Transcript report_12nov2008

Monday, 10th November 2008
Preliminary results of the THGEM
characterization with several gas mixtures
for Dummy THGEM
Dummy THGEM:
Wires:
drift = wires
d=0.36 mm
pitch =0.2 mm
THGEM
d=4.5 mm
Jarda Polak and Elena Rocco
Procedure for measuring the back
scattering
The dummy chamber is disconnected from the other then the default
configuration is flushing the N2.
 Measurement @ 0.4 mbar up to 260V applied to the wires;
 Isolate the chamber and filled with the appropriate mixture of gas;
 When the gas reaches a slightly over pressure into the chamber,
the output of the chamber is opened for flushing out the gas
through a bubbler;
 Switching on of the UV lamp with the UV filter (λ =239 nm) and
measurement up the first discharge or instability or maximum
voltage attainable with the power supply;
 Gas sucked out by the vacuum pump;
 Measurement @ 0.4 mbar up to 260V applied to the wires.
2
Reproducibility of the measurements
(1/2)
Decreasing the voltage into the wires
Increasing the voltage into the wires
Current read out from anode (pA)
100
80
60
40
20
Vacuum level=0.4 mbar
0
50
100
150
200
Voltage applied to the wires (V)
3
250
300
Pure Argon in atmospheric
pressure always flushing!!
Measurement on Friday
Measurement on Monday
10
0
500
1000
1500
2000
2500
Voltage applied to the wires (V)
3000
3500
Current (pA)
Current read out from top + bottom of THGEM (pA)
Reproducibility of the measurements
(2/2)
Measurement on Friday
Measurement on Monday
10
0
4
500
1000
1500
2000
2500
Voltage applied to the wires (V)
3000
3500
Using the Optical Density filter in the
vacuum and ...
Current read out from anode (pA)
1000
Vacuum level=0.4 mbar
100
10
Optical Density 0
Optical Density 1.0
50
100
150
200
Voltage applied to the wires (V)
5
250
300
...in the gas (chamber filled and
isolated)
Current read out from anode (pA)
100
Atmospheric
pressure+
Pressure= 10
mbar 10 mbar
Ar/CO2 70/30
10
1
Optical Density 1.0
Optical Density 0
0
1000
2000
3000
4000
Voltage applied to the wires (V)
6
5000
6000
Measurements comparison in configuration of the
hold gas in the chamber or in a continuous
flushing of the gas in the chamber
Current read out from anode (pA)
100
10
flushing
kept
Ar/CO2 70/30, but with slightly
different pressures
1
0
1000
2000
3000
4000
Voltage applied to the wires (V)
7
5000
6000
The gases written in the
legend give ONLY the
indication about the
chronology followed.
HERE THERE’S NO
CONTAMINATION
OF ANY GAS, JUST
PURE METHANE
Current read out from top + bottom of THGEM (pA)
Vacuum meas. before the meas. with
the mixture gas
Ar/CO2 70/30
Neon
Pure Argon
Pure Methane
Neon/methane 77/23
1000
100
10
The usual pressure at which the measurement is performed
is 0.4 mbar. The first measurement with the mixture of the
Argon and the carbon dioxide has been made at 0.035 mbar.
50
100
150
200
Voltage applied to the wires (V)
8
250
300
These measurements
on the vacuum show
a possible
dependence of the
residuals of the gas
mixture just used
Current read out from top + bottom of THGEM (pA)
Vacuum meas. after the meas. with the
mixture gas
Ar/CO2 70/30
Neon
Pure Argon
Pure Methane
Neon/methane 77/23
Neon/methane 95/5
1000
100
10
The usual pressure at which the measurement is performed
is 0.4 mbar. The first measurement with the mixture of the
Argon and the carbon dioxide has been made at 0.035 mbar.
50
100
150
200
Voltage applied to the wires (V)
9
250
300
Current read out from top + bottom of THGEM (pA)
Back scattering measured for several gases
@ atmospheric pressure (flow 5 l/h)
100
Argon
Neon
Argon/Carbon Dioxide 70/30
Methane
Neon/Methane 77/23
Neon/Methane 95/5
10
0
1000
2000
3000
4000
5000
Voltage applied to the wires (V)
10
6000
Something to think about...
There’s a discrepancy between the
current measured on the THGEM and
the current on the wires....maybe the
tolerance of the resistor in the
picoammeter.
700
Current on the THGEM (top + bottom)
Current in the wires
600
400
300
200
100
0
50
100
150
200
Voltage applied to the wires (V)
Pressure = 0.4 mbar
250
300
Current read out from top + bottom of THGEM (pA)
Currents (pA)
500
Total current on the THGEM
Current in the wires
90
80
70
60
50
40
30
20
Back scattering measured on the Dummy THGEM in the
pure methane gas.
10
0
1000
2000
3000
4000
5000
Voltage applied to the wires (V)
11
Atmospheric pressure
6000
7000
Current read out from top + bottom of THGEM (pA)
Requested from Silvia (1/2)
Argon
Neon
Argon/Carbon Dioxide 70/30
Methane
Neon/Methane 77/23
Neon/Methane 95/5
140
120
100
80
60
40
20
0
0
1000
2000
3000
4000
5000
Voltage applied to the wires (V)
12
6000
Current read out from top + bottom of THGEM (pA)
Requested from Silvia (2/2)
80
60
Argon
Neon
Argon/Carbon Dioxide 70/30
Methane
Neon/Methane 77/23
Neon/Methane 95/5
40
20
0
0 50 1001502002503003504004505005506006507007508008509009501000
Voltage applied to the wires (V)
13