loss from the cryogenic installation.In case of opening of the QVs (quenches above 6.5 kA)the helium lost from the cold mass volume was recoveredas foreseen in the system. New learning with quenchesand recovery will be the subject of future experience forRun2 during the magnets training.

RUN2 BEAM PARAMETERS —CRYOGENIC MARGINS AND LIMITS

The detailed analysis of the beam induced heating waspresented during Evian Workshop in December 2012 [2].This chapter will summarize the work done during LSlto upgrade the system and will present key values formargins and limits for the refrigeration power.

ARC, SAMS and 113‘ beam screen circuitThe analysis of scrubbing runs (December 2012) shown

e-cloud heat deposition measured on beam screen circuits(BS). The curves in Fig. 13 show topology of the heatdeposition with existed before LSl limitations on specificBS cooling loops.

um I' m. an»: I'll n a. -m '1.'-\' I'll ui'. .--._. 52.x: ...-.- x. m. sow. .-_...

;in‘.1\rc-:r:x:;l. S3“. 3

l Lim ITI

i . _ H...‘ ,I'. -' 1] m! 1.: Lirn 53-1

anio

uaM

/mpe

apt-r

une]

"551-3'121I'x‘ [(5. [5:14 tern

Figure 13. Scrubbing run heat deposition

The hydraulic limitations on local cooling loops of thebeam screen had to be upgraded on SAM and semi-SAMmagnets over the accelerator length (38 valve poppetswere replaced during LSl). The upgrade was applied alsoon arc section in sector 3-4 where the cryogenic valvepoppets were replaced to go back to the level of coolingcapacity equal to the other sectors. The present locallimitation for beam scrubbing on all BS cooling loopsis about 2 W/m per aperture (see Table 1).

Table 1: Old and new local limitation on BS circuits.

Lcml rm :1 ‘35 :cc w; 333cm \III'RI

an rru Rem-mu Ior“VIN“ wrrrum .

11mm WW E“5~"' [w m pm I” m w henna. 1.3' I'ril ' arxmre} 3w ninr IFIIIJ .I

ammra}mi N?» Clc Nell. f‘ n I] .

The upgrade allows for full distribution of availablerefrigeration power moving the limits from local coolingloops to the limit on global refrigeration power. Takinginto account equal distribution of the availablerefrigeration power the new limitation for beam scrubbingwill be 1.6 W/m per aperture (see Table 2).

Table 2: Old and new local limitation on BS circuits.

Global limitation (Cryoplant) 25ns 2015

Qbs Remaining fortmax 25 ns 2015 beam scrubbing

kW per sector 14 8 5 3 9 5Average WCm per aperture 2 4 0 9 1 5

The distribution of the heat load on the BS andavailable cooling power for all sectors is presented inFig. 14 (Qs 7 static heat load, e i synchrotron radiation,Qic 7 image current, Qec i electron cloud).

BS cooling circuitsl Q5 l e Qic l Qec

8000 Installed power 80

S, 6000 60 3a; EV 3'© 4000 40 _o5 1;,m 2000 20 _E.9 O

U I I I I I I I 80 I I I I I 0 To

312 523 534 $45 $56 567 S78 S81 ,9

Figure 14: BS heat load and available cooling power.

138

Heat deposition on the cold mass The LS1 allowed also for relocation of the braids on all

concerned ITs which were wrongly installed before Run1. The local margin on refrigeration power with relation to the luminosity of 1.00E+34 is equal to 1.75 (for details see Table 3).

Table 3: Limitations on ITs cold masses.

The distribution of the heat load on the whole sector cold mass and available cooling power for all sectors is presented in Fig. 15 (Qs – static heat load, Qrh – resistive heating, Qbgs – beam gas scattering, Qsec – secondary particles).

Figure 15: cold mass heat load and available cooling power.

Regarding global heat load coming from the BS circuit and cold mass circuit the available margin is either 1800 W for additional cold mass cooling or 9000 W for additional BS heat load. The representation of global margin for each sector is shown in Fig. 16 combining loads coming from BS and cold mass presented in Figs. 14 and 15.

Figure 16: Global cooling margin

CONCLUSIONS Gained great experience during Run1 allowed operating

cryogenic system nearly to 95% of availability during last year of operation. The helium losses were reduced by factor of 2, down to ~22 tons/year. Large LS1 campaign is underway for maintenance, upgrade, repairs and consolidation of different subsystems and components of the LHC cryogenics. Applied study on spare parts and possible redundancies gives good sense of efficient machines operation during Run2 minimizing potential down time. The introduced upgrades on the BS local cooling loops allows for full and more flexible distribution of available global refrigeration power. The existing margin on installed cooling capacity can be used to cover excessive heat load on the LHC cooling loops.

ACKNOWLEDGMENT Many thanks to all support teams for planned

and urgent interventions during Run1 as well as their effort for preparation of Run2 operation.

REFERENCES [1] O. Bruning et al., “LHC Design Report,” Geneva, 2004. [2] L. Tavian, “Performance limitations of the LHC

cryogenics: 2013 review and 2015 outlook,” LHC Beam Operation workshop – Evian 2012.

139

Heat deposition on the cold mass The LS1 allowed also for relocation of the braids on all

concerned ITs which were wrongly installed before Run1. The local margin on refrigeration power with relation to the luminosity of 1.00E+34 is equal to 1.75 (for details see Table 3).

Table 3: Limitations on ITs cold masses.

The distribution of the heat load on the whole sector cold mass and available cooling power for all sectors is presented in Fig. 15 (Qs – static heat load, Qrh – resistive heating, Qbgs – beam gas scattering, Qsec – secondary particles).

Figure 15: cold mass heat load and available cooling power.

Regarding global heat load coming from the BS circuit and cold mass circuit the available margin is either 1800 W for additional cold mass cooling or 9000 W for additional BS heat load. The representation of global margin for each sector is shown in Fig. 16 combining loads coming from BS and cold mass presented in Figs. 14 and 15.

Figure 16: Global cooling margin

CONCLUSIONS Gained great experience during Run1 allowed operating

cryogenic system nearly to 95% of availability during last year of operation. The helium losses were reduced by factor of 2, down to ~22 tons/year. Large LS1 campaign is underway for maintenance, upgrade, repairs and consolidation of different subsystems and components of the LHC cryogenics. Applied study on spare parts and possible redundancies gives good sense of efficient machines operation during Run2 minimizing potential down time. The introduced upgrades on the BS local cooling loops allows for full and more flexible distribution of available global refrigeration power. The existing margin on installed cooling capacity can be used to cover excessive heat load on the LHC cooling loops.

ACKNOWLEDGMENT Many thanks to all support teams for planned

and urgent interventions during Run1 as well as their effort for preparation of Run2 operation.

REFERENCES [1] O. Bruning et al., “LHC Design Report,” Geneva, 2004. [2] L. Tavian, “Performance limitations of the LHC

cryogenics: 2013 review and 2015 outlook,” LHC Beam Operation workshop – Evian 2012.

139

Heat deposition on the cold massThe LSl allowed also for relocation of the braids on all

concerned ITs which were wrongly installed before Runl.The local margin on refrigeration power with relation tothe luminosity of 1.00E+34 is equal to 1.75 (for detailssee Table 3).

Table 3: Limitations on ITs cold masses.Lmax compatible withlocal margin: 1.75E3d

ES'‘1 \r.\' rx'l'n'mrr

23‘'r ._‘. hm"; 'nn1' ‘9? l'n barr'e‘. weIEe-cw-n-I T

CD. dz: eEDn'aiaed :r '42:” n

The distribution of the heat load on the whole sectorcold mass and available cooling power for all sectorsis presented in Fig. 15 (Qs 7 static heat load, t iresistive heating, ns i beam gas scattering, Qsec isecondary particles).

1.9 K cold-mass circuitsl (15 l t ns l Qsec

2400 Installed power 120 H0"

:2000 1003:3' 1600 80 EE© .g 1200 60 g

I I _“ 800 ' ' 40 “'5 l I l l I ' ' E”

IIIIIII”?0 0 E512 523 S34 545 556 867 578 581

Figure 15: cold mass heat load and available coolingpower.

Regarding global heat load coming from the BS circuitand cold mass circuit the available margin is either1800 W for additional cold mass cooling or 9000 W foradditional BS heat load. The representation of globalmargin for each sector is shown in Fig. 16 combiningloads coming from BS and cold mass presented in Figs.14 and 15.

139

Installed power200W

'_' N 90 g/s ofmargin, i.e.:Q 9 ~1800W@1.9K orno 150 .‘7'. —> ”9000W for BS coolingEB ('“1.6W/m per aperture]

3- 100 l CMI|ll|l|7.3 50

e I I I I I I I I0$12 523 S34 S45 $56 567 $78 581

Figure 16: Global cooling margin

CONCLUSIONSGained great experience during Runl allowed operating

cryogenic system nearly to 95% of availability during lastyear of operation. The helium losses were reduced byfactor of 2, down to ~22 tons/year. Large LS1 campaign isunderway for maintenance, upgrade, repairs andconsolidation of different subsystems and components ofthe LHC cryogenics. Applied study on spare parts andpossible redundancies gives good sense of efficientmachines operation during Run2 minimizing potentialdown time. The introduced upgrades on the BS localcooling loops allows for full and more flexibledistribution of available global refrigeration power.The existing margin on installed cooling capacity can beused to cover excessive heat load on the LHC coolingloops.

ACKNOWLEDGMENTMany thanks to all support teams for planned

and urgent interventions during Runl as well as theireffort for preparation of Run2 operation.

REFERENCES[1] O. Bruning et al., “LHC Design Report,” Geneva, 2004.[2] L. Tavian, “Performance limitations of the LHC

cryogenics: 2013 review and 2015 outlook,” LHC BeamOperation workshop 7 Evian 2012.

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