RPC Progress for a DHCAL Lei Xia Argonne National Laboratory

1
RPC Progress for a DHCALLei XiaArgonne
National Laboratory

• Digital readout system, multiplicity measurement
• RPC hit multiplicity and chamber configuration
  study
• Large size RPC test

2
Multi-channel digital readout system

• We have already acquired expertise in RPC
  construction and have very good understanding of
  RPC signal and running condition
• Our effort is now focused on multi-channel
  digital readout of RPC signal, which is crucial
  for a digital calorimeter
• The digital readout system is built around a 6U
  VME card
• 64 channels per card
• Each channel convert input
• analog signal to a digital bit,
• according to a pre-set
• threshold
• The card collects a digital hit
• pattern of all channels and
• assembles them into an event
• A time stamp (100ns resolution)
• is attached to each event

Analog
Digital
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Digital readout system
Trigger area
Readout pads

• Use 8x8 pad array
• Each pad is 1x1 cm2, and has an on-board
  amplifier (NEC video amp)
• Cosmic ray signal is sent to one
• channel of the VME board,
• and is readout with pad
• signals

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Test with digital readout system AIR4

• AIR4 is a 1-gap RPC built with 1.1mm glass sheet
• 1.2mm gap size
• Resistive paint layer is about 1MO/?
• Running at 6.8 KV
• Avalanche signal 5pc
• Efficiency gt97
• Total RPC rate from 64 channels lt10 Hz
• Very low noise!

(On-board amplifiers)
Pad array
Mylar sheet
Resistive paint
1.1mm Glass sheet
1.2mm gas gap
GND
1.1mm Glass sheet
Resistive paint
-HV
Mylar sheet
Aluminum foil
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Test with digital readout system AIR4

• Changing the signal threshold, one can run AIR4
  at specific efficiency, and measure the hit
  multiplicity, thus measuring it as a function of
  threshold/efficiency
• Running at 6.8KV, good hit multiplicity achieved
• For eff95 1.6 1.7
• For eff90 1.4 1.5
• Running at 7.0KV, 7.2KV, similar hit multiplicity
  achieved
• Avalanche signal 8pc at 7.0KV
• Avalanche signal 11pc at 7.2KV
• Use result from AIR4 at 6.8KV as default. All
  following results
• will be compared to it!

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Hit multiplicity and RPC configuration
1-gap/2-gap, High R/ Low R

• AIR1 and AIR2 are 2-gap RPCs
• Each gap is 0.6mm, total gap size is about the
  same as 1-gap chamber
• AIR1 0.2MO/? on its resistive paint layer
• AIR2 1MO/? on its resistive paint layer
• Running both chambers at 8.4KV
• Avalanche signal 5pc
• Both AIR1 and AIR2 have low noise

(On-board amplifiers)
Pad array
Mylar sheet
Resistive paint
1.1mm Glass sheet
0.6 mm gas gap
GND
1.1mm Glass sheet
0.6 mm gas gap
1.1mm Glass sheet
Resistive paint
-HV
Mylar sheet
Aluminum foil
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Hit multiplicity and RPC configuration
1-gap/2-gap, High R/ Low R

• Both AIR1 and AIR2 have higher hit multiplicity
  than AIR4
• Two gap design has higher hit multiplicity!
• AIR1 has higher hit multiplicity than AIR2
• Lower resistivity on the paint layer gives higher
  hit multiplicity
• This confirms results obtained with analog
  readout system

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Hit multiplicity and RPC configuration thinner
glass

• AIR5 used thinner glass
• 0.85mm glass sheet (all others were built with
  1.1mm glass sheet)
• 1-gap of 1.2mm
• 1MO/? on paint layer, comparable to AIR4
• Accidentally tested two configurations
• Pads far from chamber ( 0.3 0.4mm additional
  material)
• Pads close to chamber
• Both configurations have low chamber noise

(On-board amplifiers)
Pad array
Plastic tape
Mylar sheet
Copper tape
Resistive paint
Copper tape
0.85mm Glass sheet
1.2mm gas gap
GND
0.85mm Glass sheet
Resistive paint
-HV
Mylar sheet
Aluminum foil
Pads far from chamber
(On-board amplifiers)
Pad array
Mylar sheet
Resistive paint
0.85mm Glass sheet
1.2mm gas gap
GND
0.85mm Glass sheet
Resistive paint
-HV
Mylar sheet
Aluminum foil
Pads close to chamber
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Hit multiplicity and RPC configuration thinner
glass

• Run AIR5 at 7.0KV
• Avalanche signal 5pc
• Compare the two configurations, the one with pads
  close to chamber clearly gives lower hit
  multiplicity
• Signal pads should be as close as possible to the
  avalanche signal!

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Hit multiplicity and RPC configuration thinner
glass

• Compare to AIR4, AIR5 gives slightly lower hit
  multiplicity
• For eff 95, 1.6
• For eff 90, 1.4 - 1.5
• Again, pads closer to avalanche give lower hit
  multiplicity

Trigger area
spacer

• 3 efficiency correction applied to AIR5 results
• A fishing line spacer passed through the center
  of trigger area, causing 3-4 dead region

Readout pads
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Hit multiplicity and RPC configuration one paint
layer

• AIR7 was built with only one resistive paint
  layer. The pads sit directly on the glass sheet
• The resistivity of the paint layer is 1MO/?
• Compare to AIR4, AIR7 gives slightly lower hit
  multiplicity
• The noise rate of AIR7 is significantly higher
  than AIR4 ( x5 higher)
• To be understood

(On-board amplifiers)
Pad array
GND
1.1mm Glass sheet
1.2mm gas gap
1.1mm Glass sheet
Resistive paint
-HV
Mylar sheet
Aluminum foil
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Hit multiplicity and RPC configuration no paint
layer

• AIR8 was built with two bare glass sheets no
  paint layer
• HV applied through aluminum foil attached to one
  glass sheet
• Pads sit directly on the other glass sheet
• Compare to AIR4, AIR8 has a little higher hit
  multiplicity
• Resistive paint layer does help to reduce
  avalanche size
• RPC with this configuration might be able to run
  at high event rate need test!
• Noise rate is higher than AIR4, and is similar
  to AIR7

(On-board amplifiers)
Pad array
1.1mm Glass sheet
1.2mm gas gap
1.1mm Glass sheet
Aluminum foil
-HV
Mylar sheet
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Hit multiplicity and RPC configuration one glass
sheet

• AIR9 was built with only one glass sheet, the
  multi-pad PC board (with on-board amps) was built
  into RPC as part of the detector
• No resistive layer painted on the glass sheet
• HV applied through copper tape
• Signal pads directly face avalanche signal, which
  is the closest possible position
• RPC with this configuration might be able to run
  at high event rate
• Need to be tested!

(On-board amplifiers)
1.6mm PC board
Pad array
1.2mm gas gap
1.1mm Glass sheet
Copper tape
-HV
Mylar sheet
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RPC with only one glass sheet corrections

• Defects during PC board production
• One dead channel at the center of trigger area
• Two channels are connected, and always give hits
  simultaneously
• Corrections
• Made 6-8 corrections on efficiency, based on
  trigger rates of surrounding pads
• No correction made to hit multiplicity, due to
  the dead channel should be a very small effect
• No correction made to the connected channels hit
  multiplicity is slightly over estimated
• Will fix the problems and do the measurement again

Trigger area
Readout pads
Dead channel
Connected channels
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RPC with only one glass sheet preliminary result

• AIR9 has amazingly low hit multiplicity!
• 1.1 1.2 throughout measured region
• Noise rate higher than AIR4 ( x2-3)
• Total rate 20Hz, noise hit pattern is different
• Source need to be identified
• More study will be done

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RPC with only one glass sheet preliminary result
AIR4
AIR9
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Large size RPC towards test beam section

• AIR6 is the very first large size RPC we built
• 1 gas gap of 1.2mm
• Size of glass sheet 30.5cm x 91.5cm x 1.1mm
• Resistivity of paint layer 1MO/?
• Electrostatic force from HV compensated gas
  pressure, as we expected
• When HV is not on, deformation of glass sheet due
  to gas flow pressure is quite significant
• AIR6 was tested with single readout pad and
  analog read out system
• Readout pad has a size of 20cm x 20cm

AIR6
AIR5
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Large size RPC single readout pad

• AIR6 performs exactly the same as smaller size
  RPCs, with the same gap configuration
• Expect the same hit multiplicity as AIR4

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Conclusion

• Built 10 RPCs with different designs
• Built single and multiple channel analog readout
  system for RPC test, result has been reported in
  previous workshops
• Built multi-channel digital readout system
• Extensively studied RPC digital signal and
  explored different chamber configuration,
  acquired excellent understanding of hit
  multiplicity
• Excellent hit multiplicity achieved
• Built large size RPC with excellent performance
• We have acquired all the expertise to build RPCs
  for a 1 m3 Prototype Section to be tested in a
  particle beam