Mineral insulated coaxial cable

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Thermocoax is widely used at millikelvin temperatures, such as quantum bi= t experiments. The lossy version makes nice distributed wideband filters to= block blackbody radiation (recall that the blackbody peak is roughly 20 GH= z at 20 mK) from the experiment.=20

The mineral insulation in general is nice for refrigerator use, because t= he center conductor of an ordinary coax is difficult to cool - the cold pla= te where the experiment resides is in vacuum, and in plastic insulated coax= es there tends to be enough gap for the vacuum to creep in between. Mineral= grains seem always to make some percolated thermal path between the jacket= and the core, so that it is enough just to anchor the jacket thermally.

Regards, Mikko

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It's not only faster, but also smaller - the thinnest example is only

1mm O.D. Sadly, it's still not the really thin stuff that I thought that I could remember.

m bit experiments. The lossy version makes nice distributed wideband filter= s to block blackbody radiation (recall that the blackbody peak is roughly 2=

0 GHz at 20 mK) from the experiment.

se the center conductor of an ordinary coax is difficult to cool - the cold= plate where the experiment resides is in vacuum, and in plastic insulated = coaxes there tends to be enough gap for the vacuum to creep in between. Min= eral grains seem always to make some percolated thermal path between the ja= cket and the core, so that it is enough just to anchor the jacket thermally= .

Cute. Most of the applications I found were for the nuclear industry or for very high temperature application.

-- Bill Sloman, Nijmegen

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Be careful. We used to install mineral insulated power cables in explosion proof environments. 'Pyrotenax' comes to mind. It does the job exceedingly well. The problem is that the 'mineral' insulation is actually compressed powdered asbestos.

I would check out the coax to see if history repeats itself.

mike

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The "mineral insulation" can be any one of quite a number of different materials. Asbestos may have been popular in the past, but it doesn't seem to feature in the stuff I've just been looking at.

-- Bill Sloman, Nijmegen

You sure about that? AFAIR, it's powdered aluminum oxide.

--
"For a successful technology, reality must take precedence 
over public relations, for nature cannot be fooled."
                                       (Richard Feynman)

Usually MgO or Alumina.

Alumina = aluminum oxide ;-) AKA Aloxite (usually related to abrasives).

I once saw a magic machine that automatically welded junctions in mineral insulated thermocouples, then welded the jacket over the end to form a hermetic seal. All in a few seconds. Guaranteed vacuum tight.

--
"For a successful technology, reality must take precedence 
over public relations, for nature cannot be fooled."
                                       (Richard Feynman)

Yes, I was agreeing with you, even if it didn't look like it.

In keeping with the Alumina name- MgO can apparently be called Magnesia (and, like certain types of bees, can yield a type of milk).

Custom machine, I assume. That's a horrible, fiddly job to do by hand.

What sort of bee gives milk?

I only know about bee pee;-)

--
"For a successful technology, reality must take precedence 
over public relations, for nature cannot be fooled."
                                       (Richard Feynman)

Boo-bees

I'm sure you're right. I have no idea when they changed over. The following page gives a respectable history of the stuff.

=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D The first patent for MI cable was issued to the Swiss inventor Arnold Francois Borel in 1896. Initially the insulating mineral was described in the patent application as pulverized glass, silicious stones, or asbestos, in powdered form.

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mike

I may be wrong, but I think it actually said "Pyrotenax" on it.

From the spool, roller straightened, welded, capped, and cut to length.

They made several hundred made-to-order 'couples a week. Traceable calibration, if required.

--
"For a successful technology, reality must take precedence 
over public relations, for nature cannot be fooled."
                                       (Richard Feynman)

So the machine spent about 99% of its time waiting for the humans to make demands of it. Do you remember how they cleaned the insulation off before welding? Sand blast?

Very interesting thread! As a Radio Amateur (G0TLP) I have seen but not use d Mineral Insulated Coaxial, I am also partner in a business that manufactu res accessories for Mineral Insulated power cables and also distributes the cable as well. Over the years I have dealt with BICC pyrotenax now under t he Tyco thermal group. The cable is still manufactured in the UK but by the seam welding process from strip. The traditional method is from cast tubes drawn down to size. The insulant is magnesium oxide. The cable is produced by Wrexham Mineral Cables in the UK and they also supply Tyco. KME produce in Italy and supply AEI as well as our business. Unsurprisingly China is a lso starting to produce as well. Just thought I would add this for interest ! Best Regards