GLAST Large Area Telescope: Tracker Subsystem WBS 4.1.4 7F: On-Orbit Calibration and Test

1. Gamma-ray Large Area Space Telescope GLAST Large Area Telescope: Tracker Subsystem WBS 4.1.4 7F: On-Orbit Calibration and Test Bill Atwood Santa Cruz Institute for Particle Physics University of California at Santa Cruz atwood@scipp.ucsc.edu

2. Relevant Documents • Applicable LAT documents to this review: • LAT-TD-00249 - Tracker Front-end Readout ASIC Wafer Test Procedure • LAT-TD-00248 - Tracker Readout Controller ASIC Wafer Test Procedure • LAT-TD-00249 - Tracker Multi-Chip Module Test Plan These Plans are in a formative state – This report is meant to convey our present thinking only.

3. Logic Functionality GLAST Tracker Front End ASICs are a specialized, programmable “computer.” Two ASICs GTFE (analog and digital sections) GTRC (digital section only) Functional Testing Developed as part of parts testing during construction Load & Read-Back Control Registers & DAC Settings (TEM GTRC GTFE) - Trigger Masks - Data Masks - Threshold DAC’s & Charge Calibration DAC’s

4. Analog Testing Calibration Run - Setting the Charge Injection Masks - Setting the Charge Injection DACs - Cycling through Threshold DAC settings - Record the number of hits from each channel - Compare with results obtained prior to launch Example from First Tests of Flight GTFE Flight Chips For On Board Testing – a linear fit to the transistion Region would be made and the results sent to the ground.

5. Analog Testing Noise Occupancy Check - Fire random trigger - Accumulate counts per channel distribution - Check for (new) noisy channels Example from Mini-MCM Testing Lines are the average channel noise For each of the 6 chips (one SSD Ladder’s worth) Shows threshold setting corresponding to ¼ MIP.

6. Online Monitoring Output from Tracker is minimal: 1) Address of an SSD channel indicating the presence of the passage of a charged particle through the active area associated with it (i.e. a “hit”) 2) The address of each X & Y plane of silicon strip detectors with the collective OR of all the strips in that plane set - used for triggering 3) Time-over-threshold (TOT) for the entire layer – for the OR’d signal. This time is correlated with the amplitude of the largest single SSD single in that layer.

7. Online Monitoring Hit Strip Distributions - 884736 channels - 2 bytes/channel ( 2 MB storage) - Expect: ~ 200 counts/channel/orbit (3900 counts/ch/day) Layered OR Distributions - 1152 Layered OR’s (all GFRC working) – 4 bytes/channel (4.5 KB storage) Tower Trigger Distributions - 16 Towers – which initiated the trigger TOT Distributions - 1152 channels – keep mean and RMS for each ( 9 KB storage).

8. Online Monitoring House Keeping Items(Periodically read, monitored & downlinked) - Temperatures (18 Thermistors per Tower) - Voltages (SSD Bias, various Analog & Digital supply voltages)

9. Alignment High energy cosmic rays (mostly protons at several GeV) produce straight trajectories in GLAST Boot-Strap proceedure - Fit 3D straight lines to Tracker Hits - Off-sets in Fit Residuals tray-to-tray alignment off-sets - Linear Dep. Of Fit Residuals tray-to-tray rotations Align Trays within Towers Align Towers-to-towers Procedure being developed in conjunction with I & T ( H. Tajima et al)

10. Turn-on and First Triggers • Perform Logic Check-out and Test • Perform Analog Check-out • - Enable 3-In-A-Row trigger • - Accumulate cosmics into online monitoring histograms • - Check rates • - Select MIP subset to downlink (for alignment checks) • Enable Gamma Triggering & Filtering • Initial Operation may toggle between “gamma” data and • “straight-through” cosmic ray data. • Helpful to have capability of several downlinks/day during • this phase.