LAT FSW System Checkout TRR

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GLAST Large Area Telescope LAT Pre-Shipment
Review LAT Performance Test Results
Trends J. Eric Grove Naval Research Lab LAT
Commissioner
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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

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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

EMI/EMC
Reconfig. LAT
Acoustic
Mount Radiators
Sine Vibe
Receive, Unpack
Perform Reference CPT (at SLAC)
C
L
L
L
L
L
L
L
4X
T-Cycle
T-Bal
Remove Radiators
Weight, CG
Ship to Spectrum
Pack LAT
C
S
C
S
L
C
C
S
Final CPT
LAT Environmental Test Sequence
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Performance Test During TVAC

• TVAC performance test plan

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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

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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

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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

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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

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TDF Performance

• Trigger and Data Flow (TDF) 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-08585
• 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

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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 gt90 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

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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

Baseline established for all quantities All PHA,
Veto, and CNO chans within spec
MIP spectra (PHA)
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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

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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

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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

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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

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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

Baseline established for all quantities All
spectr chans and thresholds in spec
Hit occupancy
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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

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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 gt25 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)
Pedestal FWHM (ADC units)
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CAL Trending
Percentage change

• 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

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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

Baseline established for all quantities Efficienc
y, bad chan count within spec
Hit occupancy
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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.

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TKR Performance Noise Flares

• Whats 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

• 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

Note LAT occ Layer occ / 576
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TKR Performance Noise Flares

• LAT noise occupancy at NRL
• Muon runs during 30-day period, June/July 2006
• 301 runs, 20-min avg duration
• Mean occupancy 1.310-6 including flaring
  episodes
• Mean drops to 810-7 when flaring is excluded
• Worst 90-minute period 1.510-5
• LAT can support sustained noise occupancy of
  110-4
• 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

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TKR Performance Bad Strips

• Three major categories
• Hot strips unusually high occupancy
• Historically anything gt10-4 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

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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
• lt0.3 of channels are bad
• Recall TKR trigger efficiency 99 with Level III
  spec gt90.

• Disconnected channel trend
• Miniscule increase in disconnected channel count
  during environmental test

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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
• the adverse schedule and cost impact of redoing
  1/3 of the MCM production
• 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

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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.

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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