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 24.10.2018 Strasbourg

Nitrogen Infusion – Fermilab’s discovery DESY will do infusion, not doping [A Grassellino et al 2017 Supercond. Sci. Technol. 30 094004]

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)

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

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

1DE18 – Results – Q vs E

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 800°C @ 3h, p ≈10-6 mbar 800°C @ 2h, p=1x10-5 mbar, 120°C @ 48h with 120°C @ 48h pN2≈10-2 mbar w/o Nitrogen

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

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

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 Infusion @ DESY | LCWS 2018

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 Infusion @ DESY | LCWS 2018

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

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 Infusion @ DESY | LCWS 2018

Marc Wenskat | N Infusion @ DESY | LCWS 2018

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