1. SCT Readiness for Heavy Ion Collisions Dave Robinson on behalf of SCT 15/9/101Dave Robinson Heavy Ion Review

2. SCT HI Operation : Homework Questions 1.Number of Samples = 3 ( in pp operation = 3) 2.Specific dead time requirements = (see below) 3.Setting different from pp operation = NONE 4.Modified Voltages = NONE 5.Enhanced Risk = NONE (protected by BLM) 6.Read Out limitations (see below) 7.Specific Calibration Requirements = NONE 8.If your system provides a trigger..... (We Don’t) 15/9/10Dave Robinson Heavy Ion Review2

3. Bottlenecks in SCT DAQ ABCD (front-end ASIC) buffer – 8 events deep, read out at 40MHz One ABCD hit is 17 bits header and trailer 19 and 16 bits respectively Event size = 19 + N*17 + 16 bits ROD input decoder & FIFO – 512 events deep S-Link Readout – 40MHz x 32bit One ABCD hit in BS is (reduced to) 16 bits 16bit header per link ROD header is 9x32bit words, trailer is 5x32bit words 15/9/103Dave Robinson Heavy Ion Review

4. Implications for Event Size and Data Throughput Occupancy (%)Rate Limit (kHz)Complex DTEvent Size/ROD (kB) ABCDS-Link 075420008/530.056 1233898/1702 1028108/139515.6 2014.55.28/275531 Other Considerations: Simple dead-time = 3 (L1A is 3 clocks) + 1 contingency ROS event size limit is (currently configured to be) 65kB  Event truncation above ~46% occupancy 15/9/104Dave Robinson Heavy Ion Review

5. Verification of Limits Ran >100kHz with noise only (~10 -5 occupancy) Can artificially increase occupancy – By running with ROD simulator Confirmed limit of ~10% occupancy at 10kHz Ran at 80kHz with 0.1% occupancy (not limited by SCT) Does not exercise chips, so independent of complex DT – By reducing HV – By reducing threshold 15/9/105Dave Robinson Heavy Ion Review

6. Summary SCT DAQ bottlenecks are known and have been verified in high rate tests within ATLAS partition and at SR1 SCT standard operational run settings can comfortably cope with 10% occupancy levels for trigger rates below 10kHz SCT is ready for heavy ion collisions using nominal (standard) run settings 15/9/10Dave Robinson Heavy Ion Review6

7. Backup – Rate Calculations Eg, 1% occupancy – ABCD: 19 + 17*8 + 16 = 171 bits Max sustainable rate = 754 kHz ERROR if get 8 triggers within next 4.3  s (while first is read out) Time to read put = 171 clocks -> Complex dead-time 8/171 – ROD (one link) 1 header + 8 16bit words = 9x16bit words = 5x32bit words – ROD (all links): 9x2x48 16 bit words = 432 32-bit words + 14header/trailer 32bit words = 446 32bit words Max sustainable rate = 40MHz/446 = 89kHz 15/9/107Dave Robinson Heavy Ion Review