Thilo Pauly, CERN/PH, LECC Heidelberg 2005 Sept 13, 2005 ATLAS Level-1 Trigger Timing-In Strategies On behalf of S. Ask 1), P. Borrego Amaral 1), N. Ellis

Thilo Pauly, CERN/PH, LECC Heidelberg 2005 Sept 13, 2005

ATLAS Level-1 Trigger Timing-In Strategies

On behalf of

S. Ask1), P. Borrego Amaral1), N. Ellis1), P. Farthouat1), P. Gallno1), J. Haller1), A. Krasznahorkay1)2), T. Maeno1),

T. Pauly1), H. Pessoa Lima Jr.3)4), I. Resurreccion Arcas1),

G. Schuler1), J. M. de Seixas3), R. Spiwoks1), R. Torga Teixeira1), T. Wengler1)

1) CERN, Switzerland2) University of Debrecen, Hungary3) Federal University of Rio de Janeiro, Brazil4) Brazilian Center for Research in Physics, Brazil

Thilo Pauly, CERN/PH, LECC Heidelberg 2005 2Sept 13, 2005

Timing Concept in the Trigger System

Synchronous

Asynchronous

Identifier-based(L1ID, BCID)

Timing-based

(Subject of this talk)

TriggerDelay

L1ADelay


USA 15

•Time of flight (bunches every 25ns = 7.5m)•Detector response•Cable lengths (10m = 100ns)

The Problem

Need well-defined procedures to do the timing-in.

BC 2

BC 1

BC 1


Overview

• Timing Signals at ATLAS– Distribution– Local Trigger Processor– Timing Tasks

• ATLAS Timing-In Strategy:– Test Pulses Decent initial timing– Beam Pick-Up Detectors

Filled-Bunch Trigger Bunch-Crossing Trigger

• NEW: Read-out of the Beam Pick-Up Detectors– Beam Pick-up Signal– Global BC Identification with Filled-Bunch Trigger– Clock phase: Read-out system, test results

• Conclusions


Timing Signals from the CTP

• Level-1 Accept (L1A) • BC = Bunch Clock with 40.08 MHz• Orbit Signal:

– 1 μs long pulse every revolution (89 μs)– Is used as bunch counter reset (BCR) to synchronise the

BC counters in the sub-detector front-ends, i.e. BCID– An LHC cycle consists of 3 564 bunches, each uniquely

identified by a BCID number.

– As reference point the abort gap in the bunch train can be used.


Distribution of Timing Signals

•CTP distributes L1A, BC, Orbit through CTP_OUT

(see R. Spiwoks “The ATLAS Level-1 Central Trigger Processor”)

•Local Trigger Processor (LTP):– Interface to CTP when running in

global mode– Important tool for sub-system

timing-in– Replaces the CTP when running in

local mode (test-pulses)•Via the TTC system (Timing,

Trigger and Controls)•New Multiplexer Module for

combining partitions

CTPUp to 20 Links

Partitions


Local Trigger Processor

CTP

Local

CalibrationRequest

TriggerType

LTP2

Interface to CTP+

CTP Replacement for Local Mode

(Local Inputs, Pattern Generator)

+Programmable Switch

Manual: ATL-DA-ES-0033

max 30 m

TTC


Typical Timing TasksSub-detector-specificTiming Tasks

Global TimingAdjustments

BC Counterfor BCID

Processing

TTCDistribution

Data Forming (Phase between BC & Signal)

Data Alignment (in steps of 25ns)

BC Identification(BCR delay)

Triggered BCIdentification(L1A delay)

BC

BCR

L1A

Sub-detector


Scenarios for Timing-In

• Timing-in with test-pulses:– Local mode: Stand-alone sub-detector timing-in, without

the CTP, only with LTP– Global mode with CTP

Will already give a decent initial timing set-up (up to a few bunch crossings)

• Single Beams: – Beam pick-ups to see filled bunches– CTP can be programmed to trigger on specific filled

bunches: filled-bunch trigger, bunch-crossing trigger

• Collisions:– Scintillation-counter hodoscopes in front of the end-cap

calorimeter– Coincidence between the two ends will give minimum

bias trigger (also combination with bunch-crossing trigger)


Timing-In with Test-Pulses in Local Mode

• LTP issues a L1A a fixed time Δt after a pre-pulse, synchronised with the ORBIT

• LTP should simulate CTP (same phase with Orbit as for global mode)

• Predict beam-beam timing (dgen) with simulation of:– Time-of-flight– Detector response– Calibration system specific

delays• Also account for expected trigger

latency and propagation of L1A signal

• Adjust L1A delay (dL1A): scan and recover test-pulse data

Test-SignalGenerator

dgen

dL1A

LTP

Pre-pulse

L1A

Δt

Sub

-dete

ctor


Timing-In with Test-Pulses in Global Mode

• Central Trigger Processor (CTP) triggers on a fixed BCID.

• LTP now in transparent mode• BC identification by comparing

BCIDs of event fragments in the read-out events (BCR offsets)

• Good initial timing setup for beam-beam collisions (up to a few bunch crossings)

• Leaves only the global timing to be established later:– Single beams: global BCR delay– Collisions: clock phase, global

L1A


LTP


LTP

CTP


Timing-In With Beam

• Need to “see” the bunches• BPTX = Beam position monitors

for timing purposes• Timing reference wrt bunches• 1 per incoming beam, 175 m

from IP• Electro-static button electrodes• Read-out currently under study


Usage of the BPTX Signal

BPTX are very powerful:1. Filled-bunch trigger, Bunch-crossing trigger2. Very precise time reference (clock monitoring)

“TTCMachine

Interface”

BC-Ref

BC-RF1

BC-RF2

BPTXRead-outSystem

(Oscilloscopes+ Computer)

BC-RefOrbitBC-RF1BC-RF2

BPTX1/2

Optical Electrical

Apps

Database

Configuration/Steering

Discr. CTP

USA15Electrical

Orbit

200m

(few ns)

(20 ps)

Filled-Bunch Trigger

Monitoring



1) Filled-bunch trigger: Global BC Identification

Trigger input for CTP for filled-bunch trigger (Discrimination of the bunch signals by preserving the time information of each bunch at the level of a few ns)

Detection of gaps in the bunch train with CTP bunch-to-bunch scalers of trigger inputs (CTPMON)

BCID

BC=0



2)Clock Monitoring:• Check the phase of each individual

bunch with the phase of the clock (accuracy: ~20ps)

• Monitoring of the clock from the machine. Detection of clock drift, due to

Problems in the signal chain Temperature drifts in optical fibres

• Check for satellite bunches in RF buckets (2.5ns)

• Monitoring frequency ~ once per minute


Expected BPTX Signal

• Very clean signal +20V ... -10V on 50Ω per button (from calculation, no transmission line yet)

• After transmission line: 20% of amplitude• Simple discrimination:

– Zero-crossing independent of bunch intensity– Zero-crossing depends on bunch length: – Bunch length fluctuations at 7 TeV will be %-level

Nominal LHC intensity: 1.15 x 1011 p/bunch

7 TeV


Information in the BPTX Signal

– Complete signal description exists, and can be used as a fit function. Fit parameters:

• t0 Time of closest approach of bunch to BPTX,

•N Number of protons in bunch

•σ Bunch length (Gaussian σ)

– Background is expected to be small and under control (noise, reflections, etc.)


Clock Phase wrt LHC Bunches

• Resolution to be 20 ps• NEW: Read-out with oscilloscopes

– Relatively cheap (several 10 kCHF), no hardware and low-level software development

– Guaranteed support– Signal is fully visible, no signal discrimination

before read-out: necessary for debugging– Usually maximum of 4 Channels: 2 scopes

required for 6 signals. For instance:• Scope 1: Orbit, BC-Ref, BC-RF1, BPTX1• Scope 2: Orbit, BC-Ref, BC-RF2, BPTX2


Test system with Tektronix TDS 3054B

– 5 GS/s real-time sampling rate, i.e. measurements every 200ps

– Memory depth: 10k, i.e. 2μs (Read out 45 chunks of 2μs)

– Max voltage on 50Ω: 5VRMS with peaks < ±30V– 8-bit vertical resolution, ~0.3%– 4 channels– Trigger on long-gap with hold-off time to

88.924μs-x (with x < 2.75μs)– BPTX Test signal: Shaped output from a

pattern generator (Local Trigger Processor)– Built-in ethernet port: configuration and read-

out through HTTP1.1– Data analysis with ROOT and MINUIT


Test Result: Proof of Principle with TDS 3054B

Clock

BPTX Test Signal

Clo

ck fit Clo

ck fit

Sig

nal

fit Sig

nal

fit

Read out via HTTP1.1


•BPTX resolutions:Toy-Simulation, 1000 samples, TDS3054B resolutions (vertical resolution: 0.2V)t0 = 0 ± 2.6psσ = 252ps ± 3.0psN = (1.150 ± 0.015) x 1011

t0 uncorrelated to σ, NCorrelation between σ and N: 0.68

Test Result: Resolutions

•Clock Phase resolution:– Difference of two consecutive

clock signals– Resolution of phase

measurement: 20ps– Resolution of single time

measurement: 20ps/√2 = 14ps

Measured

Simulated


BPTX Read-Out: Conclusions

• The read-out requirements for the ATLAS BPTX can be fulfilled with 2 modern off-the-shelf sampling oscilloscopes with:– 4 channels each– Sampling rate ≥ 5 GS/sec– Memory deep enough to accommodate

89μs– Communication via ethernet


Conclusion

• I have presented strategies for timing in the sub-detectors– With test-pulses in local and global mode a

good initial timing setup can be achieved: up to a few bunch crossings

• ATLAS beam pick-up detectors are very powerful for timing-in with beam:– Filled-bunch trigger: Global BC

identification– Measuring and monitoring of the clock

phase wrt LHC bunches


Backup slides


Minimum-bias trigger:One hodoscope plane on each side replacing part of the JM moderator between Inner Detector and LAr

Scintillator Counter Hodoscope

η coverage: z = ± 3.5 m~25 cm < R <

~115 cm ~1.8 < η < ~3.3

φ segmentation: probably 8

Very high efficiency for minimum bias events


The CTP is timed-in using the beam pick-ups as timing

reference:

• CTP can generate triggers with a fixed latency for specific bunch crossings using the beam pickups

• Using the scintillatior hodoscopes, the CTP can restrict triggers to crossings with interactions

Timing-In CTP Using the Beam Structure

Adjustoffset

BCID LHC

BCID CTP


1) Sub-detector chooses a quantity with high rate due to

interaction products and small background from other

sources

2) Map out the LHC bunch structure by plotting activity vs.

BCID using random triggers or scanning all BCID values with

L1As

3) Compare to (known) LHC bunch structure, e.g. position of

long gap

Timing Check Using the Beam Structure

Adjust for offsets

But: this procedure can take several days for certain sub-detectors with low rate and acceptance.


Global BC Identification with Filled-Bunch Trigger

• Discriminate BPTX signal (at the ns level)• Propagation of BPTX signal into CTP is

known• ToF from BPTX position to z=0 is known• CTP has scalers for each PIT bit and each

single bunch: find abort gap for the BPTX trigger signal

BC=0

BCID


BPTX Signal Expectation

• Longitudinally Gaussian-shaped bunch produces a current of mirror charge on the button surface, which gives a voltage signal on the transfer impedance:Basic model: “Differentiated Gaussian convolved with

an exponential due to the RC”

TransferImpedanceZT = 1.04Ω

Read-out50Ω

BPTX

BunchN protonslength σ

16pF

uR(t)

(no transmission line yet)


Expected BPTX Signal

• Very clean signal +20V ... -10V on 50Ω per button (from calculation, no transmission line yet)

• Zero-crossing independent of bunch intensity• Zero-crossing depends on bunch length:

– 100ps effect between injection and 7 TeV– Bunch length fluctuations at 7 TeV will be %-level

Nominal LHC intensity: 1.15 x 1011 p/bunch At Injection

At 7 TeV

7 TeV 5 x 109 p/bunch


Acquisition Mode/Scope Trigger

• Acquisition modes:– Real-time sampling (single shot, averaging mode)

– Equivalent-time sampling (only for repetitive signals)

• Different trigger possibilities:– For a real-time single shot mode, any trigger can be used: whole

bunch train is read out.– For averaging or equivalent-time sampling, a trigger signal with

small jitter is needed. Possibilities:• Orbit signal• Combination: First Orbit, then clock edge• BPTX signal itself, with trigger hold-off time set to find particular gaps

in the bunch train

Documents

Thilo Pauly, CERN/PH, LECC Heidelberg 2005 Sept 13, 2005 ATLAS Level-1 Trigger Timing-In Strategies On behalf of S. Ask 1), P. Borrego Amaral 1), N. Ellis