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*
3
*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..
4
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
5
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
6
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)
7
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
8
“LIMIT” = 0.36
7x
63x
0.3 0.32 0.34 0.36 0.38 0.4 0.420
5
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.
9
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
10
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!
11
Top Related