WG-1 Summary · Arely Cano - New insights on the SRF Nb cavities performance from spectroscopic...

WG-1 SummaryKensei Umemori, Ari Palczewski, Marc Wenskat

TTCWorkshop@CERN2020

Teaser:

Highly subjective summary – put together in short amount of time – sorry if I missed

something you found important – all mistakes or unclear slides are my fault

• We have a set of approved methodes to make a cavity work

• We accepted hypotheses on why they work and moved on to

production

• We start to look at those methodes again – in the light of new

discoveries/recipes but also we simply want to understand

• Material/surface physics + state-of-the-art techniques become

more and more important

Some Facts

• 4 Sessions (3 on Tuesday, 1 on Wednesday)

o R&D involving Cavities (1Session)

o R&D involving Samples (2Session)

o R&D regarding flux trapping (1Session)

o Of course some overlap

• 19 Speaker

o 15m/4w

o America:10 Asia:3 Europe: 6

• 1 Sample Survey

o Was sent to labs prior the workshop

o Try to compare intention/material/preparation/handling/analysis

Kensei Umemori - New results of KEK infusion and mid-T bake

Sam Posen - The In-Situ Mid-T Bake

Infusion-like N profile

Lea Steder - Recent SRF cavity treatment R&D @ DESY

Chao Dong - High Q&G activity at IHEP• Many activities

o Vacuum furnaces for doping and Nb3Sn

o New Tuning Machine

o Optical inspection cameras

o CBP

o TX-Mapping & 2nd Sound

Only BCP!

David Longuevergne - Status of infusion studies at IJCLab/IRFU

• New Furnace purchased

• Commissioning studies showed a nice,

clean furnace

• First cavities outgassed looked good

• First 150°C infusion run failed

• Cleanliness of N is investigated

Pashupati Dhakal - Status of Infusion Studies at Jlab

• Restart R&D after furnace upgrade

• Systematic study on

o Actual cavity T

o Injection T

o Frequency dependence

• fvsT data used to track changes in

ζ/ℓ

Daniel Bafia – Progress in N-Doping at FNAL – New Higher Gradient Insights

• Investigated T-map for different quench patterns or N-doped cavities.

• Higher quench fields quenched closer to the equator with a mechanism that is likely of magnetic origin

• Lowest quench field (18MV/m) quenched near the iris and is likely due to the heating of a nitride

M. Checchin - LCLS-II investigation of failed LCLS-II HE prototype cavities EP analysis

o Final EP temperature is the principal parameter controlling the maximum accelerating gradient in N-doped cavities

o The colder the EP the higher the maximum gradient achievable

o Cold EP (< 16 C) is most likely allowing for an etch-free EP process and a smoother surface

Phillipp Kolb - Test Results from the TRIUMF Multi-Mode Coaxial Resonators

𝑅𝑆 (𝐵, 𝑇) =𝐴 𝐵𝑝, 𝜔

𝑇exp −

𝐶 𝐵𝑝, 𝜔

𝑇+ 𝑅𝑇𝑖(𝐵𝑝, 𝜔)

R vs B data

collected from

QWR and HWR

for wide range of

frequency from

200 ~ 1200 MHz

Attempted

N-infusion

for QWR

Flux expulsion for QWR

Alexander Romanenko - Oxygen role in the high field Q-slope / mild baking –revealed by TOF-SIMS + cavity surface engineering studies

Oxygen diffusion at 120C Oxygen diffusion at

205C

200C, 1h works just as well

as 120C, 48h for HFQS

elimination

BCS & residuals for 120 –

200 C BCS & residuals for 400 –

500 C

Effect of oxygen diffusion during baking process was investigated.

Baking

temperature and

duration time

change cavity

performance,

R_BCS, Rres,

quench field etc.

Small sample survey – Tuesday afternoon

• Thank you very much for your cooperation.

• Still welcome survey data from missing Labs.

Embedded survey data in

the file link below. Click to

open in Excel

Palczewski/Umemori/Wenskat WG1 Review 15

Anton Ivanov - Flux Expulsion Measurement with Flux Lens


• Some deformation structures could

persist even after 900°C, 950°C...

Strength of the structure and

mechanical stability needs to be

considered while increasing heat

treatment temperature.

• Upstream processing activities need

attention for future high-Q high-G

cavities.

• We are working on establishing vendor

relationships to create variations in Nb

sheet material.

Shreyas Balachandran - Microstructure correlations and flux-trapping in SRF

Nb- Role of initial microstructures


• Possible pinning change from nitrogen doping, but questions about heat treatments

• Strong pinning tested in Nbti cavities, could be used in high magnetic field environments

Hai-Hu Wen - Vortex penetration and dynamics of Nb, N-doped Nb and NbTi

plates


• We see a trend at 900C that correlated grain size and measured flux expulsion

• Still need to verify if this is a “Possible method for sorting material at Nb vendor”

Paulina Kulyavtsev - Flux expulsion on small samples for LCLS-II HE

Márton Major - Material studies on High-T Doping


Original 1983 in

Wuppertal by G. Müller

• Using XDR to evaluate the growth of d-NbN vs growth parameters

• Similar to Nitrogen doping, but at much higher temperatures, cavity soon

Arely Cano - New insights on the SRF Nb cavities performance from

spectroscopic data


• Hydride suppression see through

Raman spectroscopy • Possible shift Nb 3d spectral seen

though XPS depth profiling

• Rough surface of cavity cutouts post EP

Dirk Lützenkirchen-Hecht - In-situ EXAFS investigation of N2 - treatment of Nb


• N2 -uptake in Nb on interstitial octahedral sites, increasing with time and pressure

• In- and ex-situ measurements agree with each other

• precision measurements foster trends (slightly increased average Nb-Nb-distance &

disorder)

Jonathan W. Angle - Challenges of SIMS Calibration for N-Doped Niobium


• Even with RSF difference, good reproducibility can be achieved with a quality surface

and a good tune.

• Implant standard becoming more simple - to systematically evaluate the different

parameters

• Path to fully calibrated SIMS measurements is becoming clear

Marc Wenskat - Sample Studies on Nitrogen- and Heat-Treatments of Niobium


• Broad spectrum of sample R&D results shown Nb2C contamination, near-surface vacancy-

clusters and flux trapping in quench spot. A NbN phase forming during 120°C.

• All results tend to say: Do not bring H into Nb (e.g. cold EP) but if it is there, try to

distribute it controlled (v+nH) or trap it (O, N) to prevent formation of Nb-hydrides.

WG-1 Summary · Arely Cano - New insights on the SRF Nb cavities performance from spectroscopic...

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