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Dear colleagues,<br>
<br>
This is a reminder of the regular biweekly gluex photon beam working
group meeting on Monday at 11:00 EST. Top on the agenda is a
discussion of the latest results from Sasha. The following questions
stand out to me in looking at the latest figures.<br>
<ol>
<li>What happens when, as we agreed last week, the microscope is
moved onto the focal plane and the fixed array and exit window are
moved inward be the same amount? This should improve the resolution in
the microscope a little, and at the same time reduce the size (and
hence cost) of the vacuum chamber.</li>
<li>So far we have only considered the focus in the dispersion (xz)
plane. Where is the focal surface in the y direction? As I remember,
the focal surface in the xz plane is mainly due to the dipole field and
weakly depends on the quadrupole. However this is not true for the
y-focus, which comes about entirely from the quadrupole field. Without
the quad, the y-focal length is negative. Dan Sober once showed using
TRANSPORT that the y-focal surface is not parallel to the x-focal
plane, so the two can be made to cross anywhere in energy simply by
dialing the strength of the quadrupole field. In Geant we can do this
by placing an imaginary cut in the field map upstream of the dipole and
rescaling the field there by some factor of order 1 such that the two
focal planes cross in the region of the microscope. Now that we have
changed the dipole optics, we need to repeat this exercise to optimize
the y-resolution. The latest figures from Sasha show that with the
reduced pole width, the y-focus is no longer optimal.</li>
</ol>
Richard Jones<br>
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