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GlueX electronics



In the spirit of Elton's email about the Start Counter, I'd like to 
summarize my recollections regarding electronics discussions at last 
week's collaboration meeting.  Some of these are taken from my notes on 
talks, and some are from personal discussions.  As the newly appointed 
"Electronics Coordinator" let me say I have no desire or intention to 
micromanage GlueX electronics R&D; my goal is make sure all relevant 
information is easily available to everyone working on this part of 
GlueX so that electronics built at different institutions will all work 
together.

Please be sure to let me know if you disagree with anything below, or 
if something should be added.

------------------
Central Tracking

3250 channels
amplifiers need gain of about 10**2 or 10**3
FADCs need 10 - 12 bits at 125 MSPS

-----------------

Forward Tracking

2856 anode channels  - F1 TDC in 120 pS mode.
5712 cathode channels - FADC; speed and resolution to be determined

-----------------

Forward Time of Flight

Current design has 140 channels; going to 2.5 meter length will 
increase this slightly.
PMTs are XP2020
Discriminators are probably "Constant Fraction" type; this will be 
settled soon.
May want hardware "Mean Timers".
May want HPTDCs instead of F1 TDCs.  JLab has some CAEN HPTDC modules 
being evaluated.

------------------

PID

Gas Cherenkov in CDR may be replace by DIRC; this is a large 
perturbation on total channel count; Stefan estimates 2340 PMTs.

------------------

Tagger

128 "fixed" counters, 64 "movable" counters; peak rate in a single 
counter is 10**6.

------------------

DAQ

Ed Jastrzembski will develop a next generation Trigger Supervisor which 
supports "blocked" event readout as well as an experiment-wide clock 
distribution system.  The distributed clock will be 62.5 MHz; crates 
will generate local clocks phase-locked to this distributed clock.

Ed, could you produce a short description of your thoughts on this 
clock distribution system?  Is it fiber optics?  I assume a global 
"reset" will be distributed as well?  The FADCs need this to 
synchronize all channels.  How about special triggers for calibration, 
etc?  Are the F1 TDCs capable of using this clock as a reference?

The current and near future work by the DAQ group assume a VME64X 
"form-factor", but other "form-factors" such as VXS, VXI, ATCA, cPCI, 
PXI, etc are not being ruled out for GlueX.

------------------

Trigger

We want the ability to use the Start Counter in the level 1 trigger.  
Other detectors such as the backward veto may also be part of the level 
1 trigger.  Dave Doughty will make the CNU student's thesis on trigger 
simulations available.  Dave is requesting NSF money to continue the 
level 1 energy sum prototype work, especially the high speed serial 
links.

---------------------

Start Counter

In level 1 trigger.
About 40 channels.
High field PMTs or SiPMs
Constant fraction discriminators.
Hardware "mean-timer"?

---------------------

 From my summary talk:

Fernando Barbosa will be working on a prototype FADC which could be 
used in the existing JLab experiments and would be suitable for the 
GlueX central and forward drift chambers.  Paul Smith will be working 
on a prototype FADC for the GlueX calorimeters which will include the 
energy sum needed for the level 1 trigger.  Paul and Fernando will 
communicate and try to keep the FADCs as similar as possible.  If it is 
possible to converge on one design for all GlueX FADCs (for example by 
stuffing different front end components) this will be done.

Here is my table of institutions responsible various electronics 
subsystems with names added.   Please let me know of any mistakes 
and/or additions:

Vertex tracking		deleted
Calorimeter FADCs	IU			Paul Smith
Tracking FADCs		JLab		Fernando Barbosa
TDCs				JLab		Fernando Barbosa
CF discriminators	Alberta		Jim Pinfold
Drift chamber amps	Alberta		Jim Pinfold
Level 1 Trigger		CNU			Dave Doughty
Clock distribution	JLab		Ed Jastrzembski
Power & grounding	JLab		Chris Cuevas
Tagger				CUA			Dan Sober
Goniometer			Glasgow		Jim Kellie
Active Collimator	UConn		Richard Jones
Track count			????
Calibration			????
Pipeline issues		????

Alex will continue to communicate with ORNL regarding their involvement 
in GlueX electronics.

I've asked Zisis to add an electronics forum to the GlueX portal.  My 
hope is that this will be the starting place for links to documents on 
GlueX electronics designs.  I will put this email there when the forum 
is available.  I encourage people to place minutes of any meetings 
where GlueX electronics are discussed there as well.  If this forum 
doesn't work out, we could consider a listserv for electronics 
discussions.

We should consider occasional electronics oriented conference calls.

Sometime after the detector review we should consider a GlueX 
electronics workshop.

Paul