[Sane-analysis] Follow-up on tracking through the reversed target field

[James Maxwell]

> So a reversed field cannot be ruled out from looking at tracking. The
> target group should confirm that the vertical adjustments of the target
> movement did compensate for the ~ 3 mm upward shift from the surveyed
> center, and report on any indications of radiation damage that may have
> been observed on the upstream bottoms or downstream tops of any cups or
> lid rims. It would also help to know how such reversal might have
> happened (PS connections?, coils mounted backwards?...)

The PS connections were always consistent, but I'm not sure how we'd
know if the magnet was mounted backwards.  As far as position, we did
the fine tuning with the cross-hairs when the beam was on. That's the
only exact way to be sure where the target was; hysteresis in the
table makes it difficult to relate that to any other position
measurement.

As far as radiation damage in the cups, we have photos of each cup
load; which are difficult to use for firm conclusions.  I can say that
most indicate heavier radiation damage at the bottom of the cup, not
the top.  Damage is indicated by discoloration and the plastic
becoming brittle.  From Oscar's plots, we'd expect more damage on the
front (downstream) top and back (upstream) bottom of the cups if the
field was reversed.

In this example, the bottom rim of the cup snapped off when the lid
was removed, indicating significant radiation damage to the front
bottom side.  You can also see some discoloration which is not present
on the top side.
http://www.jlab.org/~sanetarget/sane%20pictures/target393.html

Here's another photo showing discoloration on the bottom side of the
target cups:
http://www.jlab.org/~sanetarget/sane%20pictures/target455.html

Here's the same set of cups, with both cups seeming to show heavier
damage on the bottom as well, which was why it was taken, presumably:
http://www.jlab.org/~sanetarget/sane%20pictures/target454.html

Feel free to go through the pictures of each load as it was removed here:
https://hallcweb.jlab.org/experiments/sane/wiki/index.php/Material_Pictures

If the beam were coming in at an angle like in Oscar's plots, you'd
also think we'd see something in the cross-hair plots.  Here's an
attempt to show what I mean:
http://twist.phys.virginia.edu/~jdm2z/sane/cross-hair.png

I haven't taken a close look at this, but here are a couple slow
raster plots from the 72700's super-imposed upon a picture of the
cross-hairs.  Neither of these show the cross-hairs shifted.
http://www.jlab.org/~sanetarget/sane%20pictures/target388.html
http://www.jlab.org/~sanetarget/sane%20pictures/target389.html

And all the pictures taken during the run here:
http://www.jlab.org/~sanetarget/sane%20pictures/

I'll keep thinking if there's any other indication of a field reversal.
Thanks,
James