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High-Q Performance Martina Martinello International Workshop on Cryomodule Design and Standardization 7 th September 2018 Overview of state-of-the-art surface treatments for SRF cavities Martina Martinello | Workshop on Cryomodule Design and

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Martina Martinello International Workshop on Cryomodule Design and Standardization 7th September 2018

High-Q Performance

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Overview of state-of-the-art surface treatments for SRF cavities

Martina Martinello | Workshop on Cryomodule Design and Standardization - Sep 2018

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State-of-the-art treatments

Martina Martinello | Workshop on Cryomodule Design and Standardization - Sep 2018

High-Q0

(e.g. LCLS-II)

High-Q0 High-Eacc

(e.g. ILC)

High-Eacc

(e.g. ILC)

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High-Q0 treatments

Martina Martinello | Workshop on Cryomodule Design and Standardization - Sep 2018

High-Q0

(e.g. LCLS-II)

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N-doping treatment

800 C (3 hours)

25 mTorr (2 minutes) Example of a N-doping process (2/6 recipe):

  • Nb bulk EP cavity annealed

for 3 hours in vacuum (UHV furnace) at 800C

  • Nitrogen injected (25 mTorr)

at 800C for 2 minutes

  • Cavity stays for another 6

minutes at 800C in vacuum

  • Cooling in vacuum
  • 5 um electro-polishing (EP)

Cavity after welding EP 140 ฮผm 3 h at 800C UHV baking 48 h at 120C baking N2 injection 800C EP 5 ฮผm

Martina Martinello | Workshop on Cryomodule Design and Standardization - Sep 2018

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N-doping treatment (2/6 recipe)

Martina Martinello | Workshop on Cryomodule Design and Standardization - Sep 2018

N Nb N Interstitial

Only Nb from TEM/NED spectra: N must be interstitial

Final RF Surface

  • Y. Trenikhina et Al, Proc. of

SRF 2015

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SLIDE 7

Origin of the anti-Q-slope

Martina Martinello | Workshop on Cryomodule Design and Standardization - Sep 2018

๐‘†๐‘‡ 2 ๐ฟ, ๐ถ๐‘ˆ๐‘ ๐‘๐‘ž = ๐‘†๐ถ๐ท๐‘‡ 2 ๐ฟ + ๐‘†0 + ๐‘†๐บ๐‘š ( ๐ถ๐‘ˆ๐‘ ๐‘๐‘ž, ๐‘š )

2 4 6 8 10 12 14 16 18 4 6 8 10

standard treatment standard treatment nitrogen treatment nitrogen treatment

R

2K BCS (n๏—)

Eacc (MV/m)

5 10 15 20 25 30 35 40 10

9

10

10

10

11

Q0 Eacc (MV/m)

T= 2K

Anti-Q-slope emerges from the BCS surface resistance decreasing with field Anti-Q-slope

  • A. Grassellino et al, Supercond. Sci. Technol. 26 102001 (2013) - Rapid Communications
  • A. Romanenko and A. Grassellino, Appl. Phys. Lett. 102, 252603 (2013)
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High-Q0/High-G treatments

Martina Martinello | Workshop on Cryomodule Design and Standardization - Sep 2018

High-Q0 High-Eacc

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Example of N-infusion processing sequence

Martina Martinello | Workshop on Cryomodule Design and Standardization - Sep 2018

  • Bulk electro-polishing
  • High T furnace (with caps to avoid

furnace contamination):

  • 800C 3 hours HV
  • 120C 48 hours with N2 (25

mTorr)

  • NO chemistry post furnace
  • HPR, VT assembly

Protective caps and foils are BCPโ€™d prior to every furnace cycle and assembled in clean room, prior to transporting cavity to furnace area

  • A. Grassellino et al., arXiv:1305.2182
  • A. Grassellino et al 2017 Supercond. Sci. Technol. 30

094004

160 C 48 h 96 h 25 mTorr 10-5 mTorr

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Comparison N-doped vs N-infusion

Martina Martinello | Workshop on Cryomodule Design and Standardization - Sep 2018

80 100 120 140 160 180 200 10 20 30 40 50 0.001 0.01 0.1 1 10 100 1000

HFQS onset (mT)

EP + 120 C N-infused aes010 aes015 Double exp. fit

HFQS onset for EP

  • xide

layer

Intensity norm to Nb- Depth (nm)

EP + 120 C N-infused NbN- Nb2O5

  • EP

NbN- Nb2O5

  • N-doped N profiles

are up to ~ 50 ๐œˆ๐‘› deep

  • N-infused N profiles

are ~ 20 ๐‘œ๐‘› deep

N-doped N-infusion

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What gives the Q improvement at high field with 120C infused? Improvement stems from both lower residual and lower BCS surface resistance

Martina Martinello | Workshop on Cryomodule Design and Standardization - Sep 2018

Standard 120C baking 120C N-infusion Standard 120C baking 120C N-infusion

  • A. Grassellino et al 2017 Supercond. Sci. Technol. 30 094004
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N-infusion easily affected by furnace contamination

Martina Martinello | Workshop on Cryomodule Design and Standardization - Sep 2018

Example of N-infused cavity contaminated by furnace environment Quite high level

  • f

hydrocarbons may be absorbed by the cavity

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SLIDE 13

Modified 120C baking: 4h at 75C + 48h at 120C

  • A thermocouple went faulty and oven went to standby. Cavity lingered

around 75C for about 2 hours, then resumed the 120C 48 hours -> increase in both Q and gradient observed

  • Several cavities made after that, adding the 75C step for 4 h, confirming

the results -> work in progress to better understand treatment repeatability and physics

Martina Martinello | Workshop on Cryomodule Design and Standardization - Sep 2018

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10 20 30 40 50 109 1010 1011

120 C N-infused aes015 pav007 120 C standard acc003 acc005 120 C modified aes009 1de3

Q0 Eacc (MV/m)

120 C modified baking: new discovery

Martina Martinello | Workshop on Cryomodule Design and Standardization - Sep 2018

~1.3 times higher gradient

UP TO ~ 49 ๐‘๐‘Š/๐‘›

  • A. Grassellino et al., to be published (2018)
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Next surprise: the BCS resistance is ~ as 120C N infused

Martina Martinello | Workshop on Cryomodule Design and Standardization - Sep 2018

4 8 12 16 20 24 28 32 36 40 44 48 2 4 6 8 10 12 14 16

1DE3 - 70C/120C bake 1DE20 - 70C/120C bake TE1AES015 - 120C infused TE1AES015 - regular 120C bake

Residual resistance (nOhm) Eacc (MV/m)

  • A. Grassellino et al, https://arxiv.org/abs/1806.09824
  • BCS surface resistance is lowered compare to standard 120C baking
  • Residual resistance comparable with standard 120C baking
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High-Q preservation: from vertical test to cryomodule

Martina Martinello | Workshop on Cryomodule Design and Standardization - Sep 2018

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Surface resistance contributions

Martina Martinello | Workshop on Cryomodule Design and Standardization - Sep 2018

๐‘†๐‘ก ๐‘ˆ, ๐ถ = ๐‘†๐ถ๐ท๐‘‡ ๐‘ˆ + ๐‘†0 + ๐‘†๐‘”๐‘š ๐ถ

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Surface resistance contributions

Martina Martinello | Workshop on Cryomodule Design and Standardization - Sep 2018

๐‘†๐ถ๐ท๐‘‡ โ‡’ BCS (temperature-dependent part) surface resistance ๐‘†0 โ‡’ intrinsic residual resistance

๐‘†๐‘ก ๐‘ˆ, ๐ถ = ๐‘†๐ถ๐ท๐‘‡ ๐‘ˆ + ๐‘†0 + ๐‘†๐‘”๐‘š ๐ถ

These contributions donโ€™t change from vertical test to cryomodule, they only depends on material properties, surface treatment and temperature

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SLIDE 19

Surface resistance contributions

Martina Martinello | Workshop on Cryomodule Design and Standardization - Sep 2018

๐‘†๐‘ก ๐‘ˆ, ๐ถ = ๐‘†๐ถ๐ท๐‘‡ ๐‘ˆ + ๐‘†0 + ๐‘†๐‘”๐‘š ๐ถ

๐‘†๐‘”๐‘š = ๐œƒ๐‘ข๐‘‡๐ถโ‡’ trapped magnetic

flux surface resistance

  • ๐œƒ๐‘ขโ€”flux trapping efficiency
  • ๐‘‡ โ€”trapped flux sensitivity
  • ๐ถ โ€”external magnetic field

๐ถ

  • H. F. Hess

et al., Phys.

  • Rev. Lett.

62, 214 (1989)

Cooldown

Flux trapping efficiency and the amount of external magnetic field can significant change from vertical test to cryomodule, affecting the surface resistance depending on the trapped flux sensitivity

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Trapped flux surface resistance

Martina Martinello | Workshop on Cryomodule Design and Standardization - Sep 2018

These losses can be reduced by minimizing these contributions:

๐‘บ๐’ˆ๐’Ž = ๐‘ช ๐œฝ๐’– ๐‘ป

๐ถ

  • Magnetic shielding/hygiene

improvement

๐œƒ๐‘ข

  • Fast Cooling
  • Material Optimization

S

  • Optimizing surface treatment

(mean free path)

๐‘†๐‘ก 2 ๐ฟ, ๐ถ = ๐‘†๐ถ๐ท๐‘‡ 2 ๐ฟ + ๐‘†0 + ๐‘†๐‘”๐‘š(๐ถ)

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Trapped flux surface resistance

Martina Martinello | Workshop on Cryomodule Design and Standardization - Sep 2018

These losses can be reduced by minimizing these contributions:

๐ถ

  • Magnetic shielding/hygiene

improvement

๐œƒ๐‘ข

  • Fast Cooling
  • Material Optimization

S

  • Optimizing surface treatment

(mean free path)

External magnetic field

๐‘บ๐’ˆ๐’Ž = ๐‘ช ๐œฝ๐’– ๐‘ป

๐‘†๐‘ก 2 ๐ฟ, ๐ถ = ๐‘†๐ถ๐ท๐‘‡ 2 ๐ฟ + ๐‘†0 + ๐‘†๐‘”๐‘š(๐ถ)

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Minimization of remnant field in LCLS-II pCM

Martina Martinello | Workshop on Cryomodule Design and Standardization - Sep 2018

Demagnetization Empty vacuum vessel Assembled Cryomodule Coils for magnetic field demagnetization Demagnetization

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๐‘บ๐’ˆ๐’Ž = ๐‘ช ๐œฝ๐’– ๐‘ป

Trapped flux surface resistance

Martina Martinello | Workshop on Cryomodule Design and Standardization - Sep 2018

These losses can be reduced by minimizing these contributions:

๐ถ

  • Magnetic shielding/hygiene

improvement

๐œƒ๐‘ข

  • Fast Cooling
  • Material Optimization

S

  • Optimizing surface treatment

(mean free path)

Flux Trapping Efficiency

๐‘†๐‘ก 2 ๐ฟ, ๐ถ = ๐‘†๐ถ๐ท๐‘‡ 2 ๐ฟ + ๐‘†0 + ๐‘†๐‘”๐‘š(๐ถ)

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Fast cooldown helps flux expulsion

  • Fast cool-down lead to large thermal gradients โ†’ efficient flux

expulsion

  • Slow cool-down lead to small thermal gradients โ†’

poor flux expulsion

  • A. Romanenko et al., Appl. Phys. Lett. 105, 234103 (2014)
  • A. Romanenko et al., J. Appl. Phys. 115, 184903 (2014)
  • D. Gonnella et al, J. Appl. Phys. 117, 023908 (2015)
  • M. Martinello et al., J. Appl. Phys. 118, 044505 (2015)
  • S. Posen et al., J. Appl. Phys. 119, 213903 (2016)
  • S. Huang, Phys. Rev. Accel. Beams 19, 082001 (2016)

T1 T2

All flux trapped Efficient flux expulsion

Bsc/Bnc=1.74 after complete Meissner effect Bsc/Bnc=1 after full flux trapping

Bsc/Bnc

Q0

Martina Martinello | Workshop on Cryomodule Design and Standardization - Sep 2018

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High T baking for flux expulsion improvement

5 10 15 20 25 30 35 40 1 1.2 1.4 1.6 1.8 ๏„T During Cooldown [K] BSC/BNC

AES017 2/6 outside BCP AES017+1000C 4h + 2/6 dope AES017 additional test

  • Not all materials show good flux expulsion even with large thermal

gradient

  • High T treatments are capable to improve materials flux expulsion

properties

  • S. Posen et al., J. Appl. Phys. 119, 213903 (2016)

Full trapping Full expulsion Full expulsion

Full trapping Martina Martinello | Workshop on Cryomodule Design and Standardization - Sep 2018

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High T baking for flux expulsion improvement

5 10 15 20 25 30 35 40 1 1.2 1.4 1.6 1.8 ๏„T During Cooldown [K] BSC/BNC

AES017 2/6 outside BCP AES017+1000C 4h + 2/6 dope AES017 additional test

  • S. Posen et al., J. Appl. Phys. 119, 213903 (2016)

After 900C

Full trapping Full expulsion

After 1000C

Full expulsion

Full trapping

  • Not all materials show good flux expulsion even with large thermal

gradient

  • High T treatments are (usually) capable to improve materials flux

expulsion properties

Martina Martinello | Workshop on Cryomodule Design and Standardization - Sep 2018

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๐‘บ๐’ˆ๐’Ž = ๐‘ช ๐œฝ๐’– ๐‘ป

Trapped flux surface resistance

Martina Martinello | Workshop on Cryomodule Design and Standardization - Sep 2018

These losses can be reduced by minimizing these contributions:

๐ถ

  • Magnetic shielding/hygiene

improvement

๐œƒ๐‘ข

  • Fast Cooling
  • Material Optimization

S

  • Optimizing surface treatment

(mean free path)

Trapped Flux Sensitivity

๐‘†๐‘ก 2 ๐ฟ, ๐ถ = ๐‘†๐ถ๐ท๐‘‡ 2 ๐ฟ + ๐‘†0 + ๐‘†๐‘”๐‘š(๐ถ)

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SLIDE 28

10 100 1000 0.0 0.5 1.0 1.5 2.0

๏ฌ (nm)

Doped EP/BCP Sensitivity data @ 5 MV/m Sensitivity data @ 16 MV/m S (n๏—/mG) 120 ๏‚ฐC baked

Light doping to minimize trapped flux sensitivity

๐‘ป = ๐‘บ๐‘ฎ๐’Ž ๐‘ช๐‘ผ๐’”๐’ƒ๐’’ Trapped flux sensitivity:

  • Bell-shaped trend of ๐‘‡ as a

function of mean free path

  • N-doping

cavities present higher sensitivity than standard treated cavities

  • Light doping is needed to

minimize trapped flux sensitivity

  • M. Martinello et al., App. Phys. Lett. 109, 062601 (2016)

Martina Martinello | Workshop on Cryomodule Design and Standardization - Sep 2018

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Status of SRF Technology for PIP-II

Martina Martinello | Workshop on Cryomodule Design and Standardization - Sep 2018

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162.5 MHz Half-Wave Resonators

*HWR technology developed at ANL via ANL/FNAL PIP-II Collaboration.

  • Z. Conway, A. Barcikowski, S. Gerbik, C. Hopper, M.P. Kelly, M. Kedzie, S. Kim,
  • P. Ostroumov, T. Reid.

Bulk and light EP of jacketed HWR @ ANL

Bare HWR before jacketing

Martina Martinello | Workshop on Cryomodule Design and Standardization - Sep 2018

Surface treatments:

  • Light BCP ~ 20 ๐œˆ๐‘›
  • Deep EP ~ 120 ๐œˆ๐‘›
  • Baking at 625 ยฐ๐ท for 10 hours in UHV furnace
  • Light EP ~ 20 ๐œˆ๐‘›
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SLIDE 31

HWR 2 K Test Results

Martina Martinello | Workshop on Cryomodule Design and Standardization - Sep 2018

PIP-II specs

Curtesy of A. Lunin and Z. Conway

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SSR1: 325 MHz Single Spoke Resonators

Martina Martinello | Workshop on Cryomodule Design and Standardization - Sep 2018

Surface treatments:

  • Bulk BCP ~ 120 ๐œˆ๐‘›
  • Baking at 600 ยฐ๐ท for 10 hours in UHV

furnace

  • Light BCP ~ 20 ๐œˆ๐‘›
  • Low T baking at 120 ยฐ๐ท for 48 hours

โ†’ particularly favorable to process MP

  • L. Ristori, M.H. Awida ,P. Berrutti, T.N. Khabiboulline, M. Merio, D.

Passarelli, A. Rowe, D.A. Sergatskov, A.I. Sukhanov, Proc. of IPAC 2013, Shangai, China

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SSR1 VTS Test Result

PIP-II specs

Curtesy of A. Sukanov

Martina Martinello | Workshop on Cryomodule Design and Standardization - Sep 2018

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Fully-Integrated Tests in STC

  • 9 cavities pre-qualified after test at STC with low power

coupler

  • Some degradation observed between VTS test and STC

test that may be due to flux trapping -> some studies are being carried out to better understand trapped flux sensitivity in SSR cavities

  • 5 cavities tested with high power coupler โ†’ cavities

meet spec and are now waiting for string assembly

PIP-II specs

Martina Martinello | Workshop on Cryomodule Design and Standardization - Sep 2018 Courtesy of A. Sukhanov

STC tests with low power coupler STC tests with high power coupler

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SLIDE 35

HB650 Single-cell Test Results

Martina Martinello | Workshop on Cryomodule Design and Standardization - Sep 2018

PIP-II specs

  • 120C baked cavities not always

meet specs

  • N-doping capable to double the

Q-factor at medium field, sometimes affected by early quench

  • World record Q-factor of 7e10

at 2K,17 MV/m and 650 MHz with N-doping

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SLIDE 36

Frequency dependence of RBCS(Eacc)

Martina Martinello | Workshop on Cryomodule Design and Standardization - Sep 2018

  • N-doped cavities at 650

MHz do not show the RT reversal (anti-Q-slope) typically observed at 1.3 GHz

N-doping 120C baking

  • M. Martinello et al. SRF 2017 (TUYAA02), IPAC 2018 (WEPML013)
  • Also for 120C baked cavities, the field

dependence of RT is unfavorable at low frequencies

  • The physical mechanism underneath the

reversal of RBCS (here called RT) has a stronger effect at high frequencies

650 MHz cavities

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SLIDE 37

HB650 Single-cell R&D program

Martina Martinello | Workshop on Cryomodule Design and Standardization - Sep 2018

  • Because of the recent significant improvement in the SRF

technology, now we started an intensive R&D program for 650 MHz cavities

  • GOAL: reach the highest possible Q at medium/high

field for 650 MHz cavities

  • Flux expulsion and trapped flux sensitivity will be also

taken into account for Q preservation in cryomodule

  • Surface treatments under studies: EP, BCP for baseline

and modified 120C (75-120C baking), N-doping, N- infusion for Q improvement

  • Trapped flux sensitivity will be acquired for each treatment

to understand magnetic flux shielding requisition in cryomodule

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SLIDE 38

Martina Martinello | Workshop on Cryomodule Design and Standardization - Sep 2018

Summary RF results of 650 MHz cavities new R&D program

T=2 K T=1.4 K

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SLIDE 39

HB650 5-cells Tests Results (all N-doped + โ€œheavyโ€ EP)

Martina Martinello | Workshop on Cryomodule Design and Standardization - Sep 2018

PIP-II specs

B9A-AES-010 B9A-AES-009 B9A-AES-008

  • Light

N-doping applied to 650 MHz cavities

  • 3 N-doped 5-cells 650 MHz

cavities meet PIP-II specification

  • B9A-AES-010 is now being

dressed with He vessel

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SLIDE 40

Conclusion and Future plan

Martina Martinello | Workshop on Cryomodule Design and Standardization - Sep 2018

  • Thanks to recent advance in the SRF technology, several

treatments are suitable for high-Q at medium/high gradient

  • Since

the field dependence

  • f

Rbcs strictly varies with frequencies, N-doping in 650 MHz cavities is not as effective as in 1.3 GHz cavities

  • The optimal surface treatment for 650 MHz cavities is therefore

under investigation, taking into account the needed for low trapped flux sensitivity at medium field

  • Trapped flux sensitivity and flux expulsion to be studied to set

specification of magnetic field shielding

  • HWR

and SSR cavities meet PIP-II spec with standard BCP/baking treatment -> R&D is planned to further improve Q in SSR2 cavities

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SLIDE 41

Martina Martinello | Workshop on Cryomodule Design and Standardization - Sep 2018

Thank you for your attention!