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The YouTube video The AMAZING Design of the Parker Solar Probe - Smarter Every Day 198 is quite interesting, as is the video Destin's second "Smarter" channel's video Scientist Interview: Dr. Tony Case (Parker Solar Probe).

At about 03:15 in the second video, Instrument Scientist and Deputy-PI of the Solar Probe (Faraday) Cup, part of the Solar Wind Electrons Alphas and Protons Suite (SWEAP) and astrophysicist Dr. Tony Case describes the details of the construction of Parker's Faraday Cup, which is literally the hottest part of the mission!

The grid is made of tungsten, and the wire bringing the signal back inside the probe to be measured is made of niobium, and uses sapphire beads as insulation.

There is a nearly 90 degree bend in the high voltage feed, and at that point the wire is insulated with a sapphire elbow according to Dr. Case.

How are sapphire elbows made? Is it a cast material (fused sapphire) or is this a hunk of sapphire that's been somehow drilled and machined into a piece of elbow macaroni? Sapphire isn't an easy material to work with!

Parker's sapphire elbow

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    $\begingroup$ Synthetic sapphire crystals are made using the Kyropoulos process or by variations of the Czochralski process. $\endgroup$
    – Uwe
    Commented Apr 4, 2019 at 9:17
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    $\begingroup$ Corundum, including its variants (sapphire, ruby) is a fairly common material for applications where extreme resistance to abrasion is required; it's been used by watchmakers since 19th century for clockwork bearings in expensive watches. The technology of artificial corundum is quite mature and has widespread applications. (also, first lasers were made using large artificial ruby crystals). $\endgroup$
    – SF.
    Commented Jul 31, 2019 at 8:18
  • $\begingroup$ @SF. Yes, sometimes people will mix up terms; sapphire, alumina and possibly corundum, as also happens with quartz, fused quarts and fused silica. If it turns out to be corundum rather than synthetic sapphire that's fine, but I'd still ask if hollow 90 degree corundum elbows are quite mature, and have widespread applications as well, or if making them is in fact quite a challenge. $\endgroup$
    – uhoh
    Commented Jul 31, 2019 at 8:40
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    $\begingroup$ Sapphire tubes are grown using the Stepanov method. by changing the path of the draw the a tube can be curved $\endgroup$
    – user20636
    Commented Jul 31, 2019 at 8:42
  • $\begingroup$ @JCRM growing crystal tubes with internal and external threads (Fig. 12) is downright amazing! $\endgroup$
    – uhoh
    Commented Jul 31, 2019 at 8:46

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When wires are drawn, drawing dies are used. They are typically made of a very hard material like tool steel, tungsten carbide, or diamond.

To make a diamond drawing die, a small hole has to be drilled into the diamond. Over 50 years ago, the drilling was done using diamond powder as an abrasive just like it was used to process diamonds for jewelery.

When high power lasers were available for drilling of diamond drawing dies, a lot of traditional manufacturers vanished and only the laser was used to do in days or hours what took months or weeks before.

So I think those sapphire beads and elbows are drilled using high power lasers.

For machining the elbow I think the diamond powder method is still used.

There are very small PCB drills made from tungsten carbide available. The smallest diameters are now below 0.2 and 0.1 mm. These very small drills look like the larger ones with helical flutes and cutting edges. Again using diamond powder as an abrasive.

So if it is possible to make drawing dies from diamond and small drills from tungsten carbide, sapphire elbows may be made using the same methods too.

See this pdf for some examples what may be done using selective laser etching of sapphire. Another pdf.

Even curved holes are possible combining laser treatment with etching.

The irradiated material can be selectively removed with wet-chemical etching.

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  • $\begingroup$ any examples at all of diamond drills or lasers that can make 90 degree turns? These probably won't work in this case google.com/… $\endgroup$
    – uhoh
    Commented Jul 31, 2019 at 8:54
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    $\begingroup$ The 90 degree turn is drilled in two steps from both ends with carefully controlled drill depth. $\endgroup$
    – Uwe
    Commented Jul 31, 2019 at 9:04
  • $\begingroup$ Oh, now I see what you mean. I guess we really need to see inside here to know if it's a curved bend like elbow macaroni which is what I was imagining, or just a block drilled from two sides, which, now that I think about it, makes a lot more sense! $\endgroup$
    – uhoh
    Commented Jul 31, 2019 at 9:09
  • $\begingroup$ but would leave a sharp corner inside. $\endgroup$
    – user20636
    Commented Jul 31, 2019 at 9:37
  • $\begingroup$ an isotropic wet chemical etch would break sharp corners, as would running a abrasive-laden cord through it, so I don't think the corner is the end of the world, nor does it merit a down vote. $\endgroup$
    – uhoh
    Commented Jul 31, 2019 at 11:47

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