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									     AFP Fast Timing System
        Andrew Brandt, University of Texas at Arlington
         in collaboration with Alberta, Giessen, Stony Brook, and
                      FNAL, Louvain, LLNL (CMS)

                •Introduction and requirements
                •Detectors and test beam performance
                •Electronics, including reference timing
                •Laser tests
                •PMT lifetime
                •Cost, Schedule, TDAQ

AFP Technical Review                CERN                  April 7, 2011
 Pileup background rejection/signal confirmation
 Ex: Two protons from one interaction and two b-jets from another

                   Use time difference between protons
                   to measure z-vertex and compare with
     How?          inner detector vertex. In 220 m phase
                   this will provide crucial confirmation
                   that any observed signal is legit
           10 picoseconds is design goal
           (light travels 3mm in 10 psec!)
How        gives ~x20 fake background rejection;
           Stage I: 2014 220 m few 1033 t < 20 ps
Fast?      Stage II: 2016 add 420 m 1034 t <10 ps         2
Final Timing System Requirements
 •   10 ps or better resolution
 •   Acceptance over full range of proton x+y
 •   Near 100% efficiency
 •   High rate capability (~5 MHz/pixel)
 •   Segmentation for multi-proton timing
 •   L1 trigger Capability
 •   Radiation Tolerant
     Note: For 220 m at modest luminosity/multiple
     interactions, the requirements are not as stringent:

     20 ps resolution, perhaps 1-2 MHz/pixel, multi-protons
     on same side not a significant problem, and the Level 1
     trigger capability is not strictly necessary.
           AFP Baseline Plan

                  30 cm

Two types of Cerenkov detector are employed:
  GASTOF – a gas Cerenkov detector that makes a single
  QUARTIC – two QUARTIC detectors each with 4 rows of 8 fused
  silica bar will be positioned after the last 3D-Si tracking station
  because of the multiple scattering effects in the fused silica.
  Both detectors employ Microchannel Plate PMTs (MCP-PMTs) 4
     Components of AFP Fast Timing
Radiator                       L1 Trigger

            HV/LV                      Timing

                            ROD           5
Wonderful detector developed by
K. Piotrzkowski (U.C. Louvain).
Low index of refraction means little
time dispersion, extremely accurate,
radiation hard, little material for
Multiple scattering

                                       From joint 2010
                                       ATLAS/CMS CERN TB
                                       t(G1-G2)=14 ps implies 10
                                       ps single detector
                                       resolution! BUT… only one
                                       single measurement, no
                                       segmentation, electronics
QUARTIC is Primary AFP Timing Detector
                                                     UTA, Alberta, Giessen,
                                                     Stony Brook, FNAL
                                                    4x8 array of 5-6 mm2
                                                    fused silica bars
                                                 Only need a 40 ps
                                                 measurement if you can
                                                 do it 16 times: 2 detectors
                                                 with 8 bars each, with
                                                 about 10 pe’s per bar

Multiple measurements with “modest” resolution simplifies requirements in all
phases of system
1) We have a readout solution for this option (can plug GASTOF into this)
2) We can have a several meter cable run to a lower radiation area where
   electronics will be located (without degrading overall system resolution)
3) Segmentation and L1 trigger is natural for this detector                7
4) Possible optimization with fibers instead of bars—discuss later
  Micro-Channel Plate Photomultiplier Tube

Burle/Photonis 64
channel 10 and 25 m
pore MCP-PMTs have
been tested extensively
with test beam and
laser and would be
default for first stage
except for lifetime                    8
issues (later)
         MCP-PMT Requirements
Excellent time resolution: 20-30 ps or better for 10 pe’s
High rate capability: Imax= 3 A/cm2
Long Lifetime: Q = 10-20 C/cm2/year at 400 nm
Multi anode: pixel size of ~6 mm x 6mm
Pore Size: 10 m or smaller
Tube Size: 40 mm round, 1 or 2 inch square

    Photek                                Hamamatsu
    240 (1ch)                             SL10 (4ch)

Need to have capability of measurements in different
parts of tube between 0-2 ns apart, and in same part of
the tube 25 ns apart                                9
 2010 CMS/ATLAS Fermilab Test Beam

                                                       courtesy of
2 x2 mm
Scint                                                  Albrow

Use siPM in beam as reference for evaluating QUARTIC       10
       2010 QUARTIC Test Beam Results
                                    Time Difference between adjacent
                                    bars is <20 ps, implies <14 ps/bar
                                    including bar, PMT, CFD! Too good
                                    to be true: due to charge sharing and
                                    light sharing, bars are correlated.

Time Difference between “distant
bars” 4 and 7 is 37 ps, implies
25 ps/bar (exceeds QUARTIC design
         t(siPM – Quartic Bar)
                           siPM-(avg of 3 quartic bars ) reduced
                           from ~28 (for single bar) to 21ps
                           consistent with expectations

       t=28 ps if Q~25
       siPM <15 ps        Tails due
                          to large
Note MCP-PMT with         protons
Quartz bar in beam        amps                                 12
“Nagoya Detector” can
give ~5ps resolution
             Giessen Fiber Quartic
From Sabrina Darmawi’s thesis, Michael Dueren, Hasko et al
                       •Facilitates variable bin size
                       to optimize rate+lifetime
                       •Simulations promising
                       •Needs upgraded readout
                       electronics to fully evaluate
                       Prototype performance

           Alberta Fiber Quartic

Preliminary Fermilab tests indicate improved time resolution over
quartz bars by up to 30%, even though less total light
More studies needed including effect of fiber pigtails for better
mapping onto the MCP-PMT
Electronics Layout

ZX60 4 GHz amplifier
(we use pairs of 4, 8 GHz
amps in different combinations
to control total amplification)
We will replace with diode/amp
board that fits on tube
ALCFD (Alberta/Louvain Constant
Fraction Discriminator): 8 channel
NIM unit with mini-module approach
tuned to PMT rise time, <5 ps
resolution for 4 or more pe’s             Stony Brook upgrade in
                                          progress to add trigger
                                          capability based on
                                          coincidence of quartz
                                          bars and basic ADC for
                                          monitoring gain
         Alberta HPTDC board

                                                              12 ps resolution with
                                                              pulser including non-
                                                              linearity corrections.
                                                              Successfully tested at
                                                              UTA laser test stand
                                                              with laser/10 m
                                                              tube/ZX60 amp/LCFD

                                               LCFD_Ch01_No12_spe, high level light, May 6, 2009, UTA laser test
                                                                RMS resolution = 13.7 ps


                                             14 ps
                                      4000   TDC

Test beam data complicated            1000
                                             in laser
                                        0    tests                                                      17
by 19 ns bunch structure                 800    810     820     830      840      850
                                                                               bin number
                                                                                            860   870    880       890   900
               QUARTIC HPTDC Buffering
     Concern:HPTDC designed to operate with 40 MHz clock
     but with occupancy of <2 MHZ; at high luminosity this
     might not be sufficient
                                     Loss rate in channel buffer for
     Loss rate in channel buffer for Logic core clock = 80MHz
     Logic core clock = 40MHz
                                                          Hit rate (MHz)   Total hits   Loss hits   Loss rate
    Hit rate (MHz)   Total hits   Loss hits   Loss rate
                                                          8                53244        1           1.88e-5
    4                7190         7           9.74e-4     10               7783         2           2.57e-4
    6                5117         45          8.79e-3     12               9072         6           6.61e-4
    8                3160         107         3.39e-2     15               10713        12          1.12e-3
    10               1424         118         8.29e-2     18               5998         33          5.5e-3
    12               739          111         0.15        20               2404         27          1.12e-2
    14               306          60          0.196       22               2589         37          1.43e-2

                                                          \24              2747         79          2.88e-2

(4 useful channels/ chip instead of 8, but occupancy problem solved, except for ref
clock see below)
          Reference Timing Overview
Reference timing is needed to connect two arms ~ 0.5 km apart; what we want is TL-TR,
what we measure is (TL-Tref)-(TR-Tref), so need small jitter in Tref
Solution has been developed by SLAC/LLNL involving phase lock loop. We need only
minor modifications to use 400 MHz RF instead of 476 MHz, and circuit to convert 400
MHz to 40 MHz and multiplex clock for use in HPTDC board

    Reference Timing Test Results

SLAC test show 10 ps total variation over 20 C! Adding a
correction for temperature, or controlling temperature of
electronics (not cable) will reduce the jitter to a couple ps!)
  Ref. Timing Rate Reduction

Concern: integrating reference time into DAQ since 40 MHz rate too
high for occupancy restrictions
But actually we only need reference time for good events!
1) Form a trigger based on multiplicity of CFD signals in one row
   -example if at least 4/8 bars have a signal
2) Only send CFD signals to HPTDC board if trigger is satisfied
3) Trigger reference time signal as well, so a chip will have 4 inputs:
    three bars in the row where trigger was satisfied, and the ref time
    signal corresponding to that row
4) possibly also keep some prescaled signals for monitoring

                    L1 TRIGGER
The Trigger formed in previous slide for controlling
reference time rates can also be used for a L1 Trigger,
instead of dedicated trigger detector
In 2014-2016 simple trigger, based on hits in timing
detectors, 1 CTP term for each proton side. Use large
diameter air core cables to minimize the cable delay due to
latency concerns
For 420 can use several bins and combine with jet
information from calorimeter

                         LeCroy Wavemaster
                         6 GHz Oscilloscope
Established with DOE              PLP-10 Laser
ADR, Texas ARP funds,             Supply

                                            Laser Box

                                         beam splitter
                        MCP-PMT                  filter
                                                          lenses   laser


Beam Mode     (c)   Fiber Mode

        (b)                 24
10 pe Time Resolution from Laser Tests

Laser tests of Photonis 10 µm tube show that with sufficient amplification there is
no dependence of timing on gain (low gain operation extends lifetime of tube)     25
        Saturation from Laser Tests

             Normalized Pulse Height

                                       0.60                                                             Xoo


                                         1.0E+03   1.0E+04          1.0E+05         1.0E+06   1.0E+07
                                                             Laser Frequency (Hz)

Saturation refers to the reduction in amplitude of the output signal due to the
      No rate dependence on number of pixels hit (that’s a good thing!)
   pores becoming busy at the rate increases (typically 1 msec recovery
   time/pore). This plot shows that saturation is a local phenomena, and is
   unaffected by multiple channels being on at the same time.
                Lifetime Issues
Lifetime due to positive ions damaging the photocathode
is believed to be proportional to extracted charge:
Q/year = I*107 sec/year

Q for <I>=2 A/cm2 is 20 C/cm2/yr

Can reduce this requirement with fiber detector but still
off by at least a factor of 20, so developed an R&D plan
to pursue this

             Extending Lifetime
•Inhibit positive ions
from reaching photo-
  - Ion Barrier:
aluminum film on top
of MCP’s (had
reduced collection
efficiency side effect)
so Nagoya developed
new approach
(between MCP’s).
Factor of 5 or more
lifetime increase (~3
C/cm2) for 4x4 SL10
            Extending Lifetime
•Minimize creation of positive ions
 - Use ALD coating of MCP’s (funded SBIR proposal
with Arradiance and Photonis in progress)


•Harden photocathode or improve its composition
 - solar blind photocathode could reduce impact of
positive ions
      A Long Life MCP-PMT                               e-

Arradiance coating suppresses positive ion                             +
creation (NSF SBIR Arradiance, UTA, Photonis)
Ion Barrier keeps positive ions from
reaching photocathode                                              +
(developed by Nagoya with Hamamatsu                               +
Use Photek Solar Blind photocathode or
similar (responds only to lower
wavelength/more robust)                      photon

Improve vacuum                                                     Photocathode
Seal (Nagoya/
                        Dual MCP                      DV ~ 200V
                                                                       DV ~ 2000V
Increase anode
voltage to reduce    Gain <105
                          ~ 106
crosstalk (UTA)
Run at low gain to                                    DV ~ 200V
reduce integrated
charge (UTA)                                          Anode
Possible MCP-PMT Alterntive: SIPM

UTA laser results
consistent with
results 16 ps
for 25 pe
amount of
Light using
quartz radiator
in front of SiPM)     Albrow
But this is not       At FNAL
viable design,        have been
Radiation wise        studying
Would need a
Quartic-like design               31

Need to discuss with collaborators before
filling this out


Need to discuss with collaborators before
filling this out

Estimated Production Cost

                    380k$ for 1Q+1G

                    500k$ for 1Q+2G

                    680k$ incl. spares

                    No Gastof option
                    Removes about

                    Red numbers are
                    not as well known
Minimal coupling between timing sub-components means
development and production of all parts can proceed
essentially in parallel. System factorizes into
1) Radiator: have a quartz bar solution, would prefer
    fibers if comparable performance
2) PMT: likely modified Planacon or modified SL10, both
    have same pixel size+layout
3) Electronics chain: amplifier/CFD/HPTDC
4) Reference Clock
5) Infrastructure (HV/LV/Cable)
6) Detector integration into Hamburg pipe
7) TDAQ integration

         Timing TDAQ Integration
L1: 2 CTP terms via one long large diameter air-core
cable from each side (use ALFA integration solution)

Readout: Timing integration to be done via optomodule
providing data from HPTDC board to standard ATLAS RODs
(whichever ROD is used by Silicon system should work).
One 12 channel HPTDC board required/per 8 channels of
QUARTIC (each HPTDC board has 3 chips run at 80 MHz,
Providing 4 channels each; two chips have 3 Q channels and a clock
while the third has 2 Q’s a G and clock).

So the one GASTOF one QUARTIC option gives 48 timing
readout channels/side while adding an extra QUARTIC gives
96/side. If we add the ADC that would give an ADC
channel for each timing channel. So the minimal system
(1Q+1G no ADC) has 96 total readout channels, while the full system
would have (2Q+1G+ADC) 192+66= 258 channels
Substantial progress in all phases of fast timing, including
integrating trigger capabilities into fast timing detector/electronics
We have a prototype fast timing system for AFP that seems to be
capable of ~10 ps resolution, validated with beam and laser tests
 Significant improvements in lifetime by Nagoya/Hamamatsu ;
also through UTA collaborations with Arradiance, Photonis,
Photek on lifetime. Solution exists for modest integrated charge
(few C/cm2), 10-20 C/cm2 seems achievable on a few year
In progress: final optimization and layout of detector,
electronics, PMT; evaluating radiation tolerance/needs of all
Timing detector not on critical path assuming ATLAS approves
AFP in a timely manner and R&D, production funding is 37

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