Neutron Detector Scalers

The neutron detector scaler display can be used to display approximate rates on every phototube in the GeN neutron detector. This rate display will normally only work while the DAQ is running. (See theory of operation for why.) The display can be invoked from the adaq account by typing.

     cd ~/e02013/tdcscaler

The "Freeze" button on the display stops the rates from updating. It can be used to pause the display before making a screen capture. The Raw/Norm buttons toggle between displaying the rates in KHz and displaying rates normalized to the beam current (KHz/uA). As the size of this display is rather large, it should be run from display with a resolution of 1600x1200.

Theory of operation

Because of the large number of tubes in the neutron detector, the discriminator outputs for individual tubes are not connected to hardware scalers. However, because all the discriminators are connected to multi-hit tdcs, the average number of pulses per tdc channel per event can be determined by spying on data acquired by coda. This average count, divided by the width of the TDC gates is used to compute the rate that is displayed. The spying and calculations are done in the read-out-controllers (ROC24 for Veto counters, ROC25 for the bars.), and only functions while the DAQ is running.

If the DAQ is unavailable, rebooting ROC24 and ROC25 (gensfi1 and genvme1) will start the scaler servers in stand alone mode so that rates can be displayed. However, this mode will be disabled as soon as a CODA download is done. At this point, rates will only be available while a run is in progress. (Not between runs.)


(Hall C style) Scaler servers have been installed on genvme1 and gensfi1. When queried, these servers return lists of derived scaler counts for the multihit TDC's in these crates. The display program, bighand.tcl reads the file BIGHAND.screen to get the mapping between the locations in these lists to physical detector location. This mapping file is derived from the analyzer database file that holds the mapping between TDC channel and physical detector location. The e02013/tdcscaler directory contains the softlink db_na.nd.dat which points to latest analyzer database file. If TDC mappings in this database file are changed, then the scaler display map must be updated by running:

     cd ~/e02013/tdcscaler
     ./ > BIGHAND.screen

For more information please contact Stephen Wood.

Updated February 11, 2006