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: Tour d'force
Date: Apr 28, 12:48 pm
Poster: Gerald Morris
On Apr 28, 12:48 pm, Gerald Morris wrote:
>Now for those extra comments.
>Only one error was seen and it was of minor historical importance. The largest Spherical chamber used in the Farnsworth/ITT periond (1959-1968) was 8" not 20".
-- Thanx. It was late and I "slipped a synapse". Reckon I was thinking of Miley's or my own copper dewar dimensions.
I have again, discussed most relevant hardware issues of historical fact with the original team members in person. If one does some math at the pressures used for high density plasma work, 10"-12" would be the maximum fusor diameter size for a fusor running a 1 micron or just below at sub-micron pressures. Oh, and also, Hirsch and Meeks had a patent on the basic simple inner grid fusor. Miley just dropped the dispenser cathode and anode ionizer. Actually, they allowed the ions to be formed just at the anode shell where they are needed the most. I am thinking about including these to up the efficiency of the system by getting the bulk of the electrons formed to make ions out near the anode shell. This warrants that all ions enter the inner grid at fusion enery.
>Gerald has learned the hard way about other "stuff" in the chamber. There can be nothing in the chamber other than the inner grid and a totally inert electrical stalk and insulator. Every thing must be smooth! No screws, no nothing!
--Yep! Granted, the stuff was a mere expedient, but I editorialized on that already.
>I use a ceramic feed through insulator (modified spark plug) welded on a conflat fitting. To the tip, I silver soldered a short stainless 1/4" diameter 6-32 round threaded standoff. Into this threads the 1/8" stainless electrical stalk to which the tantalum inner grid is affixed. Prior to screwing in the stalk, a pure alumina insulating sleeve which is a very tight fit is placed on it. the outside of this sleve is 1/4" in diameter and this sleeve rests on the standoff. The base of the plug has a TIG welder ceramic insulator placed over its base which is 1/2" in outside diameter and has an inside diameter of 1/4". Thus, all pieces telescope and are a perfect slide fit together to give a well insulated alumina shell covering the electrical input stalk from where it enters my spherical 316L stainless chamber up to the exact base of the spherical inner grid geodesic. No plastics allowed!!!!!
--Are you referring to the fusor region proper or the vacuum system in general? I would point out that no OBSERVABLE outgassing has seemed to occur from the Lucite fittings per se. The stuff is used extensively in Bickel's lab on many vacuum systems. Hell, there's a Helnholtz mirror made entirely of the stuff. I will repent of Lucite if it is a mortal sin to vacuum but I have not found much reference to problems with it outgassing.
>Gerald's new "good" Sorenson supply should serve him well. Current limiting is something I gotta' work on here for my modified X-ray supply.
--Amen! I recommend CT's on the high side to monitor the current and be used to trip the contacts. You ARE using an HV contactor I hope?
>Gerald notes his current seems high for low voltages and suspects his gauge. This is reasonable. I have nursed a 2 micron D2 chamber up to 24kv and it took about 5-10ma. This process is a slow one of about 1/2 hour at the fusor glow mode self cleans and ion pumps its way to just sub-micron. I then bleed D2 back in the chamber continuosly with the pump running to a level of 1-3 microns. Scott Little and I found this works best.
-- Duly noted. I have also observed the slow decay in current with time at a given voltage and concluded some self cleaning was going on. I will spend some time nursing the voltage up, just to see how high I can get it. We also have a shiny new digital TC gauge, which I intend to calibrate on a damned reliable system.
>Gerald's theoretical treatment, echo's Hirsch's original work near the end of the ITT/Farnsworth period.
--It is so based. Hirsch refers to the derivation actually being done by the team of Elmore, Tuck and Watson in his article. I put it in my presentation to allay the doubts about the issue of virtual electrodes. The math isn't that hard to follow.
>By the way, that deuteron recirculation is just not possible in micron fusor's due to mean free path. I think I noted this in another earlier posting. With our densities, we are working with a gang o' deuterons, but they would not get a second shot at fusion on a return trip if they even get a first!
--Whoops! I think you might have mentioned something about this even in your documentary. Of course, Farnsworth discusses energy loss and recirculation at length in the patent I have found most useful.
>At reduced pressures of 10e-5 torr and lower, we lose a lot of those atoms of deuterium, but nice deuteron recirculation becomes possible. Go too low, and a dispenser cathode arrangement becomes a must.
--Yep! I haven't used the diffusion pump since December. Also, my cheap video camcorder isn't doing my star modes much justice. They are much better defined to the naked eye.
>We were trying to keep this thing simple and cheap for small time operators and experimenters. The possibilites are magnificently abundant in this system depending on budget, junk box, skills and the nerve and stamina of the experimenter.
--Don't leave out some brains Richard. One reason I sermonized on certain of my own atrocities was for the benefit of the unwary.
- Re: Tour d'force - Richard Hull Apr 29, 09:58 am