Seog Oh/ Duke University/Oct, 2002 TRT/ ATLAS week at CERN Test of the cleaning gas mixtures

Seog Oh/ Duke University/Oct, 2002 TRT/ ATLAS week at CERN Purpose  Find out the safe operating limit of the glass wire-joint in mixtures with CF 4 in case silicon cleaning is necessary.  Run parameters  Upper chamber  14 glass wire-joints – 5 were pulled out on July 25. The rest was pulled out on Sept 27. –June/July/August : Ar-CO 2 -CF 4 ( ) : 16% mixture –September : Ar-CO 2 (70-30)  Lower chamber  11 glass wire-joints – 4 were pulled out on July 25. The rest was pulled out on Sept 27 –Ar-CO 2 -CF 4 ( ) : 8% mixture  Moisture level : 700 ppm on average  Gain  June/July/August - ~30,000-40,000  September ~ 70,000-80,000  Current draw  Average : 10 nA/cm – 30 nA/cm  Around wire-joints : 30 nA-100nA/cm

Seog Oh/ Duke University/Oct, 2002 TRT/ ATLAS week at CERN Test module 2

Seog Oh/ Duke University/Oct, 2002 TRT/ ATLAS week at CERN Test setup

Seog Oh/ Duke University/Oct, 2002 TRT/ ATLAS week at CERN 16% Results  Failure (do not hold HV) occurred when the integrated charge was C/cm.  0.22, 0.19, 0.26, 0.21, 0.27, 0.34 C/cm  Tension loss proceeded the failure.  All glass beads exhibited heavy etching reasonably proportional to the integrated charge.  Despite the etching, there was no evidence of silicon deposit downstream (SEM & Gain measurement).  This test ended at the end of August. At the time, there were two surviving wire-joints (#30, #31). The gas mixture was changed to Ar-CO 2 (70-30) to study the residual effect of CF 4 (more later).

Seog Oh/ Duke University/Oct, 2002 TRT/ ATLAS week at CERN

Seog Oh/ Duke University/Oct, 2002 TRT/ ATLAS week at CERN Failed wire-joints (~0.3C/cm)16%

Seog Oh/ Duke University/Oct, 2002 TRT/ ATLAS week at CERN 16%  Wire # C/cm. Broken (8/25)

Seog Oh/ Duke University/Oct, 2002 TRT/ ATLAS week at CERN Wire-joints in 16%  Note that there is no Silicon peak. Si is replaced by F.

Seog Oh/ Duke University/Oct, 2002 TRT/ ATLAS week at CERN Wire surface scan (16%)  Left : “normal”. Right : somewhat smooth

Seog Oh/ Duke University/Oct, 2002 TRT/ ATLAS week at CERN 16%  Left : “normal”. Right : somewhat smoother

Seog Oh/ Duke University/Oct, 2002 TRT/ ATLAS week at CERN Wire  Downstream of a wire-joint. There is no silicon deposit

Seog Oh/ Duke University/Oct, 2002 TRT/ ATLAS week at CERN Wire #26 (0.27C/cm). Broken 8/18

Seog Oh/ Duke University/Oct, 2002 TRT/ ATLAS week at CERN 8% Results  One failure occurred when the integrated charge was ~0.45 C/cm.  Tension loss happened as early as ~0.3 C/cm.  Etching on the failed joint was also evident. However compare to the failed ones in 16%, the etching was less.  There was also no evidence of silicon deposit downstream (SEM & Gain measurement).

Seog Oh/ Duke University/Oct, 2002 TRT/ ATLAS week at CERN

Seog Oh/ Duke University/Oct, 2002 TRT/ ATLAS week at CERN Failed wire-joint (~0.45C/cm)8%  Wire #12

Seog Oh/ Duke University/Oct, 2002 TRT/ ATLAS week at CERN 8% (#10)  Wire # C/cm. Lost 22 grams of tension

Seog Oh/ Duke University/Oct, 2002 TRT/ ATLAS week at CERN Wire-joint (8%)  There is still some silicon peak

Seog Oh/ Duke University/Oct, 2002 TRT/ ATLAS week at CERN Wire #12 (0.45C/cm) Broken 9/14

Seog Oh/ Duke University/Oct, 2002 TRT/ ATLAS week at CERN Residual effect of CF 4  The 16% mixture was changed to Ar-CO 2 (70-30) on September 3.  The gas gain : ~70,000 (from ~30,000)  Current Draw : ~17 nA/cm (=> ~50 nA around the wire-joints)  Charge accumulation  The integrated charge at the time of the switch : ~0.15 C/cm  The integrated charge since the switch : ~0.1 C/cm  Results  The degree of etching was consistent with ~0.15C/cm rather than ~0.25 C/cm.  No gain change was observed after the switch

Seog Oh/ Duke University/Oct, 2002 TRT/ ATLAS week at CERN

Seog Oh/ Duke University/Oct, 2002 TRT/ ATLAS week at CERN 0.15C/cm in 16%+0.1C in Ar-CO 2  Wire #30, 31

Seog Oh/ Duke University/Oct, 2002 TRT/ ATLAS week at CERN 16% -> 0%  Wire #30 and #31

Seog Oh/ Duke University/Oct, 2002 TRT/ ATLAS week at CERN Wire-joint #30

Seog Oh/ Duke University/Oct, 2002 TRT/ ATLAS week at CERN 16% -> 0%  4 cm downstream of wire-joint

Seog Oh/ Duke University/Oct, 2002 TRT/ ATLAS week at CERN 16% -> 0%  20 cm downstream of wire-joint. The chunks are gold.

Seog Oh/ Duke University/Oct, 2002 TRT/ ATLAS week at CERN Wire #31

Seog Oh/ Duke University/Oct, 2002 TRT/ ATLAS week at CERN Summary  Integrated charge  From the 16% and 8% test, it seems that the failure integrated charge is roughly proportional to the CF 4 fraction when the moisture level of ~700 ppm.  16% : fail at C/cm  8% : fail at C/cm  Including the earlier measurement (CF 4 ~20%, H 2 O ~ ppm, integrated charge at the failure ~ 0.1 C/cm), it seems that the failure also roughly proportional to the H 2 O level.  There is no silicon deposit or gain change.  There is no gross residual effect when the gas is switched to non CF 4 mixture.

Seog Oh/ Duke University/Oct, 2002 TRT/ ATLAS week at CERN Proposal  Test 4% mixture – (may not be necessary)  Test the effectiveness of the cleaning mixtures  Produce silicon deposit with Ar-CO 2 (70-30) gain drop of ~10%  Bubble through silicon oil?  Use contaminated straws?  Switch the gas to one of the cleaning mixtures. Determine the integrated charge necessary to restore the gain.  Parameters  CF 4 fraction  Moisture level  Gain  Irradiation level