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<div><span style="font-family: arial,helvetica,sans-serif;"
data-mce-style="font-family: arial,helvetica,sans-serif;">Dear
User Community,</span><br>
</div>
<p style="color: rgb(0, 0, 0); font-family: "Times
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data-mce-style="color: #000000; font-family: 'Times
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text-decoration-color: initial;"><span style="font-family:
arial,helvetica,sans-serif;" data-mce-style="font-family:
arial,helvetica,sans-serif;">On the morning of Thursday July
27th, CHL1 suffered a power event that resulted in several
(but not all) CHL1 compressors tripping off. The tripped
compressors resulted in a path to atmosphere to allow for
gaseous He to escape (which is the nominal situation when <b>all
</b>compressors trip off). Unfortunately several compressors
remain active and this resulted in a large volume of air being
pulled into the CHL1 Helium space. CHL1 was severely
contaminated and inoperable at this point.</span></p>
<p style="color: rgb(0, 0, 0); font-family: "Times
New<br> Roman"; font-size: medium; font-style:
normal;<br> font-variant-ligatures: normal;
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initial;<br> text-decoration-color: initial;"
data-mce-style="color: #000000; font-family: 'Times
New<br> Roman'; font-size: medium; font-style: normal;
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normal; <br> font-weight: normal; letter-spacing: normal;
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text-decoration-color: initial;"><span style="font-family:
arial,helvetica,sans-serif;" data-mce-style="font-family:
arial,helvetica,sans-serif;">At this point in the Summer
shutdown, CEBAF was at 4K on CHL1 and CHL2 was at room
temperature for maintenance, but in an operable state
(maintenance more or less completed). The estimate was that
CEBAF could last about 48h without 4K CHL operations. CHL2
cooldown started mid-day Thursday and CEBAF slowly lost LHe
levels (clean gas was captured, dirty gas was vented). CHL2
was able to liquefy Helium Saturday afternoon at which time
several modules had past the no-return point. Cryo cooled and
maintained modules that had not passed the 50K level and those
that had were allowed to warm up to room temperature.</span></p>
<p style="color: rgb(0, 0, 0); font-family: "Times
New<br> Roman"; font-size: medium; font-style:
normal;<br> font-variant-ligatures: normal;
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initial;<br> text-decoration-color: initial;"
data-mce-style="color: #000000; font-family: 'Times
New<br> Roman'; font-size: medium; font-style: normal;
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text-decoration-color: initial;"><span style="font-family:
arial,helvetica,sans-serif;" data-mce-style="font-family:
arial,helvetica,sans-serif;">By Sunday about half of CEBAF was
cold (but not full). By Monday Cryogenics had cleaned
contaminated purifier and was in the position to purify He gas
and fill some of the modules that were cold. This effort
continues to this day. Next week Cryogenics and SRF will start
the process of cooling down the warm modules. This process
will take a bit less than one-month.</span></p>
<p style="color: rgb(0, 0, 0); font-family: "Times
New<br> Roman"; font-size: medium; font-style:
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data-mce-style="color: #000000; font-family: 'Times
New<br> Roman'; font-size: medium; font-style: normal;
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text-decoration-color: initial;"><span style="font-family:
arial,helvetica,sans-serif;" data-mce-style="font-family:
arial,helvetica,sans-serif;">At the time of the incident, two
months of shutdown work remained to be performed, including
testing/recommission cold-box SC1 which failed in March. We
are still evaluating the tasks/sequence to recover CEBAF. The
estimate is that sometime around mid-November CEBAF will be in
a position to support beam, with beams for Physics after
Thanksgiving. This is a very rough estimate. We are working on
an experiment schedule for the remaining of 2017 and all of
2018 based on this estimate.</span><br>
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<p style="color: rgb(0, 0, 0); font-family: "Times
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initial;<br> text-decoration-color: initial;"
data-mce-style="color: #000000; font-family: 'Times
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text-decoration-color: initial;"><span style="font-family:
arial,helvetica,sans-serif;" data-mce-style="font-family:
arial,helvetica,sans-serif;">This event is what Ops refers to
as a "unplanned" warmup, not to be confused with an
"uncontrolled" warmup (aka hurricane Isabel). As such the
modules warmed in a slow manner as vacuum was maintained
during the warmup (although we wish it was slower).
Nevertheless there might be some impact to SRF performance
associated with this event. We are working with Cryogenics to
develop the quickest route to 2K so that we can evaluate the
SRF performance. In the meantime, assuming worse case, we are
readying the two hottest cryomodules in the LERF to be
installed in CEBAF if it is determined that there is a need
for this action. The present sketch suggests that we might be
in a position to answer these questions by Oct.</span></p>
<p style="color: rgb(0, 0, 0); font-family: "Times
New<br> Roman"; font-size: medium; font-style:
normal;<br> font-variant-ligatures: normal;
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initial;<br> text-decoration-color: initial;"
data-mce-style="color: #000000; font-family: 'Times
New<br> Roman'; font-size: medium; font-style: normal;
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text-decoration-color: initial;"><span style="font-family:
arial,helvetica,sans-serif;" data-mce-style="font-family:
arial,helvetica,sans-serif;">The Lab Director has formed a
Root Cause Investigate team, led by COO Mike Maier to look
into the root cause of this event and recommend corrective
actions.</span></p>
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