Photon Trigger

                                                                       Carlos W. Salgado      -    Version 1.0      -     August, 2001

NOTE: Photon Trigger files should only be changed by, or with direct authorization of, the run coordinator.

1 Introduction

During CLAS photon beam runs, level 1 [L1] triggers are produced by the coincidence of the so-called "photon triggers" and "CLAS triggers. The CLAS trigger is a logic combination of CLAS detector signals made by the Tigris software and it is note addressed in this document. . The photon trigger is and input to the trigger supervisor [TS]. This note documents the hardware and software needed to set the photon trigger. There is hardware to make possible two photon trigger inputs into the TS, they are called ASYNC1 and ASYNC2.

The photon trigger provides to the TS the following information:


2  Hardware

The hardware for the photon trigger is located in part at the space frame [SF] (1st floor), and in part at the forward carriage [FC] (2nd floor).

The MOR and logic ST signals are defined in the SF hardware.

The MOR is produced by a series of "cascading" coincidences done by NIM Phillips 754 modules. See figure 1 for the general tagger system electronic diagram. These modules are to the left of the tagger electronic racks, entering the Hall to your right. There are "extra" 754 modules, more than the necessary to make just one combination of all T counters. Therefore, up to TWO MORs can be defined as any subset of T counter ranges. There are two cables of same length (about 110ns) running from the SF to the FC electronics carrying these two MOR signals for ASYNC1 and ASYNC2.

G6C: two equal MOR are defined by the 1-12 T counters Two 754 modules are used to combined [1-4,5-8,9-12].
MOR for ASYNC1 and ASYNC2 are the same in g6c.

The ST logical signals are made in the rack to the right of where the MOR signals are defined. There is the possibility for two ST combinations going to the FC (again, there are two equal length cables – also of the same length as the MOR cables). They will be combined with the MOR signals to form ASYNC1 and ASYNC2 at the FC. There are six ST signals coming to the rack. 1-2, 3-4 and 5-6 are added and sent to a NIM 740 Phillips module. See diagram in figure 2.

G6C: ASYNC1 is the logic signal of 2 out of three (2/3) hits.
ASYNC2 is the logic signal of 1 out of three (1/3) hits.

The discrimination, relative delays and logical handling of the MOR, ST and TAC (PS) signals are made at the FC through CAMAC modules (located in crate #2). The modules are at CAMAC1, top of rack that contains the TS.
MoModule slot description
4413 3 MOR discriminator (test input behind)
4413 5 ST discriminator (test input behind)
4418 4 ST delay (MOR is currently not delay)
4516 9 MOR ST logic AND
2313 20 MOR discriminator (input at address 0)
2313 21 ST discriminator (input at address 8)
4418 22 ST delay (MOR is currently not delay )
4516 23 MOR ST logic AND

  The photon trigger software (see section 3) controls the values (widths, thresholds and logic sets) for these units. Modules 4413 allow only threshold control, however, widths and thresholds can be control for the 2313 units. There are two photon triggers made in parallel. Normally, Both will make use of a MOR· ST coincidence with adjustable widths, thresholds and relative delays.
  ASYNC1: The modules for the ASYNC1 trigger are to the left of the CAMAC unit (crate 2). The MOR signal from the SF enters a 4413 discriminator unit (from the test input, therefore, the signal is available in all 16 channels). Input 1 goes directly to the logic module (i.e. no delay) (level 1) and input 16 goes directly to bit 7 of TS. The ST signal enters another 4413 discriminator unit but also through the test input. The ST signal goes through a 4418-delay unit where the relative timing is adjusted (during commissioning in steps of 2 ns from 2 to 32 ns).
The TAC signal enters a 2313 discriminator (no currently in use).

ASYNC2: The modules for the ASYNC2 trigger are to the right of the CAMAC unit (crate 2). The MOR signal from the SF enters a 2313 discriminator unit (from the input #1 (address 0). Input 1 goes directly to the logic module (no delay) (level 1). The ST signal enters another 2313 discriminator unit but through channel #9 (address 8). The ST signal goes through a 4418-delay unit where the relative timing is adjusted (during commissioning in steps of 2 ns from 2 to 32 ns).
There is not TAC signal related to ASYNC2.


    3 Software

    The FC CAMAC electronics is controlled from the CLON machines using the photon gui or editing and setting the photon trigger files "by hand".

    The photon gui function is an interface to produce the photon trigger file. The trigger configuration from the DAQ run the setting of the photon trigger electronics as specified by this file at the initiation of each experimental run.

    ["by hand"]
    Files related to the photon triggers are at:


    for g6C the file is:


    that file can be set "manually" using the command: (from the above directory):

    photon_setup camac1 check

    4 Commissioning the photon trigger

A "time curve" using the ST delay modules need to be performed during commissioning (or any change of hardware configuration that could affect the MOR-ST timing relation) to find the optimum MOR-ST coincidence timing.

One way to make this curve is using the information on the TLV1 banks

Use: /home/clasrun/tlv1/bin/tlv1

5 Production Running with the photon trigger

The "photon trigger file" setting the electronics in the FC is controlled by the DAQ configuration file. It is run at the initialization of each run. Normally, it should not be change after commissioning – consult the run coordinator to make any changes.