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Re: CDC Gas Flow



Hi Curtis,

I also concur that's a great idea. It makes the flow through the straws 
less problematic due to any possible leakages around the connectors on 
the upstream end.

I support Slava's design and with some additional refinements it will 
work well. I emphasize that the design should minimize any operations 
that may cause future gas contamination and also minimize the length of 
the connections from the straws to the electronics. After talking to 
Slava, it became apparent to me that the cable/connector assemblies can 
be prepared prior to installation and the length can be made very short.

The issue of accessibility and maintenance is obviously very important. 
The FDC has a document on failure modes and their impact on operations. 
This could be a starting point for the CDC. But you may already have a 
plan that also addresses which straws connect to which connectors and 
based on tracking and tolerance to broken wires. In other words, we 
would like to know the normal maintenance intervals (once, twice a 
year?) and when there is an absolute need to fix the detector (how many 
inoperative channels?).

The other issue to consider is the cooling of the preamps. Forced 
convection may work but, given all the cables and hardware around the 
preamps, it may be hard to predict the efficiency of such a scheme. The 
preamp card temperature must not exceed 31 degree Celsius. I have 
measured and simulated its thermal operation for the FDC and I will 
simulate its operation under forced convection conditions. This will 
tell us the air flow and air temperature requirements.

I will modify the HVB to incorporate features that will allow 
disconnecting individual straws. In normal hall operation, a map would 
tell us which channels on a particular HVB would need to be off and a 
spare card would be prepared in advance of detector maintenance/access.

Regards,
Fernando



Curtis A. Meyer wrote:
> Hi Tim 
> Actually, I think we wanted to bring the gas through some support rods inside
> the chamber volume. We simply reverese the flow direction of what we are
> currently planning. Then we do not break trhough the down-stream plenum
> at all, and it is "easy" to seal.
>
>
>      curtis
> On Tue September 30 2008, Tim Whitlatch wrote:
>   
>> Sounds too simple!
>> We would bring 1/4" plastic tubing along the outside and bring it in 
>> through the downstream Mylar bag?
>>
>> Tim
>>
>> Curtis A. Meyer wrote:
>>     
>>> Hi Elke -
>>>
>>> My understanding of how we plan to do this is that we simply reverse the
>>> "in" and "out" gas line somewhere outside of the chamber. I don't think
>>> that anything else changes.
>>>
>>>   Curtis
>>>
>>> On Tue September 30 2008, Elke-Caroline Aschenauer wrote:
>>>   
>>>       
>>>> On Tue, 30 Sep 2008, Curtis A. Meyer wrote:
>>>>
>>>> Dear Curtis,
>>>>
>>>> that sounds like a very very nice idea. the only discussion point I could
>>>> see is do we increase any material in the detector by this. I would not
>>>> think so, but just to ask the obvious question.
>>>>
>>>> cheers elke
>>>>
>>>>
>>>>
>>>>     
>>>>         
>>>>> Date: Tue, 30 Sep 2008 12:52:57 -0400
>>>>> From: Curtis A. Meyer <cmeyer@ernest.phys.cmu.edu>
>>>>> To: GlueX Tracking <tracking@gluex.org>
>>>>> Cc: Gary Wilkin <wilkin@andrew.cmu.edu>
>>>>> Subject: CDC Gas Flow
>>>>>
>>>>> Hi Everyone -
>>>>>
>>>>>   after our connector discussion today, I got to thinking about
>>>>> the gas flow through the CDC, and leaks. For reasons which
>>>>> I do not believe we ever really justified, we always talked about
>>>>> flowing the gas in the upstream end of the chamber, and out
>>>>> the down stream end. This choice requires good seals around
>>>>> all the wire feed throughs.
>>>>>
>>>>>    I started wondering why we do not reverse the flow direction.
>>>>> The down stream plenum is extremely easy to gas tight (nothing
>>>>> comes through it), and if we take the gas out of the upstream
>>>>> plenum, a small leak there is probably  not a disaster.
>>>>>
>>>>>    We should follow up on this, in particular does anyone have
>>>>> a good reason why this can't work?
>>>>>
>>>>>   thanks - Curtis
>>>>> --
>>>>> Professor Curtis A. Meyer        Department of Physics
>>>>> Phone:  (412) 268-2745          Carnegie Mellon University
>>>>> Fax:    (412) 681-0648            Pittsburgh PA 15213-3890
>>>>> cmeyer@ernest.phys.cmu.edu  http://www.curtismeyer.com/
>>>>>
>>>>>       
>>>>>           
>>>>  ( `,_' )+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=
>>>>   )    `\                                                  -
>>>>  /    '. |                                                  +
>>>>  |       `,              Elke-Caroline Aschenauer            =
>>>>   \,_  `-/                                                    -
>>>>   ,&&&&&V         Jefferson Lab                                +
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>>>> ,&&&&&&&&&&;      Suite 8                 Hampton, VA 23664      -
>>>> |  |&&&&&&&;\     12000 Jefferson Ave                             +
>>>> |  |       :_) _  Newport News, VA 23606  Tel.:  001-757-224-1216  =
>>>> |  |       ;--' | Mail:  elke@jlab.org    Mobil: 001-757-256-5224   -
>>>> '--'   `-.--.   |                                                    +
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>>>>
>>>>     
>>>>         
>>>
>>>   
>>>       
>
>
>
>   
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