STAR PXL status

1. STAR PXL status • Construction Status / Installation • Cosmic ray run • 15 GeV/c and 200 GeV/c running • Sensor damage • Operational procedures implemented for remediation • Testing and possible implications • Outlook ALICE-ITS meeting April 25, 2014

2. Construction Status • First PXL detector was completed and shipped to BNL in February 2014. • Second PXL detector is under construction. Estimated completion in June 2014. • 20 spare inner and 20 spare outer replacement ladders under construction. Estimated completion June 2014. • Project CD-4 technical review date is scheduled for mid July 2014. ALICE-ITS meeting April 25, 2014

3. Detector Installation PXL assembled and under test in the STAR assembly area. • Pxl installation pics • Clean room • Installed and cabled PXL inserted into the STAR TPC inner field cage. Cabling, power and cooling air system installed. ALICE-ITS meeting April 25, 2014

4. Status after installation • PXL was installed with all sensors (400) working. < 2k bad pixels out of 356 M pixels. • 38 ladders with Cu FPC, 2 inner ladders with Al FPC. • Automated threshold setting scripts applied (1600 thresholds need to be set). Noise rate is ~1-2 x 10-6 per sensor for most of the sensors. Last few sensors were tuned manually. • Readout is working well. We have tested it through DAQ at trigger rates up to 3kHz. • Dead time at 1kHz < 5% • Interfaces to trigger, DAQ working well. Interface to slow controls still being completed. • LU thresholds at default ~400mA above operating current of ~800 mA. • Cooling working well. ALICE-ITS meeting April 25, 2014

5. Cosmic Ray running • Detector working well. • All parameters stable and alignment with cosmic ray tracks in progress. • Some misalignment in the kinematic mounts (~1mm). • Sensor positions on detector halves appear to be as measured in the CMM before installation. ALICE-ITS meeting April 25, 2014

6. PXL preliminary half-to-half pointing residuals Inner layer Preliminary Preliminary Preliminary outer layer Preliminary Preliminary Preliminary Consistent with expectations for alignment and momentum of muons. Preliminary alignment by Alex Schmah ALICE-ITS meeting April 25, 2014

7. 15 GeV/c and 200 GeV/c running - status Apr 23 Jan 25 Feb 14 Mar 14 Jul 2 now End of run 200 GeV start 15 GeV start PXL install • The HFT (PXL + IST) was used only intermittently in the 15 GeV/c Au+Aurun. • The HFT (PXL + IST) has been operated in the 200 GeV/c Au+Au since the start. • The SSD is still commissioning and is expected to join the data taking in some weeks. • We have 300M events stored and are on track to take 1G events in this run. This should meet physics requirements. Projection of current data rate to end of run ALICE-ITS meeting April 25, 2014

8. Preliminary DCA Pointing resolution TPC + IST + PXL Preliminary 750 MeV Kaon 750 MeV Kaon 200 GeV/c Au-Au data (Cu FPC) Simulation with Al FPC * Alignment and calibrations still not complete ALICE-ITS meeting April 25, 2014

9. 15 GeV and 200 GeV running – sensor damage • The 15 GeV beams appear to be very unstable. There have been at least 7 beam events that have tripped off the cathode power supply to the TPC. This dumps a LOT of radiation into the PXL detector. • First sensor damage was observed in the last week of the 15 GeV running after 7 beam loss events. Increase in digital current on S9L1 and S1L1. Two sensors exhibited operational damage. Damage to sensors continued into the 200 GeV run. • Sensor damage takes many forms – increased current draw, loss of intact header, loss of columns, damaged columns, damaged JTAG registers, loss of full and partial sub-arrays, etc. • Current increases are always found in the digital power supply and the damage is concentrated in the inner ladders. The analog supply current is stable. • In addition, we observe current excursions ( that do not trigger LU) and sensor malfunctions that are recoverable with a power cycle or JTAG refresh that are attributed to SEU. • Now all inner ladders show increased current draw as do 3 outer ladders. This damage has occurred primarily during the 200 GeV running. • The LU rate with existing thresholds is ~15 / run (30 minutes) for the detector. • Current status of detector is 8 bad inner sensors. 3 bad outer sensors. Still under analysis. ALICE-ITS meeting April 25, 2014

10. Possible Mechanisms • Non-ionizing (Neutron) damage? – Dislocation of atoms in the matrix generally results in permanent damage to silicon. This is consistent with what we observe. In discussions with Matt Durham who worked on the Phenix FVTX detector, he indicated that the beam tune into Phenix had some component of scraping against a magnet or beam pipe surface that caused spallation neutron based damage in their detector and that the neutron rate was nearly 3 orders of magnitude above what was calculated. In our case, we have no information about the neutron flux at low radii from the beamline. • Ionizing radiation damage? – The primary source of ionizing radiation damage is expected to come from the transit of MIPs through the sensors. This is expected to show up in hits registered in sensor pixels. The occupancy of charged tracks is approximately what was projected in the simulations ( ~300 hits per frame on the inner ladders and ~100 hits per frame in the outer ladders). The likelihood of normal beam activities causing the damage observed is judged to be low. There have been, however, a significant number of non-standard events during this run. Particularly during the 15 GeV run period. • LU related damage? – It is possible that LU events could cause damage in the silicon. This would need to be a phenomenon particular to thinned silicon and/or high resistivity epi. We did extensive testing of full thickness sensors at the BASE facility at the 88” cyclotron at LBNL where we exposed sensors to many thousands of LU events to measure the LU LET onset and cross-section. ALICE-ITS meeting April 25, 2014

11. Operational procedures implemented for remediation • For ionizing and non-ionizing damage there is very little that can be done to mitigate damage using operational methods. • Current operational procedures: • Power detector off when not in use (particularly during high intensity running early in fill where there is too much pileup). • We implemented a full detector reset (power off and reconfiguration) that occurs every 15 minutes (settable) • We have changed the way that we set the LU thresholds such that the LU limit is now 6 DAC counts (120mA) above the measured operating current for the ladder for all ladders. (previously this was up to 400mA above operating current) ALICE-ITS meeting April 25, 2014

12. NOW Amps Digital current on the inner ladders Before operational optimizations Amps ALICE-ITS meeting April 25, 2014

13. PXL increased current consumption IPHC-LBL Phone conference April 1, 2014 ALICE-ITS meeting April 25, 2014 13

14. Latch-up? • LU initial default thresholds were ~1.2A for digital power with initial ladder current of 800mA. This was the case for the time when most of the damage occurred. • LU threshold control implemented by 2nd week of 200GeV run but we needed time to find the running currents. • Thresholds at 120mA over operating currents and global reset implemented for ~3 weeks, no or minimal additional damage since then (but this is not a guarantee, only an observation) • The new LU limits also limit SEUs that cause increased current. • It appears that a damage mechanism may be dependent on the amount of energy available to be dissipated in a LU event. • LU itself is not a problem. We expect it and have mechanisms to deal with it. Damage from LU events (if this is what is happening) is quite unexpected and needs further study. ALICE-ITS meeting April 25, 2014

15. Proposed Testing Plan Proton Irradiation The testing done for ionizing radiation dose was done with gamma rays. This is a generally accepted method of assessing the radiation tolerance of silicon designs. The proton irradiation more closely mimics the environment at the operating STAR experiment and adds displacement damage to the mix. We propose to expose an existing powered PXL ladder to proton beams at the 88” cyclotron at LBNL at various rates up to 300 kRadas well as testing the latch-up cross section due to proton irradiation (if possible, the primary proton LU mechanism of energy deposition from recoil only turns on at ~100 MeV). Latch-up Testing It is possible that the damage observed is related to latch-up. The fact that the sensors are now thinned to 50um could give opportunity for other failure mechanisms such as micro-fracturing due to higher LU point temperature excursions. We propose to expose an existing PXL ladder and thinned sensor on testing cards to heavy ion beams at the 88” Cyclotron BASE facility for up to 5k latch-up events on a sensor. We will also measure the voltage discharge profile on the ladder to understand the profile of energy deposition in the silicon LU area. The production sensors have high resistivity epi and the initial LU test sensors were standard epi. Neutron Irradiation It is possible that we are being exposed to a much higher neutron flux than has been anticipated. We propose to irradiate some sensors to doses of 1013, 1014 and 1015 1MeV Neq / cm2 . These sensors have already been sent to Sandia for irradiation with a batch of ATLAS sensors. ALICE-ITS meeting April 25, 2014

16. Possible Implications • Depending on the rate of damage, it is possible we could lose some significant part of the functional detector by the end of the run. If the damage rate is too high, we may envision inserting the spare detector for the remainder of the run. • The damage appears to be stable for the moment. There is little reason to expect that we can change the existing design as most of the second detector and spare ladders are already fabricated. • It is important to determine the mechanism since this could affect new detector designs based on MAPS. • This may have implications for sensor designs that have a high dynamic range in current draw and are less amenable to LU threshold adjustments. ALICE-ITS meeting April 25, 2014

17. outlook • The DCA pointing resolution performance of the installed detector appears to be as expected. • If the damage can be minimized by operational methods (as it appears now), we expect to be able to deploy the spare detector (with Al conductor FPC on the inner ladders) for the next run and repair the damage to the existing detector. • At this point, it appears that the installed PXL detector will be able to complete the physics goals for this run. • The spare detector should be ready in ~1.5 months. ALICE-ITS meeting April 25, 2014

18. Lessons learned (or already known) • Build testing functionality into the sensor design from the start optimized for probe testing/module testing. Develop the parametric testing requirements first and implement them in the design. • Probe testing • Proper probe pins for thinned sensors • spend time on whole system yield (ours varied between 35% - 55%) • Engineering run • Do a proper full system test (if possible) in the correct environment with partial full detector and infrastructure. • Spend time optimizing full yield through all production steps. • Full LU/rad environment testing of thinned production sensors/modules for all expected conditions. • Have backup solutions – e.g. Cu rather than Al conductor FPC • Implement as much remote configuration of sensor/module and detector operating parameters as possible to allow for remediation of surprises. ALICE-ITS meeting April 25, 2014

19. end ALICE-ITS meeting April 25, 2014

20. Run 15090063 - Mon Mar 31 21:16:0 Sector 1 L1 = 1.75 A L2 = 0.78 A L3 = 0.78 A L4 = 0.78 A IPHC-LBL Phone conference April 1, 2014 ALICE-ITS meeting April 25, 2014 20

21. Run 15090063 - Mon Mar 31 21:16:0 Sector 2 L1 = 1.34 A L2 = 0.78 A L3 = 0.78 A L4 = 0.78 A IPHC-LBL Phone conference April 1, 2014 ALICE-ITS meeting April 25, 2014 21

22. Run 15090063 - Mon Mar 31 21:16:0 Sector 3 L1 = 2.44 A L2 = 1.31 A L3 = 0.78 A L4 = 0.78 A IPHC-LBL Phone conference April 1, 2014 ALICE-ITS meeting April 25, 2014 22

23. Run 15090063 - Mon Mar 31 21:16:0 Sector 4 L1 = 1.51 A L2 = 1.31 A L3 = 0.78 A L4 = 0.78 A IPHC-LBL Phone conference April 1, 2014 ALICE-ITS meeting April 25, 2014 23

24. Run 15090063 - Mon Mar 31 21:16:0 Sector 5 L1 = 1.32 A L2 = 0.78 A L3 = 0.78 A L4 = 0.92 A IPHC-LBL Phone conference April 1, 2014 ALICE-ITS meeting April 25, 2014 24

25. Run 15090063 - Mon Mar 31 21:16:0 Sector 6 L1 = 1.13 A L2 = 1.36 A L3 = 0.78 A L4 = 0.78 A IPHC-LBL Phone conference April 1, 2014 ALICE-ITS meeting April 25, 2014 25

26. Run 15090063 - Mon Mar 31 21:16:0 Sector 7 L1 = 1.23 A L2 = 0.78 A L3 = 0.78 A L4 = 0.78 A IPHC-LBL Phone conference April 1, 2014 ALICE-ITS meeting April 25, 2014 26

27. Run 15090063 - Mon Mar 31 21:16:0 Sector 8 L1 = 0.78 A L2 = 1.07 A L3 = 0.92 A L4 = 0.78 A IPHC-LBL Phone conference April 1, 2014 ALICE-ITS meeting April 25, 2014 27

28. Run 15090063 - Mon Mar 31 21:16:0 Sector 9 L1 = 1.22 A L2 = 0.78 A L3 = 0.78 A L4 = 0.78 A IPHC-LBL Phone conference April 1, 2014 ALICE-ITS meeting April 25, 2014 28

29. Run 15090063 - Mon Mar 31 21:16:0 Sector 10 L1 = 1.57 A L2 = 0.78 A L3 = 0.78 A L4 = 0.78 A IPHC-LBL Phone conference April 1, 2014 ALICE-ITS meeting April 25, 2014 29