Transcript ppt

GLAST LAT Project
Gamma-ray Large
Area Space
Telescope
Instrument Analysis Meeting– Dec 9, 2005
Noisy Strip determination
Takuya Kawamoto (Hiroshima Univ)
Hiro Tajima (SLAC)
TKR
[email protected]
Takuya Kawamoto , TKR Noisy Strip determination
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GLAST LAT Project
Instrument Analysis Meeting– Dec 9, 2005
Noisy Strip Specification
Before…
– Strip occupancy > 10-4  Noisy strip.
• Easy to identify , too conservative.
• Common to both data and trigger mask.
New definition
• Minimize the number of noisy strips.
– Closely conform to specifications.
– Data Mask and Trigger Mask have different specifications.
• Specification for Data Mask.
– Tower average strip occupancy > 5.0*10-5
• This value comes from the data volume specification by flight
software.
• Specification for Trigger Mask
– Layer average strip occupancy > 10-5
• This value is derived from trigger occupancy specification (<8%).
• 8% trigger occupancy corresponds to 50 kHz layer trigger rate for
OR_STRECH=1.6 us.
• Use observed correlation between strip occupancy and layer
trigger rate to determine layer strip occupancy limit.
–
1.5* 10-5 is a real specification. Apply 10-5 to be slightly conservative.
Takuya Kawamoto , TKR Noisy Strip determination
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GLAST LAT Project
Instrument Analysis Meeting– Dec 9, 2005
How to define Noisy strips
• Identification of Noisy strip candidates from each run.
– Remove noisiest strips until tower or layer level average strips
occupancy specification is satisfied.
• Improve stability of noisy strip definition.
– Account for history.
• Each tower has few ~ 26 output files
– If a strip is a noisy strip candidate for more than 10%
of runs  defined as Noisy Strip!
Takuya Kawamoto , TKR Noisy Strip determination
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GLAST LAT Project
Instrument Analysis Meeting– Dec 9, 2005
Noisy Strips for Data Mask
• All noise-occupancy-test data for TKR FMA-FM15 were analyzed.
• Three noisy strips are found in FM7 and four noisy strips are
found in FM11.
– Much reduced from ~ 30 noisy strips per tower with previous
definition.
• After Noisy strips are masked:
– FM7: 3 Noisy strips were Masked
• One run exceeded tower level specification.
– 7.3*10-5 (45% above specification)
– FM11: 4 Noisy strips were Masked
• One run exceeded tower level specification
– 5.2*10-5 (barely above specification)
• We consider 50% above speciation is acceptable.
– Easily compensated by other towers with lower occupancies.
Takuya Kawamoto , TKR Noisy Strip determination
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GLAST LAT Project
Instrument Analysis Meeting– Dec 9, 2005
Noisy Strips for Trigger Mask
• Before Masked
– 124 layer out of (36layer*17TWR) exceeded Noise occupancy
specification: 20% of layers.
– 430 noisy strips identified.
• After Noisy strips are masked.
– 16 layers were still way above the specification.
Those excesses were due to the Unstable strips
• To Mask these unstable strips
– New condition:
• If strip occupancy > 1536*10-5 even once,
it will be defined as Noisy.
•After Masked these unstable strips:
– just 6 layers are above specification now!
Stay in < 10% above specification.
Takuya Kawamoto , TKR Noisy Strip determination
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GLAST LAT Project
Instrument Analysis Meeting– Dec 9, 2005
Summary
• We redefined noisy strips.
– Different definitions for data and trigger mask.
– Closely conform respective specifications.
• Improve stability of noisy strips by considering history.
• New noisy strip definitions meet specifications for various runs.
• Need to consider to incorporate occupancies results from cosmic
ray data. (physics data on orbit.)
Takuya Kawamoto , TKR Noisy Strip determination
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