Re: CDC design (fwd)

[Gerard Visser <gvisser@indiana.edu>]

Indeed, I have one small comment -->

	- Gerard

Elton Smith wrote:
> Hi all,
> 
> I think this discussion should go to the listserver, both to inform a
> larger audience, as well as for archiving.
> 
> Cheers, Elton.
...
>>>> 4. How many channels need to be dead before a wire replacement
>>>> attempt is made?
>>> If one wire breaks and stays shorted to ground, 24 channels will be
>>> inoperative (minimum segmentation). Under the best of hypotheses,
>>> obviously other wires breaking within this same group won't impact
>>> the detector any further. So, it is important to select which wires
>>> are connected to one preamp card to get a minimal impact on tracking.
>>> Ultimately, the tracking efficiency and re-work logistics will
>>> dictate the maintenance period.

Well, if a wire breaks and stays shorted to ground, you can at some 
small access opportunity pull the HVB/preamp assembly, remove the one 
bias resistor, and reinstall, restoring the other 23 straws without 
opening the detector itself. Now, I may be overoptimistic in thinking 
how easy or often such an access will come... But, still, I believe we 
should be very careful before defining any "minimal failure impact" 
mapping of straws to HVB's, if the tradeoff is longer connecting wire 
lengths. Fernando, I think you share my concern about any more wire 
length than we can barely get away with. It raises the crosstalk and 
especially the EMI or feedback issues. Of course if there are choices 
like HVB orientation that affect the "failure impact" while leaving the 
connecting wire length minimized, that is great.