Magnetic Field Diagnostics at the DESY Vertical Teststands TTC Meeting at TRIUMF – 05.02.2019 M. Wenskat – on behalf of the SRF Team

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

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)

First DAQ Run Bsc/Bnc = 1.4 MF1 MF2 MF3

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

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

Influence of shielding RT Start Closing Closed Start Opening Open B [mG]

Influence of shielding 2K Closed Start Closing B [mG]

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

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 …)

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

1DE3 Fast Cooldown

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, 234103 (2014) A. Romanenko et al., J. Appl. Phys. 115, 184903 (2014) Sam Posen 10/15/2019

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

1DE7 Normal cooldown

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

1DE27 - MF2 – Tequator

1DE27 – MF3 – Tequator

1DE27 - MF1 - pHe Δt=11s

1DE27 - MF1 - pHe Δt=11s

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

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