1. Digital Calorimetry for FCC Detectors
Yasar Onel1, Burak Bilki1,2
1 University of Iowa, Iowa City, USA
2 Beykent University, Istanbul, Turkey

2. Trend in Calorimetry Imaging calorimetry Tower geometry ET
Large number of calorimeter
readout channels (~107)
Option to minimize
resolution on individual
channels
Particles in a jet are
measured individually
Tower geometry
Energy is integrated over
large volumes into single
channels
Readout typically with
high resolution
Individual particles in a
hadronic jet not resolved ET

3. Particle Flow Algorithms (PFAs)
Particles in jets
Fraction of energy
Measured with
Resolution [σ2]
Charged
65 %
Tracker
Negligible
Photons
25 %
ECAL with 15%/√E
0.072 Ejet
Neutral Hadrons
10 %
ECAL + HCAL with 50%/√E
0.162 Ejet
Confusion
If goal is to achieve a resolution of 30%/√E →
≤ Ejet
Attempt to measure the energy/momentum of each particle with the detector subsystem providing the best resolution
Maximum exploitation of precise tracking measurement
Large radius and length to separate the particles
Large magnetic field for high precision momentum measurement
“no” material in front of calorimeters (stay inside coil)
Small Moliere radius of calorimeters to minimize shower overlap
High granularity of calorimeters to separate overlapping showers
Emphasis on tracking capabilities of calorimeters 3
High lateral and longitudinal segmentation

4. Digital Hadron Calorimeter
Development of the
Digital Hadron Calorimeter
Develop a tracking Hadron Calorimeter
Implement digital readout (1-bit) to maximize the number of readout channels
Place the front-end electronics in the detector
The active medium should:
Be planar and scalable to large sizes
Not necessarily be proportional (only yes/no for the traversing particle)
Be easy to construct, robust, reliable, easy to operate, …
Resistive Plate Chambers

5. The Digital Hadron Calorimeter (DHCAL) I
Active element
Thin Resistive Plate Chambers (RPCs)
Glass as resistive plates
Single 1.15 mm thick gas gap
Readout
1 x 1 cm2 pads
1-bit per pad/channel → digital readout
100-ns level time-stamping
Calorimeter
54 active layers
1 x 1 m2 planes with each 9,216 readout channels
3 RPCs (32 x 96 cm2) per plane
Absorber
Either Steel or Tungsten 9

6. The Digital Hadron Calorimeter (DHCAL) II
DHCAL = First large scale calorimeter prototype with
Embedded front-end electronics
Digital (= 1 – bit) readout
Pad readout of RPCs
Extremely fine segmentation with 1 x 1 cm2 pads
DHCAL = World record channel count for calorimetry
World record channel count for RPC-based systems
~500,000 readout channels
DHCAL construction
Started in 2008
Completed in 2010
Test beam activities
In the Fermilab testbeam (Steel absorber / No absorbers)
In the CERN testbeams (Tungsten absorber)
This is only a prototype
For a colliding beam detector multiply by ×100 10

7. Resistive Plate Chambers (RPCs)
Gas: Tetrafluorethane (R134A) : Isobutane : Sulfurhexafluoride (SF6) with the following ratios 94.5 : 5.0 : 0.5
High Voltage: 6.3 kV (nominal)
Average efficiency: 96 %
Average pad multiplicity: 1.6
Gap size and gas flow uniformity is maintained via fishing line channels 11

8. Resistive Plate Chambers (RPCs)
All geometries probed
Default design
(32 cm x 96 cm)
First generation RPCs (20 cm x 20 cm) 11
One-glass RPCs
(32 cm x 48 cm)

9. DHCAL Construction Stages of Construction RPC Painting
RPC Construction
Front-end electronics
Cassette Assembly
Back-end electronics
Gas System

10. RPC Painting Challenges/Requirements
Provide uniform surface resistivity
1-5(10) MΩ/☐ on thin (thick) glass
high R reduces rate capability
low R increases multiplicity
Maximize coverage of paint (HV) across RPC
Produce ~ 500 sheets
The Paint
2-component artist (airbrush) paint
needs to be mixed and sprayed
(paint booth and spray gun)
Paint Booth:
Large structure to exhaust fumes and instrument step motors for gun control
Spray Gun:
Commercial paint gun with fine control and rugged construction (easy to clean)
Uses nitrogen (dry gas) to carry paint
Production Procedure
Mix paint
Clean glass
Mask rims
Operate booth  8 sheets/day
Clean tools

11. RPC Assembly and Quality Control
Cut frames (sets gap size)
Assemble and glue chambers
1 RPC/day/tech
RPC Quality Control and Validation
Pressure tests – chambers are sealed
Gap size measurement – maintain uniform electric field in gas gap
HV tests – tests connections in cassette environment
Cosmic Ray Test Stand (9 RPCs stacked vert.)
validate production
test front-end electronics
noise measurements
HV scans  multiplicity and efficiency
> 95% of the RPCs pass the quality control tests

12. Electronics Overview

13. Readout System Overview
VME Interface
Data Collectors – Need 10
Timing Module
Double Width
- 16 Outputs
Ext. Trig In
master IN
6U VME Crate
To PC
Data
Concentrator
Front End Board
with DCAL Chips
& Integrated DCON
Chambers – 3 per plane
Data Collectors – Need 10
VME Interface
master IN
Ext. Trig In
To PC
Timing Module
Double Width
- 16 Outputs
Communication Link
- 1 per Front-End Bd
6U VME Crate
Square Meter Plane

14. The DCAL Chip Developed by Input Threshold Readout Versions
Threshold (DAC counts)
Hits/100 tries
The DCAL Chip
Developed by
FNAL and Argonne
Input
64 channels
High gain (GEMs, micromegas…) with minimum threshold ~ 5 fC
Low gain (RPCs) with minimum threshold ~ 30 fC
Threshold
Set by 8 – bit DAC (up to ~600 fC)
Common to 64 channels
Readout
Triggerless (noise measurements)
Triggered (cosmic, test beam)
Versions
DCAL I: initial round (analog circuitry not optimized)
DCAL II: some minor problems (used in vertical slice test)
DCAL III: no identified problems (final production)
Production of DCAL III
11 wafers, 10,300 chips, fabricated, packaged, tested
Threshold (DAC counts) 14

15. Front-end Electronics and Gluing
Front-end board (FEB) assembly
Build electronics and pad boards separately to avoid blind and buried vias
Each FEB contains 1536 channels
A data concentrator is implemented
Test electronics (noise rates, threshold curves,…)
Glue Robot
Glue is a conductive epoxy
Robot precisely places glue dots
0.001” thick plastic film used as spacers
dried in oven over night
10 boards/day
>300 FEB fabricated

16. Cassette Design structurally hold RPCs within the absorber structure
large copper and steel sheets
3 RPCs for each cassette
6 FEBs readout RPCs
maintain FEB contact with RPC (badminton strings
cool electronics (Cu)

17. Cassette Assembly Assembly Cassette Testing
- Cassette is compressed horizontally with a set of 4 (Badminton) strings
- Strings are tensioned to ~20 lbs each
- ~45 minutes/cassette
Cassette Testing
- Cassettes are tested in the cosmic
ray test stand

18. Peripheral Systems Gas System - HV mixer and bubbler racks
1 channel feeds 6 RPCs
leaky layers have individual supply
Wiener power supply with ISEG HV modules. Custom slow control software
Low voltage distribution for FEBs
Wiener power supply
Back-end Electronics
(2 VME crates)
2 Trigger and Timing Modules
20+ Data Collectors
bubbler
mixer
TTM
DCOL

19. DHCAL in Test Beams CERN May 12 June 12 July 12 Nov 12 > 40M events
FNAL
Oct 10
Jan 11
Apr 11 (w/ CALICE SiW ECAL)
June 11
> 20M events
FNAL
Nov 11
~ 2M events

20. Event Displays: Muons

21. Event Displays: Positrons
32 GeV
20 GeV
16 GeV
12 GeV

22. Event Displays: Pions
8 GeV
60 GeV
10 GeV

23. Event Displays: Protons
120 GeV

24. 3D Event Display w/SiW ECAL
40 GeV π+

25. A Few Test Results 0.04 – 2 cc/min/RPC  1.2 – 60 vol/day
JINST 5, 02007, 2010
Too many to list. Please see references in the last slide.

26. Recent R&D: 1-glass RPCs
Offers many advantages
Pad multiplicity close to one
→ easier to calibrate
Better position resolution
→ if smaller pads are desired
Thinner
→ t = tchamber + treadout = ~1.5 mm
→ saves on cost
Higher rate capability
→ roughly a factor of 2
Status
Built several large chambers
Tests with cosmic rays very successful
→ chambers ran for months without problems
Both efficiency and pad multiplicity look good
Good performance in the test beam 65
Efficiency
Pad multiplicity cm
JINST 5, 05003, 2015

27. Rate capability of RPCs
Measurements of efficiency
With 120 GeV protons
In Fermilab test beam
Rate limitation
NOT a dead time
But a loss of efficiency
Theoretical curves
Excellent description of effect
Rate capability depends
Bulk resistivity Rbulk of resistive plates
(Resistivity of resistive coat) 66
JINST 4 P06003, 2009

28. There is a gap between 10-9 and 10-3
Here is the problem
There is a gap between and 10-3 67
C. Pecharromán X. Workshop on RPC and related Detectors (Darmstadt)

29. Development of semi-conductive glass
Co-operation with COE college (Iowa) and University of Iowa
World leaders in glass studies and development
Vanadium based glass
Resistivity tunable!
Procedure aimed at industrial manufacture (not expensive) 75
See M. Affatigato’s talk.
International Journal Of Applied Glass Science, 6, 26, 2015

30. Development of semi-conductive glass75
Soda-lime
Soda-lime
Schott
SchottGlassTechnologiesInc., 400 York Ave, Duryea, PA18642, U.S.A.
JINST 10 P10037, 2015

31. (trigger-less acquisition)
High Voltage Distribution System
Generally
Any large scale system will need to distribute power
in a safe and cost-effective way
HV needs
RPCs need of the order of 6 – 7 kV
Specification of distribution system
Turn on/off individual channels
Tune HV value within restricted range (few 100 V)
Monitor voltage and current of each channel
Status
Iowa started development
First test with RPCs encouraging
Work stopped due to lack of funding 77
Size of noise file
(trigger-less acquisition)

32. Gas Recycling System DHCAL’s preferred gas
Development of ‘Zero Pressure Containment’ System
Work done by University of Iowa/ANL
Status
First parts assembled…
Gas
Fraction [%]
Global warming potential (100 years, CO2 = 1)
Fraction * GWP
Freon R134a
94.5
1430
1351
Isobutane
5.0 3
0.15
SF6
0.5
22,800
114
Recycling mandatory for larger RPC systems 78
Work stopped due to lack of funding

33. Summary The Digital Hadron Calorimeter concept is validated.
Extensive and unique experience with RPCs: We operated an RPC-based calorimeter for several years
Many R&D issues ahead for future systems, mostly under control but all stopped due to lack of funds

34. References
B. Bilki, et.al., Calibration of a digital hadron calorimeter with muons, JINST 3 , P05001, 2008.
B. Bilki, et.al., Measurement of positron showers with a digital hadron calorimeter, JINST 4, P04006, 2009.
B. Bilki, et.al., Measurement of the rate capability of Resistive Plate Chambers, JINST 4, P06003, 2009.
B. Bilki, et.al., Hadron showers in a digital hadron calorimeter, JINST 4, P10008, 2009.
Q. Zhang, et.al., Environmental dependence of the performance of resistive plate chambers, JINST 5, P02007, 2010.
J. Repond, Analysis of DHCAL Muon Data, CALICE Analysis Notes, CAN-030, CAN-030A, 2011.
L. Xia, CALICE DHCAL Noise Analysis, CALICE Analysis Note, CAN-031, 2011.
B. Bilki, DHCAL Response to Positrons and Pions , CALICE Analysis Note, CAN-032, 2011.
J. Repond, Analysis of Tungsten-DHCAL Data from the CERN Test Beam, CALICE Analysis Note, CAN-039, 2012.
B. Bilki, The DHCAL Results from Fermilab Beam Tests: Calibration, CALICE Analysis Note, CAN-042, 2013.
B. Bilki, et.al., Tests of a novel design of Resistive Plate Chambers, JINST 10, P05003, 2015.
M. Affatigato, et.al., Measurements of the rate capability of various Resistive Plate Chambers, JINST 10, P10037, 2015.
N. Johnson, et.al., Electronically Conductive Vanadate Glasses for Resistive Plate Chamber Particle Detectors, International Journal Of Applied Glass Science, 6, 26, 2015.
B. Freund, et.al., DHCAL with minimal absorber: measurements with positrons, JINST 11, P05008, 2016.
C. Adams, et.al., Design, construction and commissioning of the Digital Hadron Calorimeter — DHCAL, JINST 11, P07007, 2016.