The outputs from the photomultiplier tubes for trigger counters A and B were sent to NIM linear fanout modules.  One output from the linear fanout was sent through 200 ns of delay line and then to a Lecroy 2249A to encode the total charge.   A second output was sent to Ortec 934 constant fraction discriminators and then to a 4-fold logic module.  Readout of the prototype calorimeter tower photomultiplier tubes (PMT) and the shower-maximum detector (SMD) multi-anode photomultiplier tubes (MAPMT) was initiated when a coincidence was observed between trigger counters A and B.  In the overlap coincidence, trigger counter A defined the timing. 


A second logic gate was used to define the condition A.B.not busy, using a busy signal from the data acquisition system.  Given the 0.1 s interval between SLAC pulses, the data acquisition system was virtually never too busy to accept an A.B coincidence.   The A.B.not busy signal was used as


*        a trigger to the computer to initiate readout.


*        a signal to drive a programmable gate generator (Lecroy 2323), used to remotely control the (wide) gate to a Lecroy 2249W, used to encode the pulse height from the calorimeter tower PMT.  The typical (wide) gate width used for most of the measurements was 3.0 microseconds.


*        a signal to the second channel of the LeCroy 2323, used to remotely control the (narrow) gate to a LeCroy 2249A, used to encode the current from the fast component of the calorimeter tower PMT.  The typical  (narrow) gate width used for most of the measurements was 100 ns.


*        a signal to a LeCroy 821 leading edge discriminator, used to generate a 400 ns wide gate to a LeCroy 4301.  The LeCroy 4301 distributed gate pulses to the ten 4300B (FERA) analog-to-digital converters.  The FERA encoded the charge produced by individual anodes of the Hamamatsu 6568 multi-anode photomultipliers, used to read out the 160 scintillator strips of the shower-maximum detector.


*        a common start to a Lecroy 2228 time-to-digital converter.  Separate TDC stops were derived from all trigger counters and the SLAC clock, suitably adjusted in phase.



The figure shows the typical pulse height spectrum from the three trigger counters (see figure of the T-438 setup) for the 10-GeV running with focused beam.  Observed for counters A,B are multiple peaks corresponding to events where 1,2,3 or more 10-GeV electrons passed through the scintillators.  For most of the events, trigger counter C (with a 2.54 cm diameter hole) records no pulse height, indicating that the electrons from the beam passed through the hole of the detector.


Send comments to:

L.C. Bland (IUCF), for the T-438 collaboration


Last revised: 31 October 1999