Brief report of the hardware commissioning activities

The challenges for getting the nominal cryogenic conditionsL. Tavian, AT.CRG CERN 14 May 2008 Academic Training:Commissioning of the LHC superconducting magnet systemIntroduction to LHC cryogenic system (layout, architecture)Preparation before cool-down (Purge, flushing)Transient operations to reach nominal operating condition (Cool-down, filling)Tuning of the cryogenic system:With an without electrical circuit poweringCoping with resistive transitionAvailability for poweringConclusion

Contents14 May 2008L. Tavian - LHC Cryogenics2Introduction14 May 2008L. Tavian LHC Cryogenics3

Main cryogenic requirement:Cooling of 24 km of superconducting magnets @ 1.9 K, 8.33 TWhy 1.9 K ?14 May 2008L. Tavian LHC Cryogenics4

With Nb-Ti as technical superconductor, to get sufficient current density above 9 T, cooling below 2 K is requiredTrade-off between magnet and cryogenic complexityWhy helium as refrigerant ?14 May 2008L. Tavian LHC Cryogenics5

Helium is the only available cryogen which is not solid below 15 K14 May 2008L. Tavian LHC Cryogenics6Cryogenic system layout5 cryogenic islands8 helium cryogenic plants: 1 plant serves 1 sector (18 kW @ 4.5 K, 2.4 kW @ 1.8 K and 600 kW LN2 precooler)

(Distribution line)(Interconnection box)Cryogenic plant6Cryogenic architecture14 May 2008L. Tavian LHC Cryogenics7

Typical even-point architecture14 May 2008L. Tavian LHC Cryogenics8

Photo gallery: Refrigerators 14 May 2008L. Tavian LHC Cryogenics9

1.8 K refrigeration units(2.4 kW @ 1.8 K)4.5 K Refrigerators(18 kW @ 4.5 K)

Photo gallery: Storage and distribution14 May 2008L. Tavian LHC Cryogenics10

GHe storage LN2 storage Cryo-magnet Distribution line (QRL) Interconnection boxVertical transfer line

Superfluid helium cooling principle14 May 2008L. Tavian LHC Cryogenics11

Heat exchanger tube in copper with a diameter DN50. Overall thermal conductance: ~ 100 W/m.K (i.e., for 1W/m, a temperature difference of 10 mK)Principle of the LHC He II Cooling SchemeNormal operating conditions14 May 2008L. Tavian LHC Cryogenics12

Magnet-cell (107 m) cooling scheme14 May 2008L. Tavian LHC Cryogenics13

107 mOther tunnel equipments14 May 2008L. Tavian LHC Cryogenics14

RF cavities (P4)Feed box (DFB)Standard cell(107 m)Inner triplet

Standalone magnetIntroduction to LHC cryogenic system (layout, architecture)Preparation before cool-down (Purge, flushing)Transient operations to reach nominal operating condition (Cool-down, filling)Tuning of the cryogenic system:With an without electrical circuit poweringCoping with resistive transitionAvailability for poweringConclusion

Contents14 May 2008L. Tavian - LHC Cryogenics15Sector preparation: Purge & leak test14 May 2008L. Tavian LHC Cryogenics16

Removal of air in circuit by evacuation and He filling:400 m3 of circuits distributed over 3.3 km,He taken from medium pressure storage, at least 3 cycles to get air and humidity content below 50 ppm to be compatible with the cryoplant purification system (dryer and adsorber), 1 to 2 cycles per day,~10 kCHF of He per sector purge.Sector preparation: circuit flushing 14 May 2008L. Tavian LHC Cryogenics17

Removal of dust and debris by flushing the helium circuits with high helium flow at 300 K:all circuits flushed in series,QRL headers first to avoid migration of dust to the machine circuits (magnets and beam screens),use of refrigerator compressors for flow production,the complete return flow is passing trough a filter to stop the debris,1 to 2 week per sector depending of the circuit cleanliness.Filter inspection after flushing14 May 2008L. Tavian LHC Cryogenics18

Debris & KaptonDustPossible short in magnet diodesTravellersFoam (welding plug) But the sooner the best !Introduction to LHC cryogenic system (layout, architecture)Preparation before cool-down (Purge, flushing)Transient operations to reach nominal operating condition (Cool-down, filling)Tuning of the cryogenic system:With an without electrical circuit poweringCoping with resistive transitionAvailability for poweringConclusion

Contents14 May 2008L. Tavian - LHC Cryogenics19300 5 K cool-down of Sector14 May 2008L. Tavian LHC Cryogenics20

Cool-down of 4625 t per sector over 3.3 km:From 300 to 80 K: 600 kW pre-cooling with LN2,up to ~5 t/h,6 LN2 trailer per day during 10 days (1250 t of LN2 in total); LN2 logistics critical.From 80 to 5 K: Cryoplant turbo-expander cooling,cryoplant tuning critical (4 different types).LHe filling: 15 t of LHe in total (4 trailers).Up to 40 PID loops to control the cool-down speed of the cells, standalone magnet and DFB.

Logitics during sector cool-down 14 May 2008L. Tavian LHC Cryogenics21

Unloading of LHe & LN2:~ 200 kCHF of LN2 per sector cool-down,~ 600 kCHF of LHe per sector filling.

300-5 K cool-down time (w/o filling)14 May 2008L. Tavian LHC Cryogenics22

Totalw/o external factors & cryoplant stopsCool-down time hampered by:external factors (leaks, electrical short-circuits, electrical control plateaus),cryogenic stops (utility loss, cryogenic problems),cryogen logistics management (week-ends, nights),cryoplant and tunnel cooling loops tuning and limitations.Room for improvement !Filling & cool-down to 1.9 K14 May 2008L. Tavian LHC Cryogenics23

LHe filling and cool-down completion by using the 1.8 K refrigeration unitComplex operation of cold compressors (up to 4 in series)Filling and cooling of electrical feed boxes and their current leads (as well as RF cavity modules, if any)1 week per sector

Cold compressorsCold compressors14 May 2008L. Tavian LHC Cryogenics24

Definition of reduced parameters:

m: mass-flowTin: Inlet temperaturePin: Inlet pressureN: Rotational speedSubscript0: Design condition

andComplex operation of hydro-dynamic compressor:- high rotational speed: up to 800 Hz,- reduced operation range at constant pressure ratio.Introduction to LHC cryogenic system (layout, architecture)Preparation before cool-down (Purge, flushing)Transient operations to reach nominal operating condition (Cool-down, filling)Tuning of the cryogenic system:With an without electrical circuit poweringCoping with resistive transitionAvailability for poweringConclusion

Contents14 May 2008L. Tavian - LHC Cryogenics25Tuning of the cryogenic system14 May 2008L. Tavian LHC Cryogenics26

Commissioning at cold of instrumentation (temperature, cryo-heaters, Lhe level, valves)Commissioning of sub-systems like electrical feed boxes and superconducting links which are cold tested for the first time in the tunnelTuning of the control loops to get the required stability and conditions for allowing the magnet poweringValidate the conformity of the equipment cooling1 to 2 weeks partially in parallel with the last cold-down phaseCommissioning of instrumentation14 May 2008L. Tavian LHC Cryogenics27TypeQuantityLocationThermometers(Cernox 1.7 - 300 K)700*Magnet cold mass, QRL, DFBThermometers(Pt100, Thermocouple)500*Current lead, cryo-heater, thermal shieldLevel gauges70SSS phase separator, DFB, standalone magnetCryo-heaters300Magnet cold mass, DFB, QRL, beam screenCryogenic control valves180QRLWarm control valves (DFB)150Current leadTotal per sector1900Always on-line with the instrumentation database*: including some redundant sensors installed but not connected Commissioning of the control system14 May 2008L. Tavian LHC Cryogenics28Local Cryogenic control room

Central Control RoomOWS [1..x]PVSS DS Sector

OWS[1..x]

PROFIBUS DP networks

PROFIBUS PA networks

WFIP Networks (7)

RadTol electronicsUNICOSPLCS7-400 Siemens

FECs(FESA)

RM sector 81 RM sector 78RM sector 78PLCQUIC SchneiderReturn Module CRYO Instrumentation expert toolPVSS DS

TT, PT, LT, DI, EHCVCourtesy E. BlancoCommissioning of sub-systems14 May 2008L. Tavian LHC Cryogenics29

DFB commissioning : Level measurement and current lead temperature control and stability~ 1 week per sectorTuning of control loops14 May 2008L. Tavian LHC Cryogenics30PID control loopQuantity1.9 K cooling loop30Current lead temperature control150Level control (DFB, standalone magnet)20BS cooling loop120Total per sector320Tuning of all control loops and the corresponding control logic to get the required stability and conditions for allowing first the ELQA activity and then the magnet poweringFill-up and boil-off of standalone magnets to confirm the level and the complete wetting of the magnet coils with liquid helium.Validation of the conformity of the cooling circuits:Non conformities identified in some feeding pipes of the 1.8 K bayonet heat exchangers. Use of the built-in redundancy to cool the non-conforming cells.Validation of cooling conformity 14 May 2008L. Tavian LHC Cryogenics31Boil-off of standalone magnets

14 May 2008L. Tavian LHC Cryogenics32Cooling loop redundancy 14 May 2008L. Tavian LHC Cryogenics33

SlopeS5-6 magnet temperature stability14 May 2008L. Tavian - LHC Cryogenics34

~ 140 temperature measurements superimposed !(Validation of the thermometry quality)Introduction to LHC cryogenic system (layout, architecture)Preparation before cool-down (Purge, flushing)Transient operations to reach nominal operating condition (Cool-down, filling)Tuning of the cryogenic system:With an without electrical circuit poweringCoping with resistive transitionAvailability for poweringConclusion

Contents14 May 2008L. Tavian - LHC Cryogenics35Quench recovery14 May 2008L. Tavian LHC Cryogenics36

Recovery time: 6 hRecovery time: 4.5 h

QuenchreliefvalveIntroduction to LHC cryogenic system (layout, architecture)Preparation before cool-down (Purge, flushing)Transient operations to reach nominal operating condition (Cool-down, filling)Tuning of the cryogenic system:With an without electrical circuit poweringCoping with resistive transitionAvailability for poweringConclusion

Contents14 May 2008L. Tavian - LHC Cryogenics37Cryo-availability14 May 2008L. Tavian LHC Cryogenics38Availability for sector HWC : 80 % during weeks w/o resistive transitionTo be improved during beam commissioning: more than 95 % per sector Note : A cryogenic system takes time (hours) to recover any kind of stop !

(Considering independent origins of problems)HWCBCIntroduction to LHC cryogenic system (layout, architecture)Preparation before cool-down (Purge, flushing)Transient operations to reach nominal operating condition (Cool-down, filling)Tuning of the cryogenic system:With an without electrical circuit poweringCoping with resistive transitionAvailability for poweringConclusion

Contents14 May 2008L. Tavian - LHC Cryogenics39Time for getting nominal conditions:Presently 10 weeks for getting nominal conditions,In routine operation, about 1 month is foreseen,

LHC cryogenics is the largest, the longest and the most complex cryogenic system worldwide.Operation for the needs of Sector HWC is now demonstrated.Based on experience, together with procedures and tools being put in place, availability must be improved for the next phase: The Beam Commissioning.Conclusion14 May 2008L. Tavian - LHC Cryogenics40