GLAST LAT Project Instrument Analysis Meeting– Dec 9, 2005 Takuya Kawamoto, TKR Noisy Strip determination 1 Noisy Strip determination Takuya Kawamoto (Hiroshima Univ) Hiro Tajima (SLAC) TKR Gamma-ray Large Area Space Telescope

GLAST LAT Project Instrument Analysis Meeting– Dec 9, 2005 Takuya Kawamoto, TKR Noisy Strip determination 2 Noisy Strip Specification Before … –Strip occupancy >  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 > 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* is a real specification. Apply to be slightly conservative.

GLAST LAT Project Instrument Analysis Meeting– Dec 9, 2005 Takuya Kawamoto, TKR Noisy Strip determination 3 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! How to define Noisy strips

GLAST LAT Project Instrument Analysis Meeting– Dec 9, 2005 Takuya Kawamoto, TKR Noisy Strip determination 4 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.

GLAST LAT Project Instrument Analysis Meeting– Dec 9, 2005 Takuya Kawamoto, TKR Noisy Strip determination 5 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.

GLAST LAT Project Instrument Analysis Meeting– Dec 9, 2005 Takuya Kawamoto, TKR Noisy Strip determination 6 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.)