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

Test of the cleaning gas mixtures


Purpose Find out the safe operating limit of the glass wire-joint in mixtures

with CF4 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-CO2-CF4 (70-14-16) : 16% mixture– September : Ar-CO2(70-30)

Lower chamber 11 glass wire-joints – 4 were pulled out on July 25. The rest was pulled

out on Sept 27– Ar-CO2-CF4 (70-22- 8) : 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


Test module 2


Test setup


16% Results Failure (do not hold HV) occurred when the

integrated charge was 0.2-0.3 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-CO2 (70-30) to study the residual effect of CF4 (more later).


16% (C/cm .vs. T change)

-20

-15

-10

-5

0

5

0 0.05 0.1 0.15 0.2 0.25 0.3

C/cm

Tens

ion

loss


Failed wire-joints (~0.3C/cm)16%


16% Wire #25. 0.27C/cm. Broken (8/25)


Wire-joints in 16% Note that there is no Silicon peak. Si is replaced by F.


Wire surface scan (16%) Left : “normal”. Right : somewhat smooth


16% Left : “normal”. Right : somewhat smoother


Wire Downstream of a wire-joint. There is no silicon deposit


Wire #26 (0.27C/cm). Broken 8/18


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).


8% (C/cm .vs. T change)

-25

-20

-15

-10

-5

0

5

0 0.1 0.2 0.3 0.4 0.5

C/cm

Tens

ion

loss


Failed wire-joint (~0.45C/cm)8% Wire #12


8% (#10) Wire #10. 0.31 C/cm. Lost 22 grams of tension


Wire-joint (8%) There is still some silicon peak


Wire #12 (0.45C/cm) Broken 9/14


Residual effect of CF4 The 16% mixture was changed to Ar-CO2 (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


0.15C/cm in 16%+0.1C in Ar-CO2

Wire #30, 31


16% -> 0% Wire #30 and #31


Wire-joint #30


16% -> 0% 4 cm downstream of wire-joint


16% -> 0% 20 cm downstream of wire-joint. The chunks are gold.


Wire #31


Summary Integrated charge

From the 16% and 8% test, it seems that the failure integrated charge is roughly proportional to the CF4 fraction when the moisture level of ~700 ppm.

16% : fail at 0.2-0.3 C/cm 8% : fail at 0.4-0.5 C/cm

Including the earlier measurement (CF4 ~20%, H2O ~ 2000-3000 ppm, integrated charge at the failure ~ 0.1 C/cm), it seems that the failure also roughly proportional to the H2O level.

There is no silicon deposit or gain change. There is no gross residual effect when the gas is

switched to non CF4 mixture.


Proposal Test 4% mixture – (may not be necessary) Test the effectiveness of the cleaning mixtures

Produce silicon deposit with Ar-CO2 (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 CF4 fraction Moisture level Gain Irradiation level

seog oh/ duke university/oct, 2002 trt/ atlas week at cern test of the cleaning gas mixtures

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