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Yesterday, while troubleshooting gun high voltage problems, we found a
problem with a splice between the gun HV cable going into the gun
ceramic and the cable coming from the Ross probe tank upstairs in the
service building. The problem at the splice.....speculation is that
we suffered an arc to ground. Not so drastic that the cable was
completely shorted, rather it behaved like a small and variable
resistor to ground. As a result, we were taking away voltage from the
gun. This introduced beam steering downstream of the 15 degree dipole
bend magnet. Probably started happening on September 29 when we first
noticed via the archiver that the 100kV orbit was drifting around. So
on one hand, we regret not identifying the problem sooner. On the
other hand, maybe we have made some progress understanding the puzzling
injector drift problem (e.g., why we would need to adjust capture phase
on daily basis....we thought those days were over, and maybe they are,
once we fix our HV cable and run with constant gun bias). Granted,
this is still speculation, but if indeed we were taking away voltage
from the gun, it could explain some of our observations. And once we
fix the splice, we might find it easier to operate the Compton..... <br>
Matt<br>
<br>
<br>
Arne Freyberger wrote:
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<h1 class="title">B-team Meeting Agenda (2:00pm Wednesday MCC conf.
room)</h1>
<div id="outline-container-1" class="outline-2">
<h2 id="sec-1"><span class="section-number-2">1</span> <span
class="timestamp-wrapper"> <span class="timestamp">2009-10-21 Wed
14:00</span></span> Agenda </h2>
<div class="outline-text-2" id="text-1">
</div>
<div id="outline-container-1.1" class="outline-3">
<h3 id="sec-1.1"><span class="section-number-3">1.1</span> Compton
Status <span class="tag"><span class="Happex">Happex</span> <span
class="III">III</span></span></h3>
<div class="outline-text-3" id="text-1.1">
<p>What is the status of the electron and photon compton signals
after
the last injector optimization? </p>
<ul>
<li id="sec-1.1.1">Photon counting <br>
<ul>
<li><a
href="http://opweb.acc.jlab.org/CSUEApps/elog/entry/1492644">Injector
tuning on October 15th</a> resulted in good photon rates.
Compton photon rates are very sensitive to the settings of the
injector. </li>
<li><a
href="http://opweb.acc.jlab.org/CSUEApps/elog/entry/1493141">Retune
required on October 19th</a> to get photon rates back to
acceptable.
<p>– orbits were adjusted
– capture gset by 2 out of 6000
– increased prebuncher by 0.02
– capture phase by 1.3 degrees
– A laser phase by 0.5 degrees </p>
</li>
<li>new spectrum look similar to old spectrum (for my crude
eyes) </li>
</ul>
</li>
<li id="sec-1.1.2">Electron counting <br>
<ul>
<li>electron data appears to be a bit cleaner. </li>
<li>electron detector moved closer to the beam (about 6mm). </li>
<li>zero crossing clearly observed. </li>
</ul>
</li>
<li id="sec-1.1.3">Flash ADC photon data <br>
<ul>
<li>1800V operation except when beam conditions degrade and the
things
trip off. </li>
<li>Low photon rate count (number available to MCC) is not a
guarantee that the flash ADC spectrum is clean. </li>
<li>MCC has no way to know if beam quality is good enough for
the
flash
ADC analysis. </li>
</ul>
</li>
<li id="sec-1.1.4">Summary <br>
<ul>
<li>beam quality is good for photon compton </li>
<li>electron detector still has a high level background. But
there might
not be enough time to address this. Cleaning the electron
background is not as high priority as accumulating statistics. </li>
</ul>
</li>
<li id="sec-1.1.5">Q/A <br>
<ul>
<li>most sensitive signal is a PMT current. </li>
</ul>
</li>
</ul>
</div>
</div>
<div id="outline-container-1.2" class="outline-3">
<h3 id="sec-1.2"><span class="section-number-3">1.2</span> Injector
optimization for Happex-III <span class="tag"><span class="Kazimi">Kazimi</span> <span
class="Reza">Reza</span></span></h3>
<div class="outline-text-3" id="text-1.2">
<p>What knobs are best? Stability and drift?
Additional parasitic monitors? </p>
<ul>
<li>Continuously monitor the time of arrival at the YAO cavity.
Reza
is
exploring continuous readout of the 6GHz bunch length cavity to look
for changes in the arrival time at this point. </li>
</ul>
</div>
</div>
<div id="outline-container-1.3" class="outline-3">
<h3 id="sec-1.3"><span class="section-number-3">1.3</span> Hall-A
Transport optics <span class="tag"><span class="Ryan">Ryan</span> <span
class="Tief">Tief</span></span></h3>
<div class="outline-text-3" id="text-1.3">
<p>What did ray-trace tell us about Hall-A optics?
</p>
<ul>
<li>horizontal pseudo phase space looks reasonable through the
Hall-A
line </li>
<li>vertical mis-match at the beginning of the A line </li>
<li>IP02A BPM area significant distortion to the ray-trace ellipse </li>
<li>distortion is correlated with beam loss in the A line. So
scraping
is causing the distortion which starts in the compton chicane. The
ellipse excursion in this region is of order 1.8mm full width. So
there is a tight 1mm vertical issue at the front end of the compton.
The distortion shows up on the negative side, so the tight aperture
is below the beam. </li>
<li>Detail look at the vertical plots, suggests that the problem
resides
somewhere between 1C16 and 1P02A. Better data would help narrow
down the source of the problem. </li>
</ul>
</div>
</div>
<div id="outline-container-1.4" class="outline-3">
<h3 id="sec-1.4"><span class="section-number-3">1.4</span> Energy
change </h3>
<div class="outline-text-3" id="text-1.4">
<dl>
<dt>Date</dt>
<dd><span class="timestamp-wrapper"> <span class="timestamp">2009-10-29
Thu</span></span> </dd>
<dt>Energy(5-pass)</dt>
<dd>6.068 GeV, symmetric setup. </dd>
<dt>θ<sub>wien</sub></dt>
<dd>Equal pain, θ<sub>wien</sub>=75 </dd>
<dt>θ<sub>wien</sub></dt>
<dd>During first four days when only B is taking beam, θ<sub>wien</sub>
= 65 </dd>
<dt>Special Request</dt>
<dd>Vertical spin alignment in Hall-A for two shifts.
Hall-B will want to go to 1-pass beam during this test. PVDIS will
want this in the middle/end of the run, not at the beginning. </dd>
</dl>
<ul>
<li id="sec-1.4.1">Comments on PVDIS startup <br>
Would like to address the beam quality issues at the beginning of the
run. This includes:
<ol>
<li>phase advance from modulation coils </li>
<li>compton photon rates </li>
<li>compton electron rates </li>
<li>raster size at target </li>
<li>FFB setup </li>
<li>85μ A current </li>
<li>θ<sub>wien</sub> </li>
</ol>
<p>Most of these issues require close collaboration with Hall-A
experimenters since they provide the measurements and Q&A. The goal
is not merely to reach acceptable beam, but to achieve the requirements
with
a robust (stable) setup with minimal compromises. Time invested at
the start of the run to get things right, should pay off over the
duration of the run. </p>
</li>
<li id="sec-1.4.2">Energy Change Strawman <br>
This will be discussed in more detail at the next B-team meeting.
<ul>
<li>defer cathode bake/activation until <span
class="timestamp-wrapper"> <span class="timestamp">2009-11-02 Mon</span></span>
if possible </li>
<li id="sec-1.4.2.1">Thursday <span class="timestamp-wrapper">
<span class="timestamp">2009-10-29 Thu</span></span> <br>
<ul>
<li>A and C go offline </li>
<li>ESR T1 turbine swap out, remove FNAL turbine and
install
repaired
JLAB turbine. </li>
<li>radcon survey of A line from 1C16 to 1P02A, search for
hot spots. </li>
<li>Helicity board swap </li>
<li>energy change to 6.068 GeV.
– review last June test, is this allsave ok?
– symmetric setup
– watch the cryoload </li>
<li>5-pass A to dumplette </li>
<li>5-pass B to F-cup </li>
<li>5-pass C to BSY dump </li>
</ul>
</li>
<li id="sec-1.4.2.2">Friday–Monday <span
class="timestamp-wrapper"> <span class="timestamp">2009-10-30 Fri</span></span>–
<span class="timestamp-wrapper"> <span class="timestamp">2009-11-02
Mon</span></span> <br>
<ul>
<li>5-pass CW to B, physics </li>
<li>5-pass 5uA CW to BSY dump for stability </li>
<li>periodically 5-pass to A dumplette for quad scans with
1C05 </li>
</ul>
</li>
<li id="sec-1.4.2.3">Monday <span class="timestamp-wrapper"> <span
class="timestamp">2009-11-02 Mon</span></span> <br>
<ul>
<li>12 hours gun bake/activation </li>
<li>MO Δ f 12 GeV studies </li>
</ul>
</li>
<li id="sec-1.4.2.4">Tuesday <span class="timestamp-wrapper"> <span
class="timestamp">2009-11-03 Tue</span></span> <br>
<ul>
<li>θ<sub>wien</sub>=75 change </li>
<li>5-pass to B when possible </li>
<li>5-pass to A
– day shift, injector optimization of compton rates
– day shift, ray trace collection or other optics work
– day shift, beam will be high current for compton </li>
</ul>
</li>
<li id="sec-1.4.2.5">Wednesday <span class="timestamp-wrapper">
<span class="timestamp">2009-11-04 Wed</span></span> <br>
<ul>
<li>5-pass to B </li>
<li>5-pass to A
– day shift, more beam studies to optimize compton
– ray-trace
– aperture scans
– matching
– phase advance
– raster setup </li>
</ul>
</li>
</ul>
</li>
</ul>
</div>
</div>
<div id="outline-container-1.5" class="outline-3">
<h3 id="sec-1.5"><span class="section-number-3">1.5</span>
Optics-on-call </h3>
<div class="outline-text-3" id="text-1.5">
<dl>
<dt>Outgoing</dt>
<dd>Tiefenback </dd>
<dt>Incoming</dt>
<dd>Roblin </dd>
</dl>
<ul>
<li id="sec-1.5.1">Recent Machine issues <br>
<ul>
<li>Compton rates
– highly sensitive on injector configuration, see notes above. </li>
<li>Power outage
– 9:20pm Tuesday all power was lost on site
– 8:30am Thursday still dealing with issues </li>
<li>FFB in A is sometimes problematic to configure properly </li>
</ul>
</li>
<li id="sec-1.5.2">Upcoming Week <br>
<ul>
<li>Hall-B goes to 1-pass (from 5-pass)
– <span class="timestamp-wrapper"> <span class="timestamp">2009-10-22
Thu 11:00</span></span> start change to 1-pass
– <span class="timestamp-wrapper"> <span class="timestamp">2009-10-26
Mon ??:??</span></span> Return to 5-pass </li>
<li>Brinkman, Director of the Office of Science visits on
[2009-10-28
Wed]. The machine will go to control access for a tour of the
injector. The tour will also visit the halls. Opportunity for
short duration beam studies. </li>
<li>Prepare for energy change on <span
class="timestamp-wrapper"> <span class="timestamp">2009-10-29 Thu</span></span>
</li>
</ul>
</li>
</ul>
</div>
</div>
</div>
<div id="postamble">
<p class="date"> Date: 2009-10-22 08:47:18 EDT</p>
<p class="creator">HTML generated by org-mode 6.31trans in emacs 23</p>
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<br>
<pre class="moz-signature" cols="72">--
Arne Freyberger
Director Operations Department
Jefferson Lab Phone: (757) 269-6268
12000 Jefferson Avenue Pager: (757) 584-6268
Newport News, VA 23606 Email: <a class="moz-txt-link-abbreviated"
href="mailto:freyberg@jlab.org">freyberg@jlab.org</a>
</pre>
<pre wrap="">
<hr size="4" width="90%">
_______________________________________________
Bteam mailing list
<a class="moz-txt-link-abbreviated" href="mailto:Bteam@jlab.org">Bteam@jlab.org</a>
<a class="moz-txt-link-freetext" href="https://mailman.jlab.org/mailman/listinfo/bteam">https://mailman.jlab.org/mailman/listinfo/bteam</a></pre>
</blockquote>
<br>
<br>
<pre class="moz-signature" cols="72">--
Matt Poelker
Jefferson Lab
MS Bldg 5A, Rm 500-17
12000 Jefferson Ave.,
Newport News, VA 23606
<a class="moz-txt-link-abbreviated" href="mailto:poelker@jlab.org">poelker@jlab.org</a>
757-269-7357 office
757-584-7357 pager
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