[Halld] Hall D Solenoid Update

[Eugene Chudakov]

Dear colleagues,

There is a new development concerning the problems with the Hall D
solenoid. One of the engineers who built this solenoid at SLAC long
ago - Steve St.Loren noticed a difference in the ways liquid He is
provided to the coils between the SLAC and JLab implementations. He
explained that one of the two 3/8" pipes, which go to the bottom of
the coils, was used not for the cool-down (as we do) but was connected
to the bottom of the Helium cold box and in fact provided a
thermosyphon. The current implementation does not employ the
thermosyphon effect, which is its obvious weakness. The finding was
discussed with local experts and the general opinion is that the
effect might be significant.

We have come to a preliminary plan on making the proper modifications
in order to get closer to the SLAC configuration. We would need to
warm up the magnet and make modifications in the chimneys.  The work
is not trivial but seems doable.  The time estimate is 2 months till
the magnet is cold again.

There is a broad agreement that the modifications should be done now
rather than later. Today, the cryo group started warming
up the magnet.

Best regards,
Eugene