Re: CDC design (fwd)

[Elton Smith <elton@jlab.org>]

Hi all,

I think this discussion should go to the listserver, both to inform a
larger audience, as well as for archiving.

Cheers, Elton.

Elton Smith
Jefferson Lab MS 12H5
12000 Jefferson Ave
Suite # 16
Newport News, VA 23606
elton@jlab.org
(757) 269-7625
(757) 269-6331 fax

---------- Forwarded message ----------
Date: Wed, 24 Sep 2008 15:50:13 -0400
From: Fernando J. Barbosa <barbosa@jlab.org>
To: Tim Whitlatch <whitey@jlab.org>
Cc: Curtis Meyer <cmeyer@ernest.phys.cmu.edu>,
     Yves VanHaarlem <yvhaarle@ernest.phys.cmu.edu>,
     Vladislav Razmyslovich <vgr@jlab.org>,
     Elke-Caroline Aschenauer <elke@jlab.org>, Elton Smith <elton@jlab.org>
Subject: Re: CDC design

Hi Tim,

Tim Whitlatch wrote:
> Hi Fernando,
>
> The 4" is based on?
Capacitance.
>
> Also, is there really cross talk on HV wires?
Yes, these wires connecting to the straws feed the HV to the straw and
carry the signal to the preamp via capacitive decoupling. There is
always capacitive and inductive coupling between conductors. Crosstalk
occurs as a result of the strength of these couplings. Moving the
conductors apart and increasing shielding are two ways to decrease
crosstalk for a given frequency spectrum.
>
> Also, I need an education on what a "tiled" PCB is.
Because the size of the end-plate is larger than any PCB that can be
fabricated, a set of PCBs would be used to cover the area - so the name
tiles. Now, these PCBs may have non-regular or non-repetitive shapes
depending on the segmentation of the straws.

Regards,
Fernando
>
> Thanks,
>
> Tim
>
> Fernando J. Barbosa wrote:
>> Hi Tim,
>>
>> My responses, where applicable, follow:
>>
>> Tim Whitlatch wrote:
>>> Hi everyone,
>>>
>>> Before we can make sound decisions on the upstream end design of the
>>> CDC, I believe the following questions must be answered;
>>>
>>> 1.What is the maximum length allowed for the HV wire between the
>>> crimp pin and connector?
>> 4 inches.
>>> 2. What is the allowable gas leak in the chamber?
>>> 3. What are the maintenance requirements? Is it a requirement to be
>>> able to replace W wires individually (without taking apart the
>>> entire upstream end)?
>> No.
>>> 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.
>>> 5. Is a faraday cage required?
>> Yes.
>>>
>>> It should be kept in mind that what ever design is incorporated into
>>> the current prototype should reflect what we plan on using for the
>>> production model. It should be verifiable in the prototype as to
>>> whether or not the design will work.
>> I am in complete agreement.
>>>
>>> The prototype should apply a design based on these answers or answer
>>> the questions.
>> In principle, yes. However, this design is not a unique solution.
>>>
>>> Thoughts....?
>> Let me again suggest that a tiled PCB design is a viable option -
>> that's what I suggested at a meeting a few months ago. It may be
>> slightly more expensive in parts but much less in labor and even much
>> less in maintenance.
>>
>> Regards,
>> Fernando
>>
>>
>>>
>>> Cheers,
>>>
>>>       Tim
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