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

2 Jim 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

3 Jim 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

4 Jim Thomas - LBL 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

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

6 Jim Thomas - LBL 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

7 Jim Thomas - LBL 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 Gain Voltage

8 Jim Thomas - LBL 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

9 Jim Thomas - LBL 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

10 Jim Thomas - LBL Gas System 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.

11 Jim Thomas - LBL Summer Shutdown: usually a very tight schedule STAR runs 24/7 for weeks per year Typical schedule for shutdown period –Not a lot of time for R&D … or repair