1 STAR TPC The STAR TPC Status and Additional Issues: 2009 (There are a few issues other than wire aging, and HV trips, …) Jim Thomas

2 STAR TPC We are exploring new territory with pp 500 Luminosity is up a factor of 3 compared to 2008 pp200 run, and expected to go up 4x in coming years Trigger rates can now go up a factor of 3 or more pp500 Multiplicities are 1.25x higher than in pp200 So we are working with ~5x more charge in the TPC than ever before and STAR may ask for ~40x before we are done

3 STAR TPC pp 500 is more demanding of the TPC … Beam currents are up compared to previous pp runs –Peak luminosity at the very end of run 8 was 2 * –Peak luminosity at the end of the pp500 engineering run was 6.6 * –pp 500 goals are to achieve at least 2x higher luminosity, preferably 4x Significantly more tripping than in previous years –Shift Leaders have taken to calling them “our old friend 18-4” –Speculation as to why this may be true –This may be due to holes in our shielding in the tunnel leading to hotspots in the TPC (consistent with Carl’s observations) –It may merely be due to increased background that goes with increased beam currents –Perhaps the TPC is getting older (aka ‘aging’) or has faults (ABDB boards) This is happening even though trigger rates were held at about 150 Hz for pp500 and trying to stay below 450 Hz for pp200 –A higher trigger rate means more charge travels to the anode wires; in proportion to a background rate + the trigger rate –We have tested up to 1000 Hz. Rate limiter prevents exceeding 750 Hz.

4 STAR TPC Anode Currents in Run 8 Our tradition has been to keep the anode currents low to avoid damage to the TPC and to avoid aging the anode wires

5 STAR TPC Anode currents on the outer sector in Run 9 The charge density in the TPC ~ 1/r 2 so the outer sectors see less load

6 STAR TPC Inner Sector: Normal operation – GG triggered To be fair, the alarm limits are set at our discretion and we haven’t changed the alarm limits on these screens compared to last year. We are debating whether it is wise … or not.

7 STAR TPC Lower the gain on the inner sectors Lowering the gain from 1170 to 1135 volts dropped the gain to 66% on the inner sectors –This was required in the pp500 run due to too many HV trips –We couldn’t take data … the recovery time exceed the up time –The reduction to 2/3 gain yields approximately equivalent results to previous years operation in terms of tracking and dE/dx –New TPX electronics has 30:1 gain, while previous TPC electronics was running with 20:1 gain –The TPC was designed for 20:1 signal to noise (cluster & tracking) –We kept these settings for the succeeding pp200 run and the results appear to be successful –Elegant results from Yuri Fisyak

8 STAR TPC Other Options Add Alcohol to the gas –A long tradition … but perhaps one of the arts of the occult Add H 2 O to the gas –Also anecdotal evidence that this helps aging –Although I have some irrational concerns about this option … Turn off or reduce voltage on selected HV channels (e.g. small R) Turn off or reduce voltage on the anodes at the end of each run –Run control takes 20 seconds to start Trigger the anodes and pulse them with 100 volts for each event –If the electronics can stand the noise Alternate gas mixtures –Options somewhat limited due to limited field cage characteristics These options may help deal with the wire aging issues … but only the options to change the HV on the anodes helps with the tripping at high Luminosity

9 STAR TPC More Challenging Than Ever … TPC calibrations are more challenging than ever –The pp500 low luminosity run (12x12) was not low luminosity –Usually we try to get a very low luminosity run to calibrate our calibrations –This year we will have to calibrate the calibration run –Not to mention that the magnitude of the distortions in the physics runs will be larger than ever before The TPC is supposed to last another 10 years –One constraint: HFT takes its first data in Run 14 –Data taking sequence is 3-5 years long … run 14, 15, 16, 17,18 At some point we, as a collaboration, may decide that it is prudent to manage the luminosity of the beams –Manage the luminosity –Manage the trigger rates –Not an exact science What happens if we run the TPC until it melts? –The anode wires are the most likely component to wear out –We can replace them –Not clear that we can predict, in advance, if and when this will be necessary

10 STAR TPC Winding new grids Also an opportunity to rebuild the ABDB boards which may account for some or all of the HV tripping The STAR TPC should last a long time. However, the option to replace the wire grids on the endcaps of the TPC is an extremely valuable contingency for us. See talk by A. Lebedev

11 STAR TPC More expensive options GEM Foil readout –GEM foils do not suffer from aging on our scale of activity –Opportunity to remove ABDB boards from the system –Use of the existing pad plane would mean that spatial resolution would be degraded. GEMS are a point source of charge and don’t diffuse across several of our pads. –A new pad plane in each sector would be very expensive –Using the current electronics may be impossible due to change in polarity of the signal (?) –We should look into this option in more detail … but no doubt it will be quite expensive and would take STAR offline for at least a year.

12 STAR TPC Wire Aging isn’t the only issue Wire aging isn’t the only issue with respect to predicting whether the STAR TPC will last for another 8 to 10 years –A drop in gain of 10% is not catastrophic, even 20% is OK on the inner sectors HV Channel tripping is important, too. –HV channel tripping is a show stopper –We cannot run if the frequency of trips exceeds the recovery time –Too many trips causes permanent damage to the TPC. For example this years pp500 run has caused 1 HV channel to fail and at least one more will not reach full voltage. –HV trips may not be related to wire aging … it could be hardware inside the TPC that is breaking down (e.g. ABDB boards) Finally, let me finish my talk with a few good words about our manpower

13 STAR TPC TPC Manpower - Hardware Hardware –Alexei (BNL), Dana (BNL), Jim (LBL), Howard Wieman (The Temple Mount) –Blair does answer … but is anxious to preserve his retired status Gas System –Leonid Kotchenda (MePhi) [Alexei, Dana, Jim … in training for Lite duty] Interlocks –Jim Water –CAD, Alexei, Soja (BNL) Slow controls & Computers –Yuri Gorbunov (Creighton) & Wayne Betts(BNL) Electronics –STSG – Padrazo + Crew, Tonko, Jeff Landgraf, Bob Scheetz (BNL) Laser –Alexei

14 STAR TPC TPC Manpower - Software Pad Monitor –Jo Schambach (UT) has plans to upgrade the old pad monitor –Will require continuing support: new features, formats change … –Jeff arranged a test last year, Blair was able to see DAQ1000 files Bad Pad/Gain file –Tonko, Jeff Calibrations for Drift Velocity, dE/dx, etc. –Richard Witt (Naval Academy), Yuri (BNL), Patricia Fachini (BNL) Calibrations for Grid leak, Space Charge, Shorts etc. –Gene (BNL), Jim, Hao Qiu, Joe Seele, Grant Webb New Fast Tracker for Fast Offline –Hao Qiu (Lanzhou & BNL) + Zhangbu + Yuri

15 STAR TPC Manpower Issues Same old faces … some are wearing out –Many of these folks would like to move on to new frontiers New faces –The Spokesman’s Office has been very good about recruiting young people (esp. for calibration work) –We also need some senior faces, and people who don’t rotate so fast Slow Controls –DAQ 1000 is only one of the new systems joining STAR this year –STAR is always under-staffed in this category. Creighton does heroic work … but its only a small group … additional manpower would help ensure STAR’s future

16 STAR TPC TPC Meetings – weekly, on Wednesday TPC mailing list is very active TPC web pages – –Gene’s record of recent calibration activities – –Perhaps easier to locate via ‘experiment’ ‘sub-system’ on the STAR homepage –Hardware documentation –Procedures – expert and operator instructions Weekly TPC meetings –Coordinated by Richard Witt –Regular attendees include – Gene, Yuri, Alexei, Richard, Hao, Jim, Joe, and Grant –Additional participants are welcome!

17 STAR TPC Conclusions The TPC has performed well in 2009 –pp500 … 10 C deposited on the inner sectors in only 6 weeks –pp200 … probably another 10 C deposited on the inner sectors We are exploring new territory with the pp500 run plan –We have successfully found a strategy to deal with Luminosities up to 6 x The collaboration has run plans that will push these limits even higher –Wire aging isn’t the only hardware issue. HV channel trips may be the greater problem and the cause of these trips may not be directly related to wire aging. We have several options … including deferring some of our run plans … but only modest amounts of time to do R&D We must choose which options to pursue with care and wisdom