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

2. 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

3. MQXFS1 training history
K is A
K is 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

4. 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)

5. 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)

6. MQXFS1 quench integral
Typical high current training quenches had ~25 MIITs with the highest at MIITs
(dump resistor, heaters in protection).
The highest quench integral was seen at a high current ( 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

7. 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

8. 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: 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.

9. 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)

10. 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

11. 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

12. 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)

13. 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

14. Backup Slides

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

17. 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)