Dear Zdenek,
there are two aspects.
1. You loose about 30% of helium gas during the refill. Interesting question,
why. Nevertheless it's a rather well known value, even more, I measured multiple
times during my active time.
To tell you a consequence. For our 900 MHz Magnet we had a pipeline with an
inner diameter of 25 mm with a length Of about 50 meter until the next bigger
pipeline. The result was a filling time of 4 hours if we accept an overpressure
of 50 mBar during the filling procedure. That's a lot. Its not dangerous, but
increases the temperature of the helium by a few millikelvin. If you release
the overpressure immediately, this results in evaporating liquid helium from
100% to 93%, which is alot again. We extended the filling time to 5 hours and
released the overpressure slowly.
Everything is possible, but slow.
2. If you use any plastics material except HD-PE you get significant diffusion
of oxygen and nitrogen inside the tube. Depends on your liquefier, how much you
can accept.
Have a nice day
Rainer Haessner
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Received on Thu Aug 17 2023 - 07:16:59 MST