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<div class="moz-cite-prefix">Dan,<br>
<br>
<blockquote type="cite">Is is reasonable to assume that the
maximum channel count rates which can be handled by the SIPMs
and the fixed-array PMTs are equal (~1.5 MHz?), or is there some
additional difference that needs to be considered before I
recalculate the counter sizes and positions without gaps?</blockquote>
<br>
We should keep several things in mind in this comparison:<br>
<ol>
<li>There are different factors that control the maximum rate
for PMT's and SiPM's so it is probably not reasonable to
equate them. For PMT's, the rate limit is the degradation of
the tube over time that depends on the anode current. For the
1" tube currently under consideration, this limit is around
50uA. For SiPM's the rate limit comes from the pixel count *
charge per pixel divided by the occupation of the pixels. For
the 3mm,50um pixel devices we are using, the numbers are
3600*(0.8e6 * 1.6e-19) / 15ns = 30mA for full occupation. So
if one considers a few percent occupation to be an upper
limit, the maximum current per SiPM should be ~ 1mA >>
50uA.<br>
</li>
<li>A variety of different beam intensities (phase I, phase II,
phase III, beyond phase III) are being bandied about. For
simplicity, I would like to ask that we all stick to a
"standard reference beam intensity" figure of 10^8 tags/s on
target, which corresponds to a 20micron diamond radiator at
2.2uA. This has always been our upper limit for the tagger
design, and we should design to meet performance requirements
at that rate. Of course, if we do then we will meet them at
lower rates as well. Assuming this, the 1.5MHz you mention
should be 4MHz, right?<br>
</li>
<li>The rate in the microscope fibers is not equally divided
between the 5 fibers in a single column (energy bin). If the
spectrometer optics are optimized, about 70% of the peak rate
of 4MHz per energy bin is in the middle fiber. This means
that at the peak we expect about 3MHz for the central SiPM at
the peak in the microscope, not 1.5MHz, at the standard
intensity of 10^8.</li>
</ol>
<p>If none of that changes what you mean, then I agree with you.
Photosensor lifetime aside, what really limits the rate is time
resolution and inefficiency due to dead time. For these, both
SiPM and PMT would be affected in the same way. I would say
4-5MHz per counter would be a good upper limit, from the
standpoint of time resolution and efficiency.</p>
<p>-Richard J.<br>
<br>
</p>
<blockquote type="cite">Franz and I have decided that a more
reasonable counter displacement is 8 cm (perpendicular) behind
the nominal focal plane. Any arguments?</blockquote>
<br>
The plot you showed at the meeting pretty much demonstrate that
this is ok. It is the same order as the distance between the
Pt-Pt and Para-Pt focal planes, and the straight-line
approximation we are currently using. This sounds good to me.<br>
<br>
-Richard J.<br>
<br>
<br>
<br>
On 9/19/2012 2:37 PM, Daniel Sober wrote:<br>
</div>
<blockquote cite="mid:505A10E0.80308@cua.edu" type="cite">
Richard,<br>
Thanks for the spectrum. It confirms that, as I had been
assuming, the differential rate dN/dk at 9 GeV is about half the
maximum value on the coherent peak, and that it falls as ~1/k
above that. Thus, near 9 GeV, a 4-mm-wide counter will have about
the same rate as a 2-mm column of fibers at the peak. If we
increase the counter width to 5 mm, the count rate will be about
25% higher. Is is reasonable to assume that the maximum channel
count rates which can be handled by the SIPMs and the fixed-array
PMTs are equal (~1.5 MHz?), or is there some additional difference
that needs to be considered before I recalculate the counter sizes
and positions without gaps?<br>
Franz and I have decided that a more reasonable counter
displacement is 8 cm (perpendicular) behind the nominal focal
plane. Any arguments?<br>
Dan<br>
<br>
<br>
<div class="moz-cite-prefix">On 9/19/2012 1:17 PM, Richard Jones
wrote:<br>
</div>
<blockquote cite="mid:5059FE12.40103@uconn.edu" type="cite">
<div class="moz-cite-prefix">Dan,<br>
<br>
Just cut and paste the text from the email into your browser.
Sorry for the confusion, the text itself should be correct.<br>
<br>
-Richard J.<br>
<br>
On 9/19/2012 11:31 AM, Daniel Sober wrote:<br>
</div>
<blockquote cite="mid:5059E534.6020107@cua.edu" type="cite">
Richard,<br>
All four links actually point to the same file, "...from9.gif"<br>
Please send a file that contains the coherent peak.<br>
Thanks,<br>
Dan<br>
<br>
<br>
<div class="moz-cite-prefix">On 9/18/2012 5:23 PM, Richard
Jones wrote:<br>
</div>
<blockquote cite="mid:5058E63A.9050407@uconn.edu" type="cite">
<div class="moz-cite-prefix">Dan,<br>
<br>
Right, here they are:<br>
<ul>
<li><a href="http://zeus.phys.uconn.edu/halld/cobrems/1e8ontarg_from9.gif">http://zeus.phys.uconn.edu/halld/cobrems/1e8ontarg_from9.gif</a></li>
<li><a href="http://zeus.phys.uconn.edu/halld/cobrems/1e8ontarg_from9.gif">http://zeus.phys.uconn.edu/halld/cobrems/1e8ontarg_from9.eps</a></li>
<li><a href="http://zeus.phys.uconn.edu/halld/cobrems/1e8ontarg_from9.gif">http://zeus.phys.uconn.edu/halld/cobrems/1e8ontarg_from3.gif</a></li>
<li><a href="http://zeus.phys.uconn.edu/halld/cobrems/1e8ontarg_from9.gif">http://zeus.phys.uconn.edu/halld/cobrems/1e8ontarg_from3.eps</a></li>
</ul>
<p>-Richard J.<br>
</p>
<br>
<br>
On 9/18/2012 4:14 PM, Daniel Sober wrote:<br>
</div>
<blockquote cite="mid:5058D623.7080709@cua.edu" type="cite">
Richard,<br>
Reminder: You said you would send a typical coherent
bremsstrahlung spectrum so I could check my rate
assumptions.<br>
Dan<br>
<div class="moz-signature">-- <br>
<i>Daniel Sober<br>
Professor<br>
Physics Department<br>
The Catholic University of America<br>
Washington, DC 20064<br>
Phone: (202) 319-5856, -5315<br>
E-mail: <a href="mailto:sober@cua.edu">sober@cua.edu</a></i><br>
</div>
</blockquote>
<br>
</blockquote>
<br>
<div class="moz-signature">-- <br>
<i>Daniel Sober<br>
Professor<br>
Physics Department<br>
The Catholic University of America<br>
Washington, DC 20064<br>
Phone: (202) 319-5856, -5315<br>
E-mail: <a href="mailto:sober@cua.edu">sober@cua.edu</a></i><br>
</div>
</blockquote>
<br>
</blockquote>
<br>
<div class="moz-signature">-- <br>
<i>Daniel Sober<br>
Professor<br>
Physics Department<br>
The Catholic University of America<br>
Washington, DC 20064<br>
Phone: (202) 319-5856, -5315<br>
E-mail: <a href="mailto:sober@cua.edu">sober@cua.edu</a></i><br>
</div>
</blockquote>
<br>
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