Fusor Forums

After reading Liam David's recent thread about damage to glass viewports I was curious if anyone had any success with other materials. I know many fusioneers have had success with using ceramics on their high voltage feedthrough. Has anyone attempted to use transparent ceramics such as perlucor or transparent aluminum? Alternatively if there are other transparent materials that are not glass that are more resistant to wear and tear in the fusor environment I would appreciate knowing about them!

Looks prohibitively expensive.
Viewports being broken by an electron beam is an ultra rare occurrence. Being so, the need to look into such alternatives has never garnered much discussion.

Mark Rowley

This is not to shoot down your idea to use exotic (and likely expensive) materials, but regarding ion beam viewport damage there are simpler solutions.

First, just don't orient the grid such that gaps are inline with glass or ceramic. It's localized heating and large spacial and temporal thermal gradients, not bulk temperature, that destroys these. Regular borosilicate viewports can handle 400C, and unless you're pumping a fusor with some serious power, the chamber will likely never exceed 100-150C. Mine has heated up to about 100C in recent runs, but had my grid not rotated or I noticed the dangerous alignment of the ion beams on camera, the viewport would be fine.

Second, use a piece of sacrificial glass. Boro glass disks that fit inside 2.75" flanges are somewhere on the order of $10 at McMaster. While these are no less susceptible to the ion beams than the viewport (the lack of a glass-to-metal seal might offer an advantage though), it's better they crack than have a viewport implode and mess up your turbo/diff pump.

Third is magnetic deflection. This could be as simple as taping on some magnets outside the viewport connection flange to Andrew Seltzman's machined design. I've found that the cheap steel bolts I use for all my CF flanges retain the magnets outside the port just fine.

Fourth is to put some fine wire mesh before the viewport. I use this technique to protect o-rings when pumping conductance is important.

One of these is likely all you need. Combine two of these and you've likely got a nigh-foolproof solution.
Just my two cents
-Liam David

CF2.75" elbow with silicon front surface mirror at bend angled @45 degrees
now you have x-ray reduction and you are free from viewport electron or ion heating just replace the mirror when it isnt as good any more
transparent aluminium is saphire yes it is expensive and yes it will break just like pyrex or quartz if you hit it with electrons or ions

As someone who actually created a "transparent Aluminum" material it has its limitations (while I made 75 mm thick pieces, transparency was an issue - long story; in my thesis topic I created a process that makes any glass material (including sapphire)stronger than Al but as flexible (both tension and bending) and as tough as aluminum alloys - so, since it had all the properties of Al but was only transparent for about 100 microns it qualifies in that regard ... . It was a superior armor on a weight bases compared to even Chobham and what partly paid for my research.)

However, thick glass works very well (my view port was 3/4 inch thick and withstood electron beams) and can be obtained at good prices from a telescope supplier on line.

What people have been referring to as transparent aluminum is aluminum oxynitride (ALON) which is a transparent ceramic. Really expensive and kind of pointless for a vacuum window when there are so many other materials that will work just fine. Though it has one interesting characteristic in that it is transparent into mid-IR.

While there is no such thing as aluminum that is transparent, I can convert any glass into a material with all the basic properties of aluminium - stronger, lighter, just as tough, more flexible even in tensile elongation but with superior bend resistance so, in a sense, it is transparent aluminum. While the name "transparent aluminum is a running joke from star trek in one sense, it is very real, in that sense, relative to my thesis, however.

I just wish I could have the vacuum-compatible ceramic equivalent of Sugru or something.


Seriously, "vacuum modelling clay" that you can just wrap around wires would be awesome. You can kinda get there by mixing powdered ceramic fillers into Hysol 1C to make an even pastier mixture (Hysol 1C already has more powdered magnesium oxide than epoxy) but that isnt' really fully satisfactory.

Thank you for all the responses, it seems (as usual) that with a bit of thinking a simple solution is much better than a new and complicated/expensive one.