Study of the “Ledge” Effectin ProtoDUNE Readout
Hucheng Chen, Shanshan Gao, Veljko Radeka
10/15/2018
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Slide from Wenqiang Gu on ProtoDUNE-SP event
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Slide from Wenqiang Gu
Not all channels show the ledge from a shower event
Evaluation of Ledge Waveform
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Channel EventPrimary charge
(ADC*ticks)Primary height
(ADC)Total charge
(fC)
7205
174 20462 406 74328 24678 347 89395 23693 551 85555 19344 402 70597 18350 773 66
14876
90 25591 951 92181 26475 752 95238 27021 429 97502 21330 732 77879 31128 619 112
14855
266 22260 1092 8058 26192 390 94
400 37474 721 135778 60772 3133 219
Table from Wenqiang Gu
Most shower charge is < 100fC, few events have charge ~ 200fC
Tramp
3ms
10ms
ΔV Tw
Emulating Shower Signal in FEMB Bench Testing
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• One FEMB with Toy TPC (Cd = 150pF) in LN2
• Calibration pulse injected to the input of FE • Waveform generator 33600A
• Amp (ΔV) = Programmable• Freq = 100Hz
• Pulse width (Tw) = 3 ms
• Tramp : programmable
• Calibration Cap (Ccal) = 1.203 pF
• FE setting• 14mV/fC, 2us, 500pA,
• BL (FE) = 200mV / 900mV
FEMB
FE
C=0.022u
L = 18nH
Cd
33600A
Shower signal induces current. Ramp signal through capacitor to emulate the current
Generator Output
Ccal = 1.203pF
Tramp
10ms
ΔI Tw = 3ms
Q = ΔV * Ccal
ΔI = Q / Tramp
Ledge is reproduced with FE baseline of 200mV
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Sample Ticks
4800 6000
AD
C O
utp
ut
/ LS
B
1800
2250
350 LSBs
100 LSBs
50us~330us
Total charge ~225fC;It appears that a large and long induced current signal is more likely to create a ledge
Saturated Region
Ledge is not produced with FE baseline of 900mV
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Sample Ticks
4800 6000
AD
C O
utp
ut
/ LS
B
1800
2250
350 LSBs
50us
Total charge ~225fC
Ledge is not produced with FE baseline 900mV
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Sample Ticks
4800 6000
AD
C O
utp
ut
/ LS
B
1500
3000
900 LSBs
50us
Total charge ~580fC (about 3x large shower signal)
Does 900mV baseline solve the ledge problem?Not entirely, but a substantial improvement over 200mV.
• A ProtoDUNE-SP FEMB has been tested• Calibration pulse is injected to test pin with built-in 185fF calibration capacitor
• V = 900mV, Tramp = 10us, Qtotal ~ 165fC• 0 out of 128 (0%) channels show ledge effect with baseline of 900mV
• V = 1200mV, Tramp = 10us, Qtotal ~ 220fC• 22 out of 128 (~17%) channels show ledge effect with baseline of 900mV
• V = 1500mV, Tramp = 10us, Qtotal ~ 275fC• 40 out of 128 (~31%) channels show ledge effect with baseline of 900mV
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Most shower charge is < 100fC, few events have charge ~ 200fC
Recommendation to ProtoDUNE• Ledge effect has been observed on some collection channels in ProtoDUNE-SP
• Most observed shower charge is < 100fC, few events have charge ~ 200fC
• Lab test has been carried out with FEMBs to study the ledge effect
• Ledge effect can be reproduced on FE ASIC with 200mV baseline in LN2
• 900mV baseline setting has higher (~x3) charge threshold to show ledge effect
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Recommendation: To change the FE ASIC baseline from 200mV to 900mV. All other settings to remain the same (gain=14mV/fC, peaking time tp=2µs, bias current=500pA).
ProtoDUNE has changed the baseline to 900mV on Thursday 10/11/2018
Shower Event with 900mV Baseline under 7Gev Beam
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Run 5194
Online Monitoring (Raw data)3000
6000
0 480
TDC
Co
un
ts
Pseudo Channel
Charge scale limited to “yellow”~ 3fC for monitoring
1 m
2.4m
A monitor software glitch (minor)
Shower Event with 900mV Baseline under 7Gev Beam
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Run 5177
Online Monitoring (Raw data)
3000
6000
TDC
co
un
ts
0 480Pseudo Channel
Charge scale limited to “yellow”~ 3fC for monitoring
2.4m 1 m
A monitor software glitch (minor)
Shower Waveforms with 900mV Baseline (no ledge)
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~ 350 fC
Multiple tracks charge collection waveform
Tick / (0.5us)
Am
plit
ud
e /
LSB
Am
plit
ud
e /
LSB
Tick / (0.5us)
ac coupling to ADC (𝞽 ~ 1ms);1 LSB ~ 135 e-
Plots from Wenqiang Gu
Summary and Next Steps
• After changing the baseline from 200mV to 900mV, ledge events have been reduced significantly in ProtoDUNE• Preliminary result from Wenqiang Gu: 107 events, ledges found on only 2 channels
• Dispersion has been found in the charge thresholds to create a “ledge”. This has escaped ASIC testing for ProtoDUNE.• No ledge behavior has been observed in MicroBooNE.
• A study of FE ASIC successive iterations will be carried out in coming weeks, including P1 FE ASIC, and V4* FE ASIC used in MicroBooNE to help identify the cause of the “ledge”.• In parallel need is to understand any consequence on the SBND.
• Further discussion of FE ASIC will be planned for a future meeting.
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