Resistive Plate Chambers for CMS (Pre-assembly Jobs done at BARC)

Archana Sharma, Suman B.BeriP.U, Chandigarh

&L.M.Pant

BARC, Mumbai

Outline

• Brief Introduction of the Work

• Soldering of FRC connectors to adaptor cards of the FEBs

• Soldering of signal cables to the adaptors

• Leak test for gas-gaps – 9 nos (CERN)

• Leakage current measurement of gas-gaps

Brief Introduction of the work done

RPC- Resistive Plate Chambers: The gaseous detectors of ionizing particles

characterized by the large area coverage (~several m²), time resolution better then 2ns & space resolution of the order of cm.

Used for the muon trigger systems in CMS operated in avalanche mode.

Gas gap of about 2 mm is generated between the two bakelite sheets (each 2 mm thick) & a thin layer of graphite coating over its surface for uniform & intense electric field in the gap.

In the end-cap region of CMS, the RPC consists of a double gap arrangement

Large gap (17357.6cm², 34715.2cm³ )

Medium gap (12445.75cm², 24891.5cm³) and

Small gap (3921.9cm², 7843.8cm³).

The Cu read-out strips are sandwiched between the Large gap and the Medium and Small gap.

Whole system is packed inside a Honey Comb Panel.

The double layer consisting three gas-gaps

Medium Gap (12445.75 cm²)

Small Gap (3921.9 cm²)

Interaction of charged particle with gases produces electric signal induced on the copper strips.

Signal is brought to adapter card by co-axial signal cables.

The FRC connector connected with adapter card goes to the input of the front end board/processing unit.

Soldering of FRC connectors to adaptor cards of the FEBs

Contd…. The Cu read-out assembly is divided into 3 sections.

Each section contain 32 strips radially pointing towards the center of the end-cap.

In total 96 read out channels for each RPC. 16 channels from each section goes to one adapter

card.

Hence 6 adapter cards & 3 front end boards (FEBs) for each RPC.

The output of 3 front end boards goes through the twisted pair cable at the back panel of the RPC.

Contd……. Soldering iron of 25 Watt (230 V) is used with 0.7

mm wire of lead free tin copper alloy for soldering adapter card with FRC connector.

On one adaptor card, there were 32 points to solder in which 16 points were for signal channels & 16 for ground channels.

Checked the continuity of each point on the adaptor card before & after soldering.

Also checked that there should be no shorting in the adjacent signal channels.

The adaptor cards were designed at NPD-BARC and were outsourced for production

Before Soldering

After Soldering

FRC Connector

Adaptor Card (signal side)

Adaptor Card (ground side)

Total number of adaptor cards after soldering – 80 nos.

Soldering of Signal cables to adaptors

First attached the ferrules to the both ends of the signal cable & then soldered these cables to the adaptor cards through the attached ferules.

Again checked the continuity on both signal side as well as in the ground side.

One end of the signal cable will go to the detector while the other to the adaptor card

Ferules

Gas Leak & Leakage Current test for gaps

To check the leak in the gaps used in assembling the RPC detectors.

Gas mixture for the leak test contains:

1) Argon : Using 20% in mixture. Kept the flow rate equal to 5 SCCM for leakage current test & 2 SCCM for gas leak test.

2) Isobutane : Using less then 5% in mixture. Kept the flow rate equal to 2.4 SCCM for leakage current test & 0.4 SCCM for gas leak test.

3) Freon : Using almost 75% in mixture. Kept the flow rate equal to 14.4 SCCM for leakage current test & 3.6 SCCM for gas leak test.

These gases pass through a Regenerative gas purifier and goes to the 4-channel gas mixer.

In the gas mixer, firstly these gases go in the solenoid valves & then to the mass flow controllers.

Solenoid valves operate by compressed air ( at 5 bar ).

In the 4 channel Gas – mixer there are 8 flow controllers :

4 in sccm & 4 in lpm for the flow of gases

Ways to use the mixed gases :

1)Online mixing

2)Premixing

We are using the online mixing to use the mixed gas.

Purpose of Mixed gases:

1) Leak Test ( static pressure )

2) Leakage Current test ( gases in flow mode)

For the Gas leak test of gas mixture

total flow rate : 6 SCCM

the pressure in gap : 25-30 mm of water

column above

atm. pressure.

Leak test of gaps

When there is a sufficient pressure of the mixed gas, valve is opened for the leak test.

Mixed gas goes in three ways.

1) In the gap for leak test & the pressure with which the gas flows shown in the manometer by the difference in the two levels of a coloured red liquid (25 cm of WC for an hour).

Manometer

Safety Bubbler

Sensor

Manometer for leak-tests at NPD-BARC

2)Safety bubbler filled with silicon oil, to ensure that the pressure does not go beyond 50 cm of water column above atmospheres. Thus saves the gap from cracking.

3) Sensor

Tested nine gaps from CERN. Results of the test shown in the table:

Leak tests for the bakelite gaps(RE*/3) CERN

SN.

Gap No. Gap Size Observation time

Mano. start

Mano. stop

Leak Rate

Remarks

1 1486 Large 30 min. 258mm 256mm 2mm Gap is ok

2 1353 Medium 75 min. 240mm 240mm 0 Gap is ok

3 1355 Small 60 min 304mm 304mm 0 Gap is ok nozzle broken after leak test

4 1355 Medium 55 min. 306mm 305mm 1mm Gap is ok

5 1471 Small 70 min. 159mm 153mm 6mm Gap is ok but does not take larger pressure (?)

6 1491 Large 75 min. 288mm 282mm 6mm Gap is ok

7 1353 Small 75 min. 292mm 287mm 5mm Gap is ok

8 1352 Medium 35 min. 304mm 298mm 6mm Gap is ok

9 1490 Large 78 min. 299mm 118mm 181mm Leakage in gap

Leakage Current Test for gaps For the testing of leakage current, we require

the mixed gases in a flow mode.

So after mixing the gases goes to 8-channel flow divider i.e. at a time we can test 8 gaps. Here we are using only six channels for six gaps.

Flow divider contains inlets & outlets for the gas. Exhaust gases goes to the atmosphere through a pipe.

Contd……

Total flow rate is 22 SCCM for the flow of the gas mixture through six channels for six gaps.

This flow rate is sufficient for the 2 times change of gas volume in a day in all six gaps.

The inlet pressure of mixed gas going in these gaps is 59mb above atm.pressure where as the outlet pressure is 15mm of water column above atm.pressure.

Contd…… Purging the gas mixture through all six gaps for

two days.

Applied the High voltage in step of 1000V up to maximum limit of 9kV & noted down the variation of leakage current with voltage.

Set the maximum leakage current limit equals to 10 µA so that if for a given voltage leakage current exceeds this limit, voltage trips to zero.

Recorded the data for large, medium & small gap & plotted it.

0 1000 2000 3000 4000 5000 6000 7000 8000 90000

1

2

3

4

5

6

RH=60% and T=21oC

Leakage C

urrent

(m

icroA

mps)

Applied High Voltage (V)

Large CMS gap, Area = 18,000 cm2

Medium CMS gap, Area = 12,466 cm2

Small CMS gap, Area = 3,922 cm2

0 1000 2000 3000 4000 5000 6000 7000 8000 90000.0

0.5

1.0

1.5

2.0

2.5

Area = 12,466 cm2

RH=60% and T=21oC

Leakage C

urr

ent

(mic

roA

mps)

Applied High Voltage (V)

Medium Gap # 1355 Medium Gap # 1353

0 2000 4000 6000 8000 100000.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

6.0Area = 3,922 cm2

RH=60% and T=21oC

Leakage C

urr

ent

(mic

roA

mps)

Applied High Voltage (V)

Small Gap # 1471 Small Gap # 1353

1000 2000 3000 4000 5000 6000 70000

1

2

3

4

5

6

Area = 18,000 cm2

RH=60% and T=21oC

Leakage C

urrent (

mic

roA

mps)

Applied High Voltage (V)

Large Gap # 1491 Large Gap # 1486

THANKS