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From: Kirk T McDonald [mailto:kirkmcd@Princeton.EDU]
Sent: Thursday, November 24, 2005 1:09
I visited CVIP today to witness part of the tests of the
vacuum jacket of the cryostat for the 15-T magnet for the MERIT experiment.
Photos that I took are at
Overall views of the magnet include
1. Recall that a pressure test of the LN2 volume had
been done last Saturday. At first there was a small leak thru the gasket of
the giant flange, but this went away after further tightening of the flange
bolts. The pressure then held at 245 psi for 10 min = duration of the test.
Apparently, one could hear creaking noises from the
interior of the cryostat during the pressure test (but not during the vacuum
test).
2. When vacuum was first applied to the vacuum jacket,
the He leak checker spotted small leaks in 2 places along the weld of the
large bellows and the main outer cylinder of the cryostat.
These bad portions of weld were ground down and patch
welds of 3-4" made.
The photo shows one of the patch welds, which is (barely)
distinguishable from the original weld by the reversal of the flow of the
weldment. You would probably not notice the weld repair unless it was
pointed out.
After the repair no further leaks were detected with the
leak checker, which showed a leak rate of < 1e-9 of standard leakage units.
While I was there, they went over all the welds with a He
sniffer with no trace of any leakage.
Also, the LN2 volume was filled with He to check for
leaks on the inside surface of the vacuum jacket.
shows the He line attached to a flange bolted onto the N2
vent port at the top of the magnet end flange.
The pressure in the vacuum jacket was monitored via a
thermocouple gauge on a small port that CVIP added to the outer wall of the
cryostat, near the bottom.
Apparently this port was not specified by Peter, but it
will be useful in the future as well.
The vacuum pump was connected to the magnet via a
commercial adapter that was attached to the top pipe of the magnet -- where
the relief valve will be during nominal operation.
The adapter in the photo was made by Cryolab, now
However, it's not clear if this part is still being made
by them.
I think that the link
shows another vendor's version of this useful item.
=> We should have one of these adapters. It is not clear
whether our negotiations with CVIP include delivery this device.
............
One item remains to be installed in the LN2 volume: the
1"-diameter "snorkel" pipe that connects to the fill/drain port such as to
be able to suck LN2 out of the low point of the tilted magnet.
shows the suction end of the pipe, with a 90-deg bend,
and 4 slots ~ 5 x 5 mm^2 to let the LN2 flow into the pipe.
=> These slots will be the limiting aperture(s) in the
LN2 flow path, so we may want to enlarge them during the MIT test.
..................
An interesting issue is how to move the magnet.
It should NOT be lifted via straps around the main
cylindrical body -- which will be tempting to riggers.
It's apparently OK to run straps under the baseplate and
up around the sides of the cylindrical cryostat.
It also appears to be possible to insert the forks of a
(large) fork lift under the downstream end of the baseplate.
......................
Dave Nyguen showed how the G-10 cylinder could be
inserted into the 6" bore of the cryostat
The cylinder he use has a longitudinal cut in it....
...................
No cold test is planned at CVIP (who called such tests
"liquid nitrogen shock"). The cold test will be done at MIT.
...................
I've lost track of what kind of tests have been done on
the magnet coils as to their magnetic function. I'm sorry that I didn't
bring my inductance meter along with me to do a low-voltage test. The leads
of the coils do look very nice physically.
CVIP will continue to pump on the vacuum jacket til next
Monday. Then they will valve off the vacuum and do a 36 hour "retention"
test to see how well the system holds vacuum over time.
They can, of course do a longer retention test, but Dave
claimed that 36 hours is their standard practice, and they charge extra for
longer tests.
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