The Alpha Magnetic Spectrometer

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• AMS Superconducting Magnet
• progress over the last 3 months
• July 2007
• Steve HarrisonScientific Magnetics

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• Helium vessel
• Cryocoat development
• Magnet testing (so far)

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Helium Vessel
In April we reported that the completed helium
vessel had just been delivered
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and that the components of the frame for
manipulating the helium tank had also just
arrived.
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The manipulation jig was assembled
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then load tested using the axle from the helium
vessel leak tester.
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Trial fitting of the axle and frame to the bore
of the helium vessel was carried out by a skilled
technician
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allowing the support locations to be welded in
place accurately.
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With the helium vessel supported from the axle,
the assembly was installed in the manipulation
jig.
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This allows the vessel to be rotated
simultaneously about two axes.
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During the cleaning process, the cap protecting
the porous plug port was cut off using a special
tool.
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Both the inner surface of the cap, and the inside
of the port, were heavily contaminated with
particulates and residues
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although fortunately not all parts of the tank
were quite so dirty.
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The tank was cleaned by part-filling with IPA
then spinning on the two axes.
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After washing, the IPA was drained out and
samples taken. These were filtered, and the
concentration of particles was calculated.
At first, there was a very large number of
particles
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including several fairly large pieces which
looked like gold.
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Eventually we recovered enough gold from the
helium vessel to upgrade Mr Bollwegs rental car.
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After 40 wash/rinse cycles the level of
particulates was becoming more manageable.
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After 6 weeks of constant flushing with IPA, the
interior of the tank was clean enough to proceed
to the next stage
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which was to dry out the tank for welding,
using clean, dry, filtered air.
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Finally, the heat exchanger loops had to undergo
the same cleaning procedure. Fortunately, these
were in a much better state and were successfully
cleaned in a few days.
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Aluminium
Stainless steel
Radial gap has closed during aluminium welding,
ovalising the stainless steel tube.
Radial gap
With the vessel back in the clean room, the caps
sealing the burst disc and porous plug ports were
cut off. We now found that the ports had been
distorted during welding of the helium tank, and
neither the burst disc nor the porous plug fitted
any longer.
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The outer diameter of the burst disc vent tube
had to be machined down to fit. The porous plug
housing had to be hand-finished to get it into
the tank.
This surface machined
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The porous plug has now been successfully fitted
and welded into the tank.
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The burst disc has also been welded in.
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Vapour return to the fill port
DV12
The first of the cryogenic valves and pipework
have been welded into the helium vessel.
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From the porous plug
DV03 (from the fill port)
Cryogenic pressure transducers
Porous plug instrumentation interface
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These welds have now been leak tested
successfully. Next the helium vessel will be
assembled into the 1.8 K leak test cryostat.