[Halla_running] Quick update on CEBAF/Hall A status

[Brad Sawatzky]

Hi all,

Just a quick update on the status of the accelerator and Hall A.  Shifts
in Hall A have been cancelled through Monday swing.  Watch your email
for further updates.

MCC managed to deliver photons to Hall D early this week for about 4--5
hours before cryo problems took down the machine (CHL crash, issues with
a couple of south linac cryomodules).  They have been working on
restoring the CHL and accelerator since then.

As of today the CHL is back up, and both linacs are cold again.
However, one of the C100 cryomodules (SL25) has a stuck JT valve and an
insulating vacuum problem that is still being investigated.  The
gradients in the remaining cavities have been rebalanced to compensate
for the loss of SL25 and preliminary tests (without beam) suggest the
trip rate will be low enough to continue the program.  We won't know
when SL25 can be returned to service until the underlying problem is
better understood -- this is being worked on today.

The current plan is to attempt beam restoration to Hall D tonight and
they will continue their ~4 day run plan starting Saturday.  This would
mean the RF separator work necessary to deliver beam to Hall A would
begin Wednesday.  _Hopefully_, that could mean beam to Hall A late next
week.

Hall A itself is basically ready for beam.  The PSS has been certified,
and the beamline + dump is (basically) ready to go.  The ESR has been
brought online and I'm told that the HRS magnets are starting to cool.
If all goes well they should also be ready next week.

NOTE: There are a still a lot of unknowns.  The loss of SL25 means that
      the remaining cavities are being pushed harder than MCC would
      prefer, so it's not clear how the machine will behave with beam in
      the ring.  We'll know better by Monday.

So, it's 2 steps forward + 1 back, but progress is being made :-)

All the best,
-- Brad