Partha Dhara Data Acquisition & Development Section ...symposium.vecc.gov.in/sacet09/public_html/downloads... · Partha Dhara. Data Acquisition & Development Section, Variable Energy

Partha DharaData Acquisition & Development Section,

Variable Energy Cyclotron Centre,Kolkata

29/10/2009 SACET09 - VECC Kolkata

Contents

Nuclear Process and its effects Dead time calculation Trigger system DAQ features Conclusion


Nuclear Process

Radioactive decay process follows Poisson-exponential distribution

The probability of time interval T ≥ t is given by


( ) τin time events ofNumber Mean τμ Where

n!μe

τPnτ

μ

n

τ

→

=−

( ) τµt

etTP−

=≥

Effect of randomness Variable time gap

between two consecutive events

Dead Time loses The DAQ read-out time

should be kept as low as possible even for low average rate

Multi-module / multi-crate synchronization problem


Input

Dead time t

Dead Time Detector Dead Time

Extendable (Example GM Counter) Non Extendable (Scintillation det., solid state

det.)


τ

Input

Total Dead time

Non-extendable

Extendable

Effect on detectors Non extendable dead-time detector

Leads to pile-up○ Tail pile up could be resolved: Second pulses

occur with well after charge collection time○ Peak pile up could saturate amplifier: Close

energy isotopes could not be separated Discriminators could discard bad pulses


Pre-amp Tail ~ 1ms

Shaper ckt output 3µs

The extendable dead-time detector Dead time is variable High input rate saturates the detector The input rate should be controlled Low field radiation monitoring application Pulse Counting process may employ

correction for counting losses for dead time


Analysis of Total Dead Time Best Case: The max of all

dead times Worst Case: Addition of all

dead times Depends on Trigger

Generation Logic, read-out logic, data rate

Difficult to study analytically.


Det1

Det2

Det3

FEE

FEE

FEE

ADC DAQ

τ11

τ12

τ13

τ21

τ22

τ23

τ3 τ4

( )432131

τττττ +++==

iitoi

MAXSystem Dead time

Detectors < 1μsFEE 3-4μsVME ADC 5.7μsCAMAC 1.5μs

VME 160 ns

Observed Rate Non Extendable Dead Time

system R is actual event rate, R’

observed rate. T is average fixed dead time


τ

τ

RRRor

RR

+=

=+

1',

'11

Extendable Dead Time system

R is actual event rate, R’ observed rate. T is average fixed dead time

τReRR −×='

Trigger Generation Scheme

To identify the signature of an interesting event.

General methods are coincidence, multiplicity, current sum or Logical OR.

The collected data corresponding to each accepted trigger forms one event

Integrity of event data must be maintained


Single DAQ Common Dead Time Single trigger Common Dead

Time Sequential Read-

out


Discr

Discr

Discr

Delay

Trig

Delay

Delay

a

b

cVeto

ADC1

ADC2

ADC3

Trig

busy

amp

Multiple DAQ, multiple triggers

One Master trigger Multiple Slave

Triggers Parallel sub event

read-out Event number

distribution Event

reconstruction


Det1 Det2

Mastertrig

Ev num

SlaveTrig

DAQ1 DAQ2

Event Builder

valid

Sub-ev1 Sub-ev2

Complete Event

Multiple DAQ Autonomous Trigger

Each DAQ works with own trigger rate

Events are marked with a universal timestamp

The event reconstructed by matching the timestamp value.


Det1 Det2

Trig1 Universal Timestamp

Trig2

DAQ1 DAQ2

Event BuilderSub-ev1 Sub-ev2

Complete Event

Event Synchronization The event is fragmented over

multiple modules/crates. Sub-events should be reconstructed

back into complete event Zero suppressed data must have

proper header and trailer tag Each sub-event should be marked

with unique event number or timestamps

Events may be read horizontally or vertically across the module, whichever will yield the highest throughput.


ev01

ev11

ev21

ev02

ev12

ev22

ev03

ev13

ev23

trig

Common busy

M1 M2 M3

Windows CAMAC DAQ t4: First PC based Win16 Win3.1 t32 for Win32 systems Windows

98/2000/NT/XP Both offline (st32) and online (t32) version Hytec controller and List processor


DAQ Software VME DAQ

Online and offline version Muti-threaded Object-oriented

design Controller: PCIVME, SIS3100

controller, CES 8064WD RIO3 Modules: CAEN VME785 ADC,

VME792 QDC, VME775 TDC, Mesytec MDI2

Support for VME BLT32, CBLT32 Average 840KParam/Sec transfer

rate under application


VME CAMAC Integration CAMAC integration under

same framework Hytec 5331 Controller &

LP1341 List Processor 256KB memory

Available on both Linux (2.4 series kernel) & Windows2000/XP/2003

Driver and ESONE standard library developed inhouse

Performance Read: 10μs 16bit Single Block: 2.4μs Interrupt: 40μs


DAQ features The Multiple threads for parallel read, event-generation &

processing of data Better encapsulation for module support. Zero suppressed list format for storage.


Read Out

Event Gen

Process

buf0

buf1

buf0

buf1

VM

E/C

AM

AC

C

rate

Store

DET. + FEE

Parallel Stages


Read Out

The sub-events from multiple modules are read in BLT mode, checks validity with the event number tag. Rejects bad events

Event Gen

Sorts the sub-events, reconstructs the whole event sequentially, reformats the event in our zero suppressed format,

ProcessEvent one by one passes through a list of function executers (add, if, 1d, 2d, user), Place for Virtual ADCs,

Process List


1D spectr

umCH 0

1D Spectrum CH 1

if (1 & 2 )

1D Spectrum CH 3

2D Spectru

mCH4 Vs

CH3

if(3)

VC0=CH0 * g1 + CH1 * g2 + off

1D spectrum VC0

2D SpectrumCH10 Vs

CH0

gate (1) : 100 < CH0 < 2000

banana_gate (3) : <filename>

Configuration File C-style Single configuration file for complete

configuration, compatible to both offline and online


module{module_type=vme785;base_address=0x800000;instance=0;channel=32;conversion_gain=4096;event_size=34;geographical_address=4;

}

function{func_type=oned;spec_len=4096;gain=1.0;offset=0.0;channel_no0{

module_type=vme785;

instance=0;channel=0;

}}

if(1 & 2){function{

func_type=twod;x_len=512;y_len=512;

channel_no0{module_type=vme785;instance=0;channel=16;

}channel_no1{

module_type=vme785;instance=0;channel=25;

}}}

2D histogram for Particle Identification


Courtesy: T.K. Rana CPDA Lab, TIFR Experiment 2009

OFFLINE Analysis


Conclusion

Custom made software for experimental nuclear physics

Capability to handle hundreds of signal channel

Support for both CAMAC and VME PC based system are migrating to

distributed system with embedded hardware



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Partha Dhara Data Acquisition & Development Section ...symposium.vecc.gov.in/sacet09/public_html/downloads... · Partha Dhara. Data Acquisition & Development Section, Variable Energy