The need for more outgassing data of materials for accelerators and storage ring experiments
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The need for more outgassing data of materials for accelerators and storage
ring experiments
E. HedlundUppsala University, Sweden
SP-Swedish Testing and Research Institute
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Outline
• Outgassing properties of materials• Recommended practices for
outgassing measurements• Measurement accuracy• Create a database for outgassing
measurement• Outlook
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16th IUVSTA Workshop Outgassing properties of materials
Conclusions:• Better correlation between outgassing
measurements and the morphology and chemical structure of the surface and near surface layers
• Identification of the chemical state of H2O on or near the surface.
• Measurement of the sticking coefficient of H2O on practical surfaces (steel and Al) as a function of surface conditions
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Conclusions…
• Influence of deposited passivation layers of outgassing
• Measurements and corresponding modeling of outgassing from model systems
• Experiments that could identify and quantify the role of diffusion in the near-surface region of vacuum materials
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From this we can conclude:
– Lack of published outgassing data– Need for a freely available database
with e.g. following parameters:Precise material, surface and bulk treatments, surface structure, cleaning, heat treatment etc.
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Outgassing methods
• Throughput method• Conductance modulation method• Two-path method• Gas ackumulation method• Mass-loss measurements
”Recommended practices for measuring and reporting outgassing data” by P. A. Redhead in J. Vac. Sci. Technol. A 20(2002) 1667-1675
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CHICSi
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Outgassing methods
• Method: pump down for a certain time and observe the final pressure.
• Must know the pumping speed at the chamber, which gives larger uncertainty.
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CHICSi
• Problem to find data for conductive and non-conductive glue, printed circuit boards and insulators
• NASA: Total Mass Loss (TML)Collected Volatile
Condensable Material (CVCM)
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Type Weight
Bake-out in air Bake-out in vacuum
H2 H2O CO CO2 CH4
Total out-gassing rate
(g]
Temp(ºC ]
Time (h ]
Temp (ºC)
Time (h)
(mbar l /s g)
(mbar l
/s g)
(mbar l
/s g)
(mbar l
/s g)
(mbar l
/s g)
rate(mbar l /s g)
377 1.15 90 1.5 1.410-
6
377 1.15 90 1.5 150
24 1.310-9
1.810-10
2.010-10
410-11
610-
11
410-9
H20E
2.16 90 1.5 410-
7
1.6 10-7
610-
8
810-9 610-7
H20E
2.16 90 1.5 150
24 410-11
1.210-9
310-10
210-10
1.410-10
7 10-9
H27D
3.90 90 1.5 1.110-
6
H27D
3.90 90 1.5 150
24 3 10-7
Outgassing from glue
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Printed circuit boardsKapton
Ceramics
FR-4
Glass reinforced kapton
Kapton insulated band cable
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Materials Area Bake-out H H2O CO Total outgassing rate
cm2 Air ºC
Time h
Vacuum ºC
Time h
mbar l/
cm2s
mbar l/
cm2s
mbar l/
cm2s
mbar l/cm2s
Pyralux (2 layers)
19 150 20 210-8 410-
10
310-9 310-8
AP (2 layers) 98 150 20 210-
10
410-
11
310-
10110-9
Epoxy-Acrylic (2 layers)
30 150 20 110-
10
310-
10
310-
10310-9
Epoxy-Glass fibre, 1 layer
36 150 20 410-
10
410-
11
410-
11210-9
Alumina (14 layer electrical print)
32 150 20 3·10-10
Glass reinforced Kapton
74 150 24 210-11
FR4 (4 layers) 475 150 30 1.510-11
FR4 331 150 24 610-10
FR4 331 150 24 150 23 210-
13610-11
FR4 331 150 24 150 77 410-12
FR4 – 6 layers 120 150 30 <110-
10510-10
Outgassing from printed circuit boards
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Outlook
• Increase bakeout temperature for the whole system to 200 ˚C or possibly 300 ˚C.
• Search for conductive and non-conductive glue with lower outgassing rate
• Find a new type of a flexible multi-layer bandcable
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Outgassing metrology
• Round robin study of outgassing:- materials from same batch, - same surface treatment- run at experimental facilities in
different laboratories
• Create a database (only UHV?)