[PPT] - In-orbit Performance of the Silicon-Tungsten Tracker of the DAMPE PowerPoint Presentation

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In-orbit Performance of the Silicon-Tungsten Tracker of the DAMPE Mission

Xin Wu

n behalf of the DAMPE Collaboration

Department of Nuclear and Particle Physics University of Geneva, Switzerland

35th International Cosmic Ray Conference (ICRC) 12 – 20 July, 2017, BEXCO, Busan, Korea

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Conclusions

2 Xin Wu

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

f the DAMPE Mission”, 34th International Cosmic Ray Conference

(ICRC), July 30 - August 6, 2015, The Hague, The Netherlands

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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

DAMPE

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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

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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

5

Detection of 1 GeV - 10 TeV e/γ, 100 GeV - 100 TeV cosmic rays with excellent energy resolution, direction reconstruction (γ) and charge measurement

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Neutron Detector (NUD) Plastic Scintillator Detector (PSD) Silicon-Tungsten Tracker (STK) BGO Calorimeter (BGO)

The DAMPE detector

6 Xin Wu

high energy γ-ray, electron and cosmic ray telescope

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ü Thick imaging calorimeter (BGO of 32 X0 ) ü Precise tracking with Si strip detectors (STK) ü Tungsten photon converters in tracker (STK) ü Charge measurements (PSD and STK) ü Extra hadron rejection (NUD)

➠

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Silicon-Tungsten Tracker (STK)

Outer envelop 1.12m x 1.12m x 25.2 cm
Detection area 76 x 76 cm2
Total weight: 154.8 Kg
Total power consumption: ~85W

7 Xin Wu ICRC2017, 19/7/2017

Sunday April 18th 2015

UniGE, INFN (Perugia, Bari, Lecce), IHEP

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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 X0 for photon conversion

The STK structure

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73,728 channels 768 silicon sensors 95 x 95 x 0.32 mm3 1,152 ASICs 192 ladders

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STK silicon sensors

Single-sided Silicon strip detectors produced by Hamamatsu

– 9.5 x 9.5 cm2, 768 strips, 121 µm pitch – 320 µm thick – Resistivity 5-8 kΩ, Vfd 10-80 V

150 SSDs for EQM (Engineering and Qualification Model)
865 SSDs for FM (Flight Model)

– Excellent quality – <Ileak> ~120 nA @150V (spec: <900 nA) – Very few bad channels – Cut precision: ~ few µm

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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

10

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

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Noise [ADC counts] 2 4 6 8 10 12 14 16 18 20 Entries 1 10

2

10

3

10

4

10

After production After payload integration After satellite integration

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)

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Number of channels Noise (ADC) Track incidence angle Position resolution

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In-orbit thermal stability of the STK

The thermal management system for 73k readout channels works very well!

Ave. radiator temperature since launch
Ave. Si ladder temperature since launch

Temperature (anti) correlated with orbit angle

Day to day variation ≪ 1°
Max. variation since launch ~6°
Max. ΔT between ladders ~2°
ΔT between STK and radiators is

~ constantly 10°

2016.01.01 2017.07.03

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Noise Runs 100 200 300 400 500

Number of Channels

50 100 150 200 250 300 350 400 450

Fraction of Total [%]

0.1 0.2 0.3 0.4 0.5 0.6

J F M A M J J A S O N D J F M A M J noise>5 ADC 10>noise>5 ADC noise>10 ADC (1 PED run per day)

Dec. 30, 2015 - July 3, 2017

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Detector started in good shape, and steadily improving in the

first year due to stabilization effect

Channel noise categories since Dec. 30, 2015

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Noisy channels now <0.3%, better than on ground (~0.4%)

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Entries 73728 Noise [ADC] 10

2

10 Entries 1 10

2

10

3

10

4

10 Entries 73728

On-ground (Shanghai), Nov. 6, 2015 On-orbit, July 03, 2017

Noise comparison

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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

STK noise: July 03, 2017 vs. on-ground

86 channels (0.12%) noise > 10 199 channels (0.27%) noise > 5 98 channels (0.13%) noise > 10 303 channels (0.41%) noise > 5

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Noise Runs 100 200 300 400 500

Average Noise

2.8 2.81 2.82 2.83 2.84 2.85 2.86 2.87 2.88

J F M A M J J A S O N D J F M A M J

average noise of all channels with noise < 5 ADC

Dec. 30, 2015 - July 3, 2017

Noise Runs 100 200 300 400 500

Average Noise

9 10 11 12 13 14 15 16 17 18 19

J F M A M J J A S O N D J F M A M J

average noise of all channels with noise > 5 ADC

Dec. 30, 2015 - July 3, 2017

15 Xin Wu

Noisy channels stabilized to lower

noise values – small temperature effect

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Bulk of noise correlated with temperature

– Very small temperature coefficient

~0.01 ADC per 2°
Simplification for operation

– data compression thresholds updated

nly once on Feb. 22, using average

noise of Feb. 13-17

Evolution of average noise : bulk and noisy channels

Range of variation (0.3 ADC) more precise than the on-board pedestal calculation (2 ADC)!

99.7% of channels 0.3% of channels

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365 day shift [ADC]

40
30
20
10

10 20 30 40 Number of channels 1 10

2

10

3

10

4

10 pedDiff

Entries 1.34185e+07 Mean

0.01349

RMS 2.458

Without 5 sigma cut With 5 sigma cut

Dec. 30, 2015 - July 3, 2017

180 day shift [ADC]

40
30
20
10

10 20 30 40 Number of channels 1 10

2

10

3

10

4

10 pedDiff

Entries 2.705818e+07 Mean

0.006448

RMS 1.626

Without 5 sigma cut With 5 sigma cut

Dec. 30, 2015 - July 3, 2017

30 day shift [ADC]

15
10
5

5 10 15 Number of channels 1 10

2

10

3

10

4

10 pedDiff

Entries 3.811738e+07 Mean 0.003412 RMS 0.7938

Without 5 sigma cut With 5 sigma cut

Dec. 30, 2015 - July 3, 2017

1 day shift [ADC]

15
10
5

5 10 15 Number of channels 1 10

2

10

3

10

4

10 pedDiff

Entries 4.025549e+07 Mean

6.061e-05

RMS 0.5139

Without 5 sigma cut With 5 sigma cut

Dec. 30, 2015 - July 3, 2017

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Pedestal stability : Dec. 30 2015 – July 3 2017

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1-day shift rms 0.5 ADC 30-day shift rms 0.8 ADC 180-day shift rms 1.6 ADC 365-day shift rms 2.5 ADC

2 updates per

rbit sufficient

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Good thermal stability guaranteed a good mechanical stability

– Same good position resolution recovered as on ground recovered after alignment

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In-orbit alignment

Unbiased hit residual distribution of 6 x-layers after alignment. Tracks of all inclinations within the STK acceptance (<60°) are used.

Larger extrapolation errors Larger extrapolation errors

January 2016

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June 23, 2017

In-orbit position resolution

Intrinsic position resolution of 30-40 µm

Unbiased hit residual distribution of inner layers fitted to double Gaussians

in angular bins

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Position resolution and alignment

10 20 30 40 50 20 30 40 100 200 300 400 1000

10 20 30 40 50 40 50 60

) (deg)

y

θ (

x

θ m) µ Effective resolution (

x2 x3 x4 x5 y2 y3 y4 y5 x1 x6 y1 y6

Data Not Aligned Data Aligned

Position resolution vs angle

Before alignment After alignment

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June 23, 2017

Stability of alignment

Alignment every 2 weeks is sufficient

Use alignment of Jan. 2016 Use alignment of Jan. 2016 Use bi-weekly alignment Use bi-weekly alignment 10-20° 10-20° >50° >50°

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STK charge measurement

STK charge measurement : need to correct for floating strip readout

scheme, also the saturation effect for high Z (>8)

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Tracking efficiency for electrons

Kalman Filter based track reconstruction algorithm
Tracking efficiency ~97%, constant over energy
Very good MC-data agreement

– difference ~1% for energy >100 GeV Data from Dec. 27 2015 – June 8, 2017, used in the electron flux analysis

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Conclusions

The DAMPE Silicon-Tungsten Tracker (STK) provides crucial particle

detection capabilities of DAMPE – Precise track reconstruction – Photon conversion, identification and direction measurement – Charge measurement

The in-orbit performance of the STK is excellent

– Excellent thermal, mechanical and noise stabilities, <0.3% noisy channels – Position resolution better than specification – Very high tracking efficiency – Excellent charge measurement for light nuclei

The STK is playing important role in DM searches (electron + positron flux,

gamma-ray line) and cosmic ray flux measurements