22/04/20011Wire Chamber Working Group Status on O-ring closed Prototype Foam panels from Frascati (size: 279mm*341mm) No pad structure 4 independent gas gaps Screw distance can be varied from 10 to 15cm O-ring choice :  3mm EPDM, 50 Shore A 5 mm spacers around screws define gap size

22/04/20012Wire Chamber Working Group Status on O-ring closed Prototype Bar Gluing Tool Full Frame (4 bars) is glued in one go Bars are glued with high precision (2.5mm +/-50  m) Space between bar and panel is filled up with glue => quantity of the glue depends on bar thickness and panel planarity Good transition at the bar junctions where the O-ring sits Procedure well established

22/04/20013Wire Chamber Working Group Status on O-ring closed Prototype First tests have shown enormous leaks between bars and panel. In the corners the panels are up to 500  m less thick => A lot of glue had to be used in this regions. Due to this, the glue connection broke at these places. (stress or shrinking of the glue) Additional silicon sealing has been put on from the outside. The gap precision we get from the Spacers. ->These sit as well in the border region. ->One more reason to improve the quality of the panels in this area !

22/04/20014Wire Chamber Working Group Status on O-ring closed Prototype Result of Leak tests: After improvement of the bar gluing 3 out of 4 gaps were put in a row. Overpressure of about 15mbar was applied to the gaps. The decrease of pressure was measured over time.

22/04/20015Wire Chamber Working Group Status on O-ring closed Prototype Best results were achieved in gap 26 G2 =>The O-Ring solution is leak tight in the range of 1-4mbar/h =>The screw distance does not influence much the leak rate

22/04/20016Wire Chamber Working Group Status on O-ring closed Prototype Result of Radiation test: “A sample of the EPDM O-ring has been irradiated with a dose of 10, 13, 30KGy... apparently without any damage” (Carlo Bosio) Result of Conductivity test: In 3 gaps the HV traces were covered by a Kapton layer. The one without tripped already at 100V. We realized that this O-ring is not resistive enough ! ~200K  were measured in between HV traces and ground. We exchanged the O-ring with a more isolating one (NR  3.3 mm 45 shore A) and got in contact with the company. We measured the conductivity of around 30 samples. Based on these results and the advise from the company we will order Material. Some numbers: –EPDM 50 shore A/~10M  –EPDM 27 shore A/???  –MVQ (silicon) 20 shore A/  

22/04/20017Wire Chamber Working Group Status on O-ring closed Prototype HV Behavior The HV test in air before assembly up to 4kV has been ok. The limit for the HV of the assembled chamber under gas was around 3350 V. Trips occur randomly and can not be forecasted from the dark current behavior. Gap size uniformity Uniformity tests with the Am-source have shown that the chamber tends to trip in the border regions. This is still under investigation. Possible reasons could be: –Changes in the border region because of O-ring solution –Deformations due to the O-ring (  3.3 mm) –Bad panel quality in the border region –Full copper plane pad structure with no copper at the borders

22/04/20018Wire Chamber Working Group Status on O-ring closed Prototype Old Prototypes: Copper stopped at bars or even before. O-ring Prototypes: Full copper plane. Copper passes the bars

22/04/20019Wire Chamber Working Group Status on O-ring closed Prototype Next Steps : High resistive and softer O-ring material will be ordered. A Radiation test of this new component should be envisaged. The chamber will be reassembled. Open question concerning HV behavior and gap size uniformity will be investigated.