In-orbit Performance of the Silicon-Tungsten Tracker of the DAMPE Mission Xin Wu on behalf of the DAMPE Collaboration Department of Nuclear and Particle Physics University of Geneva, Switzerland 35 th International Cosmic Ray Conference (ICRC) 12 – 20 July, 2017, BEXCO, Busan, Korea
Conclusions The Silicon-Tungsten Tracker (STK) of the DAMPE mission is based on robust • technology of single-sided silicon strip detectors with analog readout. – It will play crucial roles in charge track reconstruction, gamma-ray detection, cosmic ray charge measurement, and overall particle identification. After 2 years of intensive design, prototyping, testing and production efforts • – Engineering and Qualification Model space qualified and tested with particle beams – Flight Model completed and passed acceptance and integration tests – The quality of the FM is excellent and meets the design specifications Launch is scheduled for December 2015 “The Silicon-Tungsten Tracker of the DAMPE Mission”, 34th International Cosmic Ray Conference (ICRC), July 30 - August 6, 2015, The Hague, The Netherlands Xin Wu 2
DAMPE Launched on December 17, 2015 STK turned on 3 days after launch • DAMPE taking good data 10 days after launch • First preliminary results shown at this conference • Xin Wu ICRC2017, 19/7/2017 3
The DAMPE Collaboration China • – Purple Mountain Observatory, CAS, Nanjing – University of Science and Technology of China, Hefei – Institute of High Energy Physics, CAS, Beijing – Institute of Modern Physics, CAS, Lanzhou – National Space Science Center, CAS, Beijing Switzerland • – University of Geneva, Switzerland Italy • – INFN Perugia and University of Perugia – INFN Bari and University of Bari – INFN Lecce and University of Salento Xin Wu ICRC2017, 19/7/2017 4
Scientific objectives of DAMPE High energy particle detection in space • – Measure the high energy cosmic electron and gamma spectra and search for Dark Matter signatures – Study of cosmic ray spectrum and composition – High energy gamma ray astronomy Detection of 1 GeV - 10 TeV e/ γ , 100 GeV - 100 TeV cosmic rays with excellent energy resolution, direction reconstruction ( γ ) and charge measurement Xin Wu ICRC2017, 19/7/2017 5
The DAMPE detector Plastic Scintillator Detector (PSD) Silicon-Tungsten Tracker (STK) BGO Calorimeter (BGO) Neutron Detector (NUD) ü Thick imaging calorimeter (BGO of 32 X 0 ) high energy γ -ray, ü Precise tracking with Si strip detectors (STK) ➠ electron and cosmic ü Tungsten photon converters in tracker (STK) ray telescope ü Charge measurements (PSD and STK) ü Extra hadron rejection (NUD) Xin Wu ICRC2017, 19/7/2017 6
Silicon-Tungsten Tracker (STK) Outer envelop 1.12m x 1.12m x 25.2 cm • Detection area 76 x 76 cm 2 • Total weight: 154.8 Kg • Total power consumption: ~85W • UniGE, INFN (Perugia, Bari, Lecce), IHEP Sunday April 18 th 2015 Xin Wu ICRC2017, 19/7/2017 7
The STK structure 12 layers (6x, 6y) of single-sided Si strip • detector mounted on 7 support trays Tungsten plates (1mm thick) integrated • in trays 2, 3, 4 (from the top) – Total 0.85 X 0 for photon conversion 192 ladders 768 silicon sensors 95 x 95 x 0.32 mm 3 1,152 ASICs 73,728 channels Xin Wu ICRC2017, 19/7/2017 8
STK silicon sensors Single-sided Silicon strip detectors produced by Hamamatsu • – 9.5 x 9.5 cm 2 , 768 strips, 121 µm pitch – 320 µm thick – Resistivity 5-8 kΩ, V fd 10-80 V 150 SSDs for EQM (Engineering and Qualification Model) • 865 SSDs for FM (Flight Model) • – Excellent quality – <I leak > ~120 nA @150V (spec: <900 nA) – Very few bad channels – Cut precision: ~ few µm Xin Wu ICRC2017, 19/7/2017 9
STK readout electronics Readout every other channel, readout pitch 242 µm • – ASIC: VA140 from IDEAS, updated version of VA64hdr of AMS • Low power (0.3 mW/channel) and large dynamic range (200 fC) – Analog readout • Charge measurement • Better position resolution with charge sharing Tracker Front-end Hybrid (TFH) • – Thin bias circuit integrated with a PCB housing 6 ASICs, and a readout cable (“pigtail“) – Vias and cupper bands for heat transfer Xin Wu ICRC2017, 19/7/2017 10
STK on-ground calibration Extensively tested and calibrated with particle beams at CERN and with • cosmic ray muons STK remained in excellent quality through ~6 months of transportation, • integration, space environmental tests, … – Number of noisy channels <0.4 % before launch Large amount of cosmic data collected to align the STK • – Excellent position resolution achieved before launch • 40 – 50 µm for vertical entry particles (requirement 75 µm) Entries Number of channels After production 4 10 Position resolution After payload integration After satellite integration 3 10 2 10 10 1 0 2 4 6 8 10 12 14 16 18 20 Noise [ADC counts] Noise (ADC) Xin Wu ICRC2017, 19/7/2017 11 Track incidence angle
In-orbit thermal stability of the STK Ave. radiator temperature since launch Ave. Si ladder temperature since launch 2016.01.01 2017.07.03 Day to day variation ≪ 1 ° • Temperature (anti) correlated with orbit angle Max. variation since launch ~6 ° • Max. Δ T between ladders ~2 ° • Δ T between STK and radiators is • ~ constantly 10 ° The thermal management system for 73k readout channels works very well! Xin Wu ICRC2017, 19/7/2017 12
Channel noise categories since Dec. 30, 2015 450 0.6 noise>5 ADC 400 10>noise>5 ADC Dec. 30, 2015 - July 3, 2017 noise>10 ADC 0.5 (1 PED run per day) 350 Number of Channels Fraction of Total [%] 300 0.4 250 0.3 200 150 0.2 100 0.1 J F M A M J J A S O N D J F M A M J 50 0 0 0 100 200 300 400 500 Noise Runs Detector started in good shape, and steadily improving in the • first year due to stabilization effect Noisy channels now <0.3%, better than on ground (~0.4%) Xin Wu ICRC2017, 19/7/2017 13
STK noise: July 03, 2017 vs. on-ground Entries Entries 73728 73728 Entries Noise comparison 4 10 On-ground (Shanghai), Nov. 6, 2015 On-orbit, July 03, 2017 303 channels (0.41%) noise > 5 3 10 199 channels (0.27%) noise > 5 2 10 98 channels (0.13%) noise > 10 86 channels (0.12%) noise > 10 10 1 2 10 10 Noise [ADC] Noise improved because of lower temperature in space and stabilization • – Bulk of noise ~2.8 ADC (vs 3 ADC on ground) – Number of noisy channels reduced by 29% after stabilization Xin Wu ICRC2017, 19/7/2017 14
Evolution of average noise : bulk and noisy channels 2.88 19 average noise of all channels with noise < 5 ADC average noise of all channels with noise > 5 ADC 18 2.87 Dec. 30, 2015 - July 3, 2017 Dec. 30, 2015 - July 3, 2017 17 2.86 99.7% of channels 0.3% of channels 16 Average Noise Average Noise 2.85 15 J F M A M J J A S O N D J F M A M J J F M A M J J A S O N D J F M A M J 2.84 14 13 2.83 12 2.82 11 2.81 10 9 2.8 0 100 200 300 400 500 0 100 200 300 400 500 Noise Runs Noise Runs Bulk of noise correlated with temperature Noisy channels stabilized to lower • • noise values – Very small temperature coefficient – small temperature effect • ~0.01 ADC per 2 ° Simplification for operation • Range of variation (0.3 ADC) – data compression thresholds updated more precise than the on-board only once on Feb. 22, using average pedestal calculation (2 ADC)! noise of Feb. 13-17 Xin Wu ICRC2017, 19/7/2017 15
Pedestal stability : Dec. 30 2015 – July 3 2017 pedDiff pedDiff Entries 4.025549e+07 Entries 3.811738e+07 4 Dec. 30, 2015 - July 3, 2017 10 Dec. 30, 2015 - July 3, 2017 Mean -6.061e-05 4 Mean 0.003412 10 RMS 0.5139 RMS 0.7938 Without 5 sigma cut Without 5 sigma cut 1-day shift 30-day shift With 5 sigma cut With 5 sigma cut 3 3 10 10 Number of channels Number of channels rms 0.5 ADC rms 0.8 ADC 2 updates per 2 2 10 10 orbit sufficient 10 10 1 1 -15 -10 -5 0 5 10 15 -15 -10 -5 0 5 10 15 1 day shift [ADC] 30 day shift [ADC] pedDiff pedDiff Entries 2.705818e+07 Entries 1.34185e+07 4 10 Dec. 30, 2015 - July 3, 2017 Dec. 30, 2015 - July 3, 2017 4 Mean -0.006448 Mean -0.01349 10 RMS 1.626 RMS 2.458 Without 5 sigma cut Without 5 sigma cut 365-day shift With 5 sigma cut 180-day shift With 5 sigma cut 3 10 3 10 Number of channels Number of channels rms 2.5 ADC rms 1.6 ADC 2 10 2 10 10 10 Xin Wu ICRC2017, 19/7/2017 16 1 1 -40 -30 -20 -10 0 10 20 30 40 -40 -30 -20 -10 0 10 20 30 40 180 day shift [ADC] 365 day shift [ADC]
In-orbit alignment Good thermal stability guaranteed a good mechanical stability • – Same good position resolution recovered as on ground recovered after alignment Larger extrapolation errors Larger extrapolation errors January 2016 Unbiased hit residual distribution of 6 x-layers after alignment. Tracks of all inclinations within the STK acceptance (<60 ° ) are used. Xin Wu ICRC2017, 19/7/2017 17
In-orbit position resolution Unbiased hit residual distribution of inner layers fitted to double Gaussians • in angular bins June 23, 2017 Intrinsic position resolution of 30-40 µm Xin Wu ICRC2017, 19/7/2017 18
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