at our meeting last week we decided that it is about time to freeze
some of the still unknown design parameters for the polarized NH3/ND3
target, so work can begin on the design of the "missing parts".
Specifically, we need to speficy:
1) The number and material of targets to be used (e.g., one NH3, one
ND3 and one dummy with either C, CO2 or N2)
2) The shape and size of the target cells and their placement on the stick.
3) The innards of the cryostat chamber which will contain the target cells.
Specifically, we need to discuss the shape and position of the microwave
trumpet, the depth and diameter of the chamber, the material and arrangement
of entrance and exit windows, etc. This will have a strong impact on the
accessible phase space for outgoing particles.
4) The beam entry channel (with windows)
5) The heat shield, especially where it can be seen by outgoing particles
and the beam.
6) The (large!) outer windows in the vaccuum chamber. Especially, we need
to discuss whether there will be different material/thickness for the beam
and the scattered particles, what the minimum and maximum theta angles
can and should be (and the overall angular coverage, also in sideways
direction), and whether we want to employ "spokes" on the window in the
coil shadows (? - note that the longitudinal field may wash out the definition
of what these are).
7) Related to the rest, where we want the target to be positioned relative
to the nominal unpolarized target point. There are good reasons to move it
back by maybe 1/2 meter to increase the coverage at low Q2.
I have arranged a meeting at JLab next Tuesday, 9/16, all afternoon. I will
give you a room number as soon as I have one. If you cannot attend but
would like to contribute to the discussion, please use our list to send
email to everyone (just send your mail to eg1_run@cebaf.gov). However,
please try to be very specific - we cannot any longer say things like
"it would be nice if the windows were as thin as possible". Try to make
estimates of what kind of window thickness would still be tolerable, and
back up your claims with (at least "back-of-the-envelope") calculations.
(Ideally a fullblown GSIM simulation should tell us what the impact of
our design decisions might be, but that's asking a lot, I know). I hope
to get at least a reference design out of this meeting, so we know what
to scrutinize for possible Physics show stoppers.
--
Hope to see you next week,
- Sebastian