The need for more outgassing data of materials for accelerators and storage

ring experiments

E. HedlundUppsala University, Sweden

SP-Swedish Testing and Research Institute

Outline

• Outgassing properties of materials• Recommended practices for

outgassing measurements• Measurement accuracy• Create a database for outgassing

measurement• Outlook

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

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

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.

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

CHICSi

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.

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)

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

Printed circuit boardsKapton

Ceramics

FR-4

Glass reinforced kapton

Kapton insulated band cable

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

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

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?)