Review of the Tests of Superconducting Magnets in

SM1814th January 2005

Review of the Cryogenic Infrastructure in SM18

Bruno Vullierme ACR-MT

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Completion of infrastructurein 2004

• Last 6 CFB in operation– February 2004: CFBD1 and D2– April 2004: CFBB1 and B2– May 2004: CFBA1 and A2

• Second CWU– The CWU formerly dedicated to the 2 Cryogenic Feeder

Units of Cluster A up to end 2003 has been integrated to the Cooldown-Warmup System.

– Resulting CWS cooldown capacity : 250 kW @ 80K (ΔT=220 K)

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Upgrade of the test station for 2004 (1/2)

• Cooldown Warmup Units Regeneration– A drawback of the continuous operation @ 80K of both CWUs

is the systematic clogging of their heat exchangers (HX).The residual water in cold masses is caught by the circulated helium and further trapped in the HP branch of the CWUs HX.

– An automatic regeneration sequence has been implemented in order to periodically heat-up and flush the HX and lower inner pipework with GHe via a new dedicated recovery circuit while the other CWU is still in operation.

• LN2 Storage– The former 50’000 l LN2 Dewar has been replaced by a new

(more safe and reliable) one with higher operating pressure and remote control.

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Upgrade of the test stationfor 2004 (2/2)

• Subcooling capacity– The Warm Pumping Unit 2 has been connected in parallel

with the 1st pumping branch (WPU1 and Cold Compressor):26 g/s @ 12 mbar.

– All maintenance interventions were done on WPUs without any loss of production (redundancy WPU1/WPU2).

– The end of bearing plates of the 3 WPU2 roots blowers have been replaced by water-cooled ones: Less problems expected.

• Cryo_OK flags– Conditions for powering @ 4.5 K, powering @ 1.9 K and

cold HV test, has been clarified and respective flags implemented in the CFB control system.

– Improved global availability of cryo_OK conditions, better understanding and diagnostic for operators.

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Improvements of operating conditions in 2004 (1/3)

• Pumpdown time:– Most of the overtime formerly spent for pumping down of the

cryostat was due to an accumulation of liquid water in the exhaust flange of the CFB roughing pumps (IPX100 Edwards). Liquid water was directly feeding the dynamic leak of the dry pump, limiting inexorably the suction pressure in the mbar range.

– The 12 IPX pumps have been modified (additional drain).

• Leak search time– The go/no go criteria for acceptance of on-bench external and

double sealed connections leaks have been clarified– Improved tightness of CFB and MRB anticryostat flanges– Improved tightness of CFB built-in leak detection circuits– No more on-bench repairs to achieve the tightness criteria

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Improvements of operating conditions in 2004 (2/3)

• Cooldown/Warmup flow rate (existing systems)– Up to end-2003, the capacity of the C/W circulators was

limited because the use of CWU1 for CFUs of Cluster A (enforced lower operating suction pressure).

– For 2004, the CWS max flow rate has been increased up to 190 g/s, i.e. the limitation resulting from the pressure drop of the existing filters on suction side and of the oil removal systems on HP side of the circulators.

• LHe withdrawing from the 25’000 l Dewar– The problem of limitation at approx. 40 g/s of LHe supply

has been definitely solved.– The 2-phase LHe withdrawing can now reach approx. 100

g/s and doesn’t represents any more a limitation to the test rate.

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Improvements of operating conditions in 2004 (3/3)

• Production phase for the Tasks Tracking System– Uniform & up-to-date information of teams involved– Better reactivity (anticipation) of teams

• Production phase for the Test Benches Priority Handling– Steering of the use of cryogenic utilities at maximum

capacity:• LHe supply• Cold return to the refrigerator• 1.9 K Subcooling

– Useful tool for the formalization of the sequencing• Cooldown/Warmup

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Critical Items (Infrastructure)

• Cryogenic Valves Problems– Most of the 100 cryogenic valves of CCL, CWL and CWUs

were presenting rubbing signs and sealing or other defects.

– CV144 control cone, after self unscrewing, has been lost in CFBE2 subcooling heat exchanger. Few others were on the way, or in very bad conditions.

• Corrective actions during the shut-down– Systematic demounting and check on all the valves– Tightening/gluing of VELAN control cone assemblies– Polishing of the rubbed mobile parts (VELAN)– In situ polishing of the rubbed parts of valves bodies– In situ mechanical re-adjustment and re-configuration

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Critical Items (CFBs)

• 600 A and 15 kA Current Leads– Lost of most of the signals from CL temperature sensors.

Fall back solution: operation of Current Leads in permanent overcooling conditions (C1 repaired)

– Malfunction of over-temperature protections (thermal switches)

• 15 kA SC Current Lines– Problem identified by Andrzej Siemko in December 2004:

Degradation of many silver shoes (C1, C2, D2, B1, A2, E2…)

– Degradation of the Voltage Taps wires

• 600 A Current Lines:– Degradation of extremities of some SC cables

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Upgrade of infrastructurefor 2005

• Cooldown/Warmup System – Installation of new Filters/Oils Removal Systems for the 2

existing circulators. New max flow rate: 280 g/s (in progress) – Upgrade from Siemens S5 to S7 of the control system of the

circulation station with a new control logic. Better flexibility for the operation of up to 3 circulators (in progress)

– Delivery of the 3rd Circulator +ORS in June 2005

• 1.9 K Pumping – Installation of the IHI cold compressor (end-January, hopefully)– Commissioning in June 2005 (redundancy 26 g/s @ 12 mbar)

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Improvements of Cooldown / Warmup Handling in 2005

• Temperature control for the 50 K shield during cooldown– Tracking set point = CM temperature - 10 K (see measurements)– Gradual increasing of ΔT set point when CM temperature is <200 K

• New control logic for optimizing dynamically all the He mass flow rate Set Points with respect to priorities and:– Required modes (cooldown, warmup)– Available cooling power– Available heating power– Available GHe circulation flow rate– Actual value of all cold mass temperatures

• Direct (but smooth) ramping with GHe @ 80K when starting a cooldown.– No more transient mixing of GHe @ 80 K with GHe @ 300 K

• Validation of Magnet Temperature value by gas circulation after a cooldown or warmup stop, before restart– Safety issue

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Repair of CFBs in 2005

• Silver shoes, V taps– Procedures to be defined~ 1 week /CFB

• 15 kA Current Leads Temperature Sensors– Procedure tested on CFBC1~ 3 days /CFB

• New Limit switches for HV143 and HV149– Under design~ 1 day /CFB

~ 12 CFB.week unavailability in 2005– Repairs– Preventive maintenance

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Line M2 Filter (CFB F2, 12-01-05)

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New Oil Removal Systems (10-01-05)