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: Some observations
Date: May 08, 09:23 am
Poster: Richard Hull
On May 08, 09:23 am, Richard Hull wrote:
While going back over my lab notes, I note that I have made a couple of observations which might be iteresting and that I have not reported heretofore.
First, the jets or beams from the poissor out into the inter-grid region appear to be a function of central grid geometry only! The beam or beams, depending on the operational regime obtained, almost never impact on an outer grid wire!
This is odd, at least on the surface of it, as the mean free path and other experiments with magnetic deflection indicate the beam becomes pretty much electrons by the time it traverses the chamber and the outer grid wires are postiive and should be very attractive of such beams.
This probably speaks to the success of attainment of the desired virtual spherical electrostatic field at the outer grid zone.
In addition, the spherocity of the inner grid coupled with the centration within the outer grid's field will dictate the beam's exit point. In my Fusor II, in the 6" bell jar, a lot of time was spent to not only center the inner grid, but also to make sure that it was quite spherical. These efforts have paid off with the characteristic constant jumping about of the beam, as if it "didn't know where it belonged", as the chamber is being pumped down. Finally, after a bit of protracted pumping to below 20 microns and some of the magnetic ion cleansing, the "star mode" is seen.
For those not using deuteruium, I will note that the common air pump down produces white to pinkish star mode rays at about 10-30 microns. While the deuterium/neutron fusors have red rays.
For those really going the full route and still not using a diffusion pump, a molecular sieve on the mechanical foreline is a must have item! This handy item will allow a good deal lower presure to be reached due to adsorption and trapping of water and pump oil vapor. I have zero'd my TC gauge on several occassions with this arrangement. With a dry ice packing of the sieve you might even go lower, but it hardly worth the effort. Naturally, if you use such a device, you must understand how and when to clear the zeolite sieve material of the bad stuff by bakeing it out. The sieve material can be is expensive but can be reused or recycled for years with proper care.