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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