Tungsten Cathode, no Welding Required

[Jon Rosenstiel]

The photos below should give a pretty good idea of the process.

I used 0.026" diameter tungsten wire from Small Parts Inc. (Part# TW-026-60) This particular wire was amazingly ductile for tungsten wire. I also attempted to make a grid using 0.022" wire but it was much too brittle. As the saying goes, "your mileage may vary".

The tubing is 7 gauge thin wall 304 stainless steel hypodermic tubing from Small Parts also. (Part #HTX-07T) My HV feedthrough stalk has an OD of 0.156" and the 7 gauge tubing has an ID of 0.160". Produces a nice friction fit.

I cut the slots in the end of the ss tubing using a thin cutoff wheel in my Dremel tool.

There was no difference in performance (neutron count) compared to the more traditional 5 circle grids I had been using.

This grid will take some punishment. I've run my fusor at over 1kW input for 3 to 4 minutes at a time. And she ran exceptionally stable!

Jon Rosenstiel

Edit: As the photo here was lost, I have taken the liberty of substituting a diagram of the construction. If Jon has this image as a photo he can insert it to back up the diagram or contact me to edit it in.
I have done this to make the fine grid idea of Jon's retain a visual aspect for other to see how it is done.
Richard Hull 11/29/19

[attachment=0]Tungsten Cathode.jpg[/attachment]

[Q]

what a neat grid idea! and so simple too.

Q

[Starfire]

Thanks & congrats. Jon - miniaturisation indeed, this must be the smallest grid ever made - and punches a Kilowatt. These photos should be archieved. ( what are you like at watchmaking?

[Adam Szendrey]

A great idea! Thanks Jon!

Adam

[Richard Hull]

This is how some of the grids were made by Miley's group. (they have built many systems, by many grad students, over the last 20 years.

Some were also assembled by bundling the long stems, as well, instead of the tube held method.

The other grids, (cross ways) can be attached by binding with 1mil or similarly fine W wire.

Good work Jon. Tungsten will have the same cleanup issues as Ta, but have the edge on the melting point.

I might try my hand at this method. at some point and it might just be NOW as my current grid system is faulty. I don't know if I will have time to implement a lot of stuff for fusor IV before the bash, but I am moving on some of them.

Richard Hull

[Starfire]

I like the tie-down - photo 3

[Jon Rosenstiel]

John,

The grid isn't as small as it appears in the photos. I think what may have thrown you off are the 3, nested, alumina tubes in pic #5. The OD of the outermost tube is 3/4" (19mm).

The grid is about 1.3" in diameter. (33mm). That makes it about a 5:1 ratio to the 6" ID of the outer shell.

I should have included something in the photos to indicate perspective.

Jon Rosenstiel

[Brian McDermott]

Is that the same grid shown in your recent "supernova" post to Images du Jour?

Is there any advantage to having the crosswise rings on the grid as opposed to simply the setup shown in the photos?

[Richard Hull]

I wouldn't image the cross links are critical provided enough vertical circles are used to fool the e-field into thinking it is a perfect sphere. It is sad that the better the transparency is, the worse the field uniformity is. There is a point, however, where the field is virtually perfect and yet the grid is still relatively, ion transparent.

Richard Hull

[Jon Rosenstiel]

Brian,
It's not the exact same grid as in the supernova photo, but is of the same construction and size.

Jon Rosenstiel