1. Update on the bakelite gluing Feb 2002: first warning from BaBar  13 gaps (over 48) accepted (27%) (i.e. max 2 non contiguous unglued spacers)…the remaining 73% had more than 8 unglued spacers. The gaps were produced with the new bakelite (more later on) Afterwards all other experiments had the same problem RPCs Production has been stopped and a R&D program setup to overcome the problem. Feb 2002: first warning from BaBar  13 gaps (over 48) accepted (27%) (i.e. max 2 non contiguous unglued spacers)…the remaining 73% had more than 8 unglued spacers. The gaps were produced with the new bakelite (more later on) Afterwards all other experiments had the same problem RPCs Production has been stopped and a R&D program setup to overcome the problem. The following refers to the results and conclusions of the RPC INFN committee (S.Morganti, S. Nuzzo et al.) The following refers to the results and conclusions of the RPC INFN committee (S.Morganti, S. Nuzzo et al.) CMS Week June 2002 P.Vitulo-Pavia University

2. What does it mean “New Bakelite” ? The firm that produces the bakelite for all the LHC experiments (and others) has enlarged his production capability, including.. substitution of melaminic and phenolic impregnation lines substitution of the press. i.e. The bakelite is made in the usual way but probably through new production cycles (one example: the press cycle at different temperature and time ?) Note: the factory has been producing in the new configuration since jul-sept 01 but the experiments were using old batches of bakelite What does it mean “New Bakelite” ? The firm that produces the bakelite for all the LHC experiments (and others) has enlarged his production capability, including.. substitution of melaminic and phenolic impregnation lines substitution of the press. i.e. The bakelite is made in the usual way but probably through new production cycles (one example: the press cycle at different temperature and time ?) Note: the factory has been producing in the new configuration since jul-sept 01 but the experiments were using old batches of bakelite

3. The hypothesis: The ungluing of the spacers from the new bakelite is due to surface characteristics (chemical). Two approaches: 1.Chemical/mechanical: realization of an automatic machine for the cleaning and brushing of the bakelite panels surfaces 2.Only mechanical: realization of an automatic machine that could locally mill the zone of the spacers and of the frame Solution 2 was discarded because it required > 4-5 months Solution 1 ready in 4-5 weeks The ungluing of the spacers from the new bakelite is due to surface characteristics (chemical). Two approaches: 1.Chemical/mechanical: realization of an automatic machine for the cleaning and brushing of the bakelite panels surfaces 2.Only mechanical: realization of an automatic machine that could locally mill the zone of the spacers and of the frame Solution 2 was discarded because it required > 4-5 months Solution 1 ready in 4-5 weeks

4. Working Plan Phase I Selection of the panels Brushing tests Roughness measurements Spacers gluing Tension tests Phase II Construction of real gaps Low pressure (5 mbar) tests Linseed oil Phase III I vs HV Cosmic test Bakelite selection (ARGO, CMS) Gluing tests Selection of Brushing Methods Roughness measurements brushing and gluing of the bakelite strips The entire panel is treated Gluing of spacers Spacers ungluing tests Phase II Gaps construction LOOP OVER IF BAD Today we are here

5. Does the problem belong to all the bakelite batches? How to select a bakelite panel Does the problem belong to all the bakelite batches? How to select a bakelite panel -The quality of each sheet is proven by gluing 4 to 5 spacers strips before any kind of test. -The remaining part is cut in strips on on which different surface tratments are applied. -One strip is kept for chemical analysis. - Spacers are glued to the treated strips with the gluing machine. -The quality of each sheet is proven by gluing 4 to 5 spacers strips before any kind of test. -The remaining part is cut in strips on on which different surface tratments are applied. -One strip is kept for chemical analysis. - Spacers are glued to the treated strips with the gluing machine.

6. 4 panels have been tested from a “bad” bakelite batch 4 panels have been tested from a “bad” bakelite batch PANELS not TREATED Tension values

7. -20 measurem. randomly distributed over the surface with random orientation of the meter -2 “old” ATLAS & BaBar and 1 “new” CMS -no sensible variations on the average roughness -20 measurem. randomly distributed over the surface with random orientation of the meter -2 “old” ATLAS & BaBar and 1 “new” CMS -no sensible variations on the average roughness PANELS not TREATED Roughness Measurements R z = ten-point height

8. Hard and soft brushing at 1700 r/min. Measurements were done transversally and longitudinally wrt the brushing direction. soft hard PANELS TREATED Mechanical Brushing

9. Something unexpected : the two sides are different ! Side A Side B Tension test on the two sides of the same panel Tension test on the two sides of the same panel Let’s call the two (indistinguishable) sides of each panel A and B: spacers were glued on both sides of the same panels and tension tests performed. Let’s call the two (indistinguishable) sides of each panel A and B: spacers were glued on both sides of the same panels and tension tests performed.

10. Tension tests on ARGO panels show the same behaviour ( ARGO has higher resistivity values) Tension tests on ARGO panels show the same behaviour ( ARGO has higher resistivity values) Side A Side B

11. Side A Side B B A Tension tests vs Roughness measurements do not evidence correlations Tension tests vs Roughness measurements do not evidence correlations Tension values Roughness values

12. Ry (  m) x 100 A A B B Tension tests vs Roughness measurements: CMS bakelite In this case the trend is opposite to the expected one Tension tests vs Roughness measurements: CMS bakelite In this case the trend is opposite to the expected one Tension values Roughness values

13. Roughness measurements done close to the region of the spacer mark vs Roughness vs Tension Roughness meausurements done in the same direction of the feed to the L.A. No correlation Roughness meausurements done in the same direction of the feed to the L.A. No correlation Rz(  m)

14. Automatic brushing and cleaning machine: L.A. “Automatic Laundry” Automatic brushing and cleaning machine: L.A. “Automatic Laundry”

15. BEFORE AFTER L.A. machine results on side A: ARGO 1500 r/min, 1m/min L.A. machine results on side A: ARGO 1500 r/min, 1m/min Detachment Tension values BEFORE and AFTER the L.A. treatment Detachment Tension values BEFORE and AFTER the L.A. treatment

16. BEFORE AFTER L.A. machine results on side B: ARGO 1500 r/min, 1m/min L.A. machine results on side B: ARGO 1500 r/min, 1m/min Detachment Tension values BEFORE and AFTER the L.A. treatment Detachment Tension values BEFORE and AFTER the L.A. treatment

17. With the same L.A. settings (1500 r/min; speed 1m/min) used for ARGO, samples of bakelite from other experiments were treated and gas volumes assembled: -ATLAS 5 gaps -CMS 3 gaps -ARGO 4 gaps Total number of spacers 2684 The 12 gaps were tested at low pressure before the surface treatment with linseed oil to check the number of “zero kg detachments” on the spacers. (tested at 540 gr) With the same L.A. settings (1500 r/min; speed 1m/min) used for ARGO, samples of bakelite from other experiments were treated and gas volumes assembled: -ATLAS 5 gaps -CMS 3 gaps -ARGO 4 gaps Total number of spacers 2684 The 12 gaps were tested at low pressure before the surface treatment with linseed oil to check the number of “zero kg detachments” on the spacers. (tested at 540 gr) 7 (over 2648) unglued spacers 3 gaps over 12 had at least 1 unglued spacer None of the remaining spacers disjoined during the pressure test 7 (over 2648) unglued spacers 3 gaps over 12 had at least 1 unglued spacer None of the remaining spacers disjoined during the pressure test

18. CMS: I vs HV curves in range (i.e. 2-5  A @ 8 kV), good surfaces quality after the linseed oil treatment, good spacer strength (i.e. > 56 mbar, the maximum overpressure available). Tested also 11 (9 w new bakelite and 2 w old bakelite) gaps (RB1-like) with brushed bakelite (no oiled yet) : 7 gaps ok up to 20 mbar, 1 gap had 1 disjoined spacer at 12 mbar, 1 gap had construction problem (i.e. big slit in the frame), 1 gap bad already at 1 mbar. ARGO: average I = (0.3 +- 0.1)  A @ 8 kV (wrt 0.2 +- 0.1  A) (1.4 +- 0.4)  A @ 9 kV (wrt 0.6 +- 0.2  A) ATLAS: no leakage up to 8 mbar, average I of 6.6  A @ 10.4 kV, Average rate 2 Hz/cm 2, eff @ working point greater than 94% CMS: I vs HV curves in range (i.e. 2-5  A @ 8 kV), good surfaces quality after the linseed oil treatment, good spacer strength (i.e. > 56 mbar, the maximum overpressure available). Tested also 11 (9 w new bakelite and 2 w old bakelite) gaps (RB1-like) with brushed bakelite (no oiled yet) : 7 gaps ok up to 20 mbar, 1 gap had 1 disjoined spacer at 12 mbar, 1 gap had construction problem (i.e. big slit in the frame), 1 gap bad already at 1 mbar. ARGO: average I = (0.3 +- 0.1)  A @ 8 kV (wrt 0.2 +- 0.1  A) (1.4 +- 0.4)  A @ 9 kV (wrt 0.6 +- 0.2  A) ATLAS: no leakage up to 8 mbar, average I of 6.6  A @ 10.4 kV, Average rate 2 Hz/cm 2, eff @ working point greater than 94%

19. Efficiency results from ATLAS