Tungsten needle cathode

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Richard Hull
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Re: Tungsten needle cathode

Post by Richard Hull » Tue Feb 19, 2008 5:51 pm

Opening a fusor puts it in the crapper every time! I loath opening up my device. It will take a number of runs to return to its old self. I guess that is the price of experiment.

We probably need one to show and one to go. Gee it is like a two car family back in the early 60's......They were considered rich or just showing off to the neighbors. In the 50's, some folks in my neighborhood didn't even own a car or a TV! We had a TV, but no car.

I guess a sign of opulance on this site would be a two or three fusor man.

Richard Hull

What if the hokey-pokey was really what it's all about?
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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Re: Tungsten needle cathode

Post by 001userid » Tue Feb 19, 2008 7:28 pm

Great work! I often contemplate what two needles pointed at each other, with just a fine gap would produce.

Joe Sal

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Re: Tungsten needle cathode

Post by DaveC » Tue Feb 19, 2008 10:07 pm

Jon -

I used to make tips with an "arm waving" width of a couple of microns by using a tiny drum grinder mounted in the tool post of my lathe. The grinder was simplicity itself: a 1/4 or 3/8" diameter aluminum drum about 1" long with a spiral wrap of 600 grit SiC paper. The drum mounted directly on the shaft of a small DC hobby motor, and was powered by a spare N gage train powersupply! The needles were a std "sharp" sewing needle mounted in a collet chuck in the Lathe. The lathe was run at about 100 rpm and the grinder at a few thousand. Took about 10 minutes per needle, maximum. And the results fit a general bell shaped distribution centered around a few microns radius.

I always wanted to try the electropolish method that John Futter describes.. it seemed so much more sophisticated and precise. I unerstand the tungsten microelectrodes used for biological experimentation also use the electropolish( etch) methods to reach sub-micron diameters.

The thought behind running a lower pressures was to localize the action to the very tip.
The thing we're trying to do, is presumably cause ion collisions. So the field lines need to converge steeply. I expect you might see a big increase in the ratio of neutron yield per watt, as the ineffective but energy consuming regions are restricted.

Very nicely done, experiments!!

Dave Cooper

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Re: Tungsten needle cathode

Post by cdicken » Fri Feb 22, 2008 1:40 pm

I had the same thought. Maybe an 'almost point'-potential could be realized without having the needle epxosed to center of the ion bombardement.

Wilfried Heil
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Re: Tungsten needle cathode

Post by Wilfried Heil » Fri Feb 22, 2008 5:02 pm

Very interesting experiment and well presented as always.

Maybe the effect has nothing to with the needle form at all (field emission), but the electrode is just the limit of a very small solid sphere. I suppose it allows some recirculation of the ions which go past the tip.

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