Re: Hodoscope location

[Franz Klein <fklein@jlab.org>]

Tim,
Richard's idea will be included in my drawing: James sent me the stp file 
for the magnet support structure, I wanted the hodoscope support be 
positioned on rails ... but that is, of course, open for discussion!

Coming back to the seaparation distance of vacuum window and fixed 
counters: it really depends on the frame (and bolts) around the window 
whether there will be enough space to add the shutter (I'd like to see 
more like 1 1/2"). When small maintenance jobs (e.g. PMT fixes) have to be 
done, I'd like to keep the hodoscope in place; the hodoscope structure 
should only be moved when major changes (scintillator/light guides) are 
necessary. It will require a survey when the hdoscope is moved back into 
the nominal position.

Greetings

Franz

On Fri, 6 Feb 2009, Tim Whitlatch wrote:

> Hi Franz,
>
> The thickness of the frame around the window will drive how many bolts are 
> needed to seat and seal the o-ring properly. We will come up with a 
> reasonable thickness based on this. Richards idea ov pivoting the hodoscope 
> away from the window during maintenance deserves some thought.
>
> Cheers,
>
>      tim
>
> Franz Klein wrote:
>> 
>> Tim and Richard,
>> 
>> last Friday James showed me the design drawing. My initial worry that we 
>> won't have more clearance but 2.8cm (for largest scintillator) was based on 
>> the pdf file James sent around on 1/22. However, the vacuum chamber drawing 
>> is largely conceptual: the flange for the long window is 1" thick and not 
>> detailed. It is more realistic to assume a 1/4" plate as flange, which 
>> gives enough space for a cover plate (which will be suspended from above 
>> and fall into a grooved beam).
>> 
>> Greetings
>> 
>> Franz
>> 
>> On Wed, 4 Feb 2009, Tim Whitlatch wrote:
>> 
>>> Thanks Richard.
>>> 
>>> Yes we are talking about shrinking the vacuum chamber. Right now we have 
>>> about 3cm. We can make due with this but do not have an easy way for 
>>> vacuum sealed plate. I do not think this is required, but hearing 
>>> protection would be required to work in the area at all times.
>>> 
>>> Tim
>>> 
>>> Richard Jones wrote:
>>>> Tim,
>>>> 
>>>> If you mean 20cm of open space normal to the window, I don't think we 
>>>> want that much distance between the window and the detectors.  At a 
>>>> crossing angle of 10 degrees, that would mean more than 1m of electron 
>>>> trajectory after the window.  Of course, we are talking about shrinking 
>>>> the vacuum chamber by 20cm, not moving the focal plane by 20cm, right? 
>>>> Yang can tell you that moving the focal plane is a much bigger job!  You 
>>>> could gain that space by shrinking the vacuum chamber, but it would 
>>>> affect our resolution. We could simulate it, but I am pretty sure that 
>>>> the effect would be significant degradation in the resolution.
>>>> 
>>>> Richard Jones
>>>> 
>>>> 
>>>> 
>>>> Tim Whitlatch wrote:
>>>>> Hi all,
>>>>> 
>>>>> How critical is the spacing  (air gap) between the hodoscope 
>>>>> scintillators and the vacuum window? Is 20 cm ok to allow a mechanism 
>>>>> for a window cover during maintenance? If not, we will have to slide the 
>>>>> protective plate over the window.
>>>>> 
>>>>> Thanks,
>>>>> 
>>>>>
>>>>>    Tim
>>>> 
>>> 
>> 
>> ===============================================================
>>                   Franz J. Klein, Associate Professor
>>                   CUA, Department of Physics
>>                   Washington, DC 20064
>>   office: Hannan Hall 206          phone: 202-319-6190
>>   or: Jefferson Lab,CC F-243       phone: 757-269-6671
>> ---------------------------------------------------------------
>> ------------------------------------------------------------------------
>> 
>> begin:vcard
>> fn:Timothy Whitlatch, PE
>> n:Whitlatch;Timothy
>> tel;work:757-269-5087
>> tel;fax:757-269-5279
>> version:2.1
>> end:vcard
>>
>>

===============================================================
                   Franz J. Klein, Associate Professor
                   CUA, Department of Physics
                   Washington, DC 20064
   office: Hannan Hall 206          phone: 202-319-6190
   or: Jefferson Lab,CC F-243       phone: 757-269-6671
---------------------------------------------------------------
begin:vcard
fn:Timothy Whitlatch, PE
n:Whitlatch;Timothy
tel;work:757-269-5087
tel;fax:757-269-5279
version:2.1
end:vcard