NPDGamma: Data Acquisition System

October 15th, 2010

NPDGamma Collaboration Meeting

ORNL

Reminder of LANL SNS transition issues• The asymmetry is not energy-dependent, so why do we care to preserve the

time structure of the data?– LANSCE: used a 3He polarizer, so Pn=Pn(λ)– RFSF: in its absence, can take data until run out of memory, then save

it. But, since we flip spins, need knowledge of time.

• At LANSCE: each pulse was 50ms– 10 ms of each pulse were made of up fast neutrons, not used for the

experiment (need En<15meV) – used to read out the ADCs.– 35-40ms used for pedestals

• SNS: 16.67ms pulses, all the neutrons are useful– No time to read out the ADCs!– Need a different strategy for pedestal data

Solution• Data Increment – 1 spin sequence (rather than 1 accelerator pulse)

• Read ADCs after each spin sequence, 11% dead time

• Implemented and tested with noise data

~13 hours of noise data

Accelerator Info: Proton Current

SNS Standard:

• Network Broadcasts via UDP

• DAS group uses standard software for every beamline to read and decode UDP packets

• Less than ideal for NPDGamma (reading wireless packets and reintegrating them into the data stream post-production)

Secret Alternative:

• 2 VME modules that will allow us to get whichever accelerator information we want and insert it into our data stream

• Modules acquired (FREE!!), working on software for VME1

Auxiliary Information

ETCSelected, processed signals (TTL)

Choppers, etc

Example:#39 – regardless of beam

#61 – only if there are neutrons

RTDL

(real time data link)

Event Link

“all events for a scheduled proton charge for all possible frequencies”

Beam information

Auxiliary Information

Read the appropriate register for proton current

RTDL

(real time data link)

Event Link

“all events for a scheduled proton charge for all possible frequencies”

Beam information

RTDL

VME

ModuleNew code

Saved as part of runXXXXX-1.dat event file

Putting it all together• Several data files

• One from each VME crate

• Target Info

• B-field

• Synchronize clocks on all the computers (I’d prefer if non-detector files could also have T0-based data structure)

• All data files are collected at the end of each run

• Online Analysis: read into a data “tree” – different data types make up different branches

• Online Analysis Status – large chunk of code to analyze the data (read in detector arrays, reconstruct signals, form asymmetries) has been written

• Must integrate with the altered GUI

Online Analysis

Tim reworked the GUI to include a command line interface

Team Members:

• Chris Crawford*

• Nadia Fomin

• Chad Gillis

• SeptimiuBalascuta

Online Analysis - continued• At the end of each run, a summary file is created with some key histograms as well as statistics

• Summary file is copied out from ORNL and entered into the e-log

• e-log is online at UTK and is accessible from anywhere.

• an online cumulative asymmetry is also continuously updated

• Progress: ssh tunnels set up, working on scripts to create entries

Summary

• 60 Hz operation – implemented

• Accelerator information – in progress

• Online analysis – a large part is in place, some integration necessary