1. N infusion study at DESY
C. Bate1, A. Dangwal Pandey2, A. Prudnikava1, D. Reschke2, J. Schaffran2, G. Semione1, S. Sievers2, N. Walker2, M. Wenskat2
1 University Hamburg
2 Deutsches Elektronen Synchrotron
LCWS Workshop
Strasbourg

2. Nitrogen Infusion – Fermilab’s discovery
DESY will do infusion, not doping
[A Grassellino et al 2017 Supercond. Sci. Technol ]

3. Furnace / N2 venting Full range gauge (regulation) Full range gauge
2 turbo molecular pumps (Varian, 6000 l/s each , max. intake pressure ~ 10-2 mbar)
Tmax ~ 1100°C
V = 1800 x 625 x 660 mm³
EPDM sealed
Roughing pumps:
Rotary vane & roots pump
Full range gauge (regulation)
Full range gauge
(new installation)
Penning gauge (standard)

4. Cavity Preparation
Disassembly, HPR and Nb caps in clean room, put in clean room bag
Installation into furnace with local clean room
Cavity is installed on special support to avoid movement
T-sensor installed on cavity
Add. 2 samples
After Baking: DI Rinsing & HPR & assembly for vertical test
N. Krupka – MKS3

5. Treatment T oven T cavity 800°C TMP stopped Start/stop infusion
125°C/120°C
~ 30°C
Infusion Recipe
Measured
3h, p ≈10-6 mbar
2h, p= 2x 10-5 mbar
48h with
pN2≈10-2 mbar
pN2≈10-4 mbar
← Problems with location of gauge

6. 1DE18 – Results – Q vs E

7. Treatment w/o Nitrogen
Low Nitrogen reason for deterioration?
Pollution from Nitrogen line?
Too high pressure during 800°C
Hence: Baking without N
A lot of effort to increase pressure for each new baking (and RGAs)
Infusion Recipe
Measured
3h, p ≈10-6 mbar
2h, p=1x10-5 mbar,
48h with
48h
pN2≈10-2 mbar
w/o Nitrogen

8. RF Results 1DE18 with Nitrogen, 1DE17 & 1DE16 w/o Nitrogen
Marc Wenskat | N DESY | LCWS 2018

9. RF Results
1DE16: Baseline – after 1st Bake w/o N – after 2nd Bake w/o N
Marc Wenskat | N DESY | LCWS 2018

10. SEM Images - Samples Each cavity was baked with two samples in furnace
Samples underwent BCP, Cavities EP!
Seen on all samples
Regardless of baking cycle!
Marc Wenskat | N DESY | LCWS 2018

11. D5:High resolutionTEM
Precipitates intruding
~ 200 nm deep into Nb bulk
- Look very similar to the β-Nb2N precipitates formed on N-doping, as reported by Trenikhina et. al. SRF2015
Marc Wenskat | N DESY | LCWS 2018

12. EDS of Lamella Pt C O Nb N Obviously NO Nb2N – but carbon (NbxCy ?)
Marc Wenskat | N DESY | LCWS 2018

13. Summary
Improved pressure during 800°C – still cavities deteriorate
SEM / TEM analysis shows carbon pollution – no nitrides!
Next:
1DE9 tested next – immediately in furnace after 1DE16
SEM of sample baked together with 1DE9 showed no precipitates
1DE16 will be tested with Tmap
Cut (use Tmap / 2nd Sound / OBACHT) and analyze samples
Marc Wenskat | N DESY | LCWS 2018

14. Marc Wenskat | N Infusion @ DESY | LCWS 2018

15. 1DE17 Baseline – After baking – After 20 μm EP
Marc Wenskat | N DESY | LCWS 2018