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 developed. We will repeat this with other JLab groups as needed.

Basic Requirements from Hall D Design Report

At turn-on Hall D will accept 10**7 photons/sec, with an expected trigger rate 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.

Design Goals

The DAQ design must include some headroom above the expected rates. Further, the initial design must meet the requirements of high luminosity with the exception of the L3 farm, which at turn-on will be a small prototype, used for monitoring only. Note that at high luminosity events will be written from the L3 farm to disk, while at low luminosity they will be written from an earlier stage.

Thus I propose the following design goals for the Hall D DAQ (numbers in parenthesis are for low luminosity):

• Physics trigger rate - 400 kHz (40 kHz)
• L1 rejection rate - 50% (50%)
• Accepted trigger rate - 200 kHz (20 kHz)
• Typical event size - 5 kByte (5 kByte)
• Data rate off detector - 1 GByte/sec (100 MByte/sec)
• Rate to L3 farm - 1 GByte/sec (20 MByte/sec at turn-on to prototype farm for monitoring)
• L3 rejection - factor of 10 (no rejection)
• Rate to local raid disk - 100 MByte/sec from L3 farm (100 MByte/sec from earlier stage)
• Rate to silo - 100 MByte/sec (100 MByte/sec)

Note that all other online and controls systems have no specific rate requirements.

Timelines

First beam to the hall is expected in ????, with production data taking expected to start in ????. Prototype DAQ systems for individual detector testing must be available by ????. The full DAQ must be ready for testing the complete detector with cosmic or pulser triggers by ????.