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MCBXFB prototype analysis and next steps

Explore the analysis of the MCBXFB inner and outer dipole prototypes, including quench propagation studies and next steps. Learn about powering strategies, torque issues, and findings from the cold test. Insights for improvements and future testing methodologies are discussed.

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MCBXFB prototype analysis and next steps

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  1. MCBXFB prototypeanalysis and nextsteps J. A. García Matos, F. Toral, A. Fernandez Navarro (CIEMAT) J. C. Pérez (CERN) Warm thanks to all CERN colleagues for their support: 927, M. Guinchard’s, Samer’s and SM18 teams!! 10th April 2019

  2. Index • Introduction. • First cold test analysis. • Second cold test analysis. • Quench propagation studies. • Next steps. • Conclusions. F. Toral - 10th April 2019

  3. Introduction • A cold test of the MCBXFB inner dipole prototype has been realized last December to validate the coil fabrication techniques: • The inner dipole was powered to ultimate current without quench. • The coils lost the pre-load at cold, so we decided to increase the azimuthal preload with 150 micron shims at each side of the collar nose. • The inner dipole collars were equipped with strain gauges. • The outer dipole has been assembled in February and the magnet tested in March. • The outer dipole was equipped with similar instrumentation than the inner one. • The inner and outer coils were axially preloaded and monitored using instrumented bullet gauges. F. Toral - 10th April 2019

  4. First cold test analysis: individual powering • The inner dipole was powered till ultimate current without quench. • The outer dipole experienced a slower training: • First quench at 1006 A • 7 quenches till reaching nominal current (1474 A) • 11 quenches till reaching ultimate current (1592 A) • There are two possible explanations for the different behaviour: • The resin content at the pole turns of the outer dipole coil could be higher (because of curing mould assembly procedure and thinner insulation thickness than nominal) • The azimuthal preload is higher (55 MPa outer dipole vs. 10 MPa inner) Courtesy K. Pepitone F. Toral - 10th April 2019

  5. First cold test analysis: combined powering (I) • Different powering strategies, but torque always below 50% of nominal. Higher torque when inner dipole current is larger than outer one. • Quench origin at inner dipole coils: outer layer, mid-plane block. • No significant detraining. • No noticeable difference between inverse and direct torque. • No degradation of the performance of the coils individually powered. • Strain gauges and collars behaviour as expected. Courtesy K. Pepitone F. Toral - 10th April 2019

  6. First cold test analysis: combined powering (II) • Our favourite explanation: sliding between the saddle end spacer and the half ring pushed by the bullets. • Why? • Torque limitation with different powering strategies: the problem is not coming from the cable properties or the resin. Mechanical problem linked to a stick-slip effect. • Quench origin at inner dipole coils: Lorentz axial forces of both dipoles react against the same endplate. Tangential force due to torque is higher at inner dipole. • Very low friction coefficient between both surfaces. • Not significant detraining or difference btw direct and inverse torque: the bullets are not sliding. F. Toral - 10th April 2019

  7. First cold test analysis: combined powering (III) • Nominal torque per unit length at straight section is very high: 140000 Nm/m, about 80 MPa at the inner dipole coil. It is consistent with strain gauges measurements. • The reaction force at the coil end is about 22 kN. At nominal current, the Lorentz axial force is about 76 kN. Therefore, we need a friction coefficient above 0.3 to avoid sliding. • The azimuthal preload provided by the collars of the inner dipole is still low. Coils are practically loose close to the ends. So the angular deformation of coil ends is larger than computed. F. Toral - 10th April 2019

  8. Index • Introduction. • First cold test analysis. • Second cold test analysis. • Quench propagation studies. • Next steps. • Conclusions. F. Toral - 10th April 2019

  9. Second cold test analysis: what to do? • A thermal cycle would confirm if the individual powering was fine. • We had no time for any major intervention to solve the problem with the torque. • We think that the stick/slip effect takes place at the coil ends. • Two possibilities: • To increase the axial loading, with possible risk of buckling at the coil ends during thermal transients. • To decrease the axial loading: no risk for the coil integrity. Only a small chance to improve the torque (no axial preload at low currents), but more likely worst behaviour because friction at coil ends would be reduced. • Finally, we decided to put the bullets just in contact with the inner dipole and to apply a small torque (3 Nm compared to 12 Nm in the first assembly) at the outer dipole bullets (outer dipole coils lose more axial preload because of Poisson effect during cooling down). F. Toral - 10th April 2019

  10. Second cold test analysis • Both dipoles reached ultimate current without quench when individually powered: good memory. Even more, the outer dipole reached 100 A above ultimate without quench. • Different powering strategies, but torque always below 40% of nominal. Higher torque when inner dipole current is larger than outer one. • Same behaviour than observed in the first cold test, with lower torque. It is consistent with our assumptions, since axial preload on coil ends is smaller. • Quench antennas confirmed that the quench starts always at the coil ends. Courtesy G. Willering F. Toral - 10th April 2019

  11. Index • Introduction. • First cold test analysis. • Second cold test analysis. • Quench propagation studies. • Next steps. • Conclusions. F. Toral - 10th April 2019

  12. Electro-thermal models for quench simulation • Modeled and simulated each dipole magnet independently (inner/Outer). Conservative assumption. • Induced currents (quench back) not modeled. Conservative assumption. • Modeled both transversal and longitudinal quench propagation. • Cables adiabatic to the He bath (fiber glass impregnated cables). • Quench detection voltage: Quench detection time from measurements. Quench validation time: 10 ms. • Initial quench in the pole turn conductor (highest field). SQUID ROXIE • CIEMAT in-housecode in Matlablanguage. Finitedifferencesmethod. • CERN in-housecode. Finitedifferencesmethod + BEM/FEM.

  13. Quench in the Outer Dipole at 1165 A • Quench in the coil end pole turn of the Outer Dipole powered alone at 1165 A. 0.3 Ohm dump resistor with no delay. EEOC2.6 9ms Quench 19 ms EEOC2.7 • Turn-to-turn propag. time • Longitudinal quench propagation velocity calculated with the voltage taps information plus geometry: 6.4 m/s. SQUID: 2.7 m/s. 17 ms 18 ms SQUID: 2 ms ROXIE 2D: 12 ms

  14. Quench with dump resistor with 900 ms delay • Quench starting at the Inner Dipole when both dipoles are powered at 870 A. • t=0 when the quench starts. 60 ms for quench detection (100 mV) plus 10 ms for quench validation. • Turn-to-turn propagation time 22 ms 20 ms 18 ms SQUID: 3 ms ROXIE 2D: 26 ms

  15. Quench with dump resistor with 900 ms delay • Quench in the Inner Dipole with both dipoles powered at 870 A. • t=0 at the quench triggering. 60 ms for quench detection plus 10 ms for quench validation. • 0.3 Ohm dump resistor with 900 ms delay from validated quench. • HETRTR is the correction factor in ROXIE for the transversal heat transfer coefficient.

  16. Quench with dump resistor with 900 ms delay • MIIts calculated from quench triggering. • Test currentextrapolateduntiltheend of thedischarge to properlycompare thequench integral of SQUID and ROXIE (MIItsincreasenegligible). • HETRTR is the correction factor in ROXIE for the transversal heat transfer coefficient. • Some discrepancies on the value of hot spot temperature computed by the pure adiabatic model used at SM18 under study.

  17. Quench with dump resistor with 1000 ms delay • Quench in the Inner Dipole with both dipoles powered at 848 A. • t=0 at the quench trigger. 66 ms for quench detection plus 10 ms for quench validation. • 0.3 Ohm dump resistor with 1000 ms delay from validated quench. • Included ROXIE simulations with correction factors for the transversal and longitudinal heat transfer coefficient: Hetrtr and Hetrlo respectively.

  18. Quench with dump resistor with 900 ms delay • MIIts calculated from quench trigger. • Test currentextrapolateduntiltheend of thedischarge to properlycompare thequench integral to SQUID and ROXIE. (0.02 MIItsincrease). • HETRTR and HETRLO are the correction factors in ROXIE for the transversal and longitudinal heat transfer coefficients.

  19. Index • Introduction. • First cold test analysis. • Second cold test analysis. • Quench propagation studies. • Next steps. • Conclusions. F. Toral - 10th April 2019

  20. Next steps (I) • First of all, wewillcorrectthedefectsfoundduringthemagnet test: • Increasetheazimuthalpreload of theinnerdipolecollars (likely 200 micronshim) • Decreasetheazimuthalpreload of theouterdipolecollars (likely 100 micronshim) • Increasethefrictioncoefficientbetween axial pusher and thecoilends • As analternativesolution, wehaveexploredthepossibility to removetheiron from thecoilends to reduce the torque (thanks to Paolo Fessia). F. Toral - 10th April 2019

  21. Next steps (II) • As analternativesolution, we are designing a system to allowtorsion of thecoilendswithoutslipping, basedonthe axial bearing concept. • We are planning a mock up to validatethesystem. F. Toral - 10th April 2019

  22. CIEMAT ongoing activities • MCBXF magnets will be a Spanish in-kind contribution. • The second short magnet production has already started. • The drawings of the tooling for the long prototype are well advanced. • The specifications for the series contracts are under preparation. • A new laboratory will be built at CIEMAT for magnet prototypes. F. Toral - 10th April 2019

  23. Conclusions • After several campaigns of cold tests, both dipoles performed successfully when individually powered. • When powered simultaneously, the performance was limited by the torque. The problem is likely due to stick/slip effect due to low friction at the coil ends. • The magnet will be disassembled and the azimuthal preload of each dipole will be corrected. • The friction between coil end-spacers and the bullets will be increased. • The magnet will be tested again next June. • An alternative solution to prevent the stick/slip effect will be developed in parallel and implemented in case of need after the first powering run. • First studies on quench propagation have been realized. The stored energy was not very high, but simulations are close to measurements. Further tests are necessary at the next run. F. Toral - 10th April 2019

  24. Thanksforyourattention 8th HL-LHC Collaboration Meeting – F. Toral - 18thOctober 2018

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