Transcript 2009_02_tessarotto_GDD_03_03_2009.ppt

New THGEM test in the COMPASS hall
Preparation of the test
Preliminary check with Fe source
The LED light sources
The test area in the COMPASS hall
Measurements with analog r/o
Measurements with digital r/o
GDD meeting,
CERN,
01/10/2008
Trieste
THGEM news
Fulvio TESSAROTTO
1
Motivations for this test
From:
- CsI photoelectron extraction and backscattering measurements
- first indications from simulation of fields and trajectories
- THGEM performances with different gases
we concluded that a methane based gas mixture is needed
We experienced difficulties in reaching high gains without sparks
 Decision to build a quadruple THGEM
 Test it with light source
 Obtain authorization to use flammable gas
 Try to characterize the time response
The COMPASS RICH test area seemed to be the easiest choice
GDD meeting,
CERN,
01/10/2008
Trieste
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2
Preparation of the test
Design and build a new chamber with:
- 9 HV connectors and 2 gas connectors,
- anode segmented in 16 pads,
- a fused silica window (Heraus Suprasil II)
- a flange for light source mounting
Design and build mechanics for:
- testing the LED light source behavior
- interfacing the light source to the chamber
Find low wavelength LED and best possible driver
Most important: involve many COMPASS colleagues for the test
GDD meeting,
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01/10/2008
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3
Choice of THGEM
“Standard geometry”:
- Thickness = 0.4 mm
Hole diameter = 0.4 mm
Pitch = 0.8 mm
Rim = 10 μm
Production:
- Laser + etching
- First set from ELTOS
Second best after “global
etching”
GDD meeting,
CERN,
01/10/2008
Trieste
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4
The chamber
THGEM 1
CERN,
01/10/2008
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drift
THGEM 2
2.0 mm
THGEM 3
2.0 mm
THGEM 4
E
2.0
mm
transfer
anode
GDD meeting,
CsI
Einduction
2.0 mm
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5
First test: triple THGEM, Ar-CH4 50-50
55Fe
source: rate ~ 200 Hz, primaries: ~ 200
THGEM: 30x30; 0.4, 0.4, 0.8, 10 μm
Spacings: 2.0 mm (drift sp. = 4.0 mm)
Fields:
Drift = Induction = 1.5 kV/cm
Transf.1 = Trasnf.2 = 1.0 kV/cm
THGEM voltages:
ΔV2 = ΔV3 = 1400 V
largest gain with 55Fe source so far
ΔV1 (V)
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Very interesting currents:
First test: triple THGEM, Ar-CH4 50-50
55Fe
source: rate ~ 200 Hz, primaries: ~ 200
Drift:
Top1:
Bottom1:
Top2:
Bottom2:
Top3 :
Bottom3:
Anode:
Fields:
Drift = Induction = 1.5 kV/cm
Transf.1 = Trasnf.2 = 1.0 kV/cm
THGEM voltages:
ΔV2 = ΔV3 = 1400 V
GDD meeting,
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THGEM: 30x30; 0.4, 0.4, 0.8, 10 μm
Spacings: 2.0 mm (drift sp. = 4.0 mm)
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+ 160 pA
+ 30 pA
0 pA
+ 110 pA
- 50 pA
+ 710 pA
- 610 pA
- 340 pA
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7
CsI deposited on one half only
8 pads corresponding
to the CsI coated half
CsI deposited by
Miranda Van Stenis
(A. Braem’s lab.)
on 17/02/2009
CsI coated half
GDD meeting,
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8 pads corresponding
to the uncoated half
uncoated half
01/10/2008
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8
We bought 2 LED’s of 255 nm
from “Laser 2000” company, Paris
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9
First test of “255 nm LED”
Check that the LED is properly working (no specifications available)
- power DC mode direct/inverse and check current
- try to see glow from UV light on fluorescent liquid
- characterize the LED emission spectra
- estimate and tune the LED light output in pulsed mode with PM
We then mounted it on the chamber with CsI coated THGEM:
- no measurable photocurrent seen
- with multiplication both signals and currents are seen
Conclusion: we can use it for the test
Colleagues from Freiburg bought a “270 nm LED”
able to provide pulses of 600 ns length, up to 40 MHz
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Mechanics for the LED
LED
quartz
window
THGEM
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Study of the LED with a MAPMT
LED
50 μm pin-hole
quartz
window
THGEM
MAPMT
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Emission spectra for LED “255” nm and “270” nm
Using an Avantes
spectrophotometer
we measured the
emission spectra
for both “255 LED”
and “270 laser LED”
Both seem to emit
in a region where
CsI has extremely
low Q.E., if any.
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COMPASS RICH THGEM TEST AREA
Power plugs
Gas Distribution rack
THGEM Detectors
Methane Detection Head
Methane Leaks Collector
Bottle of Ar/CH4 50/50
Bottle of Ar/CO2 70/30
Safety box for radioactive sources
Electronics Racks
Sliding door
Emergency Button
We have been authorized to use flammable gas: Ar-CH4 50-50 or pure CH4
for two weeks, after some interactions with the safety officers and filling of
a finite number of safety papers.
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14
Amplitude spectra with “255 nm LED”
“255 nm” LED continuous current:
Voltages:
7150
7150
5525
5325
3775
3575
2150
1950
620
For high rates the analog r/o piles up the signals;
lowering the rate we reach a minimum slope and
lowering it further the event rate changes without
changes in the slope of the spectra => single photon
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Amplitude spectra from pulsed LED
Pulsed LED provides single photoelectrons
with probability between 0.1% and 1%
Voltages:
GDD meeting,
7150
7150
5525
5325
3775
3575
2150
1950
620
CERN,
01/10/2008
Trieste
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16
Estimate of the gain: ~ 100,000
The chamber was very stable in these conditions
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Amplitude spectra with “Freiburg LED”
Random pulses – high frequency
Fixed frequency: 9kHz
Voltages:
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7100
7100
5500
5300
3750
3550
2150
1950
620
18
Using FREIBURG pulsed LED:
Voltages:
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7100
7100
5500
5300
3750
3550
2150
1950
620
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19
Delta V1 increased by 30V
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Zooming the low amplitude part
Saturation of Amplifier
Changing the GAIN of the Amplifier
There is no clear evidence of “Polya” shape
GDD meeting,
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21
First look at timing properties
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22
First look at timing properties
GDD meeting,
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01/10/2008
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Fulvio TESSAROTTO
23