results of the radioactive source scan of the first 17 mwpc produced at lnf
DESCRIPTION
Results of the radioactive source scan of the first 17 MWPC produced at LNF. Davide Pinci on behalf of the LNF-Roma1 MWPC group. System layout. 137 Cs source case. Gap A Gap B Gap C Gap D. Gas in. Gas out. HV. We measure the current drawing in the HV channels in 3x53=159 positions. - PowerPoint PPT PresentationTRANSCRIPT
Results of the radioactive source scan of the first 17 MWPC produced at LNF
Davide Pinci on behalf of the LNF-Roma1 MWPC group
Davide Pinci CERN 6/4/04
System layout
Gas inGas out
HV
137Cs source case
Gap AGap BGap CGap D
We measure the current drawing in the HV channels in 3x53=159 positions
Davide Pinci CERN 6/4/04
Photon flux profile
We recorded the current increase while the source was approaching the first pad edge
15 cmNo significant illumination differences among the gaps
Photon flux diameter of about 15 cm
Davide Pinci CERN 6/4/04
Hv and ground connections check
A wire pad (13 wires x 2 mm pitch) disconnected from HV
A 2.75 cm pad disconnected from ground
Althuogh the beam flux has a 15 cm diameter, the system can give very precise information
Davide Pinci CERN 6/4/04
Uniformity inside the gaps
Chamber number
Are
a in
the 0
.8-1
.25 r
an
ge (
%)
The requirement is to have on the 95% of the gap area a current in the range:
C0/1.25 and C0x1.25
The gap uniformity is going better.
The behaviour of Chamber C012 could be very interesting to be studied
Davide Pinci CERN 6/4/04
Chamber C012
Gap C
Gap D
... while the gain of the Bi-Gap CD is rather flat.
A bent panel between gaps C and D provides this situation: the gain in the gap C and D not uniform...
What about efficiency, time resolution and cluster size?
... to be investigated with test beam or cosmic rays...
Double-gap CD
Davide Pinci CERN 6/4/04
Uniformity inside the Bi-GapsA
rea in
the 0
.8-1
.25 r
an
ge (
%)
Chamber number
Limit of 95%
Some mechanics problems (e.g. bent panels) turn out to compensate.
We should study the performance of these chambers in order to get a decision on the quality assessment.
The situation of C012 is similar to other chambers (e.g.....)We decided to study the Bi-Gap uniformity too.
The Bi-Gap uniformity is better than the single Gap one.
Davide Pinci CERN 6/4/04
Uniformity between different gaps
Chamber number
Avera
ge c
urr
ent
(nA
)
Mean value = 190 nA
190 nA x 1.25 = 240 nA
190 nA : 1.25 = 152 nA
The production procedure has being optimized (mainly on the basis of the source scan feedback)
After some bugs have been fixed the quality seems to converge to a good level.Gap A = 172 23 nAGap B = 192 28 nAGap C = 212 24 nAGap D = 186 28 nANo systematic effects.
Here are the average values of the 159 current measurements made in each gap
Davide Pinci CERN 6/4/04
All the gaps together
152 nA 240 nA
In the whole checked production (17 chambers) 8 gaps out of the allowed range
In the last 10 chambers no one gap found out of the allowed range
Davide Pinci CERN 6/4/04
HV distribution proposal
On the experiment we will have a large number of indipendent HV channels. We can think to a smart HV distribution to equilize the gap gains.Our proposal, for istance, is to divide the gaps in 5 gain Classes (+ the “Hospital”):
where G0 is the nominal gain and has to be chosen on the basis of the production quality.The HV channels will be also divided in 5 Classes (+ 1 for the “Hospital”) which will provide 5 (+1) HV values.I tried to apply this scheme to the current situation. resulted to be 36 nA/190 nA, hence 20% of the nominal gain.The HV values would be:
-78 V -34 V HV0 +28 V + 51 V
G0-2 G0- G0 G0+ G0+2
Davide Pinci CERN 6/4/04
The optimized situation
Chamber number
Avera
ge c
urr
ent
(nA
)
Mean value = 190 nA
190 nA x 1.25 = 240 nA
190 nA : 1.25 = 152 nA
Here are the average values of the 159 current measurements made in each gap
Davide Pinci CERN 6/4/04
The gain distributions
With an optimized HV distribution in the current situation it would be possible to reduce the maximum gain spread from 170 nA (i. e. the 90% of the mean value) to 48 nA (i. e. the 25%).We think it could be very usefull to understand the feasibility of such a HV scheme.
Davide Pinci CERN 6/4/04
Future developments
So far we are not able to take into account the ambiental condition:
we measure the atmosferic pressure with a too low resolution (1 mbar);
we don’t measure the gas temperature inside the chamber;
The idea is to build a single MWP gap to be placed on the table, under the chamber in test and to use as a monitor.
The cosmic ray station is ready to acquire up to 128 MWPC pads.Waiting for the Mux, we will add 3x32 TDC Ch and we can start to investigate some regions of the most interesting chambers (e.g. C012).