MBRDS1 cold test results - first cooldown

1. MBRDS1 cold test results - first cooldown Franco Mangiarotti, Raphael Bouvier, Vincent Desbiolles, MichałDuda, Jerome Feuvrier, Jean-Luc Guyon, Daniel Turi,Gerard Willering WP3 meeting -- 2019 Feb 20 EDMS: 2082690

2. Test setup • MBRDS1 in Cluster D • 30 kA PC (ultimate 13.4 kA), 40 mOhm dump • Quench heaters: only 2 good, not used for protection • Voltage taps: each block

3. V2 A3-A4 Quench history V2 A2-A3 A B B A V2 V1 All quenches but one in the same location: V2 A2-A3. A training effect is seen, but this location limiting the training prompted us to do further investigation

4. Quench precursor comparison Quench in V2 A3-A4 Quenches in V2 A2-A3 Positive precursor: probably mechanical origin Negative precursors: possibly due to current redistribution Quench 3 is the only “typical” training quench, the other quenches are due to the problem in A2-A3 (probably conductor damage).

5. Example quench signals After the quench, the quenching segment V2 A2-A3 jumps up, while the voltage of the other coil segments jump down. In all non-quenching segments of coil V2A the voltage after the quench starts is lower than before, suggesting current redistribution Quench 8 A B B A V2 V1

6. Ramp rate studies V2 A2-A3 A B B A V2 V1 Atypical dependency: faster ramp rate increases the quench current The quench during the VI measurement (very slow effective ramp rate) has lower quench current Verification after the ramp rate studies does not show significant improvement

7. Holding current quench Ramped to 10.6 kA at fast ramp rate (200 A/s). After 95 s at this current, the magnet quenched. During the flat top, the voltage in the quenching segment V2 A2-A3 decayed ~11 uV, probably due to current redistribution The voltage in adjacent segment V2 A3-A4 increases slightly (~2 uV), and in the adjacent splice does not change. 10.6 kA 95 s to quench Ramp: 200 A/s

8. VI measurements The VI measurement was done with 2 minutes plateaus at several currents. Up to 9 kA, during the current plateaus the voltage in V2 A2-A3 decreases slightly (~1 uV). At higher currents the ramp is too short and its effect cannot be seen. The voltage in adjacent segment V2 A3-A4 is reduced, suggesting long range current redistribution The adjacent splice is not affected by these phenomena, and its resistance value is consistent with expectations (0.2 nΩ) Ramps: 10 A/s, plateaus: 2 min

9. Quenching segment information Coil V2 A is the first coil manufactured (“practice” coil). It had a turn-to-turn short around the coil exit and it was repaired. Segment A2-A3 includes both turns of the pole block and the winding exit, up to near the splice to coil V2 B. V2 A2 V2 A3 V2 A4 From the measurements, we cannot identify an exact location between the voltage taps. However, the test information is consistent with quenches in the repaired location

10. Other measurements RRR per coil: V1B: 199 V1A: 194 V2A: 196 V2B: 191 Magnet inductance (expected 4.8 mH @ 12.3 kA): Splice resistance: V1B-V1A: 1 nOhm V1A-V2A: 0.6 nOhm V2A-V2B: 0.2 nOhm

11. Conclusions • Test summary: • Three coils (V1A, V1B, V2B) reached 11.1 kA without quench • The magnet quenches in only one location: coil V2 A, A2-A3 (with a single quench elsewhere) • These quenches have a negative precursor • The ramp rate dependency of the quench current is inverse (higher current at higher ramp rate) • At a current plateau at 10.6 kA, the magnet quenches after 95s • The voltage in the quenching location drifts at current plateaus, from 2 kA to 10.6 kA • All this information points to cable damage in coil V2A, for example several strands broken

12. Next steps • The magnet will be tested again as a single aperture • Aperture V2 has been bypassed • Cooldown process started on Monday afternoon, training to resume soon (not the final setup)