Fusion Message Board

In this space, visitors are invited to post any comments, questions, or skeptical observations about Philo T. Farnsworth's contributions to the field of Nuclear Fusion research.

Subject: Re: Diamond electron emitters
Date: Jul 14, 1:14 am
Poster: Mark Harriss

On Jul 14, 1:14 am, Mark Harriss wrote:

>> There is a very short article at http://www.lerc.nasa.gov/WWW/RT1995/5000/5620k.htm about CsI doped diamond material which have a secondary electron emission co-efficient of 60 as opposed to 2-4 for most materials used in these applications. The article mentions they can get good current densities with 10-15 volts of power!! . I am not sure of the consequences for a fusor device but getting up to 30 times the electrons out of your device structures or only having to apply 15 volts to generate them looks pretty good! even though you'd still need a high electric field for the rest of the device to function.
>>I'd appreciate any comments as to whether this stuff is even useable for a fusor device.
>I am positive it would be just the ticket and readily beat out any other method.
>I will now be facetious and flippant and state that I just know that 1 lb tins of Cesium Iodide doped diamond emitter material is available from any normal hardware store for 98 cents per tin.
>Cutting edge stuff usually needs to be read as "bleeding edge" due to stratospheric pricing. Custom production, minimum quantity orders, etc.
>A super adroit wheeler-dealer might actually succeed in cajoling some hapless salesperson at the source supplier into giving out a free "engineering sample", (Enough for one fusor.), with the carrot of immediate orders to follow should the material work out.
>Hope springs eternal.
>Good luck on this high tech approach.
>Richard Hull

Thanks for the encouragement Richard, You see at this point i wasn't sure whether it was even worth trying or considering.... What i propose is to use my 9"x 11" (good 'ol offcut steel sizes) home-made vacuum chamber to run a few diamond coating experiments. I would first ideally build a Hirsch Meeks device (Mk IV?)inside the chamber and get it all running smoothly with measurements of neutron flux nicely graphed (only one measurement necessary??) .

Then start mucking around with getting diamond coating processes working, one i had in mind which amazed me was a glass tube with the correct 1-2% methane gas in hydrogen flowing thru it to an orange hot filament at one end which was mounted close to the substrate which ended up with a few microns per hour of diamond. The whole thing was in a low vacuum chamber in a feature article in Scientific American magazine about diamond semiconductors i think, around 1990-1993 though I'm not too sure.

I'm also not too sure how critical the cesium/iodine is to the emitter but i think it would get by without it albeit at a higher voltage level.

Another approach i plan to try is to make the grid and cathode out of a thoriated tungsten filament from an old ceramic transmitter tube, these have a cylindrical basket structure and are the filament/cathode at the same time, it seems when a tube wears out it's because the carbon material gets depleted from the wire, but is readily recharged by applying voltage to the filament, in a carbon rich gas and monitoring the filament current as the resistance increases with carbon content and voila!! a recharged electron emitting filament. There is a guy over here in Australia who does this for a living so i'd get him to do it and then try to bend/cut/spotweld the whole thing into a sphere, possibly with two low voltage connections for filament power.

Finally i would LOVE to get more information about this diamond coating process: http://www.xent.com/spring96/0270.html it seems these guys get a tenacious diamond metal bond using CO2 as the gas and lasers to scan the surface to be coated. The whole thing is done by a toolmaking company QQC in Dearborn Mich, is 1000 times faster than normal CVD methods and can be done up to 1/2 inch thick!!!. Maybe we could arrange for a bulk job lot of tungsten wires to be coated for a reasonable price to each subcriber to get a better coating than any other available anywhere.

Mark Harriss

ps the url for the coating process is: http://www.xent.com/spring96/0270.html