Our goal is to have a physics threshold of 5 MeV in our solar neutrino energy spectrum measurement. To reach this, we must be able to trigger at or above 200 Hz. The ID is capable of this. The OD is not.
There is still an uncertainty as to what the trigger rate must be in order to achieve the 5 MeV threshold. Studies are underway to determine this and the immediate goal is to trigger at 200 Hz.
The OD is capable of 75 Hz rates at this time. With the present logic, the limitation is in the VME bus loading. We have modified some hardware and when this is implemented, the maximum rate will be doubled to 150 Hz. [Please see discussion of BIP trigger below.] At this moment, we DO NOT have code that is capable of doing this.
The OD cannot robustly handle split triggers at this time. The December trial of the split trigger code found an unacceptable mismatch rate of about 0.001 between the Struck latch event number and the tdc event number. We don't know the cause of the mismatch at this time but it is larger than the mismatch rate of E-5 measured for synchronous triggers.
We have hypothesese on why the mismatch occurs and are studying them. One weakness is tha the Struck Latch ONLY latches the t0 trigger in a burst of events within the 16 microsecond TDC pipeline. It is INCAPABLE OF TAGGING EACH event in the pipeline. This was OK as long as the events were consecutively numbered. However, split trigger means that the pipelined events are likely to be separated by many events. We are tagging each event in the pipeline by using the 4 lower bits of the event number which are latched in the TDC. This should be enough to uniquely identify the events. [Please note that there is a veto of 800 ns between TRGs. This means that the maximum number of triggers that can occur in the 6 micro sec after the t0 is 6000/800 = 7.5. The 10 microsec before t0 is governed by a veto which only occasionally allows events to leak in.]
The Struck latch has yet other limitations. In order for the Struck latch to record the first event in the pipeline and also not be confused by bursts of triggers, the input is governed by a logic veto in the central hut which is an extra logical unit with its own crevices where events within a burst may sneak in. Intrinsic to the Struck latch we know that the buffering structure and busy signals are VERY different from the TDCs. In low regular rates, the synchronicity of the Struck Latch and TDCs is very good. At higher instantaneous rates, we have noticed anamolous events occuring at measureable levels. At the expected higher rates, this may be worse. We have not implemented the Struck latch bip into our vetos. This may be important in the future. [To implement the struck latch bip, we must make modifications to the FB bip logic board.]
Since the V533's, when used alone with a fast cpu, can record data in excess of 1 KHz, the obvious way to reach higher rates is to have a separate VME crate and CPU for the V533. The data from the dedicated CPU can be socketed to SUKANT for integration. At 1 KHz of triggers, the required data rate is 288 Kb/sec which is well within the ethernet capability.
If we want the OD daq to be able to robustly record above 150 Hz, we should produce a dedicated cpu/crate to readout the V533's.
With the upgrade using 16 bits to record the event number in the TDC and the dedicated cpu/crate, we will be capable of handling 1 KHz rates in the ODDAQ and also of handling the SPLIT TRIGGER to meet the situations that are likely to arise in SK.
Ken Young Tel: 206 543 4186 Dept of Physics Box 351560 FAX: 206 685 9242 University of Washington Email: young@phys.washington.edu Seattle, WA 98195-1560 http://www.phys.washington.edu/~young/