OCTUPOLE CIRCUITS Roberto Lopez Davide Tommasini CONTENT Roberto

OCTUPOLE CIRCUITS Roberto Lopez & Davide Tommasini CONTENT: Roberto Lopez & Davide Tommasini MCO magnets Circuit & power converter Integration and routing of wires Commissioning & operation Dielectric tests Splices Faults Strategic questions Conclusion LHC Task Force Splices: Octupole circuits October 2010

THE MAGNETS Design Manufacture Tests : superconducting, nested inside the MCDs : 616 India (Crompton + CAT) + 616 UK (Tesla) : all tested up to 150 A at 4. 5 K MCO Main Parameters Physical length 110 mm Nominal current @ 1. 9 K 100 A Critical current @ 1. 9 K 300 A Number of coils Wire Cu/Sc ratio Peak field 4 0. 73 x 0. 38 mm 4 2 T Inductance 0. 4 m. H Aperture 58 mm Outer diameter (MCDO) Weight (MCDO) Roberto Lopez & Davide Tommasini 115 mm 4 kg LHC Task Force Splices: Octupole circuits October 2010

THE MCO UNITS 0. 73 x 0. 38 mm middle of the coil US weld 1. 47 x 2. 28 mm 3 (internal)+2 (external) US welds + 2 soldered on MB + 2 US for interconnections Roberto Lopez & Davide Tommasini LHC Task Force Splices: Octupole circuits October 2010

THE CIRCUIT Vtap spool 1 spool 2 AMCO B spool 12 spool 11 AMCO B MBA MBB MQ DFBA LOW CURRENT HIGH CURRENT • 420 interconnection + 154 MB (soldered) + 385 internal (US) = 959 splices/circuit • measured “average” splice resistance @ 1. 9 K ~12 n (Nuria Catalan) : too high? • inductance per circuit ~ 31 m. H (77 magnets), energy stored @ 100 A : 154 J • resistance at 300 K of one magnet ~ 3 Roberto Lopez & Davide Tommasini LHC Task Force Splices: Octupole circuits October 2010

THE POWER CONVERTER 83 m LHC 120 A-10 V http: //te-epc-lpc. web. cern. ch/te-epc-lpc/converters/lhc 120 a-10 v/general. stm In case of fault (quench, Iearth > 50 m. A during > 20 ms, open circuit. . . ) the Pwr Module stops and the crowbar switches on when V > 13 V many thanks to Yves Thurel and Valérie Montabonnet Roberto Lopez & Davide Tommasini LHC Task Force Splices: Octupole circuits October 2010

INTEGRATION Roberto Lopez & Davide Tommasini LHC Task Force Splices: Octupole circuits October 2010

INTEGRATION/ROUTING Roberto Lopez & Davide Tommasini LHC Task Force Splices: Octupole circuits October 2010

PROXIMITY TO GROUND Roberto Lopez & Davide Tommasini LHC Task Force Splices: Octupole circuits October 2010

ROUTING IN THE MQ Roberto Lopez & Davide Tommasini LHC Task Force Splices: Octupole circuits October 2010

DIELECTRIC TESTS OF MCO: MAGNETS MB STEP Cold Mass Assembler TO GROUND TO OTHER CIRCUITS 1500 V 1. 0 k. V to QF/QD (resistance) Reception Cern 500 V to (MB coils, QH, MCS/MCO) During cryostating 256 V to MB coils In SM 18 @ 1. 9 K 990 V to MB coils After stripping 256 V to MB coils Remark : QF/QD bus bars checked towards ground at 5 k. V MQ STEP Cold Mass Assembler TO GROUND TO OTHER CIRCUITS 1700 V to adjacent spools & to MQ BB During Cryostating 500 V to all other circuits End of cryostating 313 V 183 V to MQ 313 V to other circuits In SM 18 @ 1. 9 K 1526 V 918 V to MQ bus bars 1526 V to other circuits Roberto Lopez & Davide Tommasini LHC Task Force Splices: Octupole circuits October 2010

DIELECTRIC TESTS OF MCO: INTERCONNECTIONS PAQ STEP TO GROUND TO OTHER CIRCUITS Half cell 500 V All other circuits grounded during the test 1/3 sector 500 V All other circuits grounded during the test Remark : current leads means : all spools and busbars Hardware Commissioning STEP TO GROUND TO OTHER CIRCUITS Sector after flushing 300 V All other circuits grounded during the test Sector @ 80 K 300 V All other circuits grounded during the test Sector @ 1. 9 K 600 V All other circuits grounded during the test 120 V ! 240 V ! TP 4 B: after flushing TP 4 D: @ 80 K TP 4 E: @ 1. 9 K Roberto Lopez & Davide Tommasini LHC Task Force Splices: Octupole circuits October 2010

HARDWARE COMMISSIONING & OPERATION All circuits checked to 100 A during hardware commissioning 2008 -2009 RCO. A 78 B 2: From HWC 2008 (NC 1029807 & NC 809944) , first event was a short circuit to ground during HV tests at 560 V, thereafter 3 consecutive quenches at 55 A RCO. A 81 B 2: From HWC 2009 (NC 955048), first observation was a too high resistance, thereafter an open circuit between B 12 L 1 and B 11 L 1 Currents presently applied in RCO circuits for operation at 3. 5 Ge. V RPLB. UA 23. RCO. A 12 B 1: 23. 45 A 32. 88 A RPLB. UA 27. RCO. A 23 B 1: -48. 01 A 31. 35 A RPLB. UA 43. RCO. A 34 B 1: -41. 01 A 31. 09 A RPLB. UA 47. RCO. A 45 B 1: -37. 29 A 27. 77 A RPLB. UA 63. RCO. A 56 B 1: 21. 72 A RPLB. UA 23. RCO. A 12 B 2: - RPLB. UA 27. RCO. A 23 B 2: RPLB. UA 43. RCO. A 34 B 2: RPLB. UA 47. RCO. A 45 B 2: RPLB. UA 63. RCO. A 56 B 2: -31. 79 A 8 th Not powered since the of August 2010. Power module changed the 1 st sept. RPLB. UA 67. RCO. A 67 B 1: 41. 75 A RPLB. UA 83. RCO. A 78 B 1: many 12 th 28. 54 A RPLB. UA 67. RCO. A 67 B 2: A RPLB. UA 83. RCO. A 78 B 2: thanks to 9. 57 Sandrine Le Naour Not powered since the of July 2010. Power module. Tommasini changed the 19 th July Roberto Lopez & Davide LHC Task Force Splices: Octupole circuits 0 A October 2010

THE SPLICES long term performance: see C. Scheuerlein also see: N. Catalan “Overview of all superconducting splices in the LHC machine”, Chamonix 2010, Roberto Lopez & Davide Tommasini LHC Task Force Splices: Octupole circuits October 2010

FAULTS 1. 2. 3. 4. quench short circuit to ground open circuit short circuit to/from another circuit Case 1. The maximum voltage remains well below 100 V. Case 2. and 3. The stored energy is only 154 J. Damage should remain localized to the circuit itself. Furthermore, TE-CRG experts recall this small energy would hardly be noticed by the instrumentation of the cryogenic system. Case 4. Involved energies may become relatively large (24 MJ if MQs are involved). Probably too pessimistic to consider MBs being affected (E~1236 MJ) Roberto Lopez & Davide Tommasini LHC Task Force Splices: Octupole circuits October 2010

STRATEGIC QUESTIONS ARE DEFECTIVE SPLICES PRESENT IN MCO CIRCUITS? CAN WE LOCALIZE THEM? SHALL WE EXPECT FAILURES OF MCO CIRCUITS? WHAT WOULD BE THE CONSEQUENCES? SHALL/CAN WE IMPROVE THE SITUATION? understand: monitor: test: enhance: Roberto Lopez & Davide Tommasini LHC Task Force Splices: Octupole circuits October 2010

CONCLUSION Findings Ø Faults already happened Ø The energy stored in the MCO circuit is extremely low Ø During HC each circuit was HIPOT tested to each other Ø The circuit resistance measured from the DFBA looks high (~12 n /splice) Ø Physical separation to ground and between circuits is questionable ØTest levels were (and are) probably on the low side Ø Power converters look sound Desirable (within the feasible) actions Ø Review HIPOT test levels and procedures at warm and before start-up Ø Perform a measurement campaign of splice resistances, with help of Vtaps Ø Perform a circuital analysis of reasonable fault scenarios Roberto Lopez & Davide Tommasini LHC Task Force Splices: Octupole circuits October 2010