ifr past, present, &future (

IFR Past, Present, &Future

(<2005)

Henry BandUniversity of Wisconsin

Nov. 14, 2002 Henry Band - U. of Wisconsin 2

Outline

Past RPC efficiency vs time 2000 Chambers Muon ID efficiency

Present Upgrade scope Installation status Planar FEC efficiency Belt chamber hits Remediation

Projections of future R&D plans

Summary of known problems Electronics

Barrel cable plant FECs

High Voltage Gas RPCs

Oil drops Whiskers Resistivity Dark currents and noise vs

time Backgrounds


RPC Efficiency 1999-2002

Summer 1999 29-33˚ C temperatures inside BABAR steel cause high currents and force many RPCs to be disconnected

RPC efficiencies did not recover fully after cooling added

RPC efficiencies continue to decline in 2000 - 2002

-0.93 %/month

-0.36 %/month

-1.2 %/month

Electronics problems


RPC efficiency 99-00

June 99

Jan. 00

July 00

Barrel Forward E.C. Backward E.C.

77% 91% 93%

81% 86% 85%

71% 81% 75%


Distribution of efficiency

Two dominant trends

Most RPCs showing slow eff. loss @ 3-4% per year

Other RPCs suddenly losing all efficiency in < 2 months

30 % of barrel RPCs have < 10% efficiency

Only a few of these understood in terms of known HV or gas problems


Efficiency Corrections True RPC efficiency during collision data is worse

Backgrounds Edge effects in algorithim

0 10

Passaggio’s talk at July Col. meeting


New style RPCS 24 new RPCs were installed

in Dec. 99 in the forward

endcap These RPCs had ~1/3 of the

linseed oil as the original construction

The outer layers were exposed to high backgrounds and have aged quickly

The RPCs in the inner endcap have experienced low background rates and have lost efficiency @ <3%/ year

Recoverable by raising HV


New chambers

Inner, layers # < 17 Outer, layers #17 and 18

Counting RatesIf the hit distributionwere uniform it wouldtranslate into:

0.2 Hz/cm2 /inner0.4 Hz/cm2 /layer141.2 Hz/cm2 /layer 172.4 Hz/cm2 /layer 18


New style RPCS

Layer 18 rates ~250 kHz with beam, ~60 kHz without

Large difference in efficiency with cosmics or only with beam

Layer 17 rates ~60 kHz with beam, ~20 kHz without

Reducing backgrounds a high priority


Efficiency plateau inner ‘new’ modules

collision

cosmics


Muon Identification

Muon identification selectors are losing efficiency as RPC efficiency drops

Impacting physics analysis

Nov. 1999 Jan. 2001 Software problems Front End

Electronics problems


Forward Endcap Upgrade

Gap #19 (new)

RPC belt

5x2.54cm brass plates(Layers 8,10,12,14,16)

10cm steel

double gap RPC


2002 Access - IFR

Forward endcap upgrade Add absorber

5 layers 1” brass 1 external 3.5” steel

plate Replace RPCs

12 single gap layers Add double gap layers

2 double gap layers Belt chambers

Replace LV power supplies

Other improvements Install new HV distribution Install new gas distribution Install new gas return

bubblers Improve background

monitoring Install shielding walls

around beamline sources Repair front end

electronics in the barrel Remediate Barrel RPCs Infrastructure

Add 2nd monitor crate Improve online

documentation Rewire barrel Canbus


Installation Status All 116 RPC chambers

installed, connected to DAQ and gas All connected to HV with no

problems 3/96 large chambers have gas

leaks Efficiency OK

5/20 belts had broken gas fittings

Repaired

Installed 58 minicrates 924 RPC to minicrate cables 232 minicrate to FEE Crate

cables 212 HV cables >100 misc. cables, trigger,

control, monitoring, temp. probes

Low voltage power supplies Operational To do – Remote power switch,

GMB readout

Barrel FEC repair Dead + noisy + hot FECs

63/1152 in layers 1-16 5.4% was 16.2%

Backgrounds Shielding installed

downstream of 2 LER collimators

Cables run for dedicated background scalars

Outer RPCs protected by 1” or thicker steel shielding


Installation Status

Gas distribution -FEC 8 supplies installed in

FEC 8 visual return bubblers

installed in FEC Electronic bubble

counting return chassis late ~ 2weeks Prototype in place All scalar cables run to

EH Can install ~1

hour/chassis as time allows

Gas distribution -barrel 5/9 supplies and visual

bubblers installed on barrel

Connected to main supply

4 sextant returns and 2 sextant supplies have been connected

• Sextant 0 – 4/19 layers bubble

• Sextant 5 -12/19 layers bubble

Install electronic return chassis as time allows


Remediation StatusHave attempted remediation of

barrel RPCs Introduce Argon Integrate ~200 C of

charge with either positive or negative HV

Prior to remediation new HV connectors and distribution boxes installed in the barrel 367 HV cables spliced 24 HV distribution chassis

built and installed All but 3 Barrel HV channels

active (was ~3%) GMB & CANBUS lines modified

Results of first remediation test in sextant 2

Gas flow problem ?


Planar Forward EndcapBefore After


Belt Chambers

Belts

Dead chamber ?

Bad Fecs or mappingFirst run


Future Barrel Next long access is

summer 2005 A linear projection of

present decay rate predicts 0% efficiency well before then

Expect ~5% improvement in barrel RPC efficiency from remediation

Expect 5% improvement in muon ID from both NN selector and fixing electronics

Gains from HV and gas improvements ?????

July 2005


R&D plans

Outstanding issues focus on gas Flow Composition Humidity

The Wisconsin/SLAC teststand will be moved to IR2 to allow tests of full sized Endcap chambers Can now measure pulse

height Addition of SF6 reduces

streamer size Will implement after

success in the test stand

Santonico has suggested another gas mix which has a much lower plateau May be useful in

recovering RPCs that have died

Tests of the optimal water content will likely be long term

On detector work Optimize gas flow per

layer Repeat temperature

dependency, popped button tests


Problems, problems, problems

RPC inefficiency has many sources not all of which are due to the RPC

Electronics The barrel cable plant has

been a continued headache (5 pigtails per FEC)

Most of the present 5% FEC failure rate is probably cable related (was 2% in 2000)

FECs in minicrates are accessible and reliable

Electronics – continued Largest risk is a repeat of

the background accident of last Jan. where a mis-steered beam dumped a large amout of charge into the RPCs. This apparently causes the ground to bounce destroying the ECL receivers and drivers. May knock out 8 FECs in a single failure. (clock chains)


Other problems

Gas Each barrel layer has 3

chambers in series in each layer with 1 input and 1 output gas line

Only 60% of the barrel circuits bubble

All connections are buried out of view

Tests in 2000 showed no no efficiency improvement by raising gas flow

Gas Again in 2000, there

was no strong correlation between efficiency and gas tightness

Tests up to now have focused on short <1 month time scales

Raising the flow in the FWT Layer 18 improved efficiency and stabilized decay


Problems continued

High Voltage 4% of the RPCs were

disconnected because of HV problems (sparking, very high currents (>200 microA)

New HV trips were .5 to 1 per month. Took down 12-18 RPCs ~1/2 due to HV

distribution box No HV problems in new

generation RPCs! Hopefully much improved

by new HV chassis

Backgrounds Old Layer 18 saw soft

HER synchrotron background.

Deeper layers sensitive to backgrounds from LER collimators

Expect factor 2-4 reduction from new shielding installation

Need a factor of 10 Will require further

iterations to bring under control


RPC inefficiency model

Linseed oil drops can span the RPC gap making a high resistance short which reduces the local E field below that required for streamers. First observed in test

chambers constructed shortly after the BaBar Linseed oil surface treatment under heat and HV has beaded up into drops.

The suspicion is that the oil of the original production which was intentionally applied thicker than L3 was never properly cured

Possible contamination by phthalates

FR4 frame

Bakelite

Linseed oil drops

SpacerGraphite

Test RPC


RPC surfacesGas inlet Debri

Whiskers

Excess oil

Opposite side


RPC radiographyMay 99 8100 V 45% Ar

May 00 8100 V 56% Ar

D. Piccolo


Bulk current increased from 1 to 200 A on thesum of 18 modules. (measured @5kV)

Streamer current increased from less than 20 Ato 80 A or so. This goes well with the increase ofsingle rates from ~0.05 Hz/cm2 to ~0.2Hz/cm2 for the inner layers

For most of the modules the integrated charge is

less than 0.1 C/cm2

I (A)Bulk current increases with integrated charge

Inner layers

“Spacer” resistivity decreases, current flows through spacers and not the frame


2000 generation RPCs still change with time

This refers to 18modules (<Layer 14)

at construction time

13 A/module @5kV22 A/module @7kV(4.5 A of streamer)

Both bulk and streamer currentincreased

At day 1 I vs HV

0.1 A @ 5000V1.1 A @ 7000V


Layer 18 opened Bulk current goes to zero

with nb of popped buttons Bakelite discoloration, dried,

oil residuals around buttons, no real correlation with inefficiency zones.

BAD#1 Visually ok, but bakelite resistance is huge, ~20 times > than nominal. Is bakelite too dry there ?? Graphite ok

BAD#2 Carbon discoloration on anode, missing graphite on some sections, seems graphite adhesion to bakelite has been lost at anode. Ok on the cathode side. Images of button in graphite, dried oil around buttons.

Signs of graphite deterioration on good regions


Summary

If efficiencies continue to decay at the present rate in summer of 2005

Barrel 0%Forward Endcap ~90%Backward Endcap ~40%

Too soon to see complete benefits of recent access improvements

Best hope is to change gas mixture/humidity


Backup slides


Detector studies Realization that the RPC efficiencies

did not recover spurred detector studies During the 99-00 data run access to

the RPCs was limited Physical removal of any RPC would

require > 1 month access Limited tests were carried out during

accesses or on a few chambers Lowered barrel temp. to 17 C. Reversed HV Increased gas flow Lowered discriminator threshold Put weights over inefficient regions

No effect Gas composition was regularly tested

No evidence of water vapor

A wide spread of plateau curves were measured.


RPC tests at Frascati, 1997

HV modules shipped to LNF.

Longitudinal strips were applied.

Modules packed into boxes

Cosmic ray tests were made to characterize each module

Gas Ar 45%, Freon 50%, isobutane 5%

0

2000

4000

6000

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12000

5000 6000 7000 8000 9000 10000

HV (kV)

IFR0234

IFR0235

IFR0236

IFR0237

IFR0238

0

200

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5000 5500 6000 6500 7000 7500 8000 8500 9000

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IFR0234

IFR0235

IFR0236

IFR0237

IFR0238

current(mA)

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5000 5500 6000 6500 7000 7500 8000 8500 9000 9500

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IFR0235

IFR0236

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IFR0238

AH

z


RPC radiography The RPC efficiency was mapped in 2D showing irregular regions of reduced efficiency.

D. Piccolo


IFR Construction QualityQuality distribution vs production box

Fraction of good chambers not uniformly distibuted in time

Production problems?

I. Peruzzi


The shifting plateau problem: a plateau collection


Efficiency - LNF

90

91

92

93

94

95

96

97

98

99

100

0 1 2 3 4 5 6 7 8

Average

Effic

ienc

y pl

atea

u

Efficiency of barrel modules

10 11


BABAR RPC

Operates in limited streamer mode Parallel high resitivity plates (Bakelite 1011

-1012 cm ) Graphite ~100 k/ According to the General Tecnica factory

the RPCs were filled 3 times with a mixture of 70% linseed oil and 30% n-pentane. Air was then flushed through the RPC for several days.

Strip pitch Barrel 20-33 mm (), 38 mm (z) Endcap 26 mm(y), 38 mm (x)

Changes from L3 RPCs Polycarbonate buttons with lip replaced G10

cylindrical button Single layer with strips on both sides No mechanical envelope Nonflammable gas - low iso-butane %, CBrF3

replaced by Freon 134a C2H2F4

Gas mixture in %Date Argon Freon 134a isobutane

99 45 50.2 4.8Sep-99 56.7 38.8 4.5J un-00 60.6 34.7 4.7

Tests 65 30.3 4.7


IFR History RPCs chosen for BaBar 1/95

Mature technology Good L3 experience

RPC Production 7/96- 10/97 RPC QA tests - Frascati

I < 18 A and efficiency > 95% Chamber assembly SLAC 12/96 -

12/97 Chamber tests at SLAC 5/97 – 12/97

Initial tests High Temperatures - 30 C High Currents ~100 A Efficiency > 95%

Assembly/test area air conditioned 7/97

Chamber insertion 6/97 -12/97 Cabling and Fecs installed from

10/97 Complete Barrel and Forward E.C.

11/98 Barrel cosmic ray tests 12/98 Sharply increasing current observed

when doors closed and LV on

Backward E.C. completed 4 / 99 First beam May 99

99% of RPCs working 96% of Fecs working

Heating from electronics & ambient hall raise steel T to 29-34

HV current limitations force reduction in # of RPCs

< I > 70 -210 A barrel ~70 Endcap

Complete barrel cooling 10/99 Install Endcap cooling 1/00 - 4/00 <I> 60A barrel ~40 Endcap Average Efficiency remain ~85%


RPC Efficiencies


Radiographies 10


Radiographies for the 24 ‘new’ modules 10

ifr past, present, &future (

Documents

new rpcs

yearother rpcs

new chambersinner

meetingnew style rpcs

rpc chambers

new style rpcslayer

aged quicklythe rpcs

inner endcap