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
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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
Anna Grassellino - ILC Cost Reduction
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%
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• 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
Anna Grassellino - ILC Cost Reduction
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%
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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}
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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
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XFEL statistics
Anna Grassellino - ILC Cost Reduction
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)
10/25/2018Anna Grassellino - ILC Cost Reduction10
-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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Anna Grassellino - ILC Cost Reduction11
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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Anna Grassellino - ILC Cost Reduction12
• 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
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Anna Grassellino - ILC Cost Reduction13
S. Posen, N. Valles, and M. Liepe, Phys. Rev. Lett. 115, 047001 (2015)
Klystron Timeline
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Anna Grassellino - ILC Cost Reduction14
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
10/25/2018Anna Grassellino - ILC Cost Reduction15
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}
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Anna Grassellino - ILC Cost Reduction16
Update on infusion and doping
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Anna Grassellino - ILC Cost Reduction17
Potential for very high Q at very high gradients
Anna Grassellino - ILC Cost Reduction
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
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Anna Grassellino - ILC Cost Reduction19
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
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Anna Grassellino - ILC Cost Reduction20
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
160C 48 hrs with N2/96
wo
34 MV/m 3e10 8e9 Q slope@25 1
170C 48 hrs with N2/48
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
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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
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• 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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Anna Grassellino - ILC Cost Reduction24
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)
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Anna Grassellino - ILC Cost Reduction25
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
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Anna Grassellino - ILC Cost Reduction26
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
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Anna Grassellino - ILC Cost Reduction27
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
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Anna Grassellino - ILC Cost Reduction
New breakthrough – 210 mT, 49 MV/m Tesla shape
aka “the magic 50-75C bake”
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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
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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
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Repeated on second cavity TE1AES009 (fine grain, AES, WC)
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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
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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
10/25/2018Anna Grassellino - ILC Cost Reduction35
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)
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Grassellino, Bafia et al
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?
10/4/2018 Daniel Bafia
Performance branching: role of 320-340K?
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After being warmed in the dewar to 320-340K, performance improved from good to
extraordinary (and remained stable for all subsequent cooldowns)
Grassellino, Bafia et al
• 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
Anna Grassellino - ILC Cost Reduction
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2.6 GHz with 75/120C – quench ~ 47 MV/m
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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)
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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)
10/25/2018Anna Grassellino - ILC Cost Reduction43
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
10/25/2018Anna Grassellino - ILC Cost Reduction44
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
10/4/2018 Daniel Bafia
• 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
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Anna Grassellino - ILC Cost Reduction46
• 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
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Anna Grassellino - ILC Cost Reduction47
Backup slides
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Anna Grassellino - ILC Cost Reduction48
Cryomodule demonstration of B< 3 mGauss
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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)
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Anna Grassellino - ILC Cost Reduction50
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
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CurvedTokyoDenkai 10974CurvedNingxia11301
Strongtrapping??
Weaktrapping??
SignificantgraingrowthinTokyoDenkaiandSOMEareasofNingxia
Anna Grassellino - ILC Cost Reduction
S. Posen, TTC 2018
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Accumulated elemental images (negative polarity)Ningxia 11301TD 10974
2.6 GHz could be used for ILC – cost savings?
Anna Grassellino - ILC Cost Reduction
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