tof issues to add to tracker

[Elton Smith <elton@jlab.org>]

Hall D PID Mail List:


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