Chamber Quality Control

Before the construction several checks are performed on: Panels (cathode and pad PCB) GEM foilTests on assembled detector concern: Gas chamber leakage Gain uniformity with X-ray

Checks on panels

All panels will be checked for planarity with a 3-D machine at LNF. The measure will be performed on a grid of 35 points.The planarity requirement is ≤ 50 µm

3-D machine

5 10 15 20 25 30 35

4 9 14 19 24 29 34

3 8 13 18 23 28 33

2 7 12 17 22 27 32

1 6 11 16 21 26 31

Preliminary measurements have been done on the panel pre-production resulting better than 30 µm

GEM foil HV test: conditioning (I)All GEM foils are tested before frame gluing in order to check their quality. The test, sector by sector, is performed in a gas tight box.

The voltage to each GEM sector is applied through a 500 M limiting resistor in order to avoid GEM damages in case of discharges.

N2 Flow

The gas tight plexiglass box is flushed for about 1 hour with nitrogen in order to reduce the humidity level @ < 5%, before the GEM test

humidity probe

HV supply

R= 500 MH

GEM foil HV test: Conditioning (II)Voltage is applied on each sector (18 steps):

1. 50 V up to 400 V (20 s)2. 25 V up to 500 V (1 min) 3. 10 V up to 600V (2 min)

acceptance requirements:

leakage current < 2nAAND

# of discharges <3The GEM sector pass the step

Yes

the voltage ramp-up on the sector is suspended and the

test will be repeated later

No

Test duration 3 hours with two test stations: up to 4 GEM foils/day

This procedure has been tuned on a pre-production of 11 GEM foils

GEM foil HV test: conditioning (III)

The average number of discharges per sector on the whole procedure comes out to be <2.2>. If the test is repeated a second time, the total number of discharges goes down to <0.3>.

This behaviour could be due to microscopic dust that are softly burned with high voltage and then removed from the GEM surfaces by N2 continuous flow.

Number of discharges

1st HV tour

2nd HV tour

Histograms are filled with the total number of discharges occurred in each sector during ramp-up (18 HV steps).

<2.2>.

<0.3>.

Ambient parameters (T and P) are monitored with additional sensors

Gas leak test (I): system set-up

Both test and reference chambers are inflated in parallel, up to an overpressure of 5 mbar.

The difference between P(S1) e P(S2) measures the gas leak rate of the test chamber Test duration 2

hour

foam box for thermal insulation

N2 Ref chamber

S1 S2

T, PChamber to testPat

m

The gas leak rate measurement of a chamber is generally referred to that one of a reference chamber (same volume, “no leak”) in order to take into account atmospheric pressure and temperature variations.

Gas leak test (II): procedure to define reference chamber

<1 mbar/day

Equal value of T/p

The fitted points at equal T/p give the leak rate of the chamber <1 mbar/day.This allows to keep humidity under 100 ppmV with a 100 cc/min gas flow.

The gas leak rate is obtained measuring the gas over pressure p inside the chamber looking at time periods with equal T/p value. The red band represents the instrument sensitivity ((T/p) 3x10-4) .

Time (min)

T/p

(°K

/mba

r)p

(m

bar)

Collimator diameter 5 mm

X-ray test(I): system setupThe gain uniformity, pad by pad, is measured with a high intensity 5.9 keV X-ray tube

Gas humidity and temperature are monitored with a probe mounted on the gas line outlet. Also atmospheric pressure is recorded

X-Y plane moved with step-motors

Test duration: 16 hours

A gain uniformity < 12% (with edge effects, 6% without)

X-ray test(II): measurements The current signal induced on the single pad is read-out with a current-meter (nA sensibility) and it is corrected for T and p variations

Due to effective beam spot in the border pads