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R. Bonomi A. Degiovanni M. Garlaschè Image studies for RF breakdowns

R. Bonomi A. Degiovanni M. Garlaschè Image studies for RF breakdowns. CLIC meeting TERA Foundation 16th June 2010. Background. A future test is foreseen for the S-band one-cell-test cavity  n o cut of the cavity!

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R. Bonomi A. Degiovanni M. Garlaschè Image studies for RF breakdowns

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

  2. Background • 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) ONR INR Image study for RF breakdowns

  3. Surface inspection set-up* *Thanks to J. Kovermann, A. Olyunin Digital camera Optical stereo microscope Software for image acquisition S-band cavity Tilt plane: every pic is taken with the same angle! Image study for breakdowns

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

  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 α β Image study for RF breakdowns

  6. Theory behind - 2 7x • 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 TIP ONR INR C F 63x Image study for RF breakdowns

  7. 1) Ellipse “enclosed” in a rectangle 7x • 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) BW limit N T W R C L B • * 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

  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 Nose tip 7x INR 63x “LIMIT” = 0.36 Image study for RF breakdowns

  9. 2) Ellipse from 5 points 7x • Image modification (grayscale, bw, ...) • Error minimization: 5 points • Implicit eq. • Canonic eq. Ax2 + Bxy + Cy2 + Dx + Ey + F = 0 [x y 1] [mat3] [x;y;1] = 0 λ1x2 + λ2y2 + λ3 = 0 Ellipse center, semi axes, rotation λ1, λ2 = eig(mat2) λ3 = det(mat3) / det(mat2) Image study for RF breakdowns

  10. 2) Ellipse from 5 points: Results α = 10º β = 0º • NO reliable results α = 21º β = 6º α = 21º β = 6º Outer nose radius α = 30º β = 0º α = 20º β = 0º Nose tip Inner nose radius Image study for RF breakdowns

  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 breakdowns

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