Università degli Studi di Cagliari
Dipartimento di Fisica
Detector Quality Control
Edoardo Cardelli
Edoardo Cardelli – Dipartimento di Fisica – Università di Cagliari
Overview
Introduction
Motivations
Gas Leak Test
• Measurement Principle
• Setup
• An example
 X-Ray Test
• Setup
• Uniformity measurement
Edoardo Cardelli – Dipartimento di Fisica – Università di Cagliari
Introduction
Quality control measurements are necessary to guarantee the
requested detector performances
Gas Leak Rate
The 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
Edoardo Cardelli – Dipartimento di Fisica – Università di Cagliari
Gas leak Test : setup (I)
The gas leak rate measurement of a chamber is referred to the pressure of
one reference chamber (same volume, no leak)
The chambers are inflated in parallel up to an overpressure of ~ 5 mbar
N2
Ref Chamber
Chamber to test
Patm
S1
T
P
S2
The difference of pressure, Δp, from the probe S2
returns the gas leak rate of the chamber under test
The probe S1 returns the relative pressure
of the chamber under test
Edoardo Cardelli – Dipartimento di Fisica – Università di Cagliari
Gas leak Test : setup (II)
Edoardo Cardelli – Dipartimento di Fisica – Università di Cagliari
Gas leak of the Chamber
We can measure the gas leak rate by measuring the
pressure Δp at time instants with equal p/T value.
Pressure and temperature sensors
The result fit make gas leak rate of
the chamber
Equal value of T/p
Edoardo Cardelli – Dipartimento di Fisica – Università di Cagliari
PP
atm
 const

const
T
T
X Ray Test: system setup
Gain Uniformity
We measure the current collected on the pads when the detector is illuminated with a
high intensity X-Ray Tube (the iron target gives two energy peaks at E1 = 6.4 keV and E2 =
7.1 keV) The current is proportional to the detector gain
X
The detector can be moved in the
XY plane by means of two stepping
motors to measure the average
sensitivity of each pad
Y
X Ray tube
Collimator
Sleds
Edoardo Cardelli – Dipartimento di Fisica – Università di Cagliari
With a 4 mm collimator 20% of the
beam illuminates 2 adjacent pads –
this is important to limit border
effects
Pressure and temperature are
used to correct the HV supply in
order to keep a constant detector
gain
X-Ray Test: A Measurement
The current collected on the pads is read-out with a Keithley 6517A
electrometer with sensitivity <<1 nA
Current Distribution on pads
Mean Current Distribution on pads
Entries
I(nA)
G
 15 %
G
X
Y
Edge effect  part of the X-Ray beam is
outside the detector sensitive area
I(nA)
Entries
The Gain uniformity is about 15 %
including edge effects
G
 8.3 %
G
Mean Current Distribution on pads
without edge effect
The Gain uniformity ~8 %
I(nA)
Edoardo Cardelli – Dipartimento di Fisica – Università di Cagliari
Conclusions
The triple-GEM detector quality control tools are now operational
in our construction site
The gas leak measurement setup allows to reach the requested
sensitivity in 12-24 hours
The X-Ray setup allows to monitor the detector gain uniformity
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,
equivalent to 3.25-6.5 hours total run time
Edoardo Cardelli – Dipartimento di Fisica – Università di Cagliari
Charging Up on one Pad
Conclusions
I
 26 %
I
t  1 hours
Edoardo Cardelli – Dipartimento di Fisica – Università di Cagliari
Charging Up on of the Pads
Charging Up on 12 Pads
Time (seconds)
Edoardo Cardelli – Dipartimento di Fisica – Università di Cagliari