CLIC meeting

TERA Foundation

16th June 2010

R. Bonomi A. Degiovanni

M. GarlaschèImage studies for RF breakdowns

• A future test is foreseen for the S-band one-cell-test cavity no cut of the cavity!

• Need to have spatial references on the inner surface for determining the area where breakdowns mainly occurred: area close to– max E field– max B field– max Poynting Vector ??

• Aim: drawing nose region lineand max fields lineson the pics taken(with MatLab programs)

Background

Image study for RF breakdowns 2

INR

ONR

Image study for breakdowns

Surface inspection set-up*

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*Thanks to J. Kovermann, A. Olyunin

S-band cavity

Software for image acquisition

Optical stereo microscope

Digital camera

Tilt plane:every pic is taken with the same angle!

Image study for RF breakdowns

Some pics..

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A-side

B-side

90x

32x

32x

Example of 2 very big craters!

(Distance btw machining lines ~20 µm)

Image study for RF breakdowns

Theory behind - 1• Bore hole circumference ellipse if the plane where it lives is

tilted• Angles α and β: indication of the tilt plane in the 3D space

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α

β

Image study for RF breakdowns

7x

63x

Theory behind - 2• Image centre is taken as a reference to

“move” from one pic to the other one• Within the same pic, ellipse centre is

always “corrected” to when referred to another plane by means of α and β

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TIPONRINRCF

Image study for RF breakdowns

1) Ellipse “enclosed” in a rectangle• Image modification (grayscale,

bw, ...)• Find Top, Bottom, Right and Left

points of enclosing rectangle• Find Centre of ellipse (with Top

and Bottom)• Find N, S, E and W points (with

Centre)• Calculation of α, β (comparison of

semi axes* with bore radius)

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BW limit

7x

T

B

C

L

RW

N

* We used segments CW and CN, since these segments differ from the semi axes just for an angle of 0.1 degrees.

Image study for RF breakdowns

1) Ellipse “enclosed”: Results

• Too blurry ellipse profile: not enough precision in the research of points

• High sensitivity to BW limit: too much variation in α,β!!

• NO reliable results

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“LIMIT” = 0.36

7x

63x

0.3 0.32 0.34 0.36 0.38 0.4 0.420

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10

15

20Alfa and Beta vs. Limit

Limit

INR

Nose tip

Image study for RF breakdowns

2) Ellipse from 5 points

• Image modification (grayscale, bw, ...)

• Error minimization: 5 points

• Implicit eq.

• Canonic eq.

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Ax2 + Bxy + Cy2 + Dx + Ey + F = 0

λ1x2 + λ2y2 + λ3 = 0

λ1 , λ2 = eig(mat2)λ3 = det(mat3) / det(mat2)

[x y 1] [mat3] [x;y;1] = 0

Ellipse center, semi axes, rotation

7x

Image study for RF breakdowns

α = 21ºβ = 6º

2) Ellipse from 5 points: Results

• NO reliable results

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α = 30ºβ = 0º

α = 10ºβ = 0º

α = 21ºβ = 6º

α = 20ºβ = 0º

Nose tip

Inner nose radius

Outer nose radius

Image study for RF breakdowns

Problems..• Profile of the bore hole too blurry low precision for the ellipse• No pics of the inner nose radius (too dark) no hints on BD

presence there

• We would have needed:– Precise instrumentation to tilt the cavity– Microscope characterization for visualization angle

• ..only solution: cut the cavity (BUT after the next test!!)

Thank you very much for your attention!

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