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IFR Past, Present, &Future (
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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
Nov. 14, 2002 Henry Band - U. of Wisconsin 3
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
Nov. 14, 2002 Henry Band - U. of Wisconsin 4
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%
Nov. 14, 2002 Henry Band - U. of Wisconsin 5
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
Nov. 14, 2002 Henry Band - U. of Wisconsin 6
Efficiency Corrections True RPC efficiency during collision data is worse
Backgrounds Edge effects in algorithim
0 10
Passaggio’s talk at July Col. meeting
Nov. 14, 2002 Henry Band - U. of Wisconsin 7
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
Nov. 14, 2002 Henry Band - U. of Wisconsin 8
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
Nov. 14, 2002 Henry Band - U. of Wisconsin 9
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
Nov. 14, 2002 Henry Band - U. of Wisconsin 10
Efficiency plateau inner ‘new’ modules
collision
cosmics
Nov. 14, 2002 Henry Band - U. of Wisconsin 11
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
Nov. 14, 2002 Henry Band - U. of Wisconsin 12
Forward Endcap Upgrade
Gap #19 (new)
RPC belt
5x2.54cm brass plates(Layers 8,10,12,14,16)
10cm steel
double gap RPC
Nov. 14, 2002 Henry Band - U. of Wisconsin 13
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
Nov. 14, 2002 Henry Band - U. of Wisconsin 14
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
Nov. 14, 2002 Henry Band - U. of Wisconsin 15
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
Nov. 14, 2002 Henry Band - U. of Wisconsin 16
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 ?
Nov. 14, 2002 Henry Band - U. of Wisconsin 17
Planar Forward EndcapBefore After
Nov. 14, 2002 Henry Band - U. of Wisconsin 18
Belt Chambers
Belts
Dead chamber ?
Bad Fecs or mappingFirst run
Nov. 14, 2002 Henry Band - U. of Wisconsin 19
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
Nov. 14, 2002 Henry Band - U. of Wisconsin 20
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
Nov. 14, 2002 Henry Band - U. of Wisconsin 21
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)
Nov. 14, 2002 Henry Band - U. of Wisconsin 22
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
Nov. 14, 2002 Henry Band - U. of Wisconsin 23
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
Nov. 14, 2002 Henry Band - U. of Wisconsin 24
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
Nov. 14, 2002 Henry Band - U. of Wisconsin 25
RPC surfacesGas inlet Debri
Whiskers
Excess oil
Opposite side
Nov. 14, 2002 Henry Band - U. of Wisconsin 26
RPC radiographyMay 99 8100 V 45% Ar
May 00 8100 V 56% Ar
D. Piccolo
Nov. 14, 2002 Henry Band - U. of Wisconsin 27
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
Nov. 14, 2002 Henry Band - U. of Wisconsin 28
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
Nov. 14, 2002 Henry Band - U. of Wisconsin 29
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
Nov. 14, 2002 Henry Band - U. of Wisconsin 30
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
Nov. 14, 2002 Henry Band - U. of Wisconsin 31
Backup slides
Nov. 14, 2002 Henry Band - U. of Wisconsin 32
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.
Nov. 14, 2002 Henry Band - U. of Wisconsin 33
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
8000
10000
12000
5000 6000 7000 8000 9000 10000
HV (kV)
IFR0234
IFR0235
IFR0236
IFR0237
IFR0238
0
200
400
600
800
1000
1200
1400
1600
1800
2000
5000 5500 6000 6500 7000 7500 8000 8500 9000
HV (kV)
IFR0234
IFR0235
IFR0236
IFR0237
IFR0238
current(mA)
0
2
4
6
8
10
12
14
16
18
20
5000 5500 6000 6500 7000 7500 8000 8500 9000 9500
HV (kV)
IFR0235
IFR0236
IFR0237
IFR0238
AH
z
Nov. 14, 2002 Henry Band - U. of Wisconsin 34
RPC radiography The RPC efficiency was mapped in 2D showing irregular regions of reduced efficiency.
D. Piccolo
Nov. 14, 2002 Henry Band - U. of Wisconsin 35
IFR Construction QualityQuality distribution vs production box
Fraction of good chambers not uniformly distibuted in time
Production problems?
I. Peruzzi
Nov. 14, 2002 Henry Band - U. of Wisconsin 36
The shifting plateau problem: a plateau collection
Nov. 14, 2002 Henry Band - U. of Wisconsin 37
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
Nov. 14, 2002 Henry Band - U. of Wisconsin 38
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
Nov. 14, 2002 Henry Band - U. of Wisconsin 39
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%
Nov. 14, 2002 Henry Band - U. of Wisconsin 40
RPC Efficiencies
Nov. 14, 2002 Henry Band - U. of Wisconsin 41
RPC Efficiencies
Nov. 14, 2002 Henry Band - U. of Wisconsin 42
RPC Efficiencies
Nov. 14, 2002 Henry Band - U. of Wisconsin 43
Radiographies 10
Nov. 14, 2002 Henry Band - U. of Wisconsin 44
Radiographies for the 24 ‘new’ modules 10
Recommended