Susana Izquierdo Bermudez

OUTLINE 1. Margin and MIITs overview 2. Quench study based on FNAL 11T tests results 1. Longitudinal quench propagation 2. Heaters delay 3. Quench Integral (QI) 4. Time budget 3. Minimize heaters delay 1. Inter-layer heaters 2. Reduce kapton thickness from heater to coil 3. Quench heater design optimization 4. Quench performance under accelerator conditions 5. Additional remarks 6. Baseline design 7. Conclusions/Future actions 2

Susana Izquierdo Bermudez 1. Margin and MIITs overview 3 11 T, T central field 14.5 K 5 K Temperature Margin T(MIITs) 11T cable ParameterMB11T MIITs to reach 400 8T MA 2 s5218 Temperature margin LF48-9 Temperature margin HF Differential Inductance, mH/m Stored energy, kJ/m567897

Susana Izquierdo Bermudez Longitudinal quench propagation 4 2D+1 thermal network Study the propagation of an initial resistive zone of 3 cm length in different turns. I = A, T bath =1.9K Element size in the longitudinal direction = 1 mm Adaptive time stepping (min = s, max = s] Pole turn IL (high field) v ≈ 30 m/s Mid-plane turn OL (low field) v ≈ 6.5 m/s The longitudinal quench propagation velocity in MBHSP01 was measured in one of the quenches in the inner-layer pole turn at 4.5 K using the time-of- flight method as ~27 m/s at 73% of SSL at 4.5 K 2.Quench study based on FNAL 11T tests: longitudinal quench propagation Experimental data courtesy of Guram Chlachidze

Susana Izquierdo Bermudez Insulation heater2coil = 114 µm kapton µm G10 Insulation heater2bath = 508 µm kapton 5 2.Quench study based on FNAL 11T tests: Quench Heaters Delay HFU voltage of 400 V ~ 65 W/cm 2 peak power density Experimental data courtesy of Guram Chlachidze ROXIE quench heater model heater Tuning factor (k) on G ij T,heater2coil/bath to fit experimental and computed heater delays k=0.42

Susana Izquierdo Bermudez 2.Quench study based on FNAL 11T tests: QI study 6 I 0 = A, T bath = 1.9 K MIITs after heater effective [MA 2 s] MIITs from heater fired until effective [MA 2 s] OL-IL delay [ ms] PH delay [ ms] Experimental data ≈27 CASE1: OL heaters t=0 (computed heat transfer from heater to coil) CASE2: OL PH measured delay (OL fully quenched at PH measured delay) Max. Temperature [K] Heaters t=0 OL measured delay Manual trips with the two operating protection heaters Dump delay 1000 ms  Self-dump Experimental data courtesy of Guram Chlachidze

Susana Izquierdo Bermudez 7 Manual trips with the two operating protection heaters Dump delay 1000 ms  Self-dump 2.Quench study based on FNAL 11T tests: QI study Remark: MATPRO database material properties. MIITs 6 % lower for CUDI/Cryocomp database (mainly due to Copper Thermal Conductivity) MIITs difference Additional time budget: 6 ms Experimental data courtesy of Guram Chlachidze QI after heaters effective

Susana Izquierdo Bermudez 8 2.Quench study based on FNAL 11T tests: Time budget QI max = 18 MA 2 s QI decay = 10.8 MA 2 s I 0 = A (experimental) Detection time: Time to get over the threshold : 3-6 ms Validation time : 10 ms Heating firing delay : 5 ms * Heater delay (experimental): 27 ms Time needed to quench: ms Non-redundant (all quench heaters fired) Redundant (half of the quench heaters fired) QI decay = 11.6 MA 2 s (experimental) We are tight!  We need to minimize heaters delay *actual value in RB circuits 30 ms

Susana Izquierdo Bermudez 3. Minimize heaters delay: inter-layer heaters 9 Parameter Case 1 (only OL) Case 6 (OL+IL) OL HF heater delay, ms OL LF heater delay, ms IL delay, ms MIITs total, MA 2 s MIITs after heater effective, MA 2 s MIITs heater fired until effective, MA 2 s Peak temperature in coil, K Peak temperature in heater, K Δ OL HF QH delay = - 31 % Δ IL Qh delay = - 88 % ΔT max = - 27 % Remarks: Thermal contact resistances (e.g. between insulation layers) not included, the same scaling factor as the one used to fit the FNAL test data is kept for this simulation. The insulation is a combination of glass fiber and Mica. At the moment in the model we use G10. CASE 1: Only Outer Layer Heaters Some technical development required before inter-layer heaters become a feasible option CASE 2: Outer Layer + Inter Layer Heaters

Susana Izquierdo Bermudez 3. Minimize heaters delay: reduce kapton thickness 10 Parameter Case 1 114µm k. Case 2 50µm k. OL HF heater delay, ms2114 OL LF heater delay, ms IL delay, ms7163 MIITs total, MA 2 s MIITs after heater effective, MA 2 s MIITs heater fired until effective, MA 2 s4.64 Peak temperature in coil, K Peak temperature in heater, K Δ OL HF QH delay = - 33 % ΔT max = - 13 % CASE 1: Insulation heater2coil = 114 µm kapton µm G10 + conductor insulation Insulation heater2bath = 508 µm kapton CASE 2: Insulation heater2coil = 50 µm kapton µm G10 + conductor insulation Insulation heater2bath = 508 µm kapton

Susana Izquierdo Bermudez 3. Minimize heaters delay: heater design optimization 11 DESIGN GUIDELINES Heaters should cover as many turns as possible Design should be suitable for a 5.5 m length magnet  heating stations Aiming to heater delays < 20 ms Two independent circuits (for redundancy). Higher power density in the LF region Circuit 1Circuit 2

Susana Izquierdo Bermudez Minimize heaters delay: heater design optimization For long magnets, the total heater resistance becomes too high  Heating stations 2 possible options: Heating stations LARP LQ example: wide section = 23 mm, narrow section 9 mm, distance between stations 100mm LHC copper plated solution MB example: 15 mm width, 400 mm plated, 120 mm un-plated Qualitative tests at CERN to understand how smooth the transition between narrow and wide section should be in order to avoid high spot temperatures. More development required to find a solution which combines smooth transition, enough coverage and distance in between heater stations small enough to allow fast quench propagation in the longitudinal direction BASELINE SOLUTION FOR THE FIRST MODEL = COPPER PLATED SOLUTION Thanks to Vladimir Datskov & Glyn Kirby

Susana Izquierdo Bermudez 13 Operation area 3. Minimize heaters delay: heater design optimization Width -> Cover as many turns as possible LF: 20 mm HF: 24 mm Power density LF ≈ 75 W/cm 2 HF:≈ 55 W/cm 2 Even if the operational current is expected to be in the range A, it would be good to have the possibility to go up to 150 A during short model tests to check the saturation of the system in terms of heater delays. Heater width: 20 mm LF, 24 mm HF ρ ss =7.8·10 -7 Ωm, RRR=1.34 Distance between heater stations -> quench propagation in between stations ≈ 5 ms LF: 90 mm HF: 130 mm Coverage: maximum coverage keeping the resistance within the allowable limits for a 5.5m magnet (depends on the number of power supplies/heater circuits) CoverageDistance between stations width

Susana Izquierdo Bermudez 14 OBJECTIVE: Stay within LHC standard quench heater supply limits V (V) I (A) C (mF) Tau (ms) Max. Energy (kJ) Power density (W/cm 2 ) (LF) 58 (HF) (LF) 52 (HF) For a 5.5 m magnet and 50 mm coverage: During first short model test  Higher currents (up to 150?) to check the saturation of the system in terms of heater delay 3. Minimize heaters delay: heater design optimization

Susana Izquierdo Bermudez Minimize heaters delay: heater design optimization Baseline solution: /130 20/24 Heater strip Heater circuit If heater delays becomes too high and/or current decay too slow…we still can: Duplicate the heater coverage (50mm  100mm) + parallel circuit Duplicate the heater coverage (50mm  100mm) + independent circuits We need 2 times more current from the power supply We duplicate the number of power supplies

Susana Izquierdo Bermudez 16 3D simulation with heater stations 1 MIITs difference Time budget 7 ms higher in case of full coverage Full coverage vs heating stations: 3. Minimize heaters delay: heater design optimization 50 90/130 20/24 Remark: ROXIE does not have adaptive mesh tracking (which is a must for practical quench simulation)

Susana Izquierdo Bermudez 4. Quench performance under accelerator conditions (I) 17 Quench initiation and protection INZ in the pole turn inner layer (high field) 3 cm length Quench detection at 100 mV (time required to reach this threshold from quench initiation = 3 ms) 1 Validation time = 10 ms Quench heaters (only outer layer heaters) Heater-firing delay = 5 ms (time from firing the heaters to heaters effective) P o = 84 W/cm 2 (LF) / 58 W/cm 2 (HF), ·tau = 55 ms Insulation heater2coil = 50 µm kapton µm G10. Insulation heater2bath = 508 µm kapton Redundant configuration (only half of the heaters fired) Cable eddy-currents are considered, using R c = 30 μΩ for the cross-over resistance in a cored cable and 0.3 μΩ for R a. Electrical network 1. The results presented later on correspond to a 2D simulation (X-Sec). 2D+1 thermal network is used only for the computation of the longitudinal propagation velocity. Simulation yields to v = 30 m/s in the pole turn and 3 ms are needed to reach 100 mV for an INZ of 3 cm length R dump = 15 mΩ Cold diode U thr =6V, R diff =0.1 µΩ L = 15.9 H Quenching magnet

Susana Izquierdo Bermudez 18 Quench initiation Quench detection Validation and power supply off Quench heater effective Quench heater provoked quench t=0t=3 ms t=13 ms t=18 ms t=31 ms 2.5 MA 2 s MIITs 1.8 MA 2 s 13.1 MA 2 s 4. Quench performance under accelerator conditions (II) TOTAL MIITs = 17.4 MA 2 s

Susana Izquierdo Bermudez 5. Final Remarks The model is a mix of optimistic and pessimistic assumptions PESSIMISTIC There is no cooling in the coil, except through the heaters once the heater temperature is lower than the coil temperature OPTIMISTIC The detection threshold is 0.1 V with 10 ms validation delay Delay between quench detection and heater firing is 5 ms (actual value in LHC RB circuits up to 50 ms) ROXIE thermal network has limitations that we try to overcome via fitting factors More detailed quench heaters model show better agreement with experimental results without any free parameters [Tiina Salmi] Inter-layer quench propagation computed in ROXIE is much slower than experimental results Adaptive mesh tracking is a must for efficient quench simulation [Luca Bottura, MT23] CERN uses mica-glass insulation (lower thermal conductivity than G10) REF: Thermal Conductivity of Mica/glass Insulation for Impregnated Nb3Sn Windings in Accelerator Magnets*. Andries den Ouden and Herman H.J. ten Kate 19

Susana Izquierdo Bermudez 6. Baseline design 20 Only outer layer heaters, not potted with the coil Copper cladded heating stations, 50 mm coverage, 90 mm in between heater stations for the low field region and 130 mm for the high field Heater to coil insulation = 50 µm kapton µm G10 Voltage tap location: x x x x x x x x x x x x x x x Nb3Sn-NbTi xxx xx x x x x x x x x x x x x x x Layer jump x Nb3Sn-NbTi Outer Layer Inner Layer (full monitoring of the mid-plane and pole turns)

Susana Izquierdo Bermudez 7. Conclusions/Future work The low Cu/SC ratio combined with the larger temperature margins make the protection of the 11T dipole a non-trivial problem Efficient heat transfer from quench heaters to coil is a must: Minimize insulation thickness assuring electrical integrity High power density and coverage require high currents and/or big number of heating firing units Efficient configuration in terms of heating stations Inter-layer heaters are an interesting: Lower margin in the inner layer  faster heater provoked quench More uniform heat propagation within the coil Simplify the requirement of having a redundant system Could AC losses trigger a quench? (discharge of capacitance) How would it impact the rest of the RB circuit? Quench-back modeling needs to be improved 21

Susana Izquierdo Bermudez References Quench heater experiments on the lhc main superconducting magnets. F. Rodriguez-Mateos, P. Pugnat,S. Sanfilippo, R. Schmidt, A. Siemko, F. Sonnemann LQ Protection Heater Test at Liquid Nitrogen Temperature. G. Chlachidze, G. Ambrosio, H. Felice1, F. Lewis, F.Nobrega, D. Orris. TD Experimental Results and Analysis from the 11T Nb3Sn DS Dipole. G. Chlachidze, I. Novitski, A.V. Zlobin (Fermilab) B. Auchmann, M. Karppinen (CERN) EDMS T protection studies at CERN. B. Auchmann Challenges in the Thermal Modeling of Quenches with ROXIE. Nikolai Schwerg, Bernhard Auchmann, and Stephan Russenschuck Quench Simulation in an Integrated Design Environment for Superconducting Magnets. Nikolai Schwerg, Bernhard Auchmann, and Stephan Russenschuck Numerical Calculation of Transient Field Effects in Quenching Superconducting Magnets. PhD Thesis. Juljan Nikolai Schwerg Thermal Conductivity of Mica/glass Insulation for Impregnated Nb3Sn Windings in Accelerator Magnets*. Andries den Ouden and Herman H.J. ten Kate Electrodynamics of superconducting cables in accelerator magnets, Arjan Peter Verweij Rossi, L. et al. "MATPRO: a computer library of material property at cryogenic temperature." Tech. Report, INFN,

Susana Izquierdo Bermudez Impact of copper RRR RRR total MITTS Peak temperature (K) Δ MITTS (%) ΔTmax (%) when RRR (for a fixed T max )

Susana Izquierdo Bermudez MB vs. 11T ParameterMB11T Magnet MIITs to reach 400 8T MA 2 s5218 Temperature margin LF48-9 Temperature margin HF Differential Inductance, mH/m Stored energy, kJ/m Quench heater circuit Operational voltage, V Peak Current, A Maximum stored energy, kJ Time constant, ms Quench Heater Pattern400 mm plated 120 mm un-plated mm plated 50 mm un-plated 25

Susana Izquierdo Bermudez Cable Parameters 26

Susana Izquierdo Bermudez Impact of conductor coverage 27 Δ Heater Delay (%) for a constant QH power density CASE 1: adjacent conductors covered by QH 0 CASE 2: only one of the adjacent conductors covered by QH + 18 CASE 2: none of the adjacent conductors covered by QH + 36 Pole turn Simulated turn to turn propagation time: 3 ms in the pole turn, 22 ms in the outer layer mid-plane Increase in QH delay in conductor 53: Case 1: adjacent conductors covered by QH Case 2: only one of the adjacent conductors is covered by QH QH case 1 QH case 2 QH case 3 Case 3: none of the adjacent conductors is covered by QH

Susana Izquierdo Bermudez Protection System LHC Magnets 28 The Protection System for the Superconducting Elements of the Large Hadron Collider at CERN K. Dahlerup-Petersen1, R. Denz1, J.L. Gomez-Costa1, D. Hagedorn1, P. Proudlock1, F. Rodriguez-Mateos1, R. Schmidt1 and F. Sonnemann2

Susana Izquierdo Bermudez STANDARD LHC HEATER POWER SUPPLIES 29 QUENCH HEATER EXPERIMENTS ON THE LHC MAIN SUPERCONDUCTING MAGNETS F. Rodriguez-Mateos, P. Pugnat,S. Sanfilippo, R. Schmidt, A. Siemko, F. Sonnemann

Susana Izquierdo Bermudez Impact of insulation material/thickness 30 kapton thickness G10 thickness OL HF heater delay (ms) ∆ OL HF heater delay (ms) ∆ OL HF heater delay (%) Kapton G10 Thermal conductivity Heat capacity

Susana Izquierdo Bermudez Impact of insulation material/thickness 31

Susana Izquierdo Bermudez ROXIE Thermal Network 32 T bath G ij T,heater2bath G ij T,heater2coil Lumped thermal network model in comparison to the coil/conductor geometry

Susana Izquierdo Bermudez T max vs MIITs 33 Experimental Results and Analysis from the 11T Nb3Sn DS Dipole “To keep the cable temperature during a quench below 400 K, the quench integral has to be less than MIITs“ G. Chlachidze, I. Novitski, A.V. Zlobin (Fermilab) B. Auchmann, M. Karppinen (CERN)