Long term behavior of MQXFS1 Stoyan Stoynev /FNAL/ Technical meeting on Nb3Sn long-term behavior and high MIITs tests 15 May 2019

MQXFS1 at FNAL MQXFS1 - the first 150 mm aperture, 1.5 m long Nb3Sn quadrupole within the CERN and LARP collaboration Coils fabricated by CERN (#103 and #104) and LARP (#3 and #5) Five tests performed since 2016 MQXFS1a: Training, mag. measurements, PH tests, energy extraction tests MQXFS1b: (increased azimuthal pre-stress) Training, mag. measurements, CLIQ and heater tests MQXFS1c: (increased axial pre-stress) Training, mag. measurements, CLIQ and heater tests MQXFS1d: (welded SS shell test ) Training, mag. measurements MQXFS1e: (Through busbar test) Magnet training, mag. measurements, busbar spot heater tests 2016 2016 2017 2018 2018 MQXFS1d test preparations Further extensive hipot tests with thermal cycles were conducted but the magnet was never powered

MQXFS1 training history SSL@1.9 K is 21 500 A SSL@4.3 K is 19 550 A 2016 2018 2018 2016 2017 20 kA TC TC 130 K TC WU 30 K 14 kA 20 40 60 80 100 Busbar test Stainless steel welded Each color represents (naturally) also a thermal cycle Increased axial pre-stress Increased azimuthal pre-stress

MQXFS1 quench/trip history 119 spontaneous quenches 230 provoked quenches and trips (above or equal to 1 kA) 48 unintended trips (above or equal to 1 kA) Total of 6 full thermal cycles, one partial (130 K) and a warm up to 30 K (not counting the ones for the hi-potting tests where the magnet was not powered) Training history (20 A/s ramps) Note also the remarkably stable performance at 4.5 K (after /re/training; the level is ~95% SSL) TC WU 30 K TC 130 K TC (each test by itself)

MQXFS1 quenches at 4.5 K It is likely that this difference came from increased axial pre-stress (all quenches here are in coil 5; technically this /location/ should also bring the normalized current 1% down, not applied) } Still during initial training (did not yet reach a plateau) Note also the remarkably stable performance at 4.5 K (after /re/training; the level is ~95% SSL)

MQXFS1 quench integral Typical high current training quenches had ~25 MIITs with the highest at 26.68 MIITs (dump resistor, heaters in protection). The highest quench integral was seen at a high current (13 180 A) manual trip with only heaters in protection (no dump), 29.5 MIITs, and this is from the start of manual tripping (not the actual quenching). Heater initiated quenches had lower MIITs. The magnet did not see more than 300 K hot spot temperature

MQXFS1a All quenches/trips shown Last training quench Those are all trips TC Training quenches (20 A/s ramps) TC Check-outs Protection studies (<23 MIITs), some trips Ramp Rates

MQXFS1b All quenches/trips shown Last training quench Training quenches (in mid-protection-tests) Highest MIITs seen overall (29.5 MIITs) (and highest current overall: 19 010 A) Training quenches (20 A/s ramps) Check-outs First CLIQ test Ramp Rates (and a trip) Protection studies (<30 MIITs), some trips There is no clear correlation observed between (relatively) high MIITs and performance.

MQXFS1c All quenches/trips shown Last training quench Training quenches (20 A/s ramps) TC 130 K TC 130 K Check-outs Partial memory loss induced by the higher pre-stress (procedure). Ramp Rates (and a trip) Protection studies (<28 MIITs), some trips From test “c” on, the magnet loses training memory after each thermal cycle and re-trains. Both happen in reproducible manner (see also slide 4)

MQXFS1d All quenches/trips shown Last training quench Training quenches (20 A/s ramps) TC TC Check-outs Check-outs Partial memory loss induced by the higher pre-stress (procedure) in test “c”. Already seen re-training pattern. Ramp Rate Trip

MQXFS1e All quenches/trips shown Last training quench Training quenches (20 A/s ramps) 1.9 K WU 30 K WU 30 K Check-outs Partial memory loss induced by the higher pre-stress (procedure) in test “c”. Already seen re-training pattern. Spot heater tests (on a bus), some trips

MQXFS1 coil training Consecutive quenches in a coil Consecutive quenches in the magnet “Mirror” magnet test in light blue Thermal cycles don’t necessarily affect coil training or training memory. Only tests “a” and “b” shown, as in Legends. “m” and coil 2 refer to the “mirror” magnet test (single coil testing in a structure)

Summary MQXFS1 hot spot temperatures were always below 300 K Thermal cycles don’t indicate change in magnet performance Observed reproducible loss of memory (and reproducible re-training) is rather linked to increased axial pre-stress in test “c” and a weak mechanical spot in one of the coils (coil 3) Both coil 3 and 5 are responsible for erratic behavior at higher current (up to Ultimate current) – both have a weak spot at similar locations Despite this feature(s), multiple thermal cycles and protection tests, the magnet performs consistently at 4.5 K with quenches at ~95% SSL

Backup Slides

From G. Vallone et al., IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, VOL. 28, NO. 3, APRIL 2018, 4003106

Heaters and CLIQ firing Heaters were fired in all ~400 quenches and trips Only in some of them (~35) heaters were delayed 1 s, in most of the rest there was no delay Due to limited number of HFUs (power) not all heater strips were included in the magnet protection In later tests IL heaters were not used at all Peak power density in OL heaters varied reaching up to 200 W/cm2 CLIQ was only used in testing mode (not for protection in natural quenches)