Re: tof issues to add to tracker (fwd)

[Tim Whitlatch <whitey@jlab.org>]

Thanks Elton,

We will see how George's magnetic field study comes out.We will add this 
to our list of things to revisit.

Thanks,

       Tim

Elton Smith wrote:
> There have been several issues that came up in preparations for the review
> which we need to add to our action item tracker.
>
> * Updated magnetic fringe field in the vecinity of the scintillators.
> (George Biallas expects to have some results in the next month).
> * The design presented at the review included a soft iron shield 2.75 mm
> thick and a mu-metal 0.4 mm thick.
> - The total size of the pmt (5.35cm max)+ 2x0.275cm + 2x0.04cm = 5.98cm.
> - Nominal size of scintillator paddle is 6 cm, which implies this only fit
> if there are no gaps between pmt and shields.
> -> This is not a realistic design for the pmt housing, as the pmt (at HV)
> must be insulated from the housing (at ground). If we want to put the
> mu-metal shield at HV this is will require additional space.
>
> Options:
> 1. Elke has suggested that we might want to overlap the scintillators
> to avoid any inefficiencies and this would allow additional room
> for a realistic housing.
> 2. An alternative possibility would be to reconsider using fine-mesh pmts.
> This option would avoid the need for magnetic shielding and could fit into
> the current space. One would need to evaluate the cost trade-off between
> vacuum pmt + magnetic shielding compared to the single wire-mesh pmt. For
> this case, a realistic assessment of any inefficiencies due to tracks
> hitting between two scintillators would have to be made.
>
>
> 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
>   
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