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Recent DC spark results

Recent DC spark results. Antoine Descoeudres, Yngve Levinsen, Sergio Calatroni, Mauro Taborelli. Outline. Surface treatments of Cu samples Evolution of b during conditioning and BDR measurements. Outline. Surface treatments of Cu samples rolled sheet (reference) heat treatment milling

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Recent DC spark results

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  1. Recent DC spark results Antoine Descoeudres, Yngve Levinsen, Sergio Calatroni, Mauro Taborelli

  2. Outline • Surface treatments of Cu samples • Evolution of b during conditioning and BDR measurements

  3. Outline • Surface treatments of Cu samples • rolled sheet (reference) • heat treatment • milling • Subu • Electro-polishing

  4. ‘‘de-conditioning’’ due to spark damages (observed only with Cu) Cu standard sample (rolled sheet) • First 2 – 3 sparks : Eb = 350 – 400 MV/m, b = 15 – 20 • After a few sparks: ~ 170 MV/m, b ~ 50 • The delay before the first spark is usually very long (ms)

  5. Quantity of gas released during a spark : slightly less, but within error bars Cu + heat treatment at 875°C • Both electrodes treated in a brazing cycle (2h) • Same results as non-heated Cu (Eb, b, BDR…)

  6. good surface state at the start, like rolled sheet Cu + milling • Sample milled in the CERN workshop (no idea what the roughness may be…) • Standard behaviour :

  7. Eb = 200 MV/m, b = 20 – 35 Cu (milled) + Subu treatment • Subu : ~ 20 mm removed • The surface state at the start is not as good :

  8. Also a good surface state, comparable to standard Cu Cu (milled) + Electro-polishing • Electro-polishing: ~ 20 mm removed

  9. The first sparks destroy rapidly the benefit of a good surface preparation Surface treatments of Cu : summary • Surface treatments on Cu only affects the very first breakdowns • After a few sparks: ~ 170 MV/m, b ~ 50 for every samples And in RF ? Sparks are distributed over a much larger surface… Treatments are maybe still useful

  10. Outline • Surface treatments of Cu samples • Evolution of b during conditioning and BDR measurements

  11. Evolution of b during conditioning measurements • In the 2nd DC spark setup: automatization of b measurements  between each spark

  12. Evolution of b during conditioning measurements • Correlation between b and the next breakdown field • No correlation between b and the previous breakdown field b · Eb = cst

  13. Evolution of b during conditioning measurements • b · Eb is much less dispersed than Eb Local field : b · Eb = cst = 9.8 GV/m (± 0.2) for Cu

  14. Are small tips pulled by the field? (we need more data) Evolution of b during BDR measurements spark • ‘calm’ period  low b • b seems to increase (a few %) during a calm period if E is sufficiently high

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