status of apd screening in bochum · after the initial screening: irradiation of apds with 37gy...
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Status of APD Screening in BochumPanda Collaboration Meeting 18/3
Jan Reher
Ruhr-Universitat Bochum
Readout of EMC crystals
Readout of crystals for the forward endcap EMC:I 768 crystals in the endcap (very close to the beam pipe)
are read out by VPTTsI Most crystals read out by two APDs each
Full EMC is read out by ≈ 30 000 APDs
8 APDs are supplied by one power supply and need to bematchedProperties vary between APDsProperties are dependant on temperatureValues provided by manufacturer were measured at 20 ◦C
⇒ Screening and matching of all APDs for T = −25 ◦C isrequired!
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APD screening setup in Bochum
Each screening board provides 16 slots to simultaneouslyscreen 15 APDs and one reference APDAPD signals read out by original Panda preamplifiers andSADCBias voltage and current measurements provided by isegHV modulesIllumination of APDs by DC light and by light pulserresembling the signal shapes of crystalsFull setup with two boards located inside climate chamber
⇒ Capacity to simultaneously screen 30 APDs⇒ Extension of screening capacity by 30 APDs in second
climate chamber in progress
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APD screening setup in Bochum
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Measurement process
Every APD is screened both at 20 ◦C and -25 ◦CPrevious studies1 showed: Measurement of dark currentsand pulse shapes can be performed in parallel.
→ Four measurements in total: DC- and dark currents at in awarm and cold environmentDuration for a a full set of measurements ≈ 10 hAt full capacity, screening 60 APDs per day is possible→300 APDs per weekWith duplicated setup: 600 APDs per week.As of today, ≈ 1000 new APDs and ≈ 350 irradiated APDswere screened and evaluated at Bochum
1Leon Knarr, Bachelor’s thesis
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Exemplary gain curve
0.1
1
10
100
1000
10000
0 50 100 150 200 250 300 350 400
M
U [V]
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Bias voltages for M = 100 and M = 200 for forward endcap
320 340 360 380 400 420 440U(M=100)[V]
0
50
100
150
200
250
300
AP
Ds
C°
T=20
C°
T=-25
320 340 360 380 400 420 440U(M=200)[V]
0
50
100
150
200
250
300
AP
Ds
C°
T=20
C°
T=-25
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Comparison to values provided by Hamamatsu atM = 100
Mean 0.6002
Std Dev 1.71
10− 8− 6− 4− 2− 0 2 4 6 8 10 [V]M=100, Bochum - UM=100,HamamatsuU
0
20
40
60
80
100
120
140
160
180
Eve
nts
/ (0.
4 V
)
Mean 0.6002
Std Dev 1.71
Slight deviation from the manufacturers values is observedDeviations are well within parameters explained bytemperature uncertainties (∆T ≤ 2 K)
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Temperature dependency of bias voltages
0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4/dT [V/K]
biasdU
0
50
100
150
200
250
300
350
even
ts /
(0.0
2 V
/K)
M=100
M=150
M=200
Distribution of difference between bias voltages atT = 20◦C and T = −25◦C is narrow→ Linear correlationbetween bias voltage and temperature
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SADC noise measurements
Noise measured at the SADCs depends on the darkcurrent in the APDMaximum acceptable dark current can be estimated fromthe noise at the SADCNoise limit of 3 · σ(M = 200) ⇒ Idark,max = 10 nA
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Slope at M = 200
0.02 0.04 0.06 0.08 0.1 0.12 0.141/M dM/dU [1/V]
0
20
40
60
80
100
120
140
160
180
200
220
even
ts /
(0.0
03 1
/V)
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Selection criteria for forward endcap
Maximum dark current at M = 800:
Idark (M = 800) < 10 nA
Matching criteria:I ∆Ubias at M = 200I dM
dU at M = 200
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Irradiation effects
After the initial screening: Irradiation of APDs with 37 GyAnnealing for 48 hours at 80 ◦C.Short circuit of the APD pins during irradiation andannealingSecond screening iteration after irradiation and annealingContinuous checks on the effects of irradiation, e.g. on biasvoltages or temperature gradient
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Summary and outlook
APD screening in Bochum ongoing, current capacity of300 APDs per week, soon to be doubled by second setupResults are in agreement with data from the manufacturerSelection criterium for APDs for the forward endcap:I IDark (M = 800) < 10 nA
Matching criteria:I ∆Ubias at M = 200I dM
dU at M = 200
Work on measurement process focussed on increasingoutput
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