S Antipov 042018 Problem Larger than expected tune shift of Mocoated TCSPM stripe MD 2193 nominal beam MD 2191 highintensity beam 4202018 Effect of surface roughness on TCSPM tune shift ID: 806015
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Slide1
Effect of surface roughness on TCSPM tune shift measurement
S. Antipov
04/20/18
Slide2Problem: Larger than expected tune shift of Mo-coated TCSPM stripe
MD 2193, nominal beam
MD 2191, high-intensity beam
4/20/2018
Effect of surface roughness on TCSPM tune shift
2
Slide3Possible sources of discrepancy
Impact of geometric impedance
Extra tune shift due to surface roughness
Higher resistivity of the coating due to its microstructure
-
Unlikely
D
ata matches well for MoGr and TiN
See also
Emanuela’s
talk
J. Guardia
J. Guardia
E. Carideo
- Focus of this talk
4/20/2018
Effect of surface roughness on TCSPM tune shift
3
Slide4Data processing procedure
Roughness might
affect on this stage
4/20/2018
Effect of surface roughness on TCSPM tune shift
4
Slide5How much extra tune shift we need to justify the measurement?
Assuming only the resistive wall contributes
Slope :
3.9
±
0.3
(2.4)
4/20/2018
Effect of surface roughness on TCSPM tune shift
5
Slide6How much extra tune shift we need to justify the measurement?
Subtracting the geometric contribution
Slope :
3.1
±
0.3
(1.4)
ρ [nΩ-m]:
250 ± 50
(
52
)
4/20/2018
Effect of surface roughness on TCSPM tune shift
6
Slide7How much extra tune shift we need to justify the measurement?
Subtracting the 3 x geometric contribution
for Mo stripe
Slope :
1
.6
± 0.3 (
1.4)
4/20/2018
Effect of surface roughness on TCSPM tune shift
7
Slide8Roughness: Macroscopic detailsStupakov model
Modelling roughness as a collection of randomly distributed bumps
Additional imaginary impedance scales as 1/gap
3
K. Bane and G. Stupakov, SLAC-PUB-8023, 1993
Chao (2.129), 1 bump:
Stupakov, per unit length:
J. Guardia
Packing factor, assume 1
Size, < 10
m
m
As resistive wall
4/20/2018
Effect of surface roughness on TCSPM tune shift
8
Slide9Stupakov model of roughness
Modelling roughness as a collection of randomly distributed bumps
Extra tune shift due to roughness is too small to explain the experimental findings
K. Bane and G. Stupakov, SLAC-PUB-8023, 1993
K. Bane and G. Stupakov, SLAC-PUB-8023, 1993
4/20/2018
Effect of surface roughness on TCSPM tune shift
9
Slide10Roughness: Microscopic detailsPhysical model
G. Gold and K.
Helmreich
,
IEEE Trans. Mic. Th. & Tech., vol. 65, no. 10, 2017Change in material skin depth due to microscopic surface details
Increases both resistivity and magnetic permeabilityModelled using the Matlab code, developed by S. Arsenyev
Model
SEM
Varying conductivity
Increase of
Im
and Re
Z
S.
Arsenyev
and D. Schulte,
submitted for publication
4/20/2018
Effect of surface roughness on TCSPM tune shift
10
Slide11A small gain in impedance can come from surface roughness
Model
SEM
Insufficient to explain a factor 2 discrepancy in the beam measurement
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Effect of surface roughness on TCSPM tune shift
11
Slide12Conclusion
Significant surface roughness has been observed in SEMs of Mo coating
It alone is insufficient to explain the higher than expected tune shift measured with beam
The microstructure of the coating should play a role in its higher impedance
Still, the effect may be significant, especially at smaller gapsCan be comparable to the geometric impedance of the tapersCancels the optimization effort
4/20/2018
Effect of surface roughness on TCSPM tune shift
12
Slide13Back-up slides
4/20/2018
Effect of surface roughness on TCSPM tune shift
13
Slide14Physical model of roughness does not explain the large discrepancy observed in the TCSPM resonant wire measurement at low frequencies
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Effect of surface roughness on TCSPM tune shift
14