Graphite and C-C materials for UHV applications J-P. BOJON, D. LE - - PowerPoint PPT Presentation

Graphite Outgassing Measurements for UHV Applications 25 June 2003

Graphite and C-C materials for UHV applications

J-P. BOJON, D. LE NGOC, B. VERSOLATTO Prepared by J.M. JIMENEZ AT/VAC/SL Section

J-P. BOJON, D. LE NGOC, B. VERSOLATTO AT Division, Vacuum Group Prepared by J.M. Jimenez Graphite and C-C materials for UHV applications 25 June 2003

Main topics

• What did we learn from past experiences ?
• Static outgassing of the Graphite R75001 and C-C

1501G2

• Thermal outgassing

– Dependence of the outgassing on the operating temperature – High temperature outgassing stimulated by e- bombardment

• Conclusions and Recommendations

1Carbone Lorraine, 2SGL Carbon Group

J-P. BOJON, D. LE NGOC, B. VERSOLATTO AT Division, Vacuum Group Prepared by J.M. Jimenez Graphite and C-C materials for UHV applications 25 June 2003

What did we learn ? (TIDVG, TPSG, Lab measurements)

• Testing the real material (composition and dimensions) is essential

Factor 10 between the materials tested

• Heat treatment in a clean vacuum or high temperature bake out help

Factor 10 in performances (pumping time)

• “Exotic” treatments could decrease performances

Factor 6 introduced by a PVD Ti coating (2 µm)

• Bake out > 300°C improve performances

Factor 10 in performances (pumping time)

• CH species are only pumped by ion pumps

Can not rely on NEG or Ti sublimations

• Design is essential (outgassing channels, direct bake out)

………..after installation, it is tooooo late !

J-P. BOJON, D. LE NGOC, B. VERSOLATTO AT Division, Vacuum Group Prepared by J.M. Jimenez Graphite and C-C materials for UHV applications 25 June 2003

Static Outgassing before bakeout

• after a heat treatment at 1000°C during 2 hours -

1.0E-10 1.0E-09 1.0E-08 1.0E-07 1.0E-06 10 100 1000 10000 Time (hours) Outgassing (mbar.l/s.cm2)

Heat treated Graphite Heat treated Graphite with outgassing holes Heat treated C-C Residual outgassing of the set-up

J-P. BOJON, D. LE NGOC, B. VERSOLATTO AT Division, Vacuum Group Prepared by J.M. Jimenez Graphite and C-C materials for UHV applications 25 June 2003

1.0E-13 1.0E-12 1.0E-11 10 100 Time (hours) Outgassing (mbar.l/s.cm2) Heat treated Graphite Heat treated Graphite with outgassing holes Heat treated C-C Residual outgassing of the set-up

Static Outgassing after bakeout

• after a heat treatment at 1000°C during 2 hours -

24 hours at 250°C 316 LN

J-P. BOJON, D. LE NGOC, B. VERSOLATTO AT Division, Vacuum Group Prepared by J.M. Jimenez Graphite and C-C materials for UHV applications 25 June 2003

Thermal outgassing expected if running above RT Graphite R7500

y = 1E-12e0.04 x 1.0E-12 1.0E-11 1.0E-10 1.0E-09 1.0E-08 1.0E-07 1.0E-06 50 100 150 200 250 300 350 Temperature (°C) Outgassing rate (mbar.l/s.cm2) 1.0E+00 1.0E+01 1.0E+02 1.0E+03 1.0E+04 1.0E+05 1.0E+06 Enhancement factor

Factor 35 ! Factor 250 !

J-P. BOJON, D. LE NGOC, B. VERSOLATTO AT Division, Vacuum Group Prepared by J.M. Jimenez Graphite and C-C materials for UHV applications 25 June 2003

Outgassing stimulated by e- bombardment

Sample: 14 cm2 Heating power: 175 W (2.5 keV, 70 mA) Bombardment duration: 3 min. Temperature reached: 1050°C Effective pumping speed: 40 l/s

• Pressure rise by 4 orders of

magnitude Gas analysis after 1 hour

• Higher ionization cross section for

CH4 and CO

23 % 30 % H2 12 % 40 % CO 15 % CH4 30 % H2O After 1 h RT At 1050°C

Schematic view of the set Schematic view of the set-

• up

up

J-P. BOJON, D. LE NGOC, B. VERSOLATTO AT Division, Vacuum Group Prepared by J.M. Jimenez Graphite and C-C materials for UHV applications 25 June 2003

Outgassing stimulated by e- bombardment

Outgassing recovery after heating Case of the C-C

1.0E-10 1.0E-09 1.0E-08 1.0E-07 1.0E-06 1.0E-05 1.0E-04 0.1 1 10 100 1000 Time (minutes) Outgassing (mbar.l/s.cm2)

1st bombardment 2nd bombardment 3rd bombardment

J-P. BOJON, D. LE NGOC, B. VERSOLATTO AT Division, Vacuum Group Prepared by J.M. Jimenez Graphite and C-C materials for UHV applications 25 June 2003

• Heat treatment under vacuum at 1000°C during 2 h

Absolutely required, gain: 2 orders of magnitude

• Static outgassing rate

– Before bake-out: 5.0x10-10 mbar.l/s.cm2 – After bake-out: 3.0x10-12 mbar.l/s.cm2 Acceptable for the LHC after the in-situ bake-out (250°C min. – 24 h)

• Gas composition at 1050°C

CH4 and CO are a problem high ionisation cross section

• Recovery after heating

– 4 orders of magnitude increase at 1050 °C – 3 orders of magnitude recovery after 1h½ Compatible with the refilling of the LHC

Graphite and C-C materials for UHV applications CONCLUSIONS

J-P. BOJON, D. LE NGOC, B. VERSOLATTO AT Division, Vacuum Group Prepared by J.M. Jimenez Graphite and C-C materials for UHV applications 25 June 2003

Conclusions and Recommendations

• LHC is an UHV system

bake out at 300°C required

• Control of the outgassing rates by an optimisation of the :

material and heat treatment under vacuum shape design component heating (heat loads) Design an efficient cooling (avoid vacuum brasing in the water circuit)

Gas densities in the LHC LSS close to the experiments will be a problem due to the higher ionisation cross section of CH species and to the limited pumping speed for CH species which are only pumped by ion pumps, not by NEG nor by the titanium sublimation pumps.