1. NPDGamma: Data Acquisition System October 15th, 2010 NPDGamma Collaboration Meeting ORNL

2. 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

3. 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

4. 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

5. Auxiliary Information Event Link “all events for a scheduled proton charge for all possible frequencies” Choppers, etc Example:#39 – regardless of beam #61 – only if there are neutrons ETC Selected, processed signals (TTL) RTDL (real time data link) Beam information

6. New code Auxiliary Information Event Link “all events for a scheduled proton charge for all possible frequencies” RTDL VME Module Read the appropriate register for proton current RTDL (real time data link) Saved as part of runXXXXX-1.dat event file Beam information

7. 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

8. Online Analysis • Team Members: • Chris Crawford* • Nadia Fomin • Chad Gillis • SeptimiuBalascuta Tim reworked the GUI to include a command line interface

9. 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

10. Summary • 60 Hz operation – implemented • Accelerator information – in progress • Online analysis – a large part is in place, some integration necessary