1. CLIC meeting TERA Foundation 16th June 2010 R. Bonomi A. Degiovanni M. Garlaschè Image studies for RF breakdowns

2. 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 line and max fields lines on the pics taken (with MatLab programs) Background Image study for RF breakdowns2 INR ONR

3. Surface inspection set-up* Image study for breakdowns3 *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!

4. Some pics.. Image study for RF breakdowns4 A-side B-side 90x 32x Example of 2 very big craters! (Distance btw machining lines ~20 µm)

5. 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 Image study for RF breakdowns5 α β

6. 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 Image study for RF breakdowns6

7. 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) Image study for RF breakdowns7 BW limit 7x T B C L R W N * We used segments CW and CN, since these segments differ from the semi axes just for an angle of 0.1 degrees.

8. 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 Image study for RF breakdowns8 “LIMIT” = 0.36 7x 63x INR Nose tip

9. 2) Ellipse from 5 points Image modification (grayscale, bw,...) Error minimization: 5 points Implicit eq. Canonic eq. Image study for RF breakdowns9 Ax 2 + Bxy + Cy 2 + Dx + Ey + F = 0 λ 1 x 2 + λ 2 y 2 + λ 3 = 0 λ 1, λ 2 = eig(mat2) λ 3 = det(mat3) / det(mat2) [x y 1] [mat3] [x;y;1] = 0 Ellipse center, semi axes, rotation 7x

10. 2) Ellipse from 5 points: Results NO reliable results Image study for RF breakdowns10 α = 21º β = 6º Nose tip Inner nose radius Outer nose radius

11. 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! Image study for RF breakdowns11