Christian J' Schmidt

1
GSI Production of ALICE TRDs Progress and
Quality Development
Alice TRD Chamber Production Meeting Darmstadt
Feb. 27th 2006

• Christian J. Schmidt

2
Homogeneity Distortions Could be Resolved

• 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).

3
Final Glueing Alters Things Slightly
4
Statistics on Homogeneity over Current Production
5
Statistics on Maximum Deviations (Histogram)
Maximaly deviating points per chamber
collected. Outlyers may be attributed to various
problems
6
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.

7
Gas Leak Determination

• Normal behaviour Time constant of Oxygen level
  12 h
• By now quite a few cases ( 8 ) with t 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.
8
Statistics on Leakage over Current Production
9
Statistics on Gain Measurements
Histogram on measured gain at 1600 V Anode voltage
Gain determination is difficult at GSI as strong
EMI disturbances are intermittendly present.
10
Mistakes on Radiator Unveiled
Just intended as an example for funny data and
straight forward explanations
Diagnosis one out of seven radiator pads
missing in one compartment
11
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
12
Proposed Reassembly Procedure
Gas Inlet
Pressure applied through slab 5 g/cm2 5 mbar
Radiator
Gas Volume
Spacer support bars
Pad- panel
13
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.