Clermont timing by renata.vivien


									ATLAS Forward Proton Electronics
  Andrew Brandt, University of Texas at Arlington

AFP concept: adds new ATLAS sub-detectors at 220 and 420 m
upstream and downstream of central detector to precisely measure the
scattered protons to complement ATLAS discovery program.
These detectors are designed to run at a luminosity of 1034 cm-2s-1 and
operate with standard optics (need high luminosity for discovery physics)

        beam         LHC magnets

     420 m                            H                     220 m
          AFP Detector

     After 1+ year of ATLAS internal review, AFP recently
     approved to proceed to Technical Proposal
                        What is AFP?
1) Impressive array of rad-hard edgeless 3D silicon with resolution
   ~10 m, 1rad
2) New Connection Cryostat at 420m
3) “Hamburg Beam Pipe” instead of Roman Pots
4) Timing detectors with ~10 ps resolution for overlap background
 Ex: Two b-jets from one interaction and two protons from another

                            Use time difference between protons
                            to measure z-vertex and compare
                            with tracking z-vertex measured
                            with silicon detector (x20 rejection
                            with 10 ps timing resolution)
     January 28, 2010   Andrew Brandt Clermont-Ferrand         2
             What does AFP Provide?
                                                • Mass and rapidity of
                     Acceptance >40% for wide     centrally system
                                                   M  12 s
                     range of resonance mass
                       Combination of 220
      420-                                            1
                                                   y  ln(1 /  2 )
                       and 420 is key to
      420              physics reach!
              420-                              • where 1,2 are the
                                      220         momentum loss of
                                                  the protons
                                                • Mass resolution of
                                                  3-5 GeV per event

Allows ATLAS to use LHC as a tunable s glu-glu or  collider
while simultaneously pursuing standard ATLAS physics program
    Timing System Requirements
• 10 ps or better resolution
• Robust: capable of operating with little or no intervention
  in radiation environment (tunnel)
• ~100% efficiency
• Acceptance over full range of proton x+y
• Segmented (multi-proton timing)
• High rate capability

• Two main options:
  1) one very precise measurement (GASTOF)
  2) multiple less precise measurements (QUARTIC)

 January 28, 2010   Andrew Brandt Clermont-Ferrand        4
                                                        UTA, Alberta,
                                                        Stonybrook, 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 (subject of this talk)
2) We can have a several meter cable run to a lower radiation area where
   electronics will be located
3) Segmentation is natural for this type of detector                     5
         MCP-PMT Requirements
Excellent time resolution: 20 ps or better for 10 pe’s
High rate capability: Imax= 3 A/cm2
Long Lifetime: Q= 30 C/cm2/year at 400 nm
Multi anode: pixel size of ~6 mm x 6mm
Tube Size: 40 mm round, 1 or 2 inch square
Pore Size: In our experience 10 m or better

We need 4/5 of tough requirements (only thing we don’t
need is large area!)

 Components of AFP Fast Timing System
                                           Louvain Custom   HPTDC
                 Mini-circuits ZX60                         board
                                           CFD (LCFD)
                 3 GHZ or equivalent                        (Alberta)

Photonis planacon                                               Reference
(10 m pore 8x8) or
40 mm Photek            HV/LV          Stonybrook               Timing
                                       AMP to
MCP-PMT                                                          Ref. time
                                                      Opto-      +LLNL
UTA QUARTIC/PMT Development                          modules/    <1 ps !

       Fourier Transform of Signal
                           10 m planacon, 40 pe’s
                                                            6 GHz
                                                            20 Gs/s

                     -whole signal is in first GHz
1 GHz                -scope bandwidth is 6 GHz
                     -cell phone/wireless noise contributions visible
                     -we use high bandwidth amp because of low noise
                     and then add filtering. A 1 GHz low noise
                     amplifier would likely be preferable, but we couldn’t
  January 28, 2010   Andrew Brandt we filter (1.5
                     find one so Clermont-Ferrand GHz filter helps a little,
                     1 GHz starts to cut into signal degrade performance)
ZX60 3 GHz amplifier
(we use pairs of 3,4, 8 GHz
amps in different combinations
to control total amplification)
LCFD (Louvain Constant
Fraction Discriminator)
•12 channel NIM unit
•mini-module approach
tuned to PMT rise time
•Excellent performance : <10
ps resolution for 4 or more pe’s

                                                              Remote control
                                                              for threshold
      January 28, 2010       Andrew Brandt Clermont-Ferrand            9
                  LCFD Performance
•Use large light signal to get narrow
pulse width and attenuators to evaluate
LCFD “sweet spot”
•LCFD prefers >200 mV
Note our scope resolution is about 2 ps
(measured using splitter after LCFD)      100 pe’s


                   LCFD Resolution

Pulses are amplified such that the mean pulse height is 500 mV
(Note: must optimize every measurement this way—any time you
                                          HV or number of PE’s must 11
vary the pulse height by changing Clermont-Ferrand
      January 28, 2010      Andrew Brandt
that you are still in the sweet spot of LCFD)
                         LCFD Performance
Using attenuators
can measure the time
shift as a function of
pulse height for a fixed
number of pe’s, and
determine a residual correction
factor as a function of
pulse height, which we can
apply for any number of pe’s:
but LCFD is so good this is not
really necessary

      January 28, 2010            Andrew Brandt Clermont-Ferrand   12
                                        V                               ps
                Alberta HPTDC Board
    • Targeting ~20 ps RMS resolution;                                                                                 Jim Pinfold
    (STAR TOF reported 24 ps, ALICE TOF reported 20 ps, Ref: 1,2)
                                                                                                                       Shengli Liu
    • 8 differential LVPECL input channels ;

    • 1 HPTDC (v1.3) chip from CERN in Very High Resolution Mode;

    • Altera Cyclone2 FPGA, Cypress USB chip for local debug;

    • Serial LVDS link to connect to the main RODs (ATLAS Readout)

    • Both USB and the Serial LVDS link provide timing and control
    signals to HPTDC
    Ref 1: J. Schambach, “Proposed STAR time of flight readout electronics and DAQ”, Computing in High Energy and Nuclear Physics, 24-28,
    March 2003, La Jolla, California.

    Ref 2: P. Antonioli, “A 20 ps TDC readout module for the ALICE time of flight system: design and test results”. 9th Workshop on Electronics
    for LHC Experiments, Amsterdam, The Netherlands, 29 Sep - 3 Oct 2003, pp.311-315

January 28, 2010                            Andrew Brandt Clermont-Ferrand                                                          13
             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

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


                                                  13.7 ps





January 28, 2010   Andrew Brandt                  signal
                                                         800    810     820     830      840      850       860   870   14
                                                                                                                         880       890   900
                                                                                               bin number
          QUARTIC HPTDC Buffering

Concern: During discussions at Photek we learned that
occupancy of HPTDC would be a problem for >2 MHz
(this is in the manual, but who reads manuals?)

Study used HPTDC Verilog model & measurement,
simulation details:

    At high luminosity, the hottest pixel would see a rate of 10-15 MHz
    The minimum spacing between triggers is 25 ns
    ATLAS L1 trigger rate 100 KHz, with a trigger latency of 2.5 s;

January 28, 2010       Andrew Brandt Clermont-Ferrand              15
          QUARTIC HPTDC Buffering

January 28, 2010   Andrew Brandt Clermont-Ferrand   16
          BufferingResults – Loss Rate
     Loss rate in channel buffer for                       Loss rate in channel buffer for
     Logic core clock = 40MHz                              Logic core clock = 80MHz
                                                          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

       Only input channel 0 is connected (4 useful channels/ chip instead of 8)

     January 28, 2010                  Andrew Brandt Clermont-Ferrand                                17
                   Buffering Test Results
Standard version of HPTDC chip works with a core clock
frequency up to 80 MHz
A special speed graded version of HPTDC chip could work with
core clock of 160 MHz.
RMS resolution is not affected when running with 80MHz clock.
Occupancy at trigger and readout FIFO’s is low enough

Modest increase in power consumption
January 28, 2010       Andrew Brandt Clermont-Ferrand      18
                         Reference Timing
Reference timing is needed to connect two arms ~1km apart; what we want is TL-
TR, what we measure is (TL-Tref)-(TR-Tref), so need small jitter in Tref
This setup has been tested to give 150 fs with 100m cable (1km cable isexpensive!)

                                         The reference system uses a phase lock loop to maintain a
                                         constant number of wavelengths in a 100m cable. This
                                         synchronizes the phase of the RF at each end of the cable. A
                                         voltage controlled oscillator (VCO) launches a signal down the
                                         cable where it is reflected and sent back. The returned signal is
                                         then interfered with an external RF reference to synchronize it
                                         with the reference. At the end of the 100m cable the signal is
                                         sampled with a directional coupler which mixes the signal to
      January 28, 2010          Andrew Brandt Clermont-Ferrand                                 19
                                         produce a DC level. That DC level is fed back to the VCO to
                                         maintain a constant number of wavelengths in the cable.
     Ref. Timing Rate Reduction

 Concern: integrating reference time into DAQ
 Planned to dedicate one channel/chip to reference time signal
 However reference time needs to be available every 25 ns:
 40 MHz (too high!)
 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) Also keep some prescaled signals for monitoring
January 28, 2010       Andrew Brandt Clermont-Ferrand               20
                    L1 TRIGGER
The Trigger formed in previous slide for controlling
reference time rates can also be used for a L1 Trigger!
The total number of trigger bits we send back to ATLAS for
L1 is a balance between:
    Optimal binning to give the lowest background trigger
   rate (when combined with jet information from
   The practical limits on the number of cable connections
   we can make, serial transmission schemes, and CTP
   input availability.
    The simplest scheme involves sending four bits directly
    over individual cables (low, intermediate, high, very
    high mass, for example).
   Large diameter air core cables are required to minimize
   the cable delay due to latency concerns.               21
   We have developed a fast timing system for AFP that seems to
   be capable of ~10 ps resolution
   Test beam is planned for this year with an 8-channel
   prototype system from the detector through to ATLAS
   Work in progress:
    1) final optimization of detector (looking into quartz
   fibers—could lower maximum rate by 2-3 by more sensible
    2) developing and testing long-life MCP-PMT
    3) evaluating radiation tolerance of all components and
   upgrading as needed
January 28, 2010       Andrew Brandt Clermont-Ferrand         22
Bonus Session on MCP-PMT Lifetime
    Satuday Jan. 30 9:00-11:30

              Comments/Questions/Suggestions:    23
              Please see Andrew Brandt (

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