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8/04

/23

Christian J. Schmidt

GSI Production of ALICE TRDs

Progress and Quality Development

Alice TRD Chamber Production Meeting

Darmstadt Feb. 27th 2006

L4 and L5 chambers often show severe gain inhomogeneities up to +- 40%

Problem can be cured by shimming side ledges with 100 or 200 micron shims, depending upon the outcome of pre-glue scan(s).

Homogeneity Distortions Could be Resolved

2 4 6 8 10 12

2

4

6

8

10

L5C1006 pre glue, no shimming

Z-Position

Phi

-Pos

ition

12 10 8 6 4 2

10

8

6

4

2

L5C1006 pre glue with various foils on ledges 200mu to 300mu on right half

Z-Position

Phi

-Pos

ition

12 10 8 6 4 2

10

8

6

4

2

L5C1006 pre glue second scan, third shimming trial

Z-PositionP

hi-P

ositi

on

0.6000

0.7000

0.8000

0.9000

1.000

1.100

1.200

1.300

1.400

Final Glueing Alters Things Slightly

12 10 8 6 4 2

10

8

6

4

2

L5C1006 pre glue third shimming trial

Z-Position

Phi

-Pos

ition

12 10 8 6 4 2

10

8

6

4

2

Z-Position

Phi

-Pos

ition

0.8600

0.9000

0.9400

0.9800

1.020

1.060

1.1001.120

L5C1006 final post glueing, deviation -14% to 12%

Statistics on Homogeneity over Current Production

Statistics on Maximum Deviations (Histogram)

Maximaly deviating points per chamber collected.Outlyers may be attributed to various problems

Leakage Currents

Apply HV immediately after chamber installation,

initial leakage currents would identify surface leakage.

Ever since the employment of the cleaning procedure, no

more leakage across glue surfaces encountered.

Leakage due to dust and dirt remains but seldom in winter

Leakage due to bad HV-cables with missing currents has

resurfaced due to bad cables that had been used in the past.

Gas Leak Determination

Normal behaviour: Time constant of Oxygen level ~ 12 h

By now quite a few cases ( ~ 8 ) with ~ 50 to 100 h

Strong indication for virtual leaks No external leaks measurable

Oxygen level scales inversely with gas flow

Taken typical initial Oxygen content of 80 ppm at 20 l/h, implying a leak of 8 mbar l/h, the time constant would indicate a hidden volume of several hundred ml.

too little for the radiator

too much for the pad plane

At GSI chambers in doubt are rapidly moved to a separate leak test stand where they can be flushed for many days.

Statistics on Leakage over Current Production

Statistics on Gain MeasurementsHistogram on measured gain at 1600 V Anode voltage

Gain determination is difficult at GSI as strong EMIdisturbances are intermittendly present.

Mistakes on Radiator Unveiled

-20 0 20 40 60 80 100 120 140 160

300

350

400

450

500

550

600

650

Anode C

urr

ent (

a.u

.)

Z-Position

scan across the top scan across center

L5C1001 final

Just intended as an example for funny data and straight forward explanations:

12 10 8 6 4 2

10

8

6

4

2

L5C1001 final post glue

Z-Position

phi-P

ositi

on

0.9000

0.9375

0.9750

1.013

1.050

1.088

1.125

1.163

1.200

Diagnosis: one out of seven radiator pads missing in one compartment

Dubna Chambers under Repair

Out of 18 chambers, 4 have a broken radiator towards the inside of the chamber

All 18 chambers need to be refurbished: Radiator needs to be carefully reworked and closed again.

Yuri and Nicolai are at GSI until March 11th to work on chambers

They are experimenting on best techniques for refurbishment

Bernd Voss (GSI) has successfully repaired one of the broken chambers

Proposed Reassembly Procedure

Pressure applied through slab: 5 g/cm2 ~ 5 mbar

Radiator

Pad-panel

GasVolume Spacer

supportbars

Gas Inlet

Conclusion on Current Situation at GSI

Production is running smoothly

Production rate at 1.5 chambers per week, limited by infrastructure

Various problems have been settled and quality is improving

Dubna chambers are under repair, no reason to be pessimistic here.