babar experience with rpcs: a snapshot of our present knowledge
DESCRIPTION
BaBar Experience with RPCs: A snapshot of our present knowledge. Henry Band University of Wisconsin. The BaBar detector at the PEPII B factory has operated a ~2000 m RPC detector since 1999 These RPCs operating in the streamer regime have proven very sensitive to temperature - PowerPoint PPT PresentationTRANSCRIPT
BaBar Experience with RPCs:A snapshot of our present knowledge
Henry BandUniversity of Wisconsin
May 11, 2001 Henry Band - U. of Wisconsin
Introduction
The BaBar detector at the PEPII B factory has operated a ~2000 m RPC detector since 1999
These RPCs operating in the streamer regime have proven very sensitive to temperature
Both RPC current and efficiency have suffered apparently irreversible changes (new results show hope of reversing changes)
Examination of opened RPCs show clear problems with the linseed oil coating
A few new RPCs with thinner oil coatings were installed in late 00
Although LHC RPCs operate in avalanche mode, our experience may be relevant to this next generation of RPC detector
IFR RPCs History of IFR construction Initial efficiency measurements Operational problems
Unstable temperature and currents
Declining efficiency Detector studies
BaBar Test stands Other
RPC Autopsy photos Inefficiency Model New RPCs
Characteristics Operation
BaBar plans
May 11, 2001 Henry Band - U. of Wisconsin
Instrumented Flux Return
Instrumented Flux Return 342 barrel RPCs 432 endcap RPCs 32 cylindrical RPCs
Electronics 3300 Front end cards
~ 40 mV threshold 16 channels connected to
alternate strips 1 TDC measurement 1 scalar
Gas 35% Freon 134a, 4.5% iso-
butane, 60.5% Argon 2-3 volume changes/day
High Voltage > 50 10 kV HV pods
May 11, 2001 Henry Band - U. of Wisconsin
IFR Collaboration
INFN Lab.-Frascati - F. Anulli, R. Baldini, A. Calcaterra, D. Falciai, G. Finocchiaro, P. Patteri,
I. Peruzzi, M. Piccolo, Y. Xie, A. Zallo, R. de Sangro INFN-Bari - A. Palano
INFN-Genova -S. Bagnasco, A. Buzzo, G. Crosetti, M. Lovetere, M. Macri, S. Passaggio, F. Pastore, M.G. Pia, E. Robutti, A. Santroni, S. Tosi
INFN-Napoli -T. Cartaro, N. Cavallo, G. DeNardo,F. Fabozzi, C. Gatto, , L Lista, P. Paolucci, D. Piccolo, C. Sciacca
LLNL - R. Bionta, V. Brigljevec, D. Lange, D. Wright
U. of Wisconsin- H. Band, A. Eichenbaum,J. Johnson U. Oregon - J. Brau, R. Frey, E. Grauges-Pous, M. Iwasaki, N. Sinev, D. Strom Yale U - T. Moore, H. Neal INFN-Roma - F. Ferroni, S. Morganti, G. Piredda, INFN-Pisa - M. Carpinelli, F. Forti
Consulting experts C. Lu -Princeton University, J. Va’vra -SLAC, M. Lazzari - Turin
May 11, 2001 Henry Band - U. of Wisconsin
IFR Construction
2RPC modules / chamber
3 chambers per layer
Endcap RPCs 0.9m 1.5-2.7 m
3 RPC modules / chamber
Barrel RPCs 1.25m 1.9-3.2 m
May 11, 2001 Henry Band - U. of Wisconsin
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 isobutane99 45 50.2 4.8
Sep-99 56.7 38.8 4.5J un-00 60.6 34.7 4.7
Tests 65 30.3 4.7
May 11, 2001 Henry Band - U. of Wisconsin
Bakelite Surface Changguo Lu
Linseed oil coating smoothes surface imperfections
BaBar originalNew Babar RPCs
No oil
May 11, 2001 Henry Band - U. of Wisconsin
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%
May 11, 2001 Henry Band - U. of Wisconsin
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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10000
12000
5000 6000 7000 8000 9000 10000
HV (kV)
IFR0234
IFR0235
IFR0236
IFR0237
IFR0238
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HV (kV)
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IFR0235
IFR0236
IFR0237
IFR0238
current(mA)
0
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4
6
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5000 5500 6000 6500 7000 7500 8000 8500 9000 9500
HV (kV)
IFR0235
IFR0236
IFR0237
IFR0238
AH
z
May 11, 2001 Henry Band - U. of Wisconsin
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
May 11, 2001 Henry Band - U. of Wisconsin
LNF data / Construction
0
500
1000
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3500
0 1 2 3 4 5 6 7 8Average rho
Sin
gle
s at
90%
eff
icie
ncy
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0 1 2 3 4 5 6 7 8Average rho
Cu
rren
t at 9
0% e
ffic
ienc
y
Neither the measured current or singles rate was found to depend on bakelite resistivity
Singles rate < 1kHz /m2
Current 3-20 A RPCs air shipped to SLAC HV modules assembled 2 or 3
to a chamber 2nd view strips applied SLAC cosmic rays tests Completed and tested
chambers inserted into BABAR steel
After erection of BABAR steel - installed
DAQ cabling HV cabling Gas connections
May 11, 2001 Henry Band - U. of Wisconsin
June 1999
By May 99 IFR cabling complete
RPC efficiencies good But - warning signs
Some RPCs with > 100 A were disconnected
Limited HV current capability FECs inside steel produce
2.3 W of heat each Total power into barrel ~2.6
kW Poor heat transfer to outside
With collision data Barrel heats up ~.4 C/day IR hall temperature climbs
during summer
77%
91%
93%
May 11, 2001 Henry Band - U. of Wisconsin
HV currents & temperatures 99
RPC current vs. time
@6000 V
@7800 V
FEC power turned off
+10%/ day
+0.4 C / day
Barrel temperatures vs. time
1 meter inside
Barrel face
May 11, 2001 Henry Band - U. of Wisconsin
RPC Efficiency 99
Climbing temperatures forced the disconnection of more RPCs
Cooling system being prototyped Average currents were
70 A(sextant 4) -210 A (sextant 0)
65 A Forward endcap 70 A Backward endcap
Because of voltage drops across a ~1.5 M resistor in the HV distribution network, the voltage on working RPCs was reduced by 100-300 volt
Additional inefficiency from more conventional sources HV shorts 3% Gas leaks <2% Dead front end electronics <2%
May 11, 2001 Henry Band - U. of Wisconsin
Water cooling
Tests of prototype cooling loops in sextant 1 started in mid June
Additional loops installed in August
Full barrel installation of copper loops brazed into BABAR steel- Oct. 99
Completed endcap cooling system - Jan. 00
Remove ~ 10kW heat Stabilized temperature
and RPC currents Barrel temps. ~19-21°,
were 29-33° in summer 99
Endcap temps 22- 24°
May 11, 2001 Henry Band - U. of Wisconsin
Cooling / HV Currents 2000
May 11, 2001 Henry Band - U. of Wisconsin
RPC efficiency 00
-1.4% /month
-1.4% /month
-0.56%/month
Gas change
May 11, 2001 Henry Band - U. of Wisconsin
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%
May 11, 2001 Henry Band - U. of Wisconsin
RPC efficiency 01
Efficiency loss is correlated with previous efficiency
May 11, 2001 Henry Band - U. of Wisconsin
Individual time histories
May 11, 2001 Henry Band - U. of Wisconsin
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.
May 11, 2001 Henry Band - U. of Wisconsin
RPC radiography
The RPC efficiency was mapped in 2D showing irregular regions of reduced efficiency.
D. Piccolo
May 11, 2001 Henry Band - U. of Wisconsin
RPC radiography (2)
May 99 8100 V 45% Ar
May 00 8100 V 56% Ar
D. Piccolo
May 11, 2001 Henry Band - U. of Wisconsin
IFR efficiencies status I. Peruzzi
May 11, 2001 Henry Band - U. of Wisconsin
IFR Construction Quality
Quality distribution vs production box
Fraction of good chambers not uniformly distibuted in time
Production problems?
I. Peruzzi
May 11, 2001 Henry Band - U. of Wisconsin
Test stands
Test stands were restarted or started at several locations Frascati Napoli SLAC U. of Oregon
SLAC test stand utilized 9 post BABAR production RPCs which had been used in background tests
The RPCs were subjected to a heating cycle at 36 C.
Permanent changes in both current and efficiency were seen
Several RPCs were opened
Large oil drops spanning the 2 mm gap were found.
May 11, 2001 Henry Band - U. of Wisconsin
SLAC/Wisconsin Test Stand
36 C. 29 C.32 C.
28 C
A
A. Soha
May 11, 2001 Henry Band - U. of Wisconsin
IFR inefficiency model
Linseed oil surface treatment under heat and HV has beaded up into drops.
Some drops span the RPC gap making a high resistance short which reduces the local E field below that required for streamers.
Both HV current and efficiency are irreversibly changed
The new shape of the buttons may be more likely to trap oil
The number and location of the blobs explains both the RPC to RPC variation and the efficiency holes
Gas leaks, HV shorts, and point discharges also contribute
FR4 frame
Bakelite
Linseed oil drops
SpacerGraphite
Test RPC
May 11, 2001 Henry Band - U. of Wisconsin
Oil Stalagmite Formation
In lab tests using freshly painted bakelite (uncured) the application of 4-5 kV resulted in the movement of the oil and the formation of stalagmites within hours.
In BaBar RPCs the oil is more viscous and the time scale is presumably much longer.
Changguo Lu
May 11, 2001 Henry Band - U. of Wisconsin
Effect of Oil bridge Changguo Lu