FAQ - Grid construction tips

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Richard Hull
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FAQ - Grid construction tips

Post by Richard Hull » Mon Jul 01, 2013 4:50 pm

Recent confusion has forced this FAQ to be offered.

Folks seem to be concerned about the shape and materials used for the inner grid.

A. The grid must be hollow in a simple fusor
B. All spherical grids work well, regardless of Fusor chamber shape, so shoot for a spherical construction.
C. All grids must be of metal, (conductive). The most resistive and least conductive of all pure metals would perform no better or worse than a grid that is made of the finest, highest electrical and thermally conducting pure metal.

Needed and demanded

1. Pure metal, hollow inner grid
2. Pure metal grid that can take some intense heating and not melt. Heating due to ion bombardment and field emission.
3. Electrical and thermal conductivity of the pure metal used is a non-issue and is never considered in any design criteria.
4. Only the melting point of the pure metal is a key issue and the weak point in any metal grid.
5. Most grids are made from wire of the selected metal.

Pure silver or gold are among the worst choices for grid material

Tungsten is the #1 choice. Rhenium, Molybdenum and Tantalum, all tied for #2, Hafnium #3 and maybe Titanium #4 as suitable for a real fusor.

Demo fusors can use simple stainless steel wire as they are not stressed to the degree encountered in a real fusing fusor.

The diameter of the wire is not critical provided it is thick enough to support its own weight and can handle the heat dissapation well without sagging or melting. (this is based on the power level of fusor operation). In general, 30 mil wire is a minimum diameter and 80 mil is heavy, though heavier wire is also just fine. In general, the larger the grid, the larger the wire can be. Again, the power level of operation and metal used will determine wire diameter. One grid seen here used 250 mil (1/4")diameter copper tubing

Cylindrical fusion chambers have had axial cylindrical grids function fine. (remember spherical grids work in any chamber)

The grids can be wound around a removable sphere (Meiro grid) or, more normally, be made up out of individual wire circles assembled into a geodesic type structure.

Most all successful fusors use a complex geodestic or spherical cage of wire hoops and are made of tungsten wire.

I have mentioned this before. Many metals, especially sintered metals, and tungsten in particular, are subject to hydrogen embrittlement. This is a terrible thing for structural strength but a get gift to fusor grids.

Put together under a bit of bending stress, a finshed grid of Tungsten, tantalum, titanium or hafnium will embrittle rapidly under deuteron bombardment this will relieve all stresses in the curved circles such that they suffer no tendency to open up if a weld or braze lets go. The entire struture is frozen forever, stress free. Nautrally it will now break like glass if stressed mechanically. Part of the stress relief early on is due to heat annealing as well, of course, assuming it reaches annealing temperatures. It can still melt, of course, under intense heat via bombardment currents. Continuous heating and cooling can also work harden many metals. Many factors enter into the equation.

Stainless steel grids will embrittle also but take a bit longer. The upshot is that if you make a grid of the above metals, all flexibilty and stresses will go away if operated in a deuterium environment. This makes all structural issues and worries about weldment release a virtual non-issue.



Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

Tom McCarthy
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Re: FAQ - Grid construction tips

Post by Tom McCarthy » Mon Jul 01, 2013 11:10 pm

This.
Was needed.
Thanks!

Tom

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Richard Hull
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Re: FAQ - Grid construction tips

Post by Richard Hull » Tue Jul 02, 2013 2:38 pm

The FAQ pile grows in each forum as required by newbie questions that beg details. It seems as if it never ends.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

Tom McCarthy
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Joined: Wed May 08, 2013 7:36 pm
Real name: Tom McCarthy
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Re: FAQ - Grid construction tips

Post by Tom McCarthy » Tue Jul 02, 2013 5:19 pm

But I suppose at some point must it stop? If I'm right the object of the website isn't to provide a recipe and say " here ya go get these arrange them like this, well done" but to give a guide? I can't really explain what I'm trying to say any more than that...

Tom

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Richard Hull
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Re: FAQ - Grid construction tips

Post by Richard Hull » Thu Dec 10, 2015 9:43 pm

Much has been done recently to speak to Tom's issues related to a re-organization of the forums so that newbies have additional guide posts. This assumes, (and this is a massive assumption), that they actually follow the paths supplied up front.

We have long known that exuberant newbies DO NOT LIKE TO READ!

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

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