A Brief Introduction to the STAR Time Projection

A Brief Introduction to the STAR Time Projection Chamber Jim Thomas Lawrence Berkeley National Laboratory June 4 th, 2009 Jim Thomas - LBL 1

The TPC Flies from LBL to BNL - Nov 6, 1997 Jim Thomas - LBL In 2009, the FEE electronics was upgraded to TPX - see talk by T. Ljubicic 2

Basic Size and Shape • 4. 2 m long • 4 m dia • Cathode at midplane of TPC • 28 k. V, norm • Readout on both ends • Anode planes, each with Inner & Outer sectors Jim Thomas - LBL 3

TPC Sector Detail • 24 sectors • 12 on each side • Large pads for good d. E/dx resolution in the Outer sector • Small pads for good two track resolution in the inner sector 60 cm 190 cm Jim Thomas - LBL See talk by Y. Fisyak 4

Sector Repair is possible but not a trivial task Jim Thomas - LBL Sector Installation & Tooling See talk by A. Lebedev 5

TPC Sector Detail • Gating Grid • Ground Shield • Anode – 4 mm pitch, no field wires – Spacing: inner outer • Pad Plane Jim Thomas - LBL See talks by A. Lebedev and R. Witt 6

A few other anode facts – 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 Jim Thomas - LBL 1 Gain • There are 8 HV channels and 6 RDOs per sector Inner 0, 1 1050 1150 1250 Voltage Outer 1350 7

Field Cage: to short or not to short … • The field cage operates at 28 k. V … limit is ~ 40 k. V • 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 Jim Thomas - LBL See talks by G. Van Buren & J. Seele 8

Gas • STAR uses P 10 – 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 k. V – Practical limit ~40 k. V • Other gases may be possible but choices limited by drift field and BNL health & safety reqs Jim Thomas - LBL 9

Gas System Jim Thomas - LBL The existing gas system works well and could be extended to include H 2 O or Alcohol. We have no experience with this and don’t know what impact it will have on the TPC and internal components. 10

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 Jim Thomas - LBL 11