[Halld-pid-upgrade] Cluster Counting and DAQ

[Lubomir Pentchev]

Hi Matt,

That was exactly the question Beni was asking when he started working on 
the DAQ for the cluster counting. Then he got it working right away 
without changing the timing of the trigger, as it was for the standard FDC 
readout. This means we were reading data from the fADCs that arrives up 
to 20 microseconds after the trigger. Beni can give you details about how and 
why does it work.

Of course this is a simplified DAQ and there will be other limitations 
for the full GlueX DAQ. Naively I would think that if the maximal trigger 
rate  is 20kHz (as I remember this is the official number) the readout rate 
should be the same, i.e. 50 microseconds per event which is 5 times more 
than the cluster counting time window. In any case I agree such a readout 
would be different from the rest of the detectors and we need to talk to 
the experts.

Lubomir





On Sat, 21 Sep 2013, Matthew Shepherd wrote:

>
> Hi Lubomir,
>
>  After thinking about it more, I don't think I phrased my question in 
the clearest way regarding the DAQ and cluster counting.
>
>  You showed that you need to count ionization clusters that arrive over 
a period of something 10 - 12 microseconds after the primary track.
>
>  I think our trigger typically arrives 2-3 microseconds after the event. 
For  all subsystems this means they must look back into their buffer some 
fixed  time and readout the event.  (In many subsystems the trigger can't 
arrive much later or else the data is lost.)
>
> For  the cluster counting scheme this means that you need retrieve data 
from  2-3 microseconds before the trigger and up to 10 microseconds after 
the  trigger.  I don't understand the intricacies of the electronics or 
trigger,  but does the fact that you won't have completely recorded an 
event  until almost 10 microseconds after the trigger is sent to the 
crates  cause a problem?  (Presumably in that 10 microseconds there is a 
decent probability that another trigger will arrive as well.)
>
> Maybe  there is not a problem, but this seems to be a readout scheme 
that is somehow fundamentally different from other subsystems.
>
> Matt
>
> ---------------------------------------------------------------------
> Matthew Shepherd, Associate Professor
> Department of Physics, Indiana University, Swain West 265
> 727 East Third Street, Bloomington, IN 47405
>
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