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Hi All,<br>
I would like to address Elton's main concern the lifetime of the
PMTs.<br>
<br>
After 1000 hours of running at 0.1mA the gain reduces by about a
factor of 2.<br>
According to my calculations below the highest current PMT is
0.062mA so <br>
after about 1400 hours of running the gain would be reduced by about
a factor<br>
of 2. The HV is about 1600V for a pristine 10-stage PMT to get a
gain of 10^6.<br>
The maximum HV is 2000V for such a PMT with a gain of about 6*10^6.
So we<br>
have some headroom to adjust the PMT high voltage to retain a gain
of 10^6<br>
for some time, but at least twice such that we can run for about
3000 hours<br>
with sufficient gain. That is not perfect but would mean we can run
for at least<br>
one year. At the end of one year running (120days full running) one
would have<br>
to assess the situation and may consider to replace the 8 PMTs of
the innermost<br>
paddles left and right of the beam hole of the two planes. At that
point we would<br>
also have enough experience with the TOF to take educated decisions
on what<br>
we need as amplifications and operating parameters for the 8-stage
PMTs in<br>
the high luminosity running.<br>
I hope this makes sense to you too.<br>
<br>
cheers,<br>
Beni<br>
<br>
<br>
<br>
<br>
<blockquote cite="mid:4EE7B2DA.4010108@jlab.org" type="cite">
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Hi all,<br>
<br>
See my comments attached. Cheers, Elton.<br>
<pre class="moz-signature" cols="72">Elton Smith
Jefferson Lab MS 12H5
12000 Jefferson Ave
Suite #16
Newport News, VA 23606
(757) 269-7625
(757) 269-6331 fax </pre>
<br>
On 12/13/11 11:54 AM, Mark M. Ito wrote:
<blockquote cite="mid:4EE78333.2000300@jlab.org" type="cite">
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Folks,<br>
<br>
Yesterday Beni sent out an email summarizing thinking on the
choice of phototubes for the TOF (see below).<br>
<br>
Recall that there is a problem with PMT lifetime for the high
rate counters near the beamline, especially at 10^8 photons/s.
The choice of PMT's is central to how we deal with this problem.
<br>
<br>
Please have a look. He is asking for feedback so that we can
make a decision soon.<br>
<br>
-- Mark<br>
<br>
-------- Original Message --------
<table class="moz-email-headers-table" border="0"
cellpadding="0" cellspacing="0">
<tbody>
<tr>
<th align="RIGHT" nowrap="nowrap" valign="BASELINE">Subject:
</th>
<td>[Halld-pid] PMT choice for TOF</td>
</tr>
<tr>
<th align="RIGHT" nowrap="nowrap" valign="BASELINE">Date:
</th>
<td>Mon, 12 Dec 2011 12:01:22 -0500</td>
</tr>
<tr>
<th align="RIGHT" nowrap="nowrap" valign="BASELINE">From:
</th>
<td>Beni Zihlmann <a moz-do-not-send="true"
class="moz-txt-link-rfc2396E"
href="mailto:zihlmann@jlab.org"><zihlmann@jlab.org></a></td>
</tr>
<tr>
<th align="RIGHT" nowrap="nowrap" valign="BASELINE">To: </th>
<td><a moz-do-not-send="true"
class="moz-txt-link-abbreviated"
href="mailto:halld-pid@jlab.org">halld-pid@jlab.org</a>,
Elton Smith <a moz-do-not-send="true"
class="moz-txt-link-rfc2396E"
href="mailto:elton@jlab.org"><elton@jlab.org></a>,
"Fernando J. Barbosa" <a moz-do-not-send="true"
class="moz-txt-link-rfc2396E"
href="mailto:barbosa@jlab.org"><barbosa@jlab.org></a></td>
</tr>
</tbody>
</table>
<br>
<br>
<pre>Dear colleagues,
In order to make a final decision on the choice and strategy with regard to
the PMTs for the TOF I put together a few facts and findings and ask for
your
opinion.
Please read the attached outline set in 4 main paragraphs:
Purpose, Facts, Calculations and Strategies
I am advocating strategy a) where we go with a two phase approach.
Let me know what you think and what makes the most sense. Depending
on your answers we will either take a decision right away or I will call
for a meeting at end of this week (beginning next) so that we can take a
decision on this matter before Christmas.
thanks everybody,
Beni
</pre>
<br>
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