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</style><article id="node-701521" class="node node-logentry contextual-links-region article ia-n clearfix" role="article"><header class="node-header"><h1 class="node-title">
<a href="https://logbooks.jlab.org/entry/3628625" rel="bookmark">FCAL LED pulser</a>
</h1>
</header><div class="contextual-links-wrapper"><ul class="contextual-links"><li><a href="https://logbooks.jlab.org/entry/3628625/edit?destination=email/send">Edit</a></li><li><a href="https://logbooks.jlab.org/entry/3628625/delete?destination=email/send">Delete</a></li></ul></div>
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<p class="author-datetime">
Lognumber <a href="https://logbooks.jlab.org/entry/3628625" class="lognumber" data-lognumber="3628625">3628625</a>. Submitted by <a href="https://logbooks.jlab.org/user/somov">somov</a> on <time datetime="2018-11-19T17:44:46-0500" pubdate="pubdate"><a href="https://logbooks.jlab.org/entries?start_date=1542663886&end_date=1542671086&book=HDFCAL&book=HDLOG&book=HDTRIGGER">Mon, 11/19/2018 - 17:44</a></time>. </p>
<p class="last-update">
Last updated on <time datetime="2018-11-19T17:45:28-0500" pubdate="pubdate">Mon, 11/19/2018 - 17:45</time></p>
<div class="comments-box">
<div class="ctools-collapsible-container"><div class="ctools-collapsible-handle"><a href="#">There are 4 comments...</a></div><div class="ctools-collapsible-content"><a id="comment-18684"></a>
<article class="comment comment-new comment-by-node-author odd first clearfix"><header class="comment-header"><h3 class="comment-title">
<a href="https://logbooks.jlab.org/comment/18684#comment-18684" rel="bookmark">Ok, these plots are more</a> </h3>
<em class="new">new</em>
</header><footer class="submitted"><p class="author-datetime">by <a href="https://logbooks.jlab.org/user/somov" title="View user profile." class="username">somov</a> on <time datetime="2018-11-19T20:40:19-0500" pubdate="pubdate">Mon, 11/19/2018 - 20:40</time></p>
</footer><div class="comment-content">
<div class="field field-name-comment-body field-type-text-long field-label-hidden view-mode-elog_email"><div class="field-items"><div class="field-item even"><p>Ok, these plots are more consistent with that, which Iliya presented during the meeting on Friday<br />
(in the sense that pi0s can at least be seen now). As I said, LEDs cannot be used for the calibration. </p>
<p>You mentioned that HVs for the inner part of the FCAL had been equalized based on LEDs on 10/25.<br />
FCAL channels with the large LED spread don't match completely with channels where the pi0 peak<br />
is shifted, I am confused. Anyway, we have calibration from Iliya, we start from there.</p>
</div></div></div> </div>
</article><a id="comment-18678"></a>
<article class="comment comment-new even clearfix"><header class="comment-header"><h3 class="comment-title">
<a href="https://logbooks.jlab.org/comment/18678#comment-18678" rel="bookmark">I would be very cautious</a> </h3>
<em class="new">new</em>
</header><footer class="submitted"><p class="author-datetime">by <a href="https://logbooks.jlab.org/user/shepherd" title="View user profile." class="username">shepherd</a> on <time datetime="2018-11-19T19:45:28-0500" pubdate="pubdate">Mon, 11/19/2018 - 19:45</time></p>
</footer><table class="field-vitals"><tr><th>Attached Files: </th><td><div><span class="file"><img class="file-icon" alt="PDF icon" title="application/pdf" src="cid:cecdd7b6e11cd5f7a3d0b02b2929447d@logbooks.jlab.org" /><a href="https://logbooks.jlab.org/files/2018/11/3628625/InnerBlocks.pdf" type="application/pdf; length=959833">InnerBlocks.pdf</a></span></div></td></tr></table><div class="comment-content">
<div class="field field-name-comment-body field-type-text-long field-label-hidden view-mode-elog_email"><div class="field-items"><div class="field-item even"><p>I would be very cautious about interpreting anything about relative channel-to-channel gain variations by looking at this plot. The system was not designed to be a uniform light source for every block. </p>
<p>In layer 1, there is significant radiation damage, as Colin noted. This varies quite a bit as one moves around the beam hole. The LED system is the most sensitive to radiation damage, much more so than measured derived from true showers. It is the canary in the coal mine. The downside is that it is hard to assess the impact on physics -- one needs to study variation of pi0 mass with run for some energy of photon.</p>
<p>The biggest problem with trying to do any channel to channel comparison using the LED is the variation of injected light. Recall that it is surface imperfections in the acrylic that cause light to get into the bar from the LEDs. There are a lot of edges around the beam hole as the corners of all four sheets meet there. Our intent was to have a light source that was time stable for each block but not one that was the same for every block. It is much different than a fiber injection system.</p>
<p>With a small change to the skim thanks to Sean and no modification of the clusterizing, Colin was able to regenerate pi0 plots and we now see pi0 peaks clearly in every block. I believe this is with production HV settings and software gains of unity for the inner three layers. So, the deviation from the pi0 mass is a measure of how unbalanced the gains are. I attach as a PDF -- you can easily see the variation isn't quite as dramatic as Sasha sees in the LED. I suspect it is because the LED source is pretty nonuniform in this area of the detector.</p>
</div></div></div> </div>
</article><a id="comment-18674"></a>
<article class="comment comment-new comment-by-node-author odd clearfix"><header class="comment-header"><h3 class="comment-title">
<a href="https://logbooks.jlab.org/comment/18674#comment-18674" rel="bookmark">This plot is for the nominal</a> </h3>
<em class="new">new</em>
</header><footer class="submitted"><p class="author-datetime">by <a href="https://logbooks.jlab.org/user/somov" title="View user profile." class="username">somov</a> on <time datetime="2018-11-19T18:52:35-0500" pubdate="pubdate">Mon, 11/19/2018 - 18:52</time></p>
</footer><div class="comment-content">
<div class="field field-name-comment-body field-type-text-long field-label-hidden view-mode-elog_email"><div class="field-items"><div class="field-item even"><p>This plot is for the nominal voltages.</p>
<p>I would not expect rad damage to be very different for adjacent cells<br />
(where amplitudes differ by a lot for some modules, see layer 3).</p>
<p>We need to look on gains. The LED is not the best tool to look on rad<br />
damage, only a small layer of the glass at the entrance can be damaged<br />
(before shower is developed).</p>
</div></div></div> </div>
</article><a id="comment-18673"></a>
<article class="comment comment-new even clearfix"><header class="comment-header"><h3 class="comment-title">
<a href="https://logbooks.jlab.org/comment/18673#comment-18673" rel="bookmark">Sasha, is this for the</a> </h3>
<em class="new">new</em>
</header><footer class="submitted"><p class="author-datetime">by <a href="https://logbooks.jlab.org/user/gleasonc" title="View user profile." class="username">gleasonc</a> on <time datetime="2018-11-19T18:18:07-0500" pubdate="pubdate">Mon, 11/19/2018 - 18:18</time></p>
</footer><div class="comment-content">
<div class="field field-name-comment-body field-type-text-long field-label-hidden view-mode-elog_email"><div class="field-items"><div class="field-item even"><p>Sasha, is this for the standard production HV settings? Or are all channels set to the same HV?</p>
<p>One thing you will need to keep in mind around the beam hole when using LEDs is the amount of radiation damage in each block (see this image <a href="https://halldweb.jlab.org/wiki/images/e/ea/4x4_array.pdf">https://halldweb.jlab.org/wiki/images/e/ea/4x4_array.pdf</a> for an image of radiation damage for each channel around the beam hole). The lower amplitude of the bottom row could be due to radiation damage and not a "wrong" HV set point (we know it's wrong in the sense that it is uncalibrated, but there may only be a small correction needed). For this row (27_30,27_29, and 27_28), the HV is set to the max EPICS value of 1800V with the production settings. </p>
<p> It would be interesting to check this with the green pulser, at say 25V, as that is not affected as much by the radiation damage. Nonetheless, I look forward to seeing the result with properly tuned HV.</p>
</div></div></div> </div>
</article></div></div> </div>
<table class="field-vitals"><tr><th>Logbooks: </th><td><a href="https://logbooks.jlab.org/book/hdfcal">HDFCAL</a> <a href="https://logbooks.jlab.org/book/hdlog">HDLOG</a> <a href="https://logbooks.jlab.org/book/hdtrigger">HDTRIGGER</a></td></tr><tr><th>Entry Makers: </th><td>somov</td></tr></table></div>
<div class="logentry node-content">
<p>FCAL FADC waveforms for 3 inner FCAL layers induced by a violet LED pulser operated at 15 V<br />
(data is taken in a raw fadc mode). Each histogram represents the FCAL module. Histograms are<br />
normalized to 500 fadc counts. FADC amplitudes have different peak values even in the 3rd FCAL<br />
layer, which can be accounted for either different light collection or PMT gains<br />
(we'll correlate amplitudes with the calibration coefficient obtained by Iliya).</p>
</div>
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<div class="image-wrapper"><img view_mode="elog_email" class="image-style-plentybig" src="https://logbooks.jlab.org/files/styles/plentybig/public/2018/11/3628625/fcal_3inner_layers.png" width="960" height="960" alt="" title="Fig. 1 FCAL signal waveforms induced by a violet LED pulser operated at 15 V" /></div> </div>
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