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: Axial Fusor
Date: Jan 07, 6:12 pm
Poster: Jim Lux

On Jan 07, 6:12 pm, Jim Lux wrote:

>I just got a copy of "Building Scientific Apparatus, 2nd Ed", and it has been quite interesting. The section on charged particle optics using electrostatic lenses has opened my thinking to axial fusor concepts, i.e. two or more particle beams focused on a single point. It is potentially more of a bear to build due to the need for small, high-current ion sources -- ones in the current range desired are fairly complicated. However, the vacuum rig can be smaller and less expensive than for a spherical fusor. Thoughts?

Gotta have that duoplasmatron, right?

I don't know about the vacuum rig being smaller and less expensive though.. Typically, with particle optics, you want the vacuum to be good enough that the mean free path is more than 10x the dimensions of the chamber. No easy feat when you are pumping in lots of gas to ionize and make particles with. The big ion beam stuff typically has differential pumping, etc.

Not to discourage you, but....It looks fairly straightforward in the book.. a lot is, as they say, "left as an exercise for the reader". Lots o' tinkering required. Then again, tinkering is fun. Many is the hour I've spent with Moore, et.al, as well as Strong ("procedures in experimental physics"), sitting by the fire thinking, wouldn't it be neat to make a precision spectrograph, no, how about a pulsed KrF laser, no, etc....

I'm in the middle of looking at TWT (Traveling Wave Tube) designs at work, and while things like an electron gun with a grid looks pretty easy to figure out, I am learning that the distance between simple theory and practice is very great, and, further, that it is an ART not a science, which is why there aren't many people in the business of making those tubes. Note: people, not companies.. Making high power cathodes is an arcane art, and it is not unusual for a company to "lose the recipe" for a few months.. Apparently, small trace contaminants are both necessary and unknown. I heard a story about a technician who gave up smoking, and his cathodes didn't work well for months afterwards.

The ITT facility (in the Farnsworth days) was one of those at the pinnacle of ion and electron gun design and manufacture. They had rooms full of people who knew the art and could spit a gun out easily.

The beauty of the straight fusor (spherical or cylindrical) is that it is SIMPLE.. You can fight all the practical details of vacuum, high voltage, radiation measurement, etc. with a relatively high probability of success (where success is defined as producing any detectable neutrons) and a low expenditure of cash. Once you've done that, you'll have more info to base a decision to try a more sophisticated machine.

Ignore all this if you happen to be a ion gun whiz, and let us know what happens.