1. Magnetic Field Diagnostics at the DESY Vertical Teststands
TTC Meeting at TRIUMF –
M. Wenskat – on behalf of the SRF Team

2. AMTF Cryostats Diagnostics during European XFEL production
3 TVO sensors outside of cryostat
Below cavity
Between E3/E4
Above cavity
No magnetic field diagnostics
Only insert 1 equipped with T-sensors; mainly used during commissioning

3. Vertical Test Insert – R&D
Equipped with Diagnostics
16 OSTs
3 Cernox sensors
3 Fluxgate sensors
3 RRR Sensors (3 coils each)
A lot of “potential problems” (cables, heaters, screws/nuts, bellows)

4. First DAQ Run
Bsc/Bnc = 1.4
MF1
MF2
MF3

5. 1DE3 Fast Cooldown MF1 MF2 MF3 300K to 4K in 1h Bsc/Bnc = 1.38 ΔT=3K
B [mG]
300K to 4K in 1h
MF1
MF2
MF3
ΔT=3K
B [mG]
Bsc/Bnc = 1.38

6. Long-Term Sensor Run MSEH = 0.2 mG (regardless of T or channel)
B [mG]
MSEH = 0.2 mG (regardless of T or channel)
DAQ has issues with long runs
Rather long time between data points (37s)
MF1 & MF3 drift apart and merge later again

7. Influence of shieldingRT
Start Closing
Closed
Start Opening
Open
B [mG]

8. Influence of shielding2K
Closed
Start Closing
B [mG]

9. MF1 – Tequator Δt=5s 3 1 2 5 4 5 3 2 1 5 4 Time Time B [mG] B [mG]

10. Summary New B-Sensors are functional – upgrade planned
First measurements on cavities are done
Slow cooldown & warm up reasonable (Bsc/Bnc ~ 1.4)
Fast cooldown shows unexpected behavior
Influence of various factors need to be studied
Shielding?
Mechanical movements?
Thermocurrents?
Flux-Relaxation?
Cool down procedure?
He-properties (flow / pressure …)

11. Thanks for Listening
Thanks to the complete DESY SRF team, I gave this talk on their behalf
Only collaboration with many partners allows for complex R&D work

12. 1DE3
Fast Cooldown

13. 2) Large thermal gradients at Tc promote expulsion of flux
Measure temp at top of cavity
Fast cool-down lead to large thermal gradients which promote efficient flux expulsion
Slow cool-down → poor flux expulsion
As middle hits Tc
Helium cooling from below
A. Romanenko et al., Appl. Phys. Lett. 105, (2014)
A. Romanenko et al., J. Appl. Phys. 115, (2014)
Sam Posen
10/15/2019

14. Vertical Test Insert – R&D
Magnetic field measurements
Förster-probe PFD-100 (differential measurement with compensation of the earth magnetic field)
Background: 0.12 µT (or 1.2 mG)
Insert 5
[µT]
Heater element (cryo) 50
Regulation screw - pump valve
4,6
Bellow stiffening (antenna)
0,8
Nuts – plate cavity support
1,3
2nd Sound OST support
2,4
Plug – Pick up
2,6
RRR sensors
outside
1,8
inside w/o. power
0,24
inside w. power
0,3
Insert 2
[µT]
Heater element (cryo) 50
Regulation screw - pump valve 10
Bellow stiffening (antenna) x
Nuts – plate cavity support
1,2
2nd Sound OST support
1,5
Plug – Pick up
3,3

15. 1DE7
Normal cooldown

16. 1DE3 - H – T
Δt=38s
Time
Time
MF1
MF1
MF3

17. 1DE27 - MF2 – Tequator

18. 1DE27 – MF3 – Tequator

19. 1DE27 - MF1 - pHe
Δt=11s

20. 1DE27 - MF1 - pHe
Δt=11s

21. AMTF Cryostats Magnetic field – central axis
|Earth magnetic field| ~ 49 µT

22. 50K Dip ≡ Cryoperm Optimum?
[M. Hollister, SCUBA-2 instrument: an application of large-format
superconducting bolometer arrays for submillimetre astronomy]