atlas forward proton electronics andrew brandt, university of texas at arlington 1 afp concept: adds...

ATLAS Forward Proton ElectronicsAndrew Brandt, University of Texas at Arlington

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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

p’

p’AFP Detector

LHC magnets

420 m 220 mH

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, 1rad 2) New Connection Cryostat at 420m3) “Hamburg Beam Pipe” instead of Roman Pots4) Timing detectors with ~10 ps resolution for overlap background rejection

2January 28, 2010 Andrew Brandt Clermont-Ferrand

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)

Ex: Two b-jets from one interaction and two protons from another

Allows ATLAS to use LHC as a tunable s glu-glu or colliderwhile simultaneously pursuing standard ATLAS physics program

What does AFP Provide?

420-420

420-220

220-220

3

• Mass and rapidity of centrally system

• where 1,2 are the fractional momentum loss of the protons

• Mass resolution of 3-5 GeV per event

1 2M s Acceptance >40% for wide range of resonance mass

1 2

1ln( / )

2y

Combination of 220and 420 is key to physics reach!

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)

Andrew Brandt Clermont-Ferrand 4January 28, 2010

4x8 array of 5-6 mm2 fused silica bars

QUARTIC UTA, Alberta, Stonybrook, FNAL

Multiple measurements with “modest” resolution simplifies requirements in all phases of system1) 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 located3) Segmentation is natural for this type of detector

proton

phot

ons

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

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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 nmMulti anode: pixel size of ~6 mm x 6mm Tube Size: 40 mm round, 1 or 2 inch squarePore Size: In our experience 10 m or better

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

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Components of AFP Fast Timing System

QUARTIC:Photonis planacon(10 m pore 8x8) or 40 mm Photek MCP-PMT

Mini-circuits ZX603 GHZ or equivalent

Louvain Custom CFD (LCFD)

HPTDC board(Alberta)

Reference Timing

Opto-modules/

ROD

HV/LV

UTA QUARTIC/PMT Development

Stonybrook AMP to HPTDC

Manchester/UCL

Ref. timeSLAC +LLNL<1 ps !

January 28, 2010 Andrew Brandt Clermont-Ferrand 8

Fourier Transform of Signal

-whole signal is in first GHz-scope bandwidth is 6 GHz-cell phone/wireless noise contributions visible-we use high bandwidth amp because of low noiseand then add filtering. A 1 GHz low noise amplifier would likely be preferable, but we couldn’tfind one so we filter (1.5 GHz filter helps a little,1 GHz starts to cut into signal degrade performance)

10 m planacon, 40 pe’s

Lecroy 8620AWavemaster6 GHz20 Gs/s

1 GHz

LCFD

LCFD (Louvain ConstantFraction Discriminator)•12 channel NIM unit•mini-module approachtuned to PMT rise time•Excellent performance : <10 ps resolution for 4 or more pe’s

Remote control for threshold

ZX60 3 GHz amplifier(we use pairs of 3,4, 8 GHzamps in different combinationsto control total amplification)

9January 28, 2010 Andrew Brandt Clermont-Ferrand

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LCFD Performance

100 pe’s

V

•Use large light signal to get narrow pulse width and attenuators to evaluate LCFD “sweet spot” •LCFD prefers >200 mVNote our scope resolution is about 2 ps (measured using splitter after LCFD)


LCFD Resolution

Pulses are amplified such that the mean pulse height is 500 mV (Note: must optimize every measurement this way—any time you vary the pulse height by changing HV or number of PE’s must check that you are still in the sweet spot of LCFD)


LCFD PerformanceUsing attenuatorscan measure the timeshift as a function ofpulse height for a fixednumber of pe’s, and determine a residual correctionfactor as a function of pulse height, which we can apply for any number of pe’s:but LCFD is so good this is notreally necessary

V ps


Alberta HPTDC Board• Targeting ~20 ps RMS resolution;(STAR TOF reported 24 ps, ALICE TOF reported 20 ps, Ref: 1,2)

• 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

Jim PinfoldShengli Liu

http://cdsweb.cern.ch/search?sysno=002402529CER

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

14January 28, 2010

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

0

1000

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800 810 820 830 840 850 860 870 880 890 900

bin number

coun

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13.7 pswith splitLCFD signalAndrew Brandt Clermont-Ferrand

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;

QUARTIC HPTDC QUARTIC HPTDC Buffering Buffering

January 28, 2010 15Andrew Brandt Clermont-Ferrand

QUARTIC HPTDC QUARTIC HPTDC Buffering Buffering


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

Hit rate (MHz) Total hits Loss hits Loss rate

4 7190 7 9.74e-4

6 5117 45 8.79e-3

8 3160 107 3.39e-2

10 1424 118 8.29e-2

12 739 111 0.15

14 306 60 0.196

\

Hit rate (MHz) Total hits Loss hits Loss rate

8 53244 1 1.88e-5

10 7783 2 2.57e-4

12 9072 6 6.61e-4

15 10713 12 1.12e-3

18 5998 33 5.5e-3

20 2404 27 1.12e-2

22 2589 37 1.43e-2

24 2747 79 2.88e-2

BufferingResults – Loss BufferingResults – Loss RateRate

Loss rate in channel buffer forLogic core clock = 40MHz

Loss rate in channel buffer forLogic core clock = 80MHz


James Pinfold

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

Buffering Test ResultsBuffering Test Results



Reference TimingReference 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 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 Ref. Timing Rate ReductionReduction

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

Select the reference timing edges and CFD signals to HPTDC board by following conditions:CFD signals arrive within 2 ns window of “Enable” ( 2ns corresponds to full vertex coverage at ATLAS +/- 30 cm (expect all events in a 2 ns window)

A predefined multiplicity coincidence “trigger” be met for above CFD signals;

The reference edges related to above CFD signals are passed.


L1 TRIGGERL1 TRIGGERThe 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 calorimeter)

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 readout.

Work in progress:

1) final optimization of detector (looking into quartz fibers—could lower maximum rate by 2-3 by more sensible binning)

2) developing and testing long-life MCP-PMT

3) evaluating radiation tolerance of all components and upgrading as needed

Conclusions

BonusBonus Session on MCP-PMT LifetimeSatuday Jan. 30 9:00-11:30

Comments/Questions/Suggestions:Please see Andrew Brandt ([email protected])

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atlas forward proton electronics andrew brandt, university of texas at arlington 1 afp concept: adds...

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