Radioactive source and cosmic-ray test for the MWPC

Davide Pinci on behalf of the Frascati-Roma1 MWPC

group

Davi

de P

inci

OutlineAt the end of the construction process we plan to perform a

quality control of the Multi-Wire Proportional Chambers.

For this purpose we built:

A table to investigate the gain and its space uniformity by means of a radioactive source of each gap of the chamber;

A cosmic ray station to study the chamber total efficiency and time performance;

The large number of chambers produced demands: Fast and automated test setup fully controlled by PC; Organized data storing;

Davi

de P

inci

Test with the radioactive source The measure of the gain of each chamber gap is performed by

means of a radioactive source; It results to be a very usefull test:

Th chamber can be tested whitout front-end electronics; The measurement is very fast: the whole chamber can be

checked in less than 1 hour; The gain uniformity provides important information on the

quality of each gap: gap thickness, wire spacing, electrical connections, gas flow uniformity;

The gain absolute value provides information on: uniformity between the different chamber gaps; uniformity in the chamber production (once corrected

for the room temperature and pressure variations);

Davi

de P

inci

System set-up We use a 137Cs source; The current drawn by each gap is measured by a nano-

amperometer built in Frascati, providing 1 nA of resolution; The source activity is about 40 mCi which means a production

of about 109 0,662 MeV photons/s over 4 (about 5 106 over a 24° cone);

With the nominal chamber gain (7.5 104) a current of about 70 nA is expected; The source is shielded in a lead case which insures a dose rate lower than 0.5 Sv/h @ 1 m far from the source.

137Cs source

Lead case

Davi

de P

inci

The measurement table

Two stepping motors control the source movement in the two directions;

The motors are fully controlled by PC via an I/O National Instrument board (6025E) and a driver;

The position precision is about 0.5 mm for both axes.

Davi

de P

inci

Gain uniformity requirements The main requirements on the gain uiformity are related to

the working point. Quoting the EDR:“If G0 is the nominal gas gain, we want the gas gain in 95% of the area of a single gap to be within G0/1.25 and G0*1.25 i. e. between 0.8G0 and 1.25G0.The remaining 5% of the area should have a gain within a factor 1.5 i.e. between 0.67G0 and 1.5G0 ”

Since the gain double each 106V, this requirements allows to have almost the entire chamber efficient by working 50 V (30% of the gain) above the nominal value of 2530 V:

HV = 2580V2530 V

Davi

de P

inci

Chamber C001

Davi

de P

inci

Chamber C002

Davi

de P

inci

Comments Chamber 01:

For the 4 gaps: 93->99 % of the gap area in the required range;

Chamber 02: The gaps 2, 3 and 4 show very good gain uniformity:

96 ->99% of the gap area in the required range; gain distribution r.m.s. resulted about 10% of the average

values;

The gap 1 shows two different gain regions; It can be due to a not perfect panel planarity. Nevertheless the 76% of the area is within the required range and

the 90% is in the range 1/1.30 and 1.30; The gain distribution r.m.s. resulted to be the 18% of the average

gain value. All the 4 gaps have 100% of the area in the range 1/1.50 and 1.50.

Davi

de P

inci

We plan to study MWPC efficiency, time performance and cross-talk;

6 MWPC layers are tested at the same time in order to shorten test duration and to perform muon tracking;

With this set-up the chamber edge performance measurement will be the most time consuming;

The cosmic ray test station

Lead layer for

shower veto

Trigger is given by 3 scintillators with double read-out: a total efficiency of 90% and a time resolution of ~1.8 ns were measured.

100

400

PM

Davi

de P

inci

Test performance We plan to investigate the performance of each physical channel; MWPC will be equipped with a readout circuitry: ASDQ or Carioca We made some simulations to evaluate the time needed:

Test time is expected to be less than required by the MWPC production rate;

Number of channels input into a multi-hit 128 ch TDC (CAEN V767) reduced via dedicated circuitry: multiplexing boards to reduce cost.

Davi

de P

inci

Channel multiplexing To multiplex many

channels from the MWPC FEB into a reduced number of TDC channels, groups of FE channels are delayed as shown in figure.

t needs to be larger than the MWPC time resolution in order to prevent a biased measurement.

Channel group 1

tt

t

t

t

t t

t t t

Ch2

Ch4

Ch5

Ch3

Implementation is on an FPGA. Signal lines can be propagated through long cascades of gates used as delay lines; t can be selected in the range 80-110 ns; Lab measurements show jitter values below 400ps over the allowed voltage and temperature operating ranges.

Davi

de P

inci

Muon station set-up situation The station mechanics drawing and materials are ready and the

station construction is foreseen by the end of december; Scintillators, PMs and electronics for data acquisition are set-up; DAQ system (Labview based) already written and working in

Roma1 university; Plan to debug the whole system (without Mux) by testing some

MWPC prototypes as soon as the mechanics is ready;

The MUX: All the material and components are in Roma1 The electronics drawings are ready and the board layout is

arriving The whole system should be working by the end of Feb 04

In the meantime we plan to test the chambers by using more than one single TDC.

Davi

de P

inci

Time, manpower and conclusions Radioactive source test:

The whole system (gas, HV, source-positioning, current readout) is working properly;

1 hour and 1 person is needed 2/3 times per week for the test;

Cosmic-ray stand:

Now: Trigger and data acquisition are ready in Roma1; Dec 03: debug (in Roma1) with some MWPC prototype; Jan 04: set-up in Frascati and start of tests with a preliminary

version (without Mux); Feb 04: Mux arrive and cosmic stand up-grade; 1 person needed fulltime.