[Halld-tracking-hw] CDC feedthrus and end plate

[Fernando J. Barbosa]

Hi Gerard and Tim,

    I am in agreement with Gerard. I have always made the point that the 
shorter the connection (any) the better and distributed throughout the 
end-plate. Slava has also made the point that a direct connection (say, 
a stud through the gas plenum) would be impossible due to the density of 
the straws and the location of the preamp card connectors.
    Ground wire (16 AWG w/FEP insulation?) connections in a regular 
pattern will work better than the peripheral connection attachment. Of 
course, the quantity of these connections will need to be determined but 
I agree that we should make provisions for as many as possible even if 
not used in the final configuration. I have not looked at the latest 
drawings in detail but I requested a large number of blind taped holes 
throughout the endplate when we were considering different alternatives 
to the straw connections in the past - maybe these were dropped along 
the way.
    The grounded disk is supposed to be copper and there are no major 
constraints on the thickness, other than cost. But this is already an 
expensive disk due to all the machining that will be required.
    Therefore, if there are no mechanical strength issues on the 
endplate, let's add the taped holes throughout the endplate and make the 
connections as Gerard suggests.

Best regards,
Fernando

Gerard Visser wrote:
> Hi Tim,
>     Yes, I know. This (152 direct lines) is what I had in mind. Maybe 
> it is too much to ask for. Your question whether we can live without 
> it is a good one, wish that I (or Fernando) knew the answer 100% for 
> sure. *Perhaps* the answer is yes. If I had to guess, I'd say better 
> than even odds.
>     One the other hand if you could for instance add the 152 features 
> (4-40 blind taped hole? or a blind hole to fit a Mill-Max press-fit 
> pin socket? or something like this?) to the endplate, then if the 
> eventual answer turns out to be no, it does not mean the finished, and 
> I imagine rather expensive, endplate is unusable.
>     It was the absence of any such features as far as I could 
> understand in your drawing, that stimulated this discussion.
>     If it is simply impossible to have 152, or even 152/2 or 152/3 or 
> 152/4 by some sharing scheme, then we must risk doing without it. If 
> it is possible, my opinion is the features should be added, they can 
> always be left unused if it turns out that we don't need them, i.e., 
> if grounds around the outside will not suffice.
>     By the way, the boards will (I really hope) be sitting on a ground 
> plane, e.g., the upstream plenum is a sheet of thin aluminum, right? 
> Because I can pretty much guarantee you that 152 preamp boards with 
> each a skinny 40 cm ground wire between the preamp and the endplate, 
> this will not work. If the connection is through a common sheet of 
> (preferably plated) aluminum, it stands a good chance but I would 
> still be nervous that the direct (152 5cm lines) plan might prove to 
> be necessary.
>     Well, I think we should consider this more and you'll have to tell 
> what you can really do. But the shorter, wider, more distributed the 
> ground connections are, the lower the risk and potentially the better 
> the performance. We must not forget this :)
>     Sincerely,
>
>         Gerard
>
> p.s. Seems this email thread should maybe pop back onto the list to 
> involve more discussion, so I did that.
>
> Tim Whitlatch wrote:
>> Hi Gerard,
>>
>> 5cm (which is really more like 10cm for the longest wires) is not 
>> feasible unless you have 152 direct lines (1 for each preamp card) 
>> through the gas plenum. Will 40cm long ground wires cause problems?
>>
>> Tim
>>
>> Gerard Visser wrote:
>>> Hi Tim,
>>>     I admit, I have not been following all the details... But, I 
>>> seem to sense a contradiction here. What do you mean by "direct"? 
>>> Going outside the gas volume is indirect (isn't it?). Direct (what I 
>>> would like to see) means also ~5cm for the ground connection as you 
>>> have achieved for the signal wire connection. Is *that* feasible?
>>>
>>>     - Gerard
>>>
>>> Tim Whitlatch wrote:
>>>> We can still make direct ground connections to the endplate outside 
>>>> of the gas volume.Is it important to be inside the gas volume?
>>>>
>>>> Tim
>>>>
>>>> Fernando J. Barbosa wrote:
>>>>> Hi Gerard,
>>>>>
>>>>> Yes, this is a subject that makes me a bit nervous also. I am told 
>>>>> this is all we can have due to the area occupied on the endplate, 
>>>>> because of gas sealing and straw connections. I would have 
>>>>> preferred to have direct connections to the endplate.
>>>>>
>>>>> Best regards,
>>>>> Fernando
>>
>>
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