Yulia Trenikhina SRF-15
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Transcript of Yulia Trenikhina SRF-15
Yulia TrenikhinaSRF 2015Whistler, Canada09/16/2015
Nanostructure of the penetration depth in Nb cavities: debunking the myths and new findings
Yulia Trenikhina SRF’15 Whistler, Canada2
50 100 150 200 250 300 350
2
4
6
8
10
12
14
16EP + 120C baking, Bpeak = 119 mT
Angle (deg)
Sens
or n
umbe
r
1016254063100159252400
∆T (mK)
3X0-10
50 100 150 200 250 300 350
2
4
6
8
10
12
14
16Electropolished, Bpeak = 119 mT
Angle (deg)
Sens
or n
umbe
r
1016254063100159252400
∆T (mK)
310-10
50 100 150
1
10
100
Nb 310-10 Nb 3X0-10
∆T (m
K)
B (mT)
50 100 150109
1010
1011
FG FGB
Q0
Bpeak (mT)
(a)
(b)
(c)
(d)
HFQS elimination in FG EP cavities after 120°C bake
HFQS-producing treatments
High Field Q-slope
HFQS recipes:EPEP+800C bake+BCPEP+800C bake
EPEP+120C
Yulia Trenikhina SRF’15 Whistler, Canada
Cavity diagnostics: EP vs. EP+120C baked
3
We used three different elliptical cavities made of highpurity niobium for our studies: two fine grain (!50 lm)cavities of TESLA shape24 with the fundamental TM010
mode at the resonant frequency f0 ¼ 1:3GHz, and one largegrain (!10 cm) cavity of Mark-III shape with f0 ¼ 1:5GHz.Fine grain cavities were electropolished for #120 lm mate-rial removal, and one of the cavities was additionally bakedunder vacuum at 120 $C for 48 h. The large grain cavitywas chemically polished (BCP) instead of electropolishing.Before rf measurements all cavities were high pressurewater rinsed, which is a standard treatment to avoidfield emission caused by microparticles. Using standardphase-lock techniques,25 the intrinsic quality factor
Q0 / 1= !Rs!Rs ¼
xl0ÐVH2dVÐ
ARsðHÞH2dA
" #was measured for each of
the cavities at 2 K as a function of the peak surface mag-netic field Bpeak. Fig. 1(a) shows corresponding excitationcurves Q0ðBpeakÞ for both fine grain cavities. The Q0ðBpeakÞ
curve for the large grain cavity was similar to the unbakedfine grain cavity.
A custom-built temperature mapping system similar to
that described in Ref. 26 was attached to the outside of the
cavity walls during the measurements. Spatial maps of the
temperature difference DT ¼ Ton ' Toff with and without rf
power in the cavity were obtained at different rf field levels.
Such DT is proportional to the local power dissipation
Pc / RsðHÞH2, where RsðHÞ is the local surface resistance
and H is the local magnetic field. In Fig. 1(f), the magnitude
of the local magnetic field at each sensor location and char-
acteristic temperature maps are shown for baked and
unbaked fine grain cavities at the same Bpeak ¼ 119mT.
Individual DTðBÞ for samples 1-EP and 3-EP-MB circled on
the maps are shown in Fig. 1(b). Samples 2-EP and 6-BCP
had DTðBÞ curves of the shape similar to 1-EP, and that for4-BCP would be expected to be the same. All mild baked
TABLE I. List of cutout samples investigated with VEPAS (EP, electropolishing; BCP, buffered chemical polishing; MB ¼ mild baking ' vacuum bake at120 $C for 48 h).
Grain size Cavity/sample treatment Sample name Microwave dissipation
50lm EP 120lm 1-EP Strong increase from !100mT (Fig. 1(b))
50lm Nb-310-10 þMB 1-EP-MB Not measured
50lm EP 120lm 2-EP Mild increase from !100mT
50lm Nb-240-10 þMB 2-EP-MB Not measured
50lm EP 120lm þ MB 3-EP-MB Low up to 160mT (Fig. 1(b))
50lm EP 120lm þ BCP 50lm 4-BCP Not measured
50lm EP 120lm þ BCP 50lm þMB 5-BCP-MB Not measured
!10 cm BCP 120lm 6-BCP Strong increase from !100mT
!10 cm BCP 120lm þ MB 7-BCP-MB Not measured
FIG. 1. (a) Results of Q0ðBpeakÞ measurements on fine grain electropolished cavities before and after mild baking; (b) individual DTðBÞ for samples 1-EP and3-EP-MB; (c) temperature mapping boards attached to the outside cavity walls; three boards are removed for demonstration purposes; (d) single individualboard with sensor numbering; (e) schematic showing how angle is measured around the rotational cavity axis; 36 boards are uniformly spaced with 10$ separa-tion; (f) local magnetic field B at sensor locations and unfolded temperature maps of DT / Rs for unbaked and baked fine grain electropolished cavities atBpeak ¼ 119mT.
232601-2 Romanenko et al. Appl. Phys. Lett. 102, 232601 (2013)
This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP:130.126.32.13 On: Fri, 07 Mar 2014 02:54:31
EP and 120C bakedEP (not baked)
T-maps @ 28 MV/m
Yulia Trenikhina SRF’15 Whistler, Canada
EP vs. EP+120C baked: what is causing HFQS?
4
few monolayers of hydrocarbons
Nb2O5 2-5nmNbOx x<2.5
Nb bulk
magnetic field penetration depth @2K <100 nm
Near-surface layer of SRF cavity after typical processing
What in the near-surface is causing different dissipation character?
Yulia Trenikhina SRF’15 Whistler, Canada
Hypothesis for the HFQS problem: what is the difference?
5
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>FP
@*."2D" K.&2.03T@<=-&8#'$H"*(#$=.*8-*3$-#H&-)#=$2<$`*'%"#()#-$*'=$G.)-#$^FV_$4*6$*'=$5S hN$#/0.1.2-.03$H-#((0-#$*'=$H&)#').*1$#().3*)#($,&-"<=-.=#$H"*(#($2*(#=$&'$)"#$=*)*$&,$A-&33$*'=$\#"'$^P9_$,&-$)"#$α *'=$α i β -#8.&'($*'=$`*'%"#()#-$*'=$G.)-#$^FV_$,&-$)"#$β i δ -#8.&'$426D
Nb hydrideprecipitation
Tool:T-dependent TEM electron diffraction
phase characterization
Why to look at Nb-H system?1. H concentration in near-surface
of cutouts > 10 at.%
2. ε, β are NOT superconducting
Difference in precipitation state of Nb-H in the near-surface?
Yulia Trenikhina SRF’15 Whistler, Canada
Hypothesis: Nb hydrides and HFQS
6
• Normal conducting Nb hydrides are SC by proximity effect up to Hcritical = HFQS onset (A. Romanenko et.al., Supercond. Sci. Technol. 26, 035003 (2013));
• Major role of vacancies and vacancy-hydrogen complexes in the 120C baking effect (A. Romanenko et.al., Appl. Phys. Lett. 10, 232601 (2013)).
NbOx
Nb2O5
Nb
H
NbOx
Nb2O5
Nb
V-nHcomplex
EP cavity 120˚C-baked EP cavity
Less/no NbHx precipitation!
~50 nm
Yulia Trenikhina SRF’15 Whistler, Canada7
30
NUANCE Center*exploring the inner space
TEM Sample Preparation with FIB @ Ben Myers - 2009
Lift-Out (4 of 4)L
0°
TiltL
Raise Omniprobe
~10�mL
Retract Pt GIS needleL
Send Omniprobe
to Eucentric
HighL
Retract Omniprobe
FIB
FIB
37
NUANCE Center*exploring the inner space
TEM Sample Preparation with FIB @ Ben Myers - 2009
Cleaning (1 of 2)J
Tilt into sample +/-
3-5°J
Application: SiJ
Shape: RectangleJ
Size: ~10�m (X) x ~2�m (Y)J
5kV, ~46pAJ
~2-5min per side
+/-
FIB -
~52+5°
tilt FIB -
~52-5°
tilt
SEM
22
NUANCE Center)exploring the inner space
TEM Sample Preparation with FIB ? Ben Myers - 2009
E-beam PtE
0°
Tilt
E
Application: Pt e-DepE
Shape: Rectangle
E
15�m (X) x 1.5�m (Y) x 200nm (Z)E
2-5kV, >1.4nA
E-beam dep
at 0°
Tilt (SEM)E-beam dep
at 52°
Tilt (SEM)
SEM
~10 μm
~3 μ
m
SEM images during the FIB sample preparation
TEM sample preparation: focused ion beamC
u grid
Pt protective layer
Courtesy of B. Meyer
Yulia Trenikhina SRF’15 Whistler, Canada
Nb near-surface at room T
8
[113] [011]
[-111]
EP and EP+120C baked at room T
SAD, NED, SEND: only Nb at room TH in solid solution (α-phase)
[100]
Pt protective layer
Nb bulk
Nb oxide
200 nm
TEM: low mag overview
Yulia Trenikhina SRF’15 Whistler, Canada
Nb near-surface at cryogenic T
9
βε
ε+β
βε
ε β β
ε ε ε+β ε+β
ε ε ε
ε
ε
ε
ε
ε ε
ε
ε
ε+β
ε+β
εε+β β_ _ _ _
EP at 94K EP+120C baked at 94K
Nb+ε(Nb4H3)
Nb+β(NbH)
Nb+ε,β
Nb hydrides precipitation
Nb
NO Nb hydrides precipitation
Nb
Yulia Trenikhina SRF’15 Whistler, Canada
Nb near-surface at cryogenic T continue
10
NED: Nb hydrides precipitation in all cutouts, amount and/or size of Nb hydrides is different
EP at 94K EP+120C baked at 94K
Nb hydrides
Nb hydrides
Yulia Trenikhina SRF’15 Whistler, Canada
Other treatments show Nb hydrides precipitationAnnealing at 800C˚ for 3h+BCP
β β β β
_ ε_ ε
β β β β
β β β β
β β β β
_ ε_ ε_ ε_ ε_ ε_ ε_ ε_ ε_ _ _ _
ε_ εε
_ ε ε ε
ε ε εε
ε ε εε
ε ε εε
ε ε εε
ε ε εε
ε ε εε
Annealing at 800C˚ for 3h
Yulia Trenikhina SRF’15 Whistler, Canada
HFQS recipes:EPEP+800C bake+BCPEP+800C bake
large size or large amount of Nb hydrides at 94K
=
HFQS-free recipe:EP+120C bake
Cause of HFQS
12
small/widely spread Nb hydrides at 94K=
Yulia Trenikhina SRF’15 Whistler, Canada
Grain boundaries in EP and EP+120C baked
13
grain 1 grain 2
SEM image of GBPt layer
Nb2O5
HRTEM image of GB
Yulia Trenikhina SRF’15 Whistler, Canada
EELS study of Nb oxides in EP and EP+120C baked cavities
14
120x103
100
80
60
40
20
0
cou
nts,
arb
. uni
ts
395390385380375370365360355 energy loss, eV
region 1 region 2 region 3 region 4
Nb
Nb oxides
Pt layer
STEM Z-contrast image
Oxygen inward diffusion during the bake
EELS Nb M2,3 edge
EP+120C
EP1
23
4
Yulia Trenikhina SRF’15 Whistler, Canada
Nb hydrides in N-doped cavity cutouts and samples
15
• Nb hydrides do precipitate in N doped cavities and samples!
Most of the probed area is affected by hydride precipitation in quench spot.
• Do Nb hydrides cause quench in N doped cavities?
Cryogenic temperature structural characterization of non-dissipating spot is needed.
More about N doped cavities in MOPB055
Quench Spot at 94K
baked with N @800C + 5 μm EP
?
Yulia Trenikhina SRF’15 Whistler, Canada
Conclusions
16
• Combination of T-dependent macro- and microscopic characterization revealed precipitation of Nb hydrides in the state-of-the-art SRF resonators for the 1st time;
• We showed that micro- and nanoscopic characterization gives a valuable insight into mechanisms that governs the performance of SC cavities;
• Routine use of micro- and nanoscopic characterization for the development of new SC materials and treatments for the SRF cavities.
Yulia Trenikhina SRF’15 Whistler, Canada
Microscopic characterization for new materials/treatments
17
We are working on: Nb3Sn coating of Nb cavities with Cornell
Nb3Sn coated Nb cavity: SEM/EDX on cavity cutouts
More about Nb3Sn in Sam Posen’s posters TUPB048, TUPB049 and
Yulia’s poster TUPB056.
Thanks for your attention!