investigation of microscopic materials limitations of superconducting rf cavities
DESCRIPTION
Steven M. Anlage Department of Physics Center for Nanophysics and Advanced Materials University of Maryland 29 October, 2008. Investigation of Microscopic Materials Limitations of Superconducting RF Cavities. SRF Materials Workshop. Questions to Address. - PowerPoint PPT PresentationTRANSCRIPT
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Investigation of Microscopic Materials Limitations of Superconducting RF Cavities
Steven M. Anlage
Department of PhysicsCenter for Nanophysics and Advanced MaterialsUniversity of Maryland29 October, 2008
SRF Materials Workshop
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Questions to Address
What new experiments shed light on limits played by topology, surface phasesand structures, chemical makeup, or physics?
How can we separate intrinsic behavior from that which is dependent on history orprocessing pathway?
Are there new studies … telling us about the intrinsic qualities of the niobium surface?
Do we still need to focus on heat transfer effects?
My Answers:
New Microscopic Techniques to link RF Properties to Local Structure
1) Near-Field Microwave Microscope
2) Laser Scanning Microscope
Use these to establish connectionsbetween surface structure and RFperformance on a microscopic scale
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Near-Field Microwave Microscope
1Create Strong ( BRF ~ 200 mT ) Highly Localized ( < 1 m ) RF ( 1 - 2 GHz )
Magnetic Fields on Nb Surfaces at Low Temperatures ( < 2 K )
2 Measure Local Response:Nonlinearity (Harmonics, Intermodulation)Sensitive to RF breakdown, flux generation, …
3 Correlate Local RF Properties to:TopographyDefects (welds, grain boundaries, …)Surface TreatmentProcessing
Microwave Microscope Probe
Intense BRF
Drive
Nb SampleLocalizedExcitationon Surface
Fundamental Response
Harmonic / Intermod Response
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-2 .0 -1 .5 -1 .0 -0 .5 0 .0 0 .5 1 .0 1 .5 2 .0-2 .5
-2 .0
-1 .5
-1 .0
-0 .5
0 .0
0 .5
X ( m m )Y
(m
m)
- 1 0 5 .0- 1 0 0 .0- 9 5 .0 0- 9 0 .0 0- 8 5 .0 0- 8 0 .0 0- 7 5 .0 0- 7 0 .0 0- 6 5 .0 0- 6 0 .0 0- 5 5 .0 0- 5 0 .0 0
GB
-2 .0 -1 .5 -1 .0 -0 .5 0 .0 0 .5 1 .0 1 .5 2 .0-2 .5
-2 .0
-1 .5
-1 .0
-0 .5
0 .0
0 .5
X ( m m )Y
(m
m)
- 1 0 5 .0- 1 0 0 .0- 9 5 .0 0- 9 0 .0 0- 8 5 .0 0- 8 0 .0 0- 7 5 .0 0- 7 0 .0 0- 6 5 .0 0- 6 0 .0 0- 5 5 .0 0- 5 0 .0 0
GB Third harmonicpower (dBm)
Near-Field Microwave MicroscopeExample Result
Localized Harmonic Generation from a single bi-crystal grain boundaryin a high-Tc (YBa2Cu3O7-) thin film
200m loop probe500Å
YBCO
STO
J
30° misorientation Bi-crystal grain boundary
P = +8 dBm
X
FundamentalTone In
HarmonicTones Out
<< Josephson junctions are strongly nonlinear >>
Superconductors have an intrinsic nonlinearity, clearly visible as J → Jc
The superfluid density is suppressed and very sensitive to perturbations
2
1)0,(),(c
ss J
JTJT
s becomes time-dependent, giving rise to harmonics and intermods
Phys. Rev. B 72, 024527 (2005)
fin = 6.5 GHzT = 60 K
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Near-Field Microwave Microscope► Next Generation for SRF Applications ◄
Magnetic Write Heads createi) Strong RF magnetic fields: ~ 1 T in existing write headsii) Highly localized RF magnetic fields (|| to surface!): 100’s of nm
Schematic of a longitudinal write head
RFDrive
Superconductors show nonlinearity due to both intrinsic and extrinsic effects
Noise Level
Temperature (K)
Example ResultSeagate Longitudinal Recording Head
3rd-Harmonic Response of a Homogeneous high-Tc film
3rd-H
arm
onic
Pow
er P
3f (
dBm
)
fin = 6.4 GHz
Goals: Achieve ~200 mT surface RF fields on Nb at microwave frequencies at 2 KImage RF breakdown fields and correlate with surface properties…
Tc
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Laser Scanning Microscope
1 Create a Microwave ( ~ GHz ) Resonance at Low Temperatures ( < 2 K )
2 Perturb the Surface with a Modulated Laser Spot to cause Local Heating
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Image:JRF(x, y) Local RF Current DensityLocal sources of Nonlinear ResponseRF vortex Entry and FlowThermal Healing Length
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Measure the change in f0 and Q as the laser spot is scanned over the surface
“Short-Sample” RF / Materials Science of Nb Surfaces
Co-planarWaveguideResonator
f0 , Q
MicrowaveInput
Ground Plane
Material of interest
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1 x 8 mm scan
Grain Boundaries
LAO
YBCO
Large Grain position
Laser Scanning Microscope“Short-Sample” RF / Materials Science of Nb Surfaces
Reflectivity Image
RF Image
100 m x 200 m
IRF
BRF
RF contrast developed from grain bdes,cracks, scratches, etch features, corners,etc.Low Temperature Physics 32, 592 (2006)
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Nb foil(160 m thickness)
RF input
Nb foil(160 m thickness)
RF input
Copper finger
Sapphire rod
Sapphire disc
RFIN
RFOUT
ground
Nb stripScanned area Pb
Nbsapp
hire
reflectivity
inductive resistive
1 m
m
Laser Scanning MicroscopePreliminary Results on Bulk Nb Surfaces
Nb foil(160 m thickness)
RF input
Nb foil(160 m thickness)
RF inputPb
Nbsapp
hire
reflectivity
inductive resistive
1 m
m
NbNb
Pb Pb
defect defect
LineScan
PbNb
7.2 K
9.2 K
5.6 K
10.6 KT
empe
ratu
re
1 mm
Line scan
LSM PR
0
+ peak
- peak
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Determination of the Thermal Healing Length
T = 79 KP = - 10 dBmf = 5.285 GHzfmod = 99.9 kHz
YBCO/LaAlO3
CPW Resonator
1 x 8 mm scan
Wstrip = 500 m
ModmThermal fc
k
k Thermal Conductivity
c Specific heat
m Mass Density
Modf Modulation Freq.
Intensity modulatedfocused laser beam
Bulk Metal
Coatingheatsource
x
z
Intensity modulatedfocused laser beam
Bulk Metal
Coatingheatsource
x
z
Fit gives
m 4 Thermal
J. Supercond. 19, 625 (2006)
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Conclusions
A proposal to DOE/HEP on SRF Materials Issues is in preparation
I am looking for materials collaborators who need to solve specificmaterials / low-T RF property problems and think that amicroscopic approach is fruitful
Some topics of interest:RF properties of grain boundaries and step edgesRF properties of etch pitsUnderstanding the microscopic physics of intrinsic RF breakdownCan coatings (S / I / S /…, or novel superconductor) prolong RF breakdown?
I believe the Near-Field and Scanning Laser Microwave Microscopes can helpto solve vexing SRF materials problems
http://www.cnam.umd.edu/anlage/AnlageHome.htm
Existing Collaborators:Dragos Mircea [Seagate → Hitachi]Alexander Zhuravel [Kharkov, Ukraine]Alexey Ustinov [Karlsruhe, Germany]
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Agilent E8362MicrowaveSynthesizer
LakeShore340Temperature Controller
Low-Pass Filters
High-Pass Filters
MicrowaveAmplifiers
Gain ~ 60dB
Directional Coupler (-6dB)
sampleWriter
Cryogenicchamber
Agilent E4407BSpectrum Analyzer
f
f, 2f, 3f,..
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f
f, 2f, 3f,…
f
MW source
Low pass filter
Directional coupler
High pass filter
sample
Cryogenic environment
2f, 3f,…
Spectrum Analyzer
Amp
f
3f
f, 2f, 3f,…
f
Port 1 Ref Out Ref In Port 2
VNA in FOM
Comb.
Gen.
f, 2f, 3f, …
Band pass filter
Low pass filter
Directional coupler
High pass filter
sample
Cryogenic environment
2f, 3f,…
13 www.answers.com/topic/read-write-head
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New Approach: inductive writer from a HDD
B ~ 1 T !!!
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Pinput
loop
coaxial probe
sample surface
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The inductive reader/writer : general concept
Attractive features :Attractive features :
• ~ T magnetic field~ T magnetic field
• sub-micron pole tipssub-micron pole tips
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An inductive magnetic writer/reader : Example
Pins for reader/writerPins for reader/writer
magnetic disk / superconducting samplemagnetic disk / superconducting sample
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An inductive magnetic writer/reader : Detail
writerwriter
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An inductive magnetic writer/reader : Detail
microcoilsmicrocoils
high-high- magnetic magnetic corecore
wiring of the wiring of the microcoils to the microcoils to the
pinspins
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An inductive magnetic writer/reader : Schematics
R. Hsiao R. Hsiao IBM J. Res. Develop.IBM J. Res. Develop., vol. 43, no.1/2, , vol. 43, no.1/2, Jan/March 1999Jan/March 1999
SAMPLESAMPLE
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2 2(2 / )'2
( , , ) (1 )L Mr r i tzLL
L
PP r z t e e e
Laser-induced signal generation model
The power distribution induced by a focused modulated laser beam can be described as:
temporalspatial
x-y z t
focused laser beam(lLAS = 670 nm, PL = 1 mW)
substrate
HTS film
d
heatsource
x
z
The thermally induced changes of S21(f) in the probe are understood as LSM photo-response (PR) that can be expressed as:
2 2 2 22 12 12 120 12
12 20 12
( ) ( ) ( )1 (1/ 2 )( )
2 (1/ 2 )
S f S f S ff SQPR S f T
f T Q T TS
inductive PR + resistive PR + insertion loss PR 2
2 1212 2 2
0
( )1 4 ( / 1)
SS f
Q f f
where
A.P. Zhuravel, S. M. Anlage and A.V. Ustinov
~2121 21
21
2121
21
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Scanning Laser Microscopy of Superconducting Microwave Devices
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Results: Power dependence of PRR(x,y)
LAO
YBCO10 mm
0 dBm
+6 dBm+4 dBm
+2 dBmLAO
Images of resistive LSM PR penetrating into HTS film (area B) at the different input HF power indicated in the images. White dotted boxes show the YBCO/LAO patterned edge. Brighter regions correspond to larger amplitude of PRR(x,y).
3D plot of resistive LSM PR at +6 dBm
LAO
YBCO
PRR(x,y)
A.P. Zhuravel, S. M. Anlage and A.V. Ustinov Scanning Laser Microscopy of Superconducting Microwave Devices
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Microwave Microscope Probe
Intense BRF
Drive
Nb SampleLocalizedExcitationon Surface
Fundamental Response
Harmonic / Intermod Response
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- YBCO film- LAO substrate
1 mm
1x1 mm
XY
XY
JRF
0
max
Frequency
Pow
er [
dBm
]
f1 f2
- 42
-14 -14
- 43
2f1 -f2 2f2 –f1
- 43- 42
- 49- 55
1x1 mm
IMD PRJrf
x
y
1x1 mm
0 max
(a) (b) (c)
RFIN
RFOUT
XY
JRF
XY
JIMD
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TM010 Resonant ModeCurrent Distribution
FiducialMaterials
Nb Strip withTwo differentTreatment
26
27
Pb
Nbsapp
hire
reflectivity
inductive resistive
1 m
m
NbNb
Pb Pb
Sapp
hire
Sapp
hire
defect defect
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Pb
Nb
reflectivity
inductive resistive
1 m
m
NbNb
Pb Pb
defect defect
29
reflectivity RF = -3dBm
Nb stripGap1 mm
F1
30
LineScan
PbNb
7.2 K
9.2 K
5.6 K
10.6 K
Tem
pera
ture
1 mm
Line scan
LSM PR
0
+ peak
- peak
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Nb foil(160 m thickness)
RF input
Pb foil(50 m) Pb foil(50 m)
Areascan
Linescan
Nb foil(160 m thickness)
RF input
Pb foil(50 m) Pb foil(50 m)
Areascan
LinescanPb foil(50 m) Pb foil(50 m)
Areascan
Linescan
Nb foil(160 m thickness)
RF input
Nb foil(160 m thickness)
RF input