last update: 050131

TRIGGER connections to RHIC

The trigger maintains two-way communication with RHIC through the RHIC rack in the DAQ room.

Information from RHIC to TRIGGER:

The signals we take from RHIC arrive through 2 V124 units in the DAQ room:
  1. the RHIC Strobe (RS) or RHIC clock signal, a 9.38 MHz signal generated from the 28 MHz RF signal of the accelerator. This is channel 7 on hte "yellow beam" V124.
  2. the Blue Ring Bunch full signal (BRB) (channel 8 blue V124)
  3. the Yellow Ring Bunch full signal (YRB) (channel 8 yellow V124)
  4. 4 spin bits
  5. fill patterns

The RS signal acts as the STAR Trigger heartbeat. We use the coincidence of the BRB and YRB in the trigger to eliminate beam-gas interactions. These signals come to STAR via two V124 VME units in the RHIC rack. Each V124 unit has 8 channels. We control the programming of the V124 units via the PET (Parameter Editing Tool) provided on the RHIC workstation in the control room. Channel 1 in each V124 is reserved for a copy of the RS signal, so it is programmed to output every 3rd click of the RF strobe. Note that each ring contains 360 buckets but that at most 120 are filled. It is this 1/3 filling factor that set the RS to be 1/3 of the RF strobe.

The MCR will tell us which of the Yellow and Blue buckets are full and we will then transfer this information to the second channel of the V124 units to give us the BRB and YRB signals.

NOTE: One of the tricky aspects of trigger setup is synchronizing the RS with our CDB ADC gates and synchronizing the BRB and YRB signals for the correct crossing. This is done via computer settable delays in the V124 units.

Information from TRIGGER to RHIC:

We also send information to the RHIC MCR to help them tune the beams at STAR. The ZDC sum signal is put thgough a discriminator on the platform and the logic levels are sent to the DAQ room. These discrimintaors are sent to RHIC along with their coincidence which is made in the DAQ room. We have also routed many signals from the last DSM board into the DAQ room and can patch these over to the MCR. For details, see RHIC scaler setup.