Digital Hadron Calorimetry

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Digital Hadron Calorimetry using Gas Electron
Multiplier Technology Andy White ALCPG, Victoria
BC, July 2004
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GEM/DHCAL development

• Started with Research Enhancement Grant from
  UTA.
• Supported by U.S. Department of Energy ADR and
  LCRD programs.
• Important contributions from UTA Electrical
  Engineering, and UTA Computer Science
  Engineering.
• Working with ANL HEP DHCAL/RPC group on readout
  electronics.
• Working with CALICE collaboration.

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Digital Hadron Calorimeter Development
Linear Collider calorimetry development path at
UTA - Motivated by the physics potential! -
Can digital energy flow approach work ?? - Gas
Electron Multipliers offer robust/low- cost/flexib
le technology to implement digital
calorimetry STEPS - Understand/operate GEM
systems (done) - Develop GEM/DHCAL design (done)
- Build/test large-scale GEM active DHCAL
layer(s) - Develop full calorimeter design for
test beam stack
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Digital calorimetry counting cells
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GEM foil etching
GEM field and multiplication
From CERN-open-2000-344, A. Sharma
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Double GEM schematic
Create ionization
Multiplication
Signal induction
From S.Bachmann et al. CERN-EP/2000-151
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Design for DHCAL using Triple GEM
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GEM/DHCAL cross-talk studies

• - High digital hit efficiency essential for
  tracking charged particles in/through
  calorimeter.
• plus minimal crosstalk to reduce confusion and
  mistakes in track following, pattern recognition.
• Need crosstalk information to set threshold(s)
  for hit definition.
• Examine hits from source particles in prototype
  on two adjacent pads.
• Study nature of crosstalk signal with generated
  signals.

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Recent cross-talk studies
Pad examined for crosstalk
Main pad
UTA GEM/DHCAL prototype
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32-channel board from Fermilab
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UTA GEM Calorimeter prototype - typical signal
Single cosmic event upper trigger, lower
preamp output
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Typical signal - source
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Typical crosstalk signal (prototype)
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Crosstalk study
Signal generator
scope
Insulator
Copper pads
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Crosstalk simulation (pulse generator)
Study by Dr. Jia Li
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Crosstalk derives from edges
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Effect of rise time
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Bigger pads larger effect
BigPad
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and vice-versa
SmallPad
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Effect of gap between adjacent pads
Large Gap
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Effect of gap between adjacent pads
Small Gap
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Usual situation no crosstalk visible
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Rare example of large crosstalk
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Effect of sharing signal between adjacent pads
Trigger252 Thr.110mV, V2000V.
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Development of module concepts
TESLA HCAL Layout
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DHCAL/GEM Module concepts
GEM layer slides into gap between absorber sheets
Include part of absorber in GEM active layer -
provides structural integrity
Side plates alternate in adjacent modules
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Development of GEM sensitive layer
Requirements - minimize overall thickness -
develop robust design - maintain 1mm, 3mm gaps
in GEM structure - maintain active layer
flatness absorber slice - minimize dead
boundary areas - maintain integrity of gas
volume - design for ease of construction!
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Development of GEM sensitive layer
Absorber strong back
Gas inlet/outlet (example)
Cathode layer
3 mm
Non-porous, double-sided adhesive strips
1 mm
1 mm
9-layer readout pc-board
Anode(pad) layer
Fishing-line spacer schematic
(NOT TO SCALE)
GEM foils
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Development of GEM sensitive layer
- Identified materials for layer construction
- Specified interlayer spacings/spacers -
Tried out assembly ideas - Built large (1ft x
2ft) mechanical prototypes - Iterating on
assembly procedures - Specify/document final
procedure prior to assembly of large, working
active layer(s).
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Details of GEM active layer construction
(Tests using Kapton foil only for now)
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Coating the absorber slice with adhesive for the
cathode layer
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Stretching the GEM layer with frame
Note the need to be able to grip the edges of the
kapton (but not the copper)
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GEM layer ready for laying down
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One form of 3mm spacer
3mm side walls and spacers installed
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GEM foil laid down over side walls and sides
weighted
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1mm side walls installed plus spacers and gas
in/outlets
Gas in/oulet
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Sealing corners of walls
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Installing 2nd 1mm walls and fishing line spacers
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Final GEM foil installed, PC board installed,
and whole assembly weighted
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Development of large-scale GEM layer

• Original plans were to use existing roll of 3M
  10cm x 10cm foils
• However, the roll no longer exists!
• Discussions on new run to produce what we
  actually need.
• Several other customers for GEM foils for
  various studies (La Tech., U.Washington,
  IHEP-Beijing,)

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3M GEM foil production

• Aim for 3 GEM foil strips/layer for 1m3
  prototype.
• Need subdivision of GEMs into separate voltage
  segments minimal no-copper gap.
• Other issues
• - use of Mylar for masks -gt hole
  slewing
• gt glass phototool better but more
  costly
• - pattern repetition/kapton gap for
  gripping edge
• - New layout (with 15cm x 15cm subunits -gt U.W.
  etc.)

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Mass Production is based on a 3M Proprietary Flex
Circuit Manufacturing Technique
3M Microinterconnect Systems Division
Reel-to-reel process, rolls of 16x16
templates of detachable GEMs in any pattern.
Optional processes possible. First batch of
1,980 GEMs recently produced. Low cost per
unit! (2 USD/GEM not counting RD) Two
fabrication techniques (additive,
substractive) tested.
Reel to reel flex circuit manufacture in clean
room conditions
Single roll of 1,000 GEMS
hep-ex/0304013
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3M GEM foil new layout
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3M GEM foil new layout (detail)
Gap in copper (both sides) for HV sector isolation
Issue providing copper-free strip to grip GEM
layer
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3M GEM foil production - issues

• Quotation - 10K for glass phototool
• cost per length of roll or per 15cm x 15cm unit?
• Refine layoutdevelop cost sharing with other
  users
• Specify QC at 3M and UTA physical inspection,
  standing current (nA),
• Delivery?

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GEM/DHCAL test beam stack issues
GEM active layer three sections

• Minimizing walls
• Joining GEM foils(?)
• One strongback/layer?
• Gas flow/supports (post vs. line)
• 3 PCBs or single pad layers?

305mm
GEM strip from 3M roll
progress towards test beam design
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Conclusions

• Progress on understanding prototype signals and
  associated crosstalk.
• Progress on large-scale GEM active layers.
• Working with ANL/Fermilab on readout electronics
  (GEM mods to RPC design).
• Working with 3M Corp. on GEM foil production.
• Issue now is the funding/timescale for test beam
  stack.