A Brief Introduction to the STAR Time Projection Chamber

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A Brief Introduction to the STAR Time Projection
Chamber

• Jim Thomas
• Lawrence Berkeley National Laboratory
• June 4th, 2009

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The TPC Flies from LBL to BNL - Nov 6, 1997
In 2009, the FEE electronics was upgraded to TPX
- see talk by T. Ljubicic
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Basic Size and Shape

• 4.2 m long
• 4 m dia
• Cathode at midplane of TPC
• 28 kV, norm
• Readout on both ends
• Anode planes, each with Inner Outer sectors

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TPC Sector Detail

• 24 sectors
• 12 on each side
• Large pads for good dE/dx resolution in the Outer
  sector
• Small pads for good two track resolution in the
  inner sector

See talk by Y. Fisyak
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Sector Repair is possible but not a trivial task
Sector Installation Tooling
See talk by A. Lebedev
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TPC Sector Detail

• Gating Grid
• Ground Shield
• Anode
• 4 mm pitch, no field wires
• Spacing inner ? outer
• Pad Plane

See talks by A. Lebedev and R. Witt
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A few other anode facts

• There are 8 HV channels and 6 RDOs per sector
• We can address anode wires by radius on, off, or
  lower the gain
• HV almost coincident with RDO divisions on the
  outer sector
• HV not coincident with RDO division in the inner
  sector

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Field Cage to short or not to short

• The field cage operates at 28 kV limit is 40
  kV
• Occasionally we will find a short between a pair
  of the Field Cage rings
• Usually (magnetic) dirt
• We had one permanent short on the East end
• Its has been repaired
• We have an intermittent short on the west end
• Approx ¼ of a 2 M resistor
• After a cluster of Main Magnet crashes this year
  we developed a full short
• Approx ring 130 (out of 182)

We have precision software to deal with these
shorts See talks by G. Van Buren J. Seele
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Gas

• STAR uses P10
• Low Drift Field
• 130 V/cm
• Good Diffusion
• DV at Peak of Curve
• Easy to mix
• He-Ethane was considered as an option
• Good Diffusion
• Lower MCS
• But DV is low and requires a higher field
• STAR designed for 85 kV
• Practical limit 40 kV
• Other gases may be possible but choices limited
  by drift field and BNL health safety reqs

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Gas System
The existing gas system works well and could be
extended to include H2O or Alcohol. We have no
experience with this and dont know what impact
it will have on the TPC and internal components.
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Summer Shutdown usually a very tight schedule

• STAR runs 24/7 for 20-30 weeks per year
• Typical schedule for shutdown period
• Not a lot of time for RD or repair