Aging, High Rate and Shielding L. Lopes Lip-Coimbra.
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Transcript of Aging, High Rate and Shielding L. Lopes Lip-Coimbra.
Aging, High Rate
and Shielding
L. Lopes
Lip-Coimbra
Outline
Aging of Glass Timing RPCs
Results and latest updates
Development of high rate Timing RPCs
Resistive material, electric properties
Detector assembling
Experimental results
Shielded RPCs
Current status of the HADES final prototype.
Aging (2002-2003) humid, cold
After accumulating 800mC/cm2 (equiv. 8.5 years of normal operation) we don't observe any systematic long-term increase of dark current with time.
made some changes on the experimental setup.
• Room temperature
• “Standard” timing
RPCs gas
85%C2H2F4+10%SF6
+5% iso-C4H10, with
10% relative humidity
• Primary charges
were created by an
UV lamp
Aging (2004) dry, warm
T= const = 30 ºC
T= const = 55 ºC
Water-free gas mixture
•After 60 days
we begin to
observe a
systematic
increase of
dark current
with time.
• It was not
observed any
ionization
current
increase.
Why ?...Accumulated 100 mC cm-2
Aging (2004)
1 Anode Glass
2 Cathode Aluminium
1 Cathode Glass
2 Anode Aluminium
1
2
1
2
•Face to face marks in
one chamber electrodes.
•The effect seems more
severe in the cathodes.
•In glass cathode the
surface is mechanical
damaged.
Aging (New Setup) • So, we return to the initial gas mixture with 10% relative humidity.
• Change the irradiation source. Substituted the UV lamp by a 60Co source.
• Keep working at 55 ºC, to reach a resistivity decrease of one order of magnitude.
•Six single gap chambers, with
an effective area of 9 cm2.
•Three with glass cathode
and the others with aluminium
cathode.
•3 kV applied to all chambers
•Average operating current of
30 nA cm-2 in all chambers.
60Co
Aluminium cathode
Glass cathode
Aging (2005) humid, warm
• After more than 80 days we don’t observe any increase of the dark current.
• Which seems to stabilize.
• In chambers that operate at more than 2 kHz cm-2.
• Accumulated 200 mC cm-2
High Rate
High Rate
Resistive material Controlled resistivity alumina, Al940CD, from Wesgo® Ceramics.
Supplier volume resistivity, 1109 cm at room temperature.
Good surface finish.
Easily produced in large amounts (fully commercial)
Resistive material, our measurements Volume resistivity, between 1109 and 2109 cm at room
temperature, in very good agreement with the supplier.
Good surface finish.
Electronic-like conductor. We don’t observe any increase of the
resistivity with time, when we applied an external electric field.
- HV10 M
1 nF
1 nF
1 M
10 M
Gas filters
Metallic cathode
Alumina anode
Shielding box
300 m gap
High Rate
The detector Assembling under clean conditions.
Both electrodes require good surface finish.
Spacerless construction.
High Rate
Benchtop test setup
22Na
Reference Chamber(identical)
Test Chamber10 cm2
(CBM granularity)
X-ray Generator
Photon conversion on RPC yields an exponential pulse-charge distribution Less favourable than the reasonable peak found in a charged beam.
High Rate
0
20
40
60
80
100
120
0 5 10 15 20 25 30 35
X-Ray Anode Current (mA)
Co
un
tin
g r
ate
(kH
z cm
-2)
2500 2600 2700 Linear (2700)
Counting rate
The counting rate was tested using a X-Ray generator, emitting 20 keV photons.
We can see that the chamber doesn’t lose efficiency at least until 100 kHz cm -2.
Threshold = 10 mVCounting rate vs.
“incident rate”. For
applied voltages
lower than 2.7 kV, at
high counting rates
the chamber lose
some efficiency
since we have a
gain reduction.
High Rate
0
50
100
150
200
250
300
2000 2200 2400 2600 2800 3000
Applied Voltage (V)
Cu
rren
t (n
A c
m-2
)
22Na X-Ray 5 mA
X-Ray 10 mA X-Ray 15 mA
X-Ray 20 mA X-Ray 24 mA
0
50
100
150
200
250
300
0 5 10 15 20 25 30 35X-Ray Anode Current (mA)
Cu
rre
nt
(nA
cm
-2)
2500 2600 2700
0
20
40
60
80
100
120
2000 2200 2400 2600 2800 3000Applied Voltage (V)
Co
un
tin
g r
ate
(kH
z cm
-2)
22Na X-Ray 5 mA
X-Ray 10 mA X-Ray 15 mA
X-Ray 20 mA X-Ray 24 mA
…as a result of the Ohmic drop in the
electrode. So depending on the
counting rate we should correct the
applied voltage.
High Rate
0
50
100
150
200
250
0 10 20 30 40 50 60
Counting rate (kHz/cm2)
Tim
ing
res
olu
tio
n (
ps)
Sigma from fitFWHM/2.362700-2900 V2500-2600 V
RandomCoincid.
Signal
But background of random coincidences fit with gaussian + symmetric exponentialHow does it affect the measurement of the real sigma? visit Rosendorf…
CBM goalwell in reach
Shielded RPCs
50
70
90
110
130
150
170
-600 -400 -200 0 200 400 600
Position (ps)
Tim
e r
es
olu
tio
n (
ps
)
Uncorrected Charge-corrected
Shielded timing RPCs
Actual parts, industrially produced.
Uniformity tests with 22Na (positron) source
Crosstalk for avalanches is below the noise level
49500
49550
49600
49650
49700
49750
49800
-600 -400 -200 0 200 400 600
Position (ps)
Me
an
Tim
e (
ps
)
Beam test in November
Final prototype of the HADES RPC-TOF wall
Designed to run warm (up to 60ºC)
Distributed temperature control system in development
Test bench with 25 elements
20 W heater
Hardware temperature limiter
1-WIRE® interface + power
Thermometer
Heating and sensing element
~1ºC accuracy
Conclusions Aging
No aging was observed operating at humid, cold conditions, during a time equivalent to 8 years at
normal conditions.
We observe severe aging in dry, warm conditions.
At the moment we are testing the effect in humid, warm conditions. No problem so far.
Water might be a useful gas mixture compound.
High rate We keep efficiency up more than 100 kHz cm-2.
50 kHz cm-2 with ~100 ps time resolution, possibly limited by statistical effects.
With a commercial material.
To be tested with 60Co, and then in beam at Rosendorf.
Shielded RPCs Final HADES prototype being now assembled for the November beam test.
Industrial production of the mechanical parts.
First tests satisfactory.
Design to run warm.