Event Mode Data Acquisition System

Event Mode Data Acquisition System

Richard Riedel, Oak Ridge National Laboratory

OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY

Event Mode In a Nutshell

Every neutron detected is time stamped and saved without histogramming.

Other variables are also time stamped producing a movie like data set at run end.


Why Event Mode?

This what detectors do (where and when a neutron is detected)

“Electronic time-focusing of pulsed-source neutron chopper data: binning to minimize effects of proton pulse and chopper opening time variations” JM Carpenter NIM vol 429 2001

Pulse Probe Techniques

Cross-Correlation Techniques.

(Corelli, which measures single crystal diffuse scattering using cross correlation to provide elastic discrimination)

Offers novel approaches to typical data acquisition problems


Histogram

Neutron Events

TOF

X,Y

Counts

Time, E, Q, d

Pixel Spectrum

T.O.F., Space bins

Frame n+1

Frame n

Original Space nor Time resolution necessarily preserved…histogramming is a destroyer of information


Also Need Hardware Gating

from preamp or shaper

gate control

Histogram neutrons only whentemperature is within some range of setpoint


Event Based System Requirements

No hardware histogramming.

Ability to timestamp detected neutrons.

Log with time/date stamp ancillary variables (i.e. temp, magnetic fields etc.).


Event Mode Paradigms

Gating is done at the reduction/analysis level not in the DAS hardware.

Histogramming is done at the reduction/analysis and can be modified as needed without affecting the underlying data.

scattering data

temperature logs

gated datasoftware with sort criteriadata from file stream

or live stream


d /sin

Pixel ID

tof

sine lookup

Event

Increment this binSoftware: a few multiplies, additions and if statements

Variables can be calculated without histogramming first.

Its easier to throw data out then to look at data that was never collected.

Could put a software gate here.


Event Mode Data Format

Time Stamp [31:0] Uncorrected time of flight

Position Index [31:0] Pixel ID of detected neutron

Standard neutron event data generated by all detector electronics at the SNS

Pulse ID [63:0] Pulse ID from accelerator

Zero Based Starting Index [63:0] Index of starting neutron event structure that was produced with the above pulse ID

Standard pointer array which associates a pulse ID with a set of event data.

Array of event structure

+

Array of pulse info structure


SNS Implementation

Detector Electronics

Detectors

Common Data Format

Independent of Detector

System

UDPBroadcast

Common C++ Code

(Command Handling

Data transfer functions.)

Class xxx

Class yyy

Class zzz

C++ Abstraction Classes


Broadcasting the Data Stream

Active Client (DFS)Passive ClientPassive ClientPreprocessor

Session Header

Header ACK

Data Packet #0

Packet #0 ACK

Guaranteed Delivery To One Point

Data Packet #n-1

Packet #n-1 ACK


Transmission Benchmarks

Round Trip Time vs. Paylaod (SNS UDP protocol)

0

500

1000

1500

2000

2500

3000

0 10000 20000 30000 40000

Payload Bytes.

Sen

d T

ime

+ A

ck T

ime

(use

c)

with switch

witout switch


Sample Live Views From Control Computer

SNAP .5M pixel Anger Camera

Mag. Refl. 2D He3 Gas Detector

Both instruments see same event format!


Additional Listeners Can Do Real Time Independent Work


Most Interesting Applications Require Additional Time Stamped Data

Preprocessor,Receives Events

from Electronics and adds

TOF correction.

Detector Electronics

Detectors

ControlComputer

P.P MasterMaintains listing of chopper

phasesPer pulse

DataFile Server

Data Streamed to both Control Computer and Data File Server (16.7 -100 msec time frame)

Both c.c. and dfsbin event data as directed

+ =

Position,TOF

Pulse Information Event DataChopper Phase

Temperature, Stress…

SNS DAS streams,event data……

Cross, AutoCorrelations,Dynamics, Phase Transitions,Kinetics and Transient Phenomenon


Adding Chopper Phases/Other Variables

Requires DAS Hardware Sync signal.

Require Access To Accelerator Time Stamp Broadcast.

Requires Computer Clock to be synced with accelerator

High Frequency Signals

Low Frequency Signals


Stress Strain Example

1000

33

1010

35

1020

31

1025

33

1000

34

1008

34

Strain Transducers

Stress Strain Preprocessor

Proton Pulses

Strain Sample Times

time

Stress Waveform

Sync. Pulse

PulseID Broadcast Data Set=two binary files

124567980

0

124568869

4

Data Set

PulseID

VULCAN will have the capability to do cross correlation technique


How Time Synchronization Is Done

Timing PC

Control Computer

Preprocessor

Satellite Computers:Chopper, Sample Environment etc.

Accelerator Time Stamp (60Hz)

Interrupt Based Driver/Service

(50usec latency)

NTP only

ETC

Tier 0Tier 1

Tier 2

NTP

NTP sets local time, UDP broadcast

sends accelerator time stamp

NTP to sync computer time,date clockUDP broadcast for computers that must associate additionaldata with accelerator time stamp (pulseid).


Final File Set

+

Pairs of binary files

Neutron data

pulseid

Chopper Phases

pulseid

X Variablepulseid

not the same!


SQL Like Queries are Possible

SELECT pulses FROM run3100 WHERE temperature > 10 AND temperature < 20;

SELECT tof FROM run3100 WHERE pixelid=1101 OR pixelid=1102;

Would require a abstraction of file system. (Embryonic SQL queries available now for current values).


Who Else Runs An Event DAQ?

Particle Physics.

Event Data

ATLAS DAQ system

Reduction,Data Sorting,

Analysis

NOMAD rates…up to 500MB/s

Event Mode Data Acquisition System

Documents

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