Updates on GEMs characterization with APV electronics

K. Gnanvo, N. Liyanage, K. Saenboonruang

• Performance of small GEM with Fe55 source and SRS electronics

• Experimental setup

• Measurement of the Fe 55 spectrum

• Estimation of the absolute gain

• Performance the SBS proto I with Sr90 source and SRS electronics

• Experimental setup

• Gain uniformity and efficiency

• Effect of the gas flow rate

• Updates on the APV25-MPD electronics

• Progress in the decoding and display software

• Debugging the daq software and other issues

outline

Setup of the Small GEM chamber with 55FeFe55

GEM Chamber

SRS DAQ

3T

470 pF

CR-110Amplifier

150 nF

LowpassFilter

Discriminator

Gate/Delay

Trigger

Vin Vout

66 Ω

220 pF

• Low pass filter used to reduce high frequency noise.

• The cut off frequency for this low pass filter is 10 MHz.

Study of the noise (rms of the apv25 channels)

APV25-SRS on GEM readout strips

• Typical rms noise of a given APV cards from a pedestal run SRS

• This rms is obtained after common mode correction of the baseline

• An average of 6-7 adc counts for apv25-SRS

• ~ 1200 to 1500 ENC

• a cut at 5 sigma for zero suppression ~ 6000 e-

55Fe spectrum

X-strips Y-strips

Photo-peak

Escape peak

• HV = 4 kV on the voltage divider

• Trigger threshold at 50 mV on GEM foil

• Distribution of strip cluster max ADC

counts the Fe55 spectrum

55Fe spectrum vs. HV

4000 V

X-strips

3950 V

3900 V 3850 V

Gain of the small triple GEM with 55Fe

• Gain from the mean ADC value of the

photo peak

• APV gain calibration = 238e- /adc channel

• Gain is about twice the gain we obtain

from direct measurement

• SRS electronics gain with external

pulse is overestimated

• strip capacitance and cross talk effect

of the GEM readout not taken into

account

Performance of the small GEM prototype with 55Fe

• Good chamber efficiency

• Strong variation of the X/Y charge sharing

with the applied voltage Gain

Setup of the SBS GEM chamber with 90Sr• The test used 90Sr source located above the 1st prototype SBS GEM chamber at different

locations to study efficiencies, ADC spectrums, charge sharing and other important

characteristics of the chamber by varying the gas flow rates, and directions

• The threshold of the scintillator was set at 135 mV throughout the test (unless specified by

other values)

GEM Chamber

2-cm thick Scintillator

90Sr Source

Active Areaof the scintillator

1-inch Diameter Hole

Aluminum Plate

1.5-inch GapHV

BCD

1 2 3 4 5

Test of the SBS GEM chamber with 90SrHit distributionCondition: 1) 200 mL/min < Gas flow rate < 300 mL/min

2) Gas Direction: 13) Position: B34) HV = 4400 V

5 Sigma Cut3 Sigma Cut

X-stripsY-strips

Test of the SBS GEM chamber with 90Sr

Efficiency Calculation

• Good events mean there are both hits in X and Y directions• The equation to calculate the efficiency is

where NG: Number of good eventsNT: Number of triggersRT: Trigger rate with the source (12 Hz)RGB: Rate of good events without source (20 % or 0.24 Hz)RB: Trigger rate without the source (1 Hz)

Test of the SBS GEM chamber with 90SrEfficiency vs HV

Condition: 1) 200 mL/min < Gas flow rate < 300 mL/min2) Gas Direction: 13) 5 sigma cut

3900 4000 4100 4200 4300 4400 4500 46000.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

Location C3Location B3Location B1Location D1Location B5Location B2

HV (V)

Rela

tive

Effici

ency

3900 4000 4100 4200 4300 4400 4500 46000.40

0.50

0.60

0.70

0.80

0.90

1.00

Relative Efficiency for different sigma cuts vs HV

5 Sigma 3 Sigma 4 Sigma 6 Sigma 7 Sigma

HV (V)

Rela

tive

Effici

ency

Test of the SBS GEM chamber with 90Sr

3900 4000 4100 4200 4300 4400 4500 46000

2

4

6

8

10

12

14

16

18

20

Total number of strips hit for different sigma cuts vs HV

3 Sigma 5 Sigma

HV (V)

Num

ber o

f Str

ips

Test of the SBS GEM chamber with 90Sr

Test of the SBS GEM chamber with 90SrAverage ADC in X direction

Condition: 1) Gas flow rate = 290 mL/min2) Gas Direction: 23) 5 sigma cut

40004050410041504200425043004350440044500.0

500.0

1000.0

1500.0

2000.0

2500.0

3000.0Mean ADC in X for flow rate = 290 mL/min vs HV

Location B5Location C3Location B1Location D1

HV (V)

Effici

ency

16

Charge Ratio (X/Y) vs HVCondition: 1) 200 mL/min < Gas flow rate < 300 mL/min

2) Gas Direction: 13) 5 sigma cut

3900 4000 4100 4200 4300 4400 4500 46000.9

1

1.1

1.2

1.3

1.4

1.5

Charge Ratio (X/Y) vs HV

Location B3Location B1Location B2Location B5Location C3Location D1

HV

Test of the SBS GEM chamber with 90Sr

17

3900 4000 4100 4200 4300 4400 4500 46000

2

4

6

8

10

12

14Number of Strips (5 sigma) vs HV

#Strip All#Strip X#Strip Y

HV

Test of the SBS GEM chamber with 90Sr

Updates on the APV25-MPD

• Paolo Musico’s group (INFN

Italy) is working on a new

version of the APV25 FE

cards with Panasonic

connectors and new

backplanesfor the new SBS

backtracker GEM

New APV25 FE with Panasonic connectors for SBS

backtracker GEMs

Design of ew backplanes for SBS back tracker GEMs

Backup slides

APV25 MPD and SRS systemWe suspect an overestimation of the gain

• Gain from external source is about 2 × the

gain with calibration pulse

• The estimate GEM gain from the APV-SRS

signal size is about twice the expected gain

We need to re-evaluate the amount of injected charges

• Try to access the effect of strip capacitances

and cross talk ...