Effect of surface roughness on TCSPM tune shift measurement - PowerPoint Presentation

Presentation on theme: "Effect of surface roughness on TCSPM tune shift measurement"— Presentation transcript

Slide1

Effect of surface roughness on TCSPM tune shift measurement

S. Antipov

04/20/18

Problem: 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

Possible 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

Data processing procedure

Roughness might

affect on this stage

4/20/2018

Effect of surface roughness on TCSPM tune shift

4

How 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

How 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

How 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

Roughness: 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

Stupakov 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

Roughness: 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

A small gain in impedance can come from surface roughness

Model

SEM

Insufficient to explain a factor 2 discrepancy in the beam measurement

4/20/2018

Effect of surface roughness on TCSPM tune shift

11

Conclusion

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

Back-up slides

4/20/2018

Effect of surface roughness on TCSPM tune shift

13

Physical model of roughness does not explain the large discrepancy observed in the TCSPM resonant wire measurement at low frequencies

4/20/2018

Effect of surface roughness on TCSPM tune shift

14