GLAST LAT Project September 15, 2006: Pre-Shipment Review Presentation 9 of 12 LAT Test Results 1 GLAST Large Area Telescope LAT Pre-Shipment Review LAT Performance Test Results & Trends J. Eric Grove Naval Research Lab LAT Commissioner Gamma-ray Large Area Space Telescope

GLAST LAT Project September 15, 2006: Pre-Shipment Review Presentation 9 of 12 LAT Test Results 2 Purpose / Contents  Demonstrate LAT functionality  Monitor LAT performance via CPT, LPT, and calibrations from Baseline forward through Environmental test –CPT, LPT Detector subsystems Copper paths, interfaces –Calibrations Detector subsystems  Performance baseline successfully established at SLAC prior to shipment –Successfully reproduced at NRL through environmental test

GLAST LAT Project September 15, 2006: Pre-Shipment Review Presentation 9 of 12 LAT Test Results 3 LAT Environmental Test Sequence  Instrument performance testing throughout Environmental –Defined in LAT-MD-02730, Performance and Ops Test Plan –Comprehensive and Limited performance tests at each step CPT on arrival and before/after TVAC LPT at all other milestones –Calibrations (“SVAC Test”) before and after TVAC Sine Vibe EMI/EMC L L Reconfig. LAT Acoustic L T-CycleT-Bal Remove Radiators Weight, CG Ship to Spectrum C C L Receive, Unpack C L L Limited Performance Comprehensive Performance SVAC Test C S L Pack LAT L Final CPT C Perform Reference CPT (at SLAC) S 4X Mount Radiators L SCS LAT Environmental Test Sequence

GLAST LAT Project September 15, 2006: Pre-Shipment Review Presentation 9 of 12 LAT Test Results 4 Performance Test During TVAC  TVAC performance test plan

GLAST LAT Project September 15, 2006: Pre-Shipment Review Presentation 9 of 12 LAT Test Results 5 Test Definitions  Comprehensive Performance Test –Purpose Verify copper paths and interfaces Basic performance metrics –Analysis EGSE Mobile Computing Rack –“Online” analysis –Outputs Pass/fail against performance specs Basic performance parameters for trending  Limited Performance Test –Purpose Same, but subset of CPT –Analysis Same as CPT –Outputs Same, but subset of CPT  Calibrations –Purpose Detailed performance metrics for flight science –Data are cosmic muons and test charge injection –Analysis SLAC computing farm –“Offline” analysis –Outputs Detector calibration constants

GLAST LAT Project September 15, 2006: Pre-Shipment Review Presentation 9 of 12 LAT Test Results 6 Data Products, Analysis, and Reports  “Online” analysis – Mobile Computing Rack, local to LAT –Latency Less than one hour –Analysis scripts and reports carried up from Subsystem development –Outputs Pass/fail evaluation against performance specs Basic performance quantities  “Offline” analysis – SLAC computer farm –Latency Typically less than 3 hours –Outputs Two reports produced for all runs, corresponding to data products –Digi report (basic detector quantities) »Trigger info: Total rate; Rates of trigger types; Arrival times »TKR: Number of strips and layers hit; Time over threshold –Reconstruction report (derived quantities) »Reconstructed energies, directions, positions LAT housekeeping telemetry –Entire LAT community has access and tools for offline products More detailed analysis for calibration or performance evaluation

GLAST LAT Project September 15, 2006: Pre-Shipment Review Presentation 9 of 12 LAT Test Results 7 Access to Data Products  Web site –Provides global access to data products Electronic shift log Diagnostic msg log Online products Offline products –Served from SLAC  Data review –All runs are inspected System Eng Subsystem expert –Review log maintained by QA, SE, and SLAC INT

GLAST LAT Project September 15, 2006: Pre-Shipment Review Presentation 9 of 12 LAT Test Results 8 Housekeeping Trending  Web access to telemetry data –All LAT telemetry points are available Plots over selected time span Numerical dumps, either raw samples or time-averaged

GLAST LAT Project September 15, 2006: Pre-Shipment Review Presentation 9 of 12 LAT Test Results 9 T&DF Performance  Trigger and Data Flow (T&DF) functionality –Trigger system demonstration in CPT and LPT Trigger primitive aliveness Scheduler, Engine, and Messaging functionality –Trigger and veto efficiency (calibration) Collected with FSW, analysis summary in LAT-TD  Detector subsystems timed-in at Baseline and NRL Pre-Ship –Trigger requests (TREQ) are aligned ACD veto and TKR time-aligned with CAL-LO –Readout times (TACK delays) are optimized ACD and CAL MIP peaks maximized TKR hit occupancy maximized

GLAST LAT Project September 15, 2006: Pre-Shipment Review Presentation 9 of 12 LAT Test Results 10 Trigger Performance  TKR trigger efficiency –Calibration data, triggered by CAL –Detailed analysis Image the track with CAL and ACD Measure efficiency for TKR trigger request for tracks passing through each Tower –Level III requirement: >90% efficiency Observed ~99% meets reqmt  Trigger condition summary –Standard plot in every Digi report –Summarizes relative rates of trigger requests among the 8 possible sources and their 256 combinations Plot shows number of triggers in each combination Table gives rates of individual trigger sources

GLAST LAT Project September 15, 2006: Pre-Shipment Review Presentation 9 of 12 LAT Test Results 11 ACD Performance  Subsystem performance –Minimum-ionizing particle (MIP) peaks –Veto rates –Veto thresholds  Electronics performance –Pedestal centroids and widths Width is measure of noise –Gain  Calibration quantities –MIP peaks –Veto thresholds MIP spectra (PHA) Baseline established for all quantities All PHA, Veto, and CNO chans within spec

GLAST LAT Project September 15, 2006: Pre-Shipment Review Presentation 9 of 12 LAT Test Results 12 ACD Performance  Aliveness –PHA All channels are alive and calibrated –Veto All channels are alive and can be set to flight thresholds –Exception: one channel that is not used in flight veto –CNO All channels are alive and can be set to flight thresholds  Performance notes –None Four NCRs carried up from subsystem test –Dispositions were to monitor through LAT TVAC »No performance anomalies were seen –All four are in process of being closed –See NCR presentation No other open NCRs on ACD performance –ACD performance is quite stable

GLAST LAT Project September 15, 2006: Pre-Shipment Review Presentation 9 of 12 LAT Test Results 13 ACD Performance at Baseline  Pedestal width baseline –Low electronic noise ~½% of MIP peak –Measured in each CPT, LPT This is a quantity to trend  MIP peak baseline –PMT gains are adequately balanced –Measured with 4 hrs of muons This is a calibration quantity

GLAST LAT Project September 15, 2006: Pre-Shipment Review Presentation 9 of 12 LAT Test Results 14 ACD Performance  Pedestal width trend –Essentially no changes to electronic noise since ACD was completed –Final phase shown is Baseline CPT  Veto occupancy –Aliveness test for all Veto signals “GEM Veto List” –Muons during LAT CPT and LPT show all channels are alive

GLAST LAT Project September 15, 2006: Pre-Shipment Review Presentation 9 of 12 LAT Test Results 15 ACD Trending  Pedestal width stability –Comparing NRL Pre-Ship to SLAC Baseline Units are ADC bins Typical rms is 2.5 bins –Mean pedestal width is unchanged to within ~1% System-level noise is stable  MIP peak stability –Comparing NRL Pre-Ship to SLAC Baseline Fractional change –Mean MIP peak is unchanged to within 0.2% System-level gain is stable

GLAST LAT Project September 15, 2006: Pre-Shipment Review Presentation 9 of 12 LAT Test Results 16 CAL Performance  Subsystem performance –Gain (“MeV/bin”) –Linearity  Electronic performance –Pedestal centroids and widths Width is measure of noise –Gains –Front-end linearity –Threshold DAC gains  Calibration quantities –Gain –Linearity Hit occupancy Baseline established for all quantities All spectr chans and thresholds in spec

GLAST LAT Project September 15, 2006: Pre-Shipment Review Presentation 9 of 12 LAT Test Results 17 CAL Performance  Aliveness –Spectroscopy All channels are alive and calibrated –Trigger All discriminators are alive and can be set to flight thresholds –Data suppression All discriminators are alive and can be set to flight thresholds  Performance notes –Front-end noise Four channels (out of 6144) out of family at room temp –No impact to flight performance –No open NCRs on CAL performance

GLAST LAT Project September 15, 2006: Pre-Shipment Review Presentation 9 of 12 LAT Test Results 18 CAL Performance Note  Pedestal width in post-TVAC CPT –Actual performance relative to spec Spec indicated by dotted line –Out of family Four low-energy channels Zero high-energy channels No issues –Measured in each CPT, LPT Run at >25 epochs at NRL  Not an issue for LAT calorimetry –Energy resolution is dominated by “shower fluctuations” Intrinsic to physics of gamma- ray showers –Pedestal width is a negligible contributor to resolution Pedestal FWHM (ADC units)

GLAST LAT Project September 15, 2006: Pre-Shipment Review Presentation 9 of 12 LAT Test Results 19 CAL Trending  Time evolution of pedestal width through environmental test –Typical FWHM ~ 8 bins (HEX8) –Plot shows stability of 32 channels –Initial phase is SLAC Baseline –Final phase is NRL Pre-Ship Pedestal noise is very stable  Gain stability through environmental testing –“Gain” is “Energy per ADC bin” –Comparing NRL Pre-Ship to SLAC Baseline Percentage change –Average gain (energy per bin) is unchanged to within 0.1% Calorimetry is very stable Percentage change

GLAST LAT Project September 15, 2006: Pre-Shipment Review Presentation 9 of 12 LAT Test Results 20 TKR Performance  Subsystem performance –Dead, noisy, and disconnected channel lists –Trigger efficiency  Electronics –Noise occupancy  Calibration quantities –Dead channel list –Noisy channel list –Disconnected channel list –Threshold –TOT gain Hit occupancy Baseline established for all quantities Efficiency, bad chan count within spec

GLAST LAT Project September 15, 2006: Pre-Shipment Review Presentation 9 of 12 LAT Test Results 21 TKR Performance  Aliveness –Data Total bad channel count ~ 0.3%, within spec –TOT All channels are alive and calibrated –Trigger Discriminators in all GTFEs are alive and can be set to flight thresholds  Performance notes (see details on following slides) –TKR “noise flares” Transient increase in noise occupancy –Noise occupancy and data volume are within spec –TKR meets science performance requirements. Not an issue. –“Bad strip” trending Strips not usable for triggering or tracking –TKR meets science performance requirements. Not an issue.

GLAST LAT Project September 15, 2006: Pre-Shipment Review Presentation 9 of 12 LAT Test Results 22 TKR Performance: Noise Flares  What’s a noise flare? –23 (of 612) layers in 17 Trackers have shown infrequent, sporadic flares of increased noise occupancy. Those 23 layers are uncorrelated in space and time –Flares are correlated across channels in a given ladder, with many or all channels in the ladder firing at once. –Flare durations are minutes to hours. A given ladder exhibits flaring episodes for days. –Averaged over the LAT, the rate of occurrence is Independent of time, vacuum, bias, and (probably) humidity Increased with increasing temperature –No flares were seen at Cold Operational temp in TVAC Note: LAT occ = Layer occ / 576  Analysis –The affected regions are fully ON and sensitive immediately before and after a flare. This rules out intermittent bias connections as a cause. –Even during flares, LAT meets noise occupancy requirements. Note that trigger rate is not affected since flaring layers are not correlated

GLAST LAT Project September 15, 2006: Pre-Shipment Review Presentation 9 of 12 LAT Test Results 23 TKR Performance: Noise Flares  LAT noise occupancy at NRL –Muon runs during 30-day period, June/July runs, 20-min avg duration –Mean occupancy = 1.3×10 -6 including flaring episodes Mean drops to ~8×10 -7 when flaring is excluded –Worst 90-minute period = 1.5×10 -5  LAT can support sustained noise occupancy of 1×10 -4 –TKR Level III reqmt  TKR buffering is configurable, tunable –Tests above used 64-hit GTRC buffer size –Flight setting is probably ~14 hits, which reduces occupancy in flares by a factor of four.  Impact on on-orbit performance –None Overall, the TKR noise performance is phenomenally good! –Observed flare rate and intensity is a factor of ~70 below sustained limit

GLAST LAT Project September 15, 2006: Pre-Shipment Review Presentation 9 of 12 LAT Test Results 24 TKR Performance: Bad Strips  Three major categories: –Hot strips: unusually high occupancy Historically anything >10 -4 occupancy, but strips well above this level can still be useful and should not be masked unnecessarily! Small numbers, with no trending issues. –Dead strips: do not respond to internal charge injection Either a dead amplifier or a broken SSD strip connected to the amplifier (usually the latter). Very small numbers, with no trending issues. –Disconnected strips: broken wire bond or trace between… (a) ladder and amplifier, mostly due to MCM encapsulation debonding from silicone contamination, or (b) SSDs within a ladder, due to Nusil encapsulation debonding in thermal cycles. The majority of the bad strips are in early towers, and the delamination definitely propagates somewhat with time. –Can reattach/detach with temperature change

GLAST LAT Project September 15, 2006: Pre-Shipment Review Presentation 9 of 12 LAT Test Results 25 TKR Performance Trending  Bad channel trend, essentially flat –Total number of bad channels after LAT env test = 3400 –Total number of TKR chans ~ 900,000 <0.3% of channels are bad  Recall TKR trigger efficiency ~99% with Level III spec >90%.  Disconnected channel trend –Miniscule increase in disconnected channel count during environmental test

GLAST LAT Project September 15, 2006: Pre-Shipment Review Presentation 9 of 12 LAT Test Results 26 TKR Bad Strips – Summary  The problem of encapsulation delamination has been well known and discussed for a long time, including the increase during Tracker TVAC testing, but the project elected to use the affected MCMs as-is because of 1.the adverse schedule and cost impact of redoing 1/3 of the MCM production 2.and the belief that future degradation would never reach a level at which the science would be compromised.  Nothing is different today: –Problem areas have expanded very slightly during LAT integration, but It is impossible to be sure at any time what channels are really disconnected, because the wires in delamination regions often make electrical contact even when the mechanical bond is gone. Many channels of the channels that appeared to be new disconnects during LAT environmental test were observed to be disconnected during TKR TVAC testing. No disconnected channels have appeared in previously unaffected regions of MCMs.  We expected that the problem regions would expand during LAT environmental testing at a level comparable to Subsystem environmental testing. –Indeed this is what was observed –Degradation has utterly negligible effect on science performance LAT environmental test caused the total count of disconnected strips to increase by 77 out of a total of 900,000 strips. We expect Observatory environmental testing to produce a similarly negligible increase

GLAST LAT Project September 15, 2006: Pre-Shipment Review Presentation 9 of 12 LAT Test Results 27 Calibration  Calibration –Datasets collected with cosmic muons and test charge injection Three epochs: SLAC Baseline, Pre-TVAC, Post-TVAC –Also calibrated at Hot and Cold in TVAC  Analysis –Combination of online (near real time) and offline processing Pre-TVAC calibration data analysis is complete –Detector settings were updated prior to TVAC, as needed Post-TVAC calibration data analysis is in progress –Output is set of calibration constants for each detector subsystem New detector settings based on these calibrations will be generated and installed after receiving CPT at GDC4.

GLAST LAT Project September 15, 2006: Pre-Shipment Review Presentation 9 of 12 LAT Test Results 28 Summary  LAT status –Performance baseline successfully established at SLAC Baseline CPT completed and signed off Calibrations from data collected under FSW –Post-environmental test performance measured at NRL Baseline performance confirmed Pre-ship CPT and calibration completed and signed off No new performance issues –Detectors have been operating with flight settings throughout environmental test at NRL Ready to operate with flight settings at GDC4 –LAT has completed environmental testing and is ready to ship