We are using helium as a variable thermal conductance between a liquid nitr=
ogen filled jacket and a calibration target that we need to vary the temper=
ature of.

Helium is about the only gas that won't go liquid around LN2 temperatures.

>=20
> Helium is too expensive compared to nitrogen.
>=20
> ATT long lines used nitrogen to pressurize long distance cables for many
> years
>=20
>=20
>=20
>=20
> > On Oct 13, 2017, at 6:04 AM, Justin Richards <justin.richards@gmail.com=
>
> wrote:
> >
> >> Is the alternative of doing the long  run in 110v AC and providing
> >> local AC-DC converters at each location too expensive.
> >> Designing high current 48v distribution for radio telescopes might
> >> account for some of my grey hairs :-)
> >
> > You should try running high voltage through a helium atmosphere ...
> >
> > See photo of result of running 240V through connector at less than 1atm=
 He
> ...
> >
> > For the theory read up on Paschen Curves.
> >
> > https://en.wikipedia.org/wiki/Paschen%27s_law
> >
> > Result is I am having to run things at 110V, which has caused a major r=
ethink
> about wire gauges etc.
> >
> > For the OP I suggest thinking about doing all your wiring with a low ha=
logen
> smoke free wire, if you have the possibility of persons trapped through a=
n
> electrical failure.
> >
> >
> > <Connector Small.jpg>--
> > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> > View/change your membership options at
> > http://mailman.mit.edu/mailman/listinfo/piclist
>=20
> Just my $0.02,
>=20
> Jean-Paul
> N1JPL
>=20
>=20
>=20
>=20
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