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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 - PowerPoint PPT Presentation
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1 / 14RF structures team meeting - 24.9.08
Recent DC spark results
Antoine Descoeudres, Yngve Levinsen,
Sergio Calatroni, Mauro Taborelli
2 / 14RF structures team meeting - 24.9.08
Outline
1. Surface treatments of Cu samples
2. Evolution of during conditioning and BDR measurements
3 / 14RF structures team meeting - 24.9.08
Outline
1. Surface treatments of Cu samples
• rolled sheet (reference)• heat treatment• milling• Subu• Electro-polishing
4 / 14RF structures team meeting - 24.9.08
Cu standard sample (rolled sheet)
• First 2 – 3 sparks : Eb = 350 – 400 MV/m, = 15 – 20
• After a few sparks: ~ 170 MV/m, ~ 50
• The delay before the first spark is usually very long (ms) ‘‘de-conditioning’’ due to spark damages (observed only with Cu)
5 / 14RF structures team meeting - 24.9.08
Cu + heat treatment at 875°C
• Both electrodes treated in a brazing cycle (2h)
• Same results as non-heated Cu (Eb, , BDR…)
slightly less, but within error bars
• Quantity of gas released during a spark :
6 / 14RF structures team meeting - 24.9.08
Cu + milling
• Sample milled in the CERN workshop (no idea what the roughness may be…)
good surface state at the start, like rolled sheet
• Standard behaviour :
7 / 14RF structures team meeting - 24.9.08
Cu (milled) + Subu treatment
• Subu : ~ 20 m removed
• The surface state at the start is not as good :
Eb = 200 MV/m, = 20 – 35
8 / 14RF structures team meeting - 24.9.08
Cu (milled) + Electro-polishing
• Electro-polishing: ~ 20 m removed
• Also a good surface state, comparable to standard Cu
9 / 14RF structures team meeting - 24.9.08
Surface treatments of Cu : summary
• Surface treatments on Cu only affects the very first breakdowns
rolled sheet / heat treatm.
milling Subu electro-polishing
before 1st spark ~ 15 - 20 ~ 20 ~ 25 - 30 ~ 15 - 20
1st brkd field [MV/m] ~ 200 - 400 ~ 300 - 500 ~ 150 - 200 ~ 300 - 400
• After a few sparks: ~ 170 MV/m, ~ 50 for every samples
The first sparks destroy rapidly the benefit of a good surface preparation
And in RF ? Sparks are distributed over a much larger surface…Treatments are maybe still useful
10 / 14RF structures team meeting - 24.9.08
Outline
1. Surface treatments of Cu samples
2. Evolution of during conditioning and BDR measurements
11 / 14RF structures team meeting - 24.9.08
Evolution of during conditioning measurements
• In the 2nd DC spark setup: automatization of measurements
between each spark
12 / 14RF structures team meeting - 24.9.08
Evolution of during conditioning measurements
• Correlation between and the next breakdown field
• No correlation between and the previous breakdown field
· Eb = cst
13 / 14RF structures team meeting - 24.9.08
Evolution of during conditioning measurements
• · Eb is much less dispersed than Eb
Local field : · Eb = cst = 9.8 GV/m (± 0.2) for Cu
14 / 14RF structures team meeting - 24.9.08
Evolution of during BDR measurements
spark
• ‘calm’ period low
• seems to increase (a few %) during a calm period if E is sufficiently high
Are small tips pulled by the field? (we need more data)