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 Graphite Outgassing Measurements for UHV Applications 25 June 2003
Main topics • What did we learn from past experiences ? • Static outgassing of the Graphite R7500 1 and C-C 1501G 2 • Thermal outgassing – Dependence of the outgassing on the operating temperature J-P. BOJON, D. LE NGOC, B. VERSOLATTO – High temperature outgassing stimulated by e- bombardment • Conclusions and Recommendations 1 Carbone Lorraine, 2 SGL Carbon Group AT Division, Vacuum Group Graphite and C-C materials for UHV applications Prepared by J.M. Jimenez 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 µ m) • Bake out > 300°C improve performances � Factor 10 in performances (pumping time) J-P. BOJON, D. LE NGOC, B. VERSOLATTO • 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 ! AT Division, Vacuum Group Graphite and C-C materials for UHV applications Prepared by J.M. Jimenez 25 June 2003
Static Outgassing before bakeout - after a heat treatment at 1000°C during 2 hours - 1.0E-06 Heat treated Graphite Heat treated Graphite with outgassing holes 1.0E-07 Heat treated C-C Outgassing (mbar.l/s.cm2) Residual outgassing of the set-up 1.0E-08 J-P. BOJON, D. LE NGOC, B. VERSOLATTO 1.0E-09 1.0E-10 10 100 1000 10000 Time (hours) AT Division, Vacuum Group Graphite and C-C materials for UHV applications Prepared by J.M. Jimenez 25 June 2003
Static Outgassing after bakeout - after a heat treatment at 1000°C during 2 hours - 1.0E-11 24 hours at 250°C Outgassing (mbar.l/s.cm2) Heat treated Graphite 1.0E-12 Heat treated Graphite with outgassing holes Heat treated C-C J-P. BOJON, D. LE NGOC, B. VERSOLATTO Residual outgassing of the set-up 316 LN 1.0E-13 10 100 Time (hours) AT Division, Vacuum Group Graphite and C-C materials for UHV applications Prepared by J.M. Jimenez 25 June 2003
Thermal outgassing expected if running above RT Graphite R7500 1.0E-06 1.0E+06 y = 1E-12e 0.04 x 1.0E-07 1.0E+05 Outgassing rate (mbar.l/s.cm 2 ) 1.0E-08 1.0E+04 Enhancement factor Factor 250 ! 1.0E-09 1.0E+03 J-P. BOJON, D. LE NGOC, B. VERSOLATTO Factor 35 ! 1.0E-10 1.0E+02 1.0E-11 1.0E+01 1.0E-12 1.0E+00 0 50 100 150 200 250 300 350 Temperature (°C) AT Division, Vacuum Group Graphite and C-C materials for UHV applications Prepared by J.M. Jimenez 25 June 2003
Outgassing stimulated by e - bombardment Sample: 14 cm 2 Schematic view of the set- Schematic view of the set -up up 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 At 1050°C After 1 h RT J-P. BOJON, D. LE NGOC, B. VERSOLATTO H 2 O 30 % H 2 30 % 23 % CH 4 15 % CO 40 % 12 % � Higher ionization cross section for CH 4 and CO AT Division, Vacuum Group Graphite and C-C materials for UHV applications Prepared by J.M. Jimenez 25 June 2003
Outgassing stimulated by e - bombardment Outgassing recovery after heating Case of the C-C 1.0E-04 1st bombardment 1.0E-05 2nd bombardment 3rd bombardment Outgassing (mbar.l/s.cm2) 1.0E-06 1.0E-07 J-P. BOJON, D. LE NGOC, B. VERSOLATTO 1.0E-08 1.0E-09 1.0E-10 0.1 1 10 100 1000 Time (minutes) AT Division, Vacuum Group Graphite and C-C materials for UHV applications Prepared by J.M. Jimenez 25 June 2003
Graphite and C-C materials for UHV applications CONCLUSIONS • Heat treatment under vacuum at 1000°C during 2 h � Absolutely required, gain: 2 orders of magnitude • Static outgassing rate 5.0 x 10 -10 mbar.l/s.cm 2 – Before bake-out: 3.0 x 10 -12 mbar.l/s.cm 2 – After bake-out: � Acceptable for the LHC after the in-situ bake-out (250°C min. – 24 h) • Gas composition at 1050°C � CH 4 and CO are a problem � high ionisation cross section J-P. BOJON, D. LE NGOC, B. VERSOLATTO • 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 AT Division, Vacuum Group Graphite and C-C materials for UHV applications Prepared by J.M. Jimenez 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) J-P. BOJON, D. LE NGOC, B. VERSOLATTO 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. AT Division, Vacuum Group Graphite and C-C materials for UHV applications Prepared by J.M. Jimenez 25 June 2003
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