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).

Davide Pinci CERN 6/4/04

Systematic differences between gaps

Average gain (nA) Average gain (nA)

Average gain (nA) Average gain (nA)

Gap A + Gap B = 364 nAGap C + Gap D = 396 nA