edoardo cardelli – dipartimento di fisica – università di cagliari università degli studi di...

Edoardo Cardelli – Dipartimento di Fisica – Università di Cagliari

Università degli Studi di Cagliari Dipartimento di Fisica

Detector Quality Control

Edoardo CardelliEdoardo Cardelli

Overview


Introduction

Motivations Gas Leak Test

• Measurement Principle• Setup• An example

X-Ray Test

• Setup• Uniformity measurement

Introduction


Quality control measurements are necessary to guarantee the requested detector performances

Gas Leak RateThe chamber leak rate below a few mbar/day allows to keep the gas mixture humidity below a few hundredth ppmV with a 100 cc/min gas flow, to reduce possible ageing effects due to HF formation

Test X-Ray Necessary to verify that the gain uniformity is at the level of 10-20%. This is important because the detector has a digital readout and all the channel thresholds are set to the same value. Large gain non-uniformities would reduce the detector operating pleateau

Gas leak Test : setup (I)


The gas leak rate measurement of a chamber is referred to the The gas leak rate measurement of a chamber is referred to the pressure of one reference chamber (same volume, no leak)pressure of one reference chamber (same volume, no leak)

The chambers are inflated in parallel up to an overpressure of ~ 5 mbarThe chambers are inflated in parallel up to an overpressure of ~ 5 mbar

The difference of pressure, The difference of pressure, ΔΔp, from the probe S2 p, from the probe S2

returns the gas leak rate of the chamber under testreturns the gas leak rate of the chamber under test

The probe S1 returns the relative pressure The probe S1 returns the relative pressure

of the chamber under testof the chamber under test

N2

S1 S2

Pat

m

T P

Ref Chamber

Chamber to test

Gas leak Test : setup (II)


constT

Patm constT

P

Pressure and temperature sensorsPressure and temperature sensors

Gas leak of the Chamber


Equal value of T/pEqual value of T/p

We can measure the gas leak rate by measuring We can measure the gas leak rate by measuring

the pressure the pressure ΔΔp at time instants with equal p/T p at time instants with equal p/T

value. value.

The result fit make gas leak rate of The result fit make gas leak rate of

the chamberthe chamber

Pressure and temperature are Pressure and temperature are

used to correct the HV supply in used to correct the HV supply in

order to keep a constant detector order to keep a constant detector

gaingain

X Ray Test: system setup


With a 4 mm collimator 20% of the With a 4 mm collimator 20% of the

beam illuminates 2 adjacent pads – beam illuminates 2 adjacent pads –

this is important to limit border this is important to limit border

effectseffects

The detector can be moved in the The detector can be moved in the

XY plane by means of two stepping XY plane by means of two stepping

motors to measure the average motors to measure the average

sensitivity of each padsensitivity of each pad

X Ray tube

Y

X

Sleds

Collimator

Gain UniformityGain UniformityWe measure the current collected on the pads when the detector is We measure the current collected on the pads when the detector is illuminated illuminated with a with a high intensity X-Ray Tube (the iron target gives two high intensity X-Ray Tube (the iron target gives two energy peaks at Eenergy peaks at E1 = 6.4 keV and E= 6.4 keV and E22 = 7.1 keV) The current is proportional = 7.1 keV) The current is proportional to the detector gainto the detector gain

En

trie

s

I(nA)

% 3.8G

G


X-Ray Test: A Measurement

En

trie

s

I(nA)

The current collected on the pads is read-out with a The current collected on the pads is read-out with a

Keithley 6517A electrometer with sensitivity <<1 nA Keithley 6517A electrometer with sensitivity <<1 nA

Mean Current Distribution on pads

The Gain uniformity is about 15 % including edge effects

Edge effect part of the X-Ray beam is outside the detector sensitive area

XY

I(nA)

Current Distribution on pads

Mean Current Distribution on pads without edge effect

The Gain uniformity ~8 %

% 15G

G

Conclusions


The triple-GEM detector quality control tools are now operational The triple-GEM detector quality control tools are now operational in our construction sitein our construction site

The gas leak measurement setup allows to reach the requested The gas leak measurement setup allows to reach the requested sensitivity in 12-24 hourssensitivity in 12-24 hours

The X-Ray setup allows to monitor the detector gain uniformity The X-Ray setup allows to monitor the detector gain uniformity with an accuracy better than 10% (or even better if we exclude the with an accuracy better than 10% (or even better if we exclude the pads on the detector perimeter) with a test time of 1-2 min / pad, pads on the detector perimeter) with a test time of 1-2 min / pad, equivalent to 3.25-6.5 hours total run timeequivalent to 3.25-6.5 hours total run time

Conclusions% 26

I

I

hours 1t


Charging Up on one Pad


Charging Up on of the Pads

Time (seconds)

Charging Up on 12 Pads

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