Post on 20-Dec-2015
New Readout Methods for LAr detectors
P. Otyugova
20.10.2006
ETH Zurich, Telichenphysik
CHIPP Workshop on Neutrino physics
Liquid Argon TPCs detect the ionization charge to create the image of the event and the scintillation light can be used for triggering or T0 definition.
To detect the ionization charge in a large noble liquid detector very low noise charge preamplifier is required (challenging, costly).For example: in ICARUS detector the signal is only 15000 electrons for a minimum ionizing particle track with 3mm wire pitch. In this case to obtain a highsignal to noise ratio the equivalent noise charge has to be less then 1000 electrons.
Signal from a MIP recordedIn the Induction plane of T600ICARUS detector.
In 100 kton detector with 20 m drift In a field 1kV/cm the drift time is about 10 ms. With a 2 ms electron lifetime , the 6000 electron/mm signal is attenuated by:
It is too low for a readout as in ICARUS (See talk of A.Rubbia)
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e−t /τ ≈1/150
How can we solve this problem?
To compensate the attenuation and to improve signal-to noise ratioone can introduce a so-called double-phase amplification and readout.
e-
Ampl. + readout
race track electrodes
Liquid Ar
Gas Ar
Extraction grid
In this type of readout the electrons are extracted from the liquid by a grid into the gas phase where they are amplified and read out by a gas multiplier technique.
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σ=3mm- the spread from the diffusion on 20m drift distance. It gives a limit on a readout granularity.
References on a Double Phase detection method: Experimental Methods for Particle Dark Matter Detection. Dolgoshein et al., Fiz.El.Chast. Atom. Yad. 4 (1973) 167
Different types of gas avalanche detectors can be proposed for a charge readout: GEM, T-GEM, LEM, MicroMEGAS, ...
We are working on the R&D of a Large Electron Multiplier (LEM) made out of standard PCB technique.
This method potentially provides a several benefits:
1. Possibility to reach electron amplification gain up to 104.2. Improvement of signal to noise ratio which results in a possibility to detect events with a lower energy threshold or long drift paths. 3. Low cost and relatively easy mode of operation.
For Dark Matter applications, this method potentially provides additional benefits:
1. Improvement of position resolution as compared to PMT readout.2. Possibility to use very low background materials.3. Takes less space than PMTs.
What is the LEM?
Diameter ofthe hole: 500 microns.
Distance betweentwo holes: 800 microns.
LEM thickness:1.5mm.
For HV supply bothsurfaces are coveredwith copper electrodes.
LEM is a thick macroscopic GEM
For obtaining a necessary gain a double-stage LEM system is required.
Multiplication factor (average gain) ~104.The simulation is madefor 100% Ar gas at temperature T=87K and pressure1bar.
The detector will consist of 2 LEM stages with 3mm separation
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Image of the hole is made with magnification x500. Edge of the hole seems to be smooth. It helps us to avoid the corona discharges which can be caused by the sharp and not
uniform edges.
Experimental setup
Tests of a single-stage LEM at room temperature
The tests• LEMs of 3 different thickness were tested:
2.4mm, 1.6mm, 1.0mm• 2 radioactive sources were used Fe55 (5.8keV
X-rays), Cd109 (22keV X-rays)• The tests were made in a pressure range
from 1bar to 3.54bar.• The value of the drift field was ~ 100V/cm
which according to the simulation provides a 100% transparency for the drifting electrons
The typical spectrum (Fe55)
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Gain curves for 3 types of the LEMobtained with Fe55 source
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500
1000
1500
2000
2500
3000
3500
1600 1800 2000 2200 2400 2600 2800 3000 3200
Gain 2.4mm 1barGain 1mm 1barGain 1.6mm 1bar
Gain
Voltage (V)
The experimental setup
Tests of double-stage setup
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Double-stage LEM system under construction.
Before the tests chamber was evacuated down to a pressure of 2*10-4 mbar.
Tests of this setup were performed in a wide range of pressures and temperatures and now it is prepared to be tested in double-phase conditions.
The High Voltage system for the LEM setup
The setup is supplied through the voltage divider:
R01=R02=100MOhm
R11=R12=500MOhm
R21=R22=100MOhm
The setup inside the container
Shapes of the signals from double-stage LEM system on the output of the preamplifier and 50 Ohm input of theoscilloscope.
The average signal rise time is about 12s.These are signals from Fe55 radioactive source (5.8 keV),event rate is about 1kHz.
Gain curves at atmospheric pressure and room temperature
Transfer field:Etransf=360V/cm
Tests in gas at cryogenic temperatures
Here you can see a plot which illustrates a shift of gain curves withtemperature changes.
Nitrogen boiling point: 77K
Argon boiling point: 87K
E (V/cm)
Preparation for the double-phase test
To make these tests we have to modify our setup.
The invar-plates levelmeter is used to monitor the liquid level inthe setup.
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Prototype Stripped LEM readout
Here is the schematic viewof a LEM prototype withstrips.The prototype which weare going to test sooncontains 10 strips on each electrode.Strips on both sides of the PCB are perpendicular.
Design of a final LEM readout for ArDM Experiment
Number of channels-1024
•Full scale measurement of long drift (5 m), signal attenuation and multiplication
• Simulate ‘very long’ drift (10-20 m) by reduced E field & LAr purity
• High voltage test (up to 500 kV)
• Measurement Rayleigh scatt. length and attenuation length vs purity
• Design & assembly:
completed: external dewar, detector container
in progress: inner detector, readout system, …
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readout
race tracks
Flange with feedthroughs
LAr
Gas Ar
grid
8” PMTET 9357FLA
Extraction from LAr to GAr and LEM readout
Field shaping electrodes
8” PMTET 9357FLA
Extraction from LAr to GAr and LEM readout
Field shaping electrodes
ARGONTUBE
Field shaping rings(10mm spaced)
Greinacher chain
LEM
Bottom view
Top view
Light pulse source
Inner detector design
Outlook
1. Switching to a double-phase technique gives us a possibility to solve a problem of signal-to-noise ratio and signal attenuation in large cryogenic detectors.
2. It is planned to use LEM in many double-phase cryogenic detector projects: ArDM, GLACIER, ARGONTUBE.3. The preliminary tests showed us, that the multi-stage LEM provides gain of 104 in pure Ar gas at a pressure of 1bar and a temperature of 90K.4. Gain curves shifts correlated with the temperature changes can be explained with the fact that the gas density increases with decrease of the temperature.5. For the moment we are already prepared to start a double-phase test of our setup.