Online Design Goals

Overview

Below I list the overall performance requirements and design goals of Hall D DAQ/Online/Control systems. All groups working on the project, e.g. JLab DAQ group, JLab Electronics group, etc, must design to meet them.

The JLab DAQ group will develop a similar document, then the two will be reconciled and dates, performance milestones, etc. will be added. We will repeat this with other JLab groups as needed.

Basic Requirements

At turn-on Hall D will accept 10**7 photons/sec, with an expected trigger rate (from the design report) of 18 kHz, assuming a L1 rejection rate of 50%. At high luminosity the beam rate will be ten times higher, or 10**8 photons/sec, giving an expected trigger rate of 180 kHz assuming the same L1 rejection rate. If the events average 5 kByte then the data rate off the detector at low luminosity will be 90 MByte/sec, and 900 MByte/sec at high luminosity. At low luminosity there will be no L3 rejection, and all events will be written to disk (at 90 MByte/sec). At high luminosity we expect a L3 rejection rate of a factor of 10, so the rate to disk will also be 90 MByte/sec.

The DAQ design must have a little headroom above the expected rates. Thus I propose the following design goals: