<html><head><meta http-equiv="Content-Type" content="text/html charset=utf-8"><meta http-equiv="Content-Type" content="text/html charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><br class=""><div class=""><blockquote type="cite" class=""><div class="">On Feb 28, 2018, at 10:50 AM, David Lawrence <<a href="mailto:davidl@jlab.org" class="">davidl@jlab.org</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><meta http-equiv="Content-Type" content="text/html charset=utf-8" class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class="">Hi All,<div class=""><br class=""></div><div class=""> Today turned out to not be a great day for most people to meet. It ended up being</div><div class="">just Ilya and I. We did have a discussion on what we would like to do with the chamber</div><div class="">and any remaining beam opportunity. Here are the ideas we came up with so others</div><div class="">may comment:</div><div class=""><br class=""></div><div class="">1. Change the gas mixture to 90/10. We have not yet spoken with Tom/Scot on how</div><div class="">difficult this is. We will do that this week.</div></div></div></blockquote><div class=""><br class=""></div>I think we’ll need to have Tom order a tank of 90/10 by volume. Then just move the gas regulator over to the new tank, open the valve to get gas flowing, that’s all we need to do. We will run the detector at a lower HV. </div><div class=""><br class=""></div><div class="">On the way home Saturday I finally got around to looking at the gas flow calibration data I took last Nov. I did a re-calibration of the gas flow tubes because we seem to have a discrepancy between gas gain at JLab and UMass, it’s higher at JLab than UMass. To make a long story short, I believe the “80:20” by volume mix I’ve been running at UMass is approximately 75:25. The bottom line is that running the detector with an actual 80:20 at +2000 V is probably over-biasing the detector somewhat. Andrew and I will need to take some measurements with the small prototype detector to find new recommended HV’s for 80:20 and 90:10. <br class=""><blockquote type="cite" class=""><div class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div class=""><br class=""></div><div class="">2. Change the scintillator paddle position to be closer to the beam line.</div><div class=""><br class=""></div><div class="">3. Machine a hole in the 10.75” steel plate and center it on the beam line. This will</div><div class="">give a much closer approximation of beam conditions. The hole should be round with</div><div class="">a diameter between 6.6cm and 8cm. According to my notes, the dead region in this</div><div class="">chamber is 3.4” in diameter (=8.64 cm). </div></div></div></blockquote><div class=""><br class=""></div><div class="">The diameter of the dead-zone in the chamber is 6.8”, the radius is 3.4”. </div><br class=""><blockquote type="cite" class=""><div class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div class="">Studies from last year set the beam hole</div><div class="">size to 2cm smaller in diameter compared to the dead region so if we follow that,</div><div class="">the hole size should be ~6.6 cm. </div></div></div></blockquote><div class=""><br class=""></div><div class="">Yes, I think the studies we did last year indicate the hole in the iron should be 2 cm smaller than the dead zone hole. </div><div class=""><br class=""></div><br class=""><blockquote type="cite" class=""><div class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div class="">The final design parameter for the dead region from</div><div class="">those same studies was 10 cm with a beam hole of 8cm diameter. </div></div></div></blockquote><div class=""><br class=""></div><div class="">Yes, that’s what I saw from our studies last year. However, the dead-zone we currently have is about 17 cm in diameter, so we would be going with a dead-zone diameter significantly smaller than what we currently have. </div><div class=""><br class=""></div><div class="">Rory</div><div class=""><br class=""></div><br class=""><blockquote type="cite" class=""><div class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div class=""><br class=""></div><div class="">One option is to try and do both by cutting the smaller hole, taking data, and then cutting</div><div class="">the larger hole. Alternatively, we could cut the larger hole and then make a plug or mask</div><div class="">to get data with the smaller hole size.</div><div class=""> </div><div class=""><div class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class="">The chamber is currently out of the beam. There may be opportunity on Monday to </div><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class="">reinstall it along with any of these modifications. There is also a possibility they will</div><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class="">extend the run for one more week.</div></div></div><div class=""><br class=""></div><div class="">Rory and Elton: please think about this and let us know what you think and if there are</div><div class="">any other things you would like to do during the remainder of this run period.</div><div class=""><br class=""></div><div class=""><div class=""><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class="">Regards,</div><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class="">-David</div><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><font color="#6a6a6a" class=""><br class=""></font></div><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><font color="#6a6a6a" class="">-------------------------------------------------------------</font></div><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><font color="#6a6a6a" class="">David Lawrence Ph.D.</font></div><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><font color="#6a6a6a" class="">Staff Scientist, Thomas Jefferson National Accelerator Facility<br class="">Newport News, VA</font></div><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><font color="#6a6a6a" class=""><a href="mailto:davidl@jlab.org" class="">davidl@jlab.org</a><br class="">(757) 269-5567 W<br class="">(757) 746-6697 C</font><br class=""><br class=""></div>
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