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Dear all, <br>
<br>
I think this might be even better than simply repeating the previous
calibration. There could be changes since the previous calibration was
performed, and the results of this procedure could be cross-compared
with what was obtained before. <br>
<br>
I believe the measurement will take longer than an hour or two to
perform. The magnet setting procedure, I think, includes a hysteresis
compensation that requires some time. If the plan is to hit the beam
onto 300+ detectors, and you take a minute per detector, that gives
300+ minutes. Also, has anyone thought about the optics? If the beam is
converging or diverging, it will have a different spot size at one end
of the array than the other. <br>
<br>
It also might be good to think about what peak rate the detectors can
handle, and whether that's compatible with what the accelerator can
deliver and monitor. In some sense, all you need to know is which
detector was hit, and if the response is not linear, it is still ok. On
the other hand, you probably don't want the signal size to be orders of
magntitude beyond the normal. And yet if the beam current is too small,
it will be hard for the accelerator to monitor its position; if its
position drifts around, it can spoil the measurement. <br>
<br>
In any case, if there are no show-stoppers, it has the very attractive
feature that it is an independent procedure from the previous one, so
it can help to understand the tagger calibration even better.<br>
<br>
Thanks, <br>
<br>
- Will<br>
<br>
<br>
<br>
On 7/2/10 12:54 PM, Larry Weinstein wrote:
<blockquote cite="mid:4C2E19AF.4060308@odu.edu" type="cite">Dear Folks,<br>
<br>
One possibility suggested by Dave Kashy (with modifications from Stepan
and Eugene) is to use the primary electron beam to calibrate the
tagger. <br>
<ol>
<li>Put a 300 MeV pulsed low-current electron through the tagger
magnet <br>
</li>
<li>Sweep the magnet field slowly. <br>
</li>
<li>Read out the tagger detector scalers and the tagger magnet
current in epics. <br>
</li>
<li>Correlate the magnet current with the location of each of the
tagger detectors.</li>
</ol>
After the TPE run, when we have replaced the detectors, repeat the
procedure to determine the precise locations of the detectors. <br>
<br>
According to Arne, it would take about 12 hours to configure the
machine in this way. It would take an hour or two to do the
measurement, so the total time required would be less than one day of
exclusive beam (ie: no other expt can run during this time). <br>
<br>
If Qweak is willing to let us do this, we can do this before the summer
shutdown. Alternatively, if Primex runs before TPE, we could do this
at the end of the Primex run. It would be better do this before the
summer shutdown to allow us the flexibility of removing low energy
tagger counters during the summer shutdown (assuming that Primex won't
use them).<br>
<br>
Note that this assumes that TPE will run this fall.<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 3038 (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.lions.odu.edu/%7Elweinste/">http://www.lions.odu.edu/~lweinste/</a></pre>
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