Upper limits for QPS thresholds for selected 600 A circuits B. Auchmann, D. Rasmussen, A. Verweij with kind help from J. Feuvrier, E. Garde, C. Gilloux, R. Denz, M. Karppinen, Q. King, Y. Thurel, G. Willering MPE technical meeting, January 24, 2013

Motivation Request: compute limits for QPS thresholds of the following circuit types (incl. current thresholds): Circuit typeU th Δt discr RQTD/F, I < 100 A2 V~190 ms RQTD/F, 100 A < I < 350 A0.1 V~190 ms RQT0.1 V10 ms RQTL0.1 V10 ms RQS0.1 V10 ms RO0.1 V10 ms RSS0.1 V10 ms

1.validation of the quench model propagation coupling losses circuit model 2.magnet protection 3.busbar protection 4.recommendation

Validation quench propagation 1/2 All concerned magnets use the same strand/insulation/impregnation – wire#3. RQTD/F and RQTL circuits are the most critical (assumption later proven by simulation). Bloc 4 data of initial voltage rise up to 2 V available at 400 A and 600 A from magnet training, as well as current decays. T op = 4.2 K, R crowb = 27 mΩ, Uth = 50 mV, Δt discr = 10 ms ROXIE thermal model: transversal discretization: 1 temperature node per turn. ROXIE longitudinal discretization: coarse (6cm) to limit computation time. QP3 used to compare longitudinal propagation velocity for 1 mm (converged) and 6 cm discretization at different current- and field levels.

Validation quench propagation 2/2 Zoom 400 A 600 A 400 A 600 A

Validation quench-back by IFCL Simulation of FPA at different current levels. Tune IFCL effective resistivity ρ eff and time constant τ to match observed quench-back.

Quenching mechanisms RQT, I q = 400 A

Quenching mechanisms RQT, I q = 600 A

Validation R(t) Comparing MQTL data from Bloc 4 to ROXIE simulation

ROXIE circuit model voltage regulated power supply V max = 10 V, Δt period = 80/100 ms crowbar triggered via QPS or if ΔI > 10 A EE switch opened by QPS after validation delay and switch delay External circuit elements; constant L d, no quenches Quenching magnet and its R //, L d (I), quench resistance QPS triggers on U res = R q I mag R // RqRq R //ext R leads R crowb R EE LdLd L d,ext

RQTD/F, ROXIE vs. PSpice Use R(t) from ROXIE in PSpice model to validate new ROXIE circuit model. Differences due to constant external magnet inductance in ROXIE. R // RqRq R //ext R leads R crowb R EE LdLd L d,ext

1.validation of the quench model 2.magnet protection 3.busbar protection 4.recommendation

Worst-case protection scenario Show that magnets are protected by FGC and parallel resistors alone, i.e., T max < 200 K. Magnet protection is virtually independent from QPS thresholds; we model for U th = 1 V, Δt discr = 200 ms. Determine maximal permissible QPS thresholds for protection of busbars. The resulting limits can only improve the protection of the magnets.

RQTD/F, I q = 600 A Circuit: 8 magnets, R // = 0.25 Ω, R EE = 0.7 Ω, R crowb = 0.05 Ω, R lead = Ω FGC: Δt period = 80 ms, V max = 10 V, ΔI max = 10 A. QPS: V th = 1 V, Δt discr = 200 ms

Summary magnet protection CaseT max RQTD/F, Iq = 600 A140 K RQTD/F, Iq = 400 A80 K RQTD/F, Iq = 600 A, R// failure235 K RQTL, Iq = 600 A140 K RQTD/F, Iq = 600 A, R// failure146 K RQTL, Iq = 400 A110 K RSS, Iq = 600 A115 K RO, Iq = 600 A120 K Due to large cu/sc ratio and low position on the loadline (max ~60%), magnets are very robust. FGC and R // provide ultimate protection, virtually independently from QPS thresholds. Failure of R // is VERY unlikely – robust design! would not be fatal. R // is dimensioned to absorb the energy of an entire RQTD/F circuit with T max = 400 K. Also studied: HF/LF quench locations; different quench timing w.r.t. FGC regulation period; neither has significant impact.

1.validation of the quench model 2.magnet protection 3.busbar protection 4.recommendation

Protection of the 600 A busbar Worst case scenario: Quench starts in a thermally insulated part of the bus. Quench propagates not or slowly outside the insulated part (so good cooling to LHe). Global voltage built-up is small even though local hot-spot can be high. Helium 6 cm long plug busbar Parameters used: Cross section bus: 2 mm 2 with Cu/Sc ratio=9 Bus insulation: 0.2 mm kapton Cooling: W/K/m 2 L circuit =0.248 H R circuit = 

Worst case scenario combined with: high QPS threshold: 0.8 and 1 V, long QPS discr time: t discr =190 ms, R circuit =0.23 . Conclusion: 0.8 V, 190 ms is safe up to 600 A, for all busbars with  EE <1.1 s.

1.validation of the quench model 2.magnet protection 3.busbar protection 4.recommendation

Recommendation The busbar protection defines the upper limit for QPS thresholds of all studied circuits: U th ≤ 0.8 V, Δt discr ≤ 190 ms Respecting these limits, set thresholds to the lowest practicable values.

Caveat? RPMBB-type has no DC cont.

Validation MIITs vs. ROXIE ROXIE temp. slightly below MIITs estimate (propagation). Calculated MIITs: kA 2 s, Tmax = 235 K, Bpeak = 4 T

RQTD/F I q = 600 A

RQTD/F I q = 400 A

RQTD/F, I q = 600 A, R // failure M. Karppinen: Failure VERY unlikely – robust design! R // is designed to absorb the energy of an entire RQTD/F circuit with T max = 400 K.

RQTL RQTL9: 2 magnets, R // = 0.2 Ω, R EE = 0.7 Ω, R crowb = 0.05 Ω, R lead = Ω RQTL7-8/10-13: 1 magnets, R // = 0.2 Ω, no EE, R crowb = 0.05 Ω, R lead = Ω FGC: Δt period = 100 ms, V max = 10 V, ΔI max = 10 A. QPS: V th = 1 V, Δt discr = 200 ms In the Δt discr = 200 ms / POWERING_FAILURE scenario, R EE is not instrumental.  We study RQTL9 as a worst case.

RQTL, I q = 600 A

Effect of 10V PC output voltage during 1 period before POWERING_FAILURE, PSpice

RQTL, I q = 400 A

RQTL, I q = 600 A, R // failure

RSS, I q = 600 A Circuit: 4 magnets, R // = 0.15 Ω, R EE = 0.7 Ω, R crowb = 0.05 Ω, R lead = Ω FGC: Δt period = 100 ms, V max = 10 V, ΔI max = 10 A. QPS: V th = 1 V, Δt discr = 200 ms

RO, I q = 600 A Circuit: 13 magnets, no R //, R EE = 0.7 Ω, R crowb = 0.05 Ω, R lead = Ω FGC: Δt period = 100 ms, V max = 10 V, ΔI max = 10 A. QPS: V th = 1 V, Δt discr = 200 ms

IFCL induced quenches during FPA in RQTD/F Preliminary study: to avoid quenches up to 600 A, REE would need to be reduced to 0.1 Ω. Any reduction in R EE reduces the number of quenches and the test voltages. Busbar protection calculation assumed R EE = 0.23 Ω.