status of ilc cost reduction r&dvia doping/infusion/modified low t bake –fnal, anl, jlab,...

Anna Grassellino, (on behalf of the collaboration)

LCWS 2018

UTA, Texas

Status of ILC Cost Reduction R&D

SRF activities towards ILC

• ILC Cost Reduction – focuses on cost cut based on cavity

performance improvement (and cavity processing

optimization)

– Fermilab, in collaboration with Cornell University and Jlab;

– Parallel/synergistic activities with KEK (and partially DESY)

• Main research directions:

• Nitrogen Infusion (High gradient doping)

• New breakthrough for high gradients/high Q via “modified

120C bake” – does not involve nitrogen

• Efficient Flux expulsion and ambient field minimization for Q

preservation

• Field emission abatement: HPP, plasma processing

10/25/2018Anna Grassellino - ILC Cost Reduction2

(see Giaccone ppt later)

• From the ILC TDR: “[the cost] is dominated by the SRF components and related

systems, together with the conventional facilities. These two elements account for

73% of the total. The main linac itself corresponds to 67% of the total project.”

• Investing in a carefully selected main linac R&D should be most efficient in

bringing the ILC cost down.

Approach to the ILC cost reduction

Anna Grassellino - ILC Cost Reduction

Main Linac Cost Breakdown from ILC TDR

10/25/201

8

3

• A cost model has been developed based on the ILC TDR and new progress in the

SRF technology on cavity achievable efficiency (Q) and acceleration (Eacc)

• Achievable cavity Q and acceleration are among the main cost drivers

• Improving simultaneously Q and gradient can give substantial cost cut >10% of the

total linac cost

ILC cost reduction – cost model and R&D pathways


26 28 30 32 34 36 38 4075%

80%

85%

90%

95%

100%

105%

110%

115%

120% Q0 = 7e9

Q0 = 8e9

Q0 = 9e9

Q0 = 1e10

Q0 = 2e10

Q0 = 3e10

ILC spec

Cost

(%

of

lin

ac)

Eacc (MV/m)

~ 10%

26 28 30 32 34 36 38 4075%

80%

85%

90%

95%

100%

105%

110%

115%

120% Q0 = 7e9

Q0 = 8e9

Q0 = 9e9

Q0 = 1e10

Q0 = 2e10

Q0 = 3e10

ILC spec

Cost

(%

of

linac

)

Eacc (MV/m)

~ 15%

10/25/201

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4

• Three crucial R&D pathways to achieve higher gradient with higher Q:

1. Achieving lowest possible trapped magnetic field in the cavity walls : potential

~1.5e10 at 31.5 MV/m

2. Nitrogen Doping/Infusion: potential >2e10 at >35 MV/m (up to 4e10, 50 MV/m

with R&D progress)

3. Reduce Field Emission (to maintain performance above and increase yield)

4. (long term): increase gradients beyond 50 MV/m via high frequency, bi-layer

structures, or Nb3Sn

ILC cost reduction –R&D pathways


Nicholas Walker ● DESY ● [email protected]

XFEL cavity results ● ECFA LC 2016 ● Santander - Spain ● 31-05-2016

11RI XFEL: Maximum Gradient Yield (2D)

≥Gmax MV/m

≥Q0

XFEL

RI XFEL cavities accepted for module assembly

(includes those cavities which have been retreated)

26 28 30 32 34 36 38 4075%

80%

85%

90%

95%

100%

105%

110%

115%

120% Q0 = 7e9

Q0 = 8e9

Q0 = 9e9

Q0 = 1e10

Q0 = 2e10

Q0 = 3e10

ILC spec

Cost

(%

of

lin

ac)

Eacc (MV/m)

~ 10%

10/25/201

8

5

1. Demonstrate increase in Q at 31-35 MV/m via flux expulsion {FY18-19}

2. Install high power klystron at FNAL Vertical test Facility to study field

emission reduction via high power pulsing (HPP) {FY18-19}

3. In parallel continue to push single cell R&D for high Q at high gradient

via doping/infusion/modified low T bake – FNAL, ANL, Jlab, Cornell

(KEK) {FY18-19}

4. Apply best High Q/high gradient recipe to nine cells – FNAL, Jlab (KEK)

{FY19-20}

5. Dress best nine cell cavity and demonstrate high Q at 35 MV/m in

cryomodule configuration (horizontal test stand) {FY19-20}

6. Build a cryomodule (CM) with high Q/high G cavities for final

demonstration of CM - ready technology- FNAL, {FY20-21}

ILC cost reduction – SRF R&D plan in US (FNAL, ANL, Jlab, Cornell)

Anna Grassellino - ILC Cost Reduction10/25/201

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6

1. Demonstrate increase in Q at 31-35 MV/m via flux

expulsion {FY18-19}

10/25/201

8

Anna Grassellino - ILC Cost Reduction7

• The SRF field has made very large progress since ILC TDR in

understanding the impact and demonstrating how to minimize trapped

magnetic field in SRF cavities

• Trapped magnetic field can be a source of very large cryogenic losses,

especially at high accelerating fields, which could also lead to degraded

quench fields in cryomodules

• Recent key findings at FNAL:

– Cooling cavities slowly traps all magnetic field , so linac has to be

cooled “fast” –A. Romanenko et al, Journal of Applied Physics 115, 184903 (2014)

– Material properties vary vendor by vendor and that causes more or

less flux trapping, even in fast cooling – but increasing bake T to 900-

950C mitigates this effect (implemented in LCLS2 cavities) - S. Posen et

al, Journal of Applied Physics 119, 213903 (2016)

– Magnetic field in cryomodule can be reduced a factor of 5 via active

cancellation coils + passive shielding – demonstrated 3 mGauss avg

in LCLS-2 cryomodules @FNAL – G. Wu et al, Overview on Magnetic Field

Management and shielding in High Q modules, Proceedings of SRF15

Trapped Magnetic Flux Minimization

Anna Grassellino - ILC Cost Reduction10/25/201

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XFEL statistics


Only about 25% of the E-XFEL production cavities reach 1 ∙ 1010

above 30 𝑀𝑉/𝑚.

N. Walker, ECFA LC (2016)

Trapped flux- induced surface resistance may be one important

cause of the spread in Q values with XFEL production9

0 10 20 30 40 50109

1010

1011

120 C baked (no flux)

E-XFEL typical

Q0

Eacc (MV/m)

E-XFEL QvsE data courtesy of N. Walker

10/25/2018

0 5 10 15 20 25 30 35 400.0

0.4

0.8

1.2

1.6

2.0

Trapped flux sensitivity

S (

n

/mG

)

Eacc (MV/m)


-Trapped flux at high gradients

can lower Q significantly

-Sensitivity is strongly field

dependent:

• 5 MV/m → ~ 0.4 nΩ/mG

• 31.5 MV/m → ~ 1.15 n𝛀/mG

• 35 MV/m → ~ 1.4 n𝛀/mG

-ILC TDR B field spec is

currently10 mGauss; no material

spec exists for high Q

Goals:

• Achieve B field <5 mGauss in

CM

• Develop material spec for

good flux expulsion

• Demonstrate improved nine

cell performance

ILCgradient

Additional recent studies at FNAL (regular 120C bake cavity)

reveal high trapped flux sensitivity at high accelerating fields

• Many lessons already learnt from US R&D and

implemented in LCLS-2 :

• Double shielding and active compensation

• Good flux-expelling material

• Fast cool-down

• Improve CM design to reduce thermal currents

Checchin et al, FNAL

• 4 Nine cells qualified under ILC R&D several years ago, were

unjacketed and re-baselined (at FNAL and Jlab); (four more

to be undressed)

• Next steps: bake at 900C, EP, 120 bake, retest

Progress – nine cells undress/re-baseline

(take an ILC cavity and make it better)

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1E-4

1E-3

1E-2

1E-1

1E+0

1E+1

1E+2

1E+3

1.0E+9

1.0E+10

1.0E+11

0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0

Rad

iati

on

(m

R/h

)

Qo

Eacc (MV/m)

AES-007, 24-Aug-2018 Run 3, 1299.68 MHz

Q0 Radiation

Low Field Decay Measurement: Qo = 3.23E+10 Qfpc = 9.23E+9 Qfp = 1.74E+12

Cavity “unjacketing”@ FNAL – picture courtesy of Chuck Grimm

Re-baseline –courtesy of Charlie Reece

2. Install high power klystron at FNAL Vertical test

Facility to study field emission reduction via high

power pulsing (HPP) {FY18-19}

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• RF station under development at FNAL

• ~3 MW, up to 100s of μs pulses at ~1 Hz

rep rate to vertical test stand

• Quickly raise fields in cavity (tens of μs)

– Push through and reduce field emission

– Outpace many thermal effects, reach

closer to fundamental limit of material

• Benefits to many programs:

– Field emission – study HPP for use in CM

– Nb3Sn, Nb/Cu, new materials – bypass

small defects to study fundamental limits

– N-infusion – investigate possible increase

of superheating field

New VTS Capability at FNAL: High Power Pulsed RF

10/25/201

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S. Posen, N. Valles, and M. Liepe, Phys. Rev. Lett. 115, 047001 (2015)

Klystron Timeline

10/25/201

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Prepare for Operational Readiness

ORC documentation and review Training of VTS personnel Preliminary tests into VTS dewar

RF Station Start Up and Top Plate Fabrication

Set up RF station and commission with dummy load

Fabricate new top plate with waveguide/doorknob

Interlocks design and setup

Installation

Bring RF station components to site

Evaluate damaged/missing items Design waveguide run

Preparation

Install trench in vertical test stand Ship RF Station from DESY Utilities: electrical, water

Oct – Nov

Dec – Feb

Mar – Jan

Feb – May

Posen, Zorzetti, FNAL

New Klystron at FNAL-VTS


Posen, Zorzetti, FNAL

3. Push single cell R&D for high Q at high gradient via

doping/infusion/modified low T bake – FNAL, ANL,

Jlab, Cornell (KEK) {FY18-19}

10/25/201

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Update on infusion and doping

10/25/201

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Potential for very high Q at very high gradients


ILC Cost

Reduction R&D

global effort will

explore doping

parameter space

to extend high Q at

the highest

gradients

High-Q0(e.g. LCLS-II)

High-Q0

High-Eacc(e.g. ILC)

Currently working on this R&D direction: FNAL, KEK, Jlab, Cornell, DESY; high rate of unsuccess in reproducing results; requires VERY high cleanliness furnace

10/25/201818

– 2017 Q degradation observed

– Nov Extensive traditional leak checks performed

– Dec Innovative gas qualification method resulted in observing signs of

air in infusion gas line

– Jan/Feb Further tests on the line revealed valve problematic

• Replaced valve & Initial cavity Q improved & per expectations

– Degradation attributed to excessive O2

Degradation issue @ FNAL resolution

10/25/201

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N2

N O2

Ar

CO2

O

H2With gas

Without gas

N2

N O2

Ar

CO2

O

H2

X

XQ0 Bad Q0 Good

RGA scans – before & after

10/25/201

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N Infusion (and going up to doping)– summary

Temperature Duration of N2

injection (@25

mTorr)

Eacc max,

average

Q @ 21

MV/m -2K

Q@ 35 MV/m -

2K

Limitation Average on #

single cell

cavities

120C 24 hrs 38 MV/m 2.5e10 1.7e10 Q slope @30 1

120C 48 hrs 43 MV/m

(max 45.6)

2.5e10 2.3e10 Quench 6

120C 48 hrs w/o N2 36 MV/m 2.5e10 1e9 Q slope @30 2

120C 60 hrs 43 MV/m

(max 44.5)

3e10 2.5e10 Quench 3

120C 60 hours (BCP) 33 MV/m 2.7e10 ~2e10 @30 Q slope @28 1

120C ** 90 hrs 42 MV/m 2.3e10 2e10 Quench/slope 2 ** (non well

annealed NX)

140C 48 hrs 35 MV/m 2.5e10 2.2e10 Quench 2

160C 48 hrs 36 MV/m 3e10 1e10 Q slope@30 1

160C 48 hrs with N2/48

wo

35 MV/m 4e10 2.5e10 Q slope@25 1


wo

34 MV/m 3e10 8e9 Q slope@25 1


wo

27 MV/m 4e10 -- Quench/Q

slope @25

2

200C 48 hrs 28 MV/m 3.5e10 -- Q slope @15 1

300C 4 hrs with N2/48 wo 28 MV/m 2e10 -- Quench,

MFQS

1

400C 30 mins -- 1e8 -- Nitrides 121 10/25/2018Anna Grassellino - ILC Cost Reduction


Q vs E @120C time exploration

~3e10 @20MV/m~2.5e10 @35MV/m

A. Grassellino et al, tbp

Exploring T, duration and pressure parameter space120C 48-60 hours best for gradients; 60 hours best for Q

Rbcs (Eacc) trend @120C


• Trend in BCS shows gradual decrease as nitrogen is injected for longer time

A. Grassellino et al, tbp

TOF-SIMS – nitrogen depth profiles on cavity

cutouts

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Nb2O5

NbN-~15-20 nm N-rich layer

0 20 40 60 80 100 120 140 160 180

1E-4

0.001

0.01

0.1

1

10

100

1000

Co

unts

no

rmaliz

ed

by N

b-

sig

na

l

Sputter time (sec)

Cutout #1

Cutout #2

Non-infused EP cavity cutout

Romanenko, FNAL

TOF-SIMS – oxygen and carbon (cavity cutouts)

10/25/201

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0 500 1000 1500 2000

0.1

1

10

100

1000

10000

Counts

norm

aliz

ed b

y N

b-

sig

nal

Sputter time (sec)

EP+120C baked cutout

120C infused cutout

EP cutout

O-

C-

Romanenko, FNAL

Cryo-AFM – directly seeing nanohydrides

10/25/201

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300 K 150 K

50 K 10 K

HydridesHydrides

Hydrides

Further study ongoing comparing with regular 120C baking cutouts (phase, size, temperature of formation) – see Z. Sung ppt

Sung, Romanenko, FNAL

TEM on FIB-prepared cutouts

10/25/201

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No nitride inclusions are seenNothing special around grain boundariesConfirms very clean furnace conditions needed for good performance

Romanenko, FNAL

• 2K, 34 MV/m

quench >3e10

Q @ 21MV/m:

• 2/6: 3.9e10

• 2/0: 4.4e10

• From 2/6 to 2/0

quench improved

+6MV/m

High T doping for higher gradients –

2/0 vs 2/6 Doping @ 800C bake

28

10/4/2018 Daniel Bafia, FNAL, LCLS-2 HE R&D, to be presented @ CERN upcoming TTC

10/25/201

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New breakthrough – 210 mT, 49 MV/m Tesla shape

aka “the magic 50-75C bake”


1DE3 – the first 49 MV/m cavity

• Cavity (fine grain) from DESY colleagues was prepared at FNAL for baseline test

before infusion, EP 60 microns + regular 120C bake (no nitrogen, low T oven)

• Results were pretty surprising/puzzling


A. Grassellino et al, https://arxiv.org/abs/1806.09824

Anomaly found during the low T bake

• A thermocouple went faulty and oven went to standby

• Cavity lingered around 50-75C for few hours, then resumed

the 120C 48 hours


Repeated on second cavity TE1AES009 (fine grain, AES, WC)


0 5 10 15 20 25 30 35 40 45 50 55109

1010

1011

ACC003: EP+120C - regular 1DE3: Modified 120C bake

1DE3: Re-calibrate/check

AES009: Modified 120C bake

AES009: cooldown #2 AES009: cooldown #3

Q0

Eacc (MV/m)

EP+ 75C 4 hrs+ 120C 48 hours

Regular 120C

A. Grassellino et al, https://arxiv.org/abs/1806.09824

Confirmation of performance @ Cornell

• TE1AES009 sent to Cornell for measurements in their dewar

• Now 49 MV/m (tesla shape) measured also at Cornell


M. Liepe, Maniscalco, Koufalis, Cornell

ILC Cost Reduction Studies at Cornell

Significant increase in quench field after 75C, 6 h vacuum bakes (reduction in Q0 is due to FE and trapped flux after quenching)!

1.3 GHz single-cell niobium cavities Liepe et al

Since then, repeated on several cavities


Modified low T bake cavities

Grassellino, Bafia et al

• More than a dozen different cavities tested; multiple tests for several cavities

– Consistently achieve excellent cavity performance

• Material : WC, TD, NX, Hareaus; cavities from AES, RI, DESY, KEK

Quench field histogram

36

KEK cavities (TD material): optical inspection indicates some potential surface flaws?

FNAL, DESY: TD, NX, WC, H

“Bunching up” of quench field observed: (44MV/m vs 49MV/m)

0

1

2

3

4

22 24 26 28 30 32 34 36 38 40 42 44 46 48 50

Num

ber

of

Cavitie

s

Quench Field (MV/m)

10/4/2018 Daniel Bafia

Some strange performance “branching” noticed as a function of

different cooldowns (cavity always under vacuum)



Observed branching behavior in cavities retested

without disassembly in between

38

Branching behavior in performance Possible Causes

for Branching

Likely Candidate?

Dewar NO – observed in 2

separate dewars

Top Plate NO

Cables NO

Calibration NO - Qext 2 does not

explain branching in

Q and G

Flux trapping NO - Cooled in zero

compensated field

Branching not linked to

experimental setup – What about

cavity cool down?


Performance branching: role of 320-340K?


After being warmed in the dewar to 320-340K, performance improved from good to

extraordinary (and remained stable for all subsequent cooldowns)


• Differences in performance come from intrinsic mechanisms

– Cooling from 320K, BCS resemble that of a nitrogen infused cavity

– Residual resistance has the separation observed in the Q vs E curves

Rs decomposition of AES022 Tests

40


10/25/201

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2.6 GHz with 75/120C – quench ~ 47 MV/m


So, what is happening?

• 70C seems to be another magic temperature in niobium

• 1960-70s literature studies suggest that 70C is associated

with changes in vacancies, while 120C changes in

dislocations (Bordoni or Hasiguti type process)


So, what is happening?

• All these finding may be suggesting that quench in Nb is

currently of extrinsic nature, possibly nano-hydrides, and that

changes via vacancies or dislocations or impurities (N) are

helping suppressing their formation, or changing their phase

and size (see Z. Sung studies, TTC Milan and later today)


At 4 K

800°C + BCP on hot spot cut-out 120°C baked cavity cut-out

Positron Annihilation Studies on Nb sample – changes

occur already at ~ 60C


A. Romanenko Ph.D. Thesis,Cornell University (2009)

• Sensitivity to magnetic

flux is improved

– AES022

• Could be consistent

with stronger

pinning (more

vacancies

introduced by 75C)

Trapped magnetic field sensitivity of 75/120 vs

120C

45


• ILC Cost Reduction activities proceeding at full speed

• US partners work in alignment with international

collaborators, periodic meetings: FNAL, Jlab, Cornell, KEK,

DESY

• New exciting developments pave the way for cavity

performance improvement for ILC

Summary

10/25/201

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• Thanks to the amazing SRF R&D team at Fermilab

• Thanks to M. Liepe and his SRF group at Cornell for

incredibly fast turnaround on cavity test

• Thanks to Jlab SRF R&D group

• Thanks to Kensei Umemori at KEK for many discussions on

test/results

• Thanks to DESY colleagues for cavity exchange and

discussions

Acknowledgements

10/25/201

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Backup slides

10/25/201

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Cryomodule demonstration of B< 3 mGauss


Fields up to 46 mG discovered after major assembly & installation work

• Cryo-piping welds, warm coupler install, etc.

• Most likely due to re-magnetization of the vacuum vessel & magnetic shields

Cryomodule successfully demagnetized using in-place coils

G. Wu, S. Chandrasekharan, FNAL

• Several 1-cell cavities were made with LCLS-II material

• We put a T-map on the 1-cell cavity that showed the worst

expulsion (RDT-NX-02) and measured after different

cooldowns – made with “stubborn” material

Towards Developing High Q Material Specs (S. Posen)

10/25/201

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800/140 in

Low Bamb

900/200 in

5-10 mG

LCLS-II Cavity Performance in VTFNAL & JLab data assembled by D. Gonnella, SLAC

Experimental Setup

10/25/201

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51

CurvedTokyoDenkai 10974CurvedNingxia11301

Strongtrapping??

Weaktrapping??

SignificantgraingrowthinTokyoDenkaiandSOMEareasofNingxia


S. Posen, TTC 2018


Accumulated elemental images (negative polarity)Ningxia 11301TD 10974

2.6 GHz could be used for ILC – cost savings?


120C baked cavities

53

Q-factor of 2.6 GHz cavity converge to the

one at 1.3 GHz at high gradients

T=2 K

10/25/2018

status of ilc cost reduction r&dvia doping/infusion/modified low t bake –fnal, anl, jlab,...

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