1Jim Thomas - LBL

A Brief Introduction to the STAR Time Projection Chamber

Jim Thomas

Lawrence Berkeley National Laboratory

June 4th, 2009

2Jim Thomas - LBL

The TPC Flies from LBL to BNL - Nov 6, 1997

In 2009, the FEE electronics was upgraded to TPX - see talk by T. Ljubicic

3Jim Thomas - LBL

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

60 cm

190 cm

• 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

Sector Operation for 20:1 signal to noise

Sector anode voltage

gas gain

inner 1170 3770 10%

outer 1390 1230 10%

• 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

Gai

n

Voltage

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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 don’t 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

R&D … or repair