22/04/2001 1Wire 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

22/04/2001 2Wire 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 +/-50m) • 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

22/04/2001 3Wire 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 !

22/04/2001 4Wire 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.

3 Gap Leak test3-4mbar/h

0

2

4

6

8

10

0 1 2Time in h

Pres

sure

in

mba

r

15cm screw distance

10cm screw distance

22/04/2001 5Wire 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

rate26 2G Leak test=> less than 1mbar/h

0

5

10

15

20

25

0 1 2 3 4

Time in h

Pres

sure

in

mba

r

15cm srew distance

10cm screw distance

22/04/2001 6Wire 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/

22/04/2001 7Wire 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

22/04/2001 8Wire 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

22/04/2001 9Wire 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.