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Dear Larry, <br>
<br>
The other position we discussed for the calorimeter was downstream of
CLAS. That would allow much more flexibility in repeated changes, but
it should be checked whether the free aperture is enough for the
collimated beams to be transported that far without hitting anything.<br>
<br>
Thanks, <br>
<br>
- Will<br>
<br>
<br>
<br>
Larry Weinstein wrote:
<blockquote cite="mid:4B731727.2030009@odu.edu" type="cite">Dear
TPE-ers,<br>
<br>
We have several beam monitors available for TPE:<br>
<ol>
<li>two quartz crystal background monitors located in the chicane
just before the PS magnet. They will give real time monitoring of
shifts in the relative intensity of the left and right beams.</li>
<li>fiber monitor plus calorimeter. The FM will be directly in
front
of the calorimeter to provide much improved position resolution. The
combination will be placed in the beam during chicane tuning to measure
the energy vs position spreads of the e+ and e- beams separately. (We
will block the individual beams to measure the other beam by itself.)
This will be done once or twice during the measurement. There are two
possible locations for the detector:</li>
<ol>
<li>upstream of the steel shield (as shown on the current
drawings). This might not give enough lever arm to measure the beams.<br>
</li>
<li>at the target (as advocated by certain people). This would
give a much better measure of the beam position vs energy at the
target, but would have a huge overhead (2 days?) for insertion and
removal.</li>
</ol>
<li>reaction vertex measurement by CLAS. This will not be a real
time measurement, but I hope we can organize near-online data analysis
to give us this information a few hours later.</li>
<li>a possible sparse-fiber monitor (1 mm fibers every 5 mm)
located
at the downstream collimator (where it was during the test run)</li>
</ol>
Open questions:<br>
<ol>
<li>where should we locate the calorimeter?</li>
<li>do we need the sparse-fiber monitor?<br>
</li>
</ol>
1. We are simulating the beam profile at the two possible locations.
We will also discuss this with Dave Kashy to see if it is even possible
to place it at the target.<br>
2. I am not sure what we will learn from the sparse-fiber monitor. It
will give us relatively poor beam centroid information and very poor
beam width information. If the italian dipole fields drift, then the
beam centroid will not change, but the width will increase slightly. I
am not sure what could change that would give a significant change in
the sparse fiber monitor. At present, I am inclined to leave it out.<br>
<br>
<br>
<pre class="moz-signature" cols="72">--
Sincerely,
Larry
-----------------------------------------------------------
Lawrence Weinstein
University Professor
Physics Department
Old Dominion University
Norfolk, VA 23529
757 683 5803
757 683 5809 (fax)
<a moz-do-not-send="true" href="mailto:weinstein@odu.edu">weinstein@odu.edu</a>
<a moz-do-not-send="true" href="http://www.physics.odu.edu/%7Eweinstei">http://www.physics.odu.edu/~weinstei</a>
</pre>
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