test on installed rpcs with the gas mixture. preliminary results
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Test on installed RPCs with the gas mixture. Preliminary results. Alessandro Paoloni on behalf of the OPERA RPC Group (Bologna, LNF, LNGS, Napoli, Padova, Zagreb) OPERA collaboration meeting Hamburg 3-5 June 2004. The first spectrometer in the Hall C. Environment parameters: - PowerPoint PPT PresentationTRANSCRIPT
Test on installed RPCs with the gas mixture.
Preliminary results.
Alessandro Paoloni
on behalf of the OPERA RPC Group
(Bologna, LNF, LNGS, Napoli, Padova, Zagreb)
OPERA collaboration meeting
Hamburg
3-5 June 2004
The first spectrometer in the Hall C
Environment parameters:• T=16 oC (at the base of the spectrometer)• P~900 mbar (few mbar higher wrt external lab)• Dry=50-60% (wetter wrt external lab)
RPC layers1 11
RPC layers12 22
Easternside
Row 1
Row 7
Hall C lateral wall
To compare experimental results with data from ext. lab, rescale applied voltages to fixed T0=293 K and P0=900 mbar:
V=Vapplied*(T/T0)*(P0/P)
Tests with nitrogen
For the installed RPCs validation, we kept the detector at 6.5 kV, below the discharge region, but above the operating voltage with the gas mixture:• Test the HV system found that an additional PET layer is needed for the insulation of HV electrodes from the strips• Test mechanical stresses by comparing the currents before and after the iron slab installation in case reduction of the filling material thickness
N2 Test
Test with gas mixture
• We have the permission to use small quantities of the mixture Ar/C2H2F4/i-C4H10/SF6=75/20/4/1 in premixed bottles
•Test a RPC row (~9 m2) at a time, flushed at 5 refills/day
• The row is covered by a panel of 32 horizontal strips, served by 2 IC boards
Up to now tested the row n.1 of layers n.9,18 and 19
Test set-up
• The strip panel is self-triggered using two Timing boards installed on the InterConnection boards • Each timing board is endowed with a double threshold discriminator acting on the analog sum of 16 strips• Threshold low = ~20 mV• Threshold high = 25 mV (40 mV in the first measurements)• 32 ADC channels used for measuring the charge induced in each strip• Also counting rates and currents are measured
Test of the set-up in Frascati
• Used a small size old RPC prototype• Higher Pressure wrt GS lab expected operating voltages below 6 kV in Hall C
Counting rate
Induced charge
Reference plots at the external lab
• RPC BES1451 under test at Ciocco facility for ‘‘ageing’’ studies at cosmic rays rate• MACRO FE boards used
Effect due to fast increase of the current with high resistivity ?
Chosen operating point:5.5 kV
Operating currents in Hall CLayer n.9
Layer n.18 Layer n.19
• The currents at the operating point are below 350 nA, lower wrt to QC tests at external GS lab• Their increase is faster for the eastern RPC (near the lateral wall of Hall C)
Counting rates in Hall C
Layer n.9
Layer n.19Layer n.18
• The counting rates at the operating point are of the order of few Hz/m2 (to be compared with 200-400 Hz/m2 at cosmic rays rate)• The counting rates are higher for the eastern RPC (near the lateral wall of Hall C)• There is not a plateau, but an exponential dependence on the operating voltage
Threshold studies
The rates have been measured at 5.5 kV with the lower threshold at 20 mV
Good higher threshold stability till 60 mV
Induced charge
The average induced charge at 5.5 kV is about 20 pC
Induced charge: layer 9
Entire row Middle + western RPCs
Induced charge: layer 18
Western RPC Middle RPC Eastern RPC
Conclusions
Up to now we have tested 9 installed RPCs with the gas mixture Ar/C2H2F4/i-C4H10/SF6=75/20/4/1, observing:
1. Very low operating currents and counting rates
2. No plateau for the counting rate vs the voltage (reference to external lab. measurements essential for determining the operating point)
3. Current and rate higher for RPCs near the lateral side of Hall C
These results are a first indication of the goodness of the RPC installation procedure
More statistics needed (first installed rows, rows with filling material substituted)
What from QC tests ? BE1074
7.9 ± 0.3
2.8 ± 0.4
2.021 ; 2.099
386 ; II
BIM1331
2.5 ± 0.6
0.92 ± 0.01
1.911 ; 1.988
464 ; II
BE1136
8.7 ± 0.2
0.45 ± 0.01
1.917 ; 1.973
568 ; OK
BES1710
1.7 ± 0.1
0.70 ± 0.01
1.965 ; 2.043
472 ; II
BI1653
3.8 ± 0.3
1.34 ± 0.04
1.864 ; 1.903
388 ; II
BES1698
5.7 ± 0.2
1.27 ± 0.02
1.950 ; 1.999
377 ; II
BES1551
2.7 ± 0.3
4.0 ± 0.3
2.004 ; 2.047
372 ; II
BI1220
14.1 ± 0.4
0.90 ± 0.02
2.031 ; 2.070
450 ; OK
BES1680
19.7 ± 0.2
0.94 ± 0.01
1.914 ; 1.977
530 ; II
Eastern side
Layer 9
Layer 18
Layer 19
RPC name di/dv (nA/kV)cm)V100 ; V500 (kV)Iop(nA); C.R. Q.R.
RPC name:Red=high temperature testGreen=low temperature test
Strip signals (I)Strip
Ground
1 M pick-up
Strip signals (II)
Adjacent strips
50 pick-up
Strip signals (III)Central strip1 M pick-up
Ground1 M pick-up
Central strip differential read-out
Far strips50 pick-up
Strip signals (IV)
Noise
Strip1 Mpick-up
Ground1 Mpick-up
Strip with differential read-out
Induced charge: layer 9
Total induced charge
Reconstructed hit position
Entire rowMiddle + western RPCs
Up Down
Induced charge: layer 18
UpDown
Western RPC Middle RPC Eastern RPC
P = 1000 mbar
P = 900 mbar
Lower operating voltages expected at GS because of the lower pressure
Frascati test of the set-up
6.25 kV
5.65 kV
T = 20 oC
Strip panel not covering the entire RPC and picking up signals outside its area (more signals at the edge of the panel)
Frascati test of the set-up
Found a miscalibration of the nanoamperometers used in hall C (not OPERA standard): the currents are lower by a factor of about 2
Current on the negative electrode from nanoamperometers
Current on the positive electrode from power supply
Further investigations needed to understand and solve the problem