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: More on Mass Spec Analysis
Date: Aug 23, 9:39 am
Poster: Richard Hull

On Aug 23, 9:39 am, Richard Hull wrote:

>>Perhaps Richard could comment about the pump locations and whether a port for a mass spec would be practical in this area.

But aren't you in a molecular flow area... As the Lesker catalog points out "Vacuum doesn't suck".. The pump just removes any molecules that happen to bounce into the inlet (why pump diameter is everything for high vacuum). It shouldn't make any difference where you hang your mass spec.


This entire post by Jim should be re-read by all vacuum heads. I just finished another of my "High Energy Amateur Science" videos which spotlighted vacuum for amateurs. The main theme is "vacuum don't suck". In molecular flow, the molecules are bouncing around like BBs in a box car. It is a crap shoot as to where they go!

A pump never pulls molecules into it whether in viscous or molecule flow regimes. The gas molecules always supply 100% of the energy to enter the pump in any mode!!! The pump just continuously offers new expanding, intrinsically empty VOLUMES for them to flow or ricochett into. Again, the molecules supply all the energy needed to enter the pump volume! The work done by the pump is strictly limited to compressing the ever falling pressure of trapped molecules in the now sealed off volume to greater than atmosperic pressure so they can be spit out on the exhaust stroke. Oh...It also works on the intake stoke, but only against the outside air and not the inside air. RH
> Was also thinking about the constituents of the fusor "star" rays that are seen. These should be relatively high in concentration of fusion reactants.

The rays are mostly electrons, and because they are low mass, they are focussed well by the grids. Actually, of course, the visible part is the result of the neutral atoms in the way getting hit by the fast moving electrons, but the idea is the same.

Again, Jim is right on. In the simple fusor, the electrons predominate and have the greatest mean free path. My first Fusor video shows this dramatically with the easy bending and 180 turn of the beams by magnets external to Fusor I. In Fusor II, I even got them to corkscrew near the walls with a Nd:Fe:B magnet. The chamber is so well electrodynamically "stirred" and thermally active, that reactants and molecules would probably be well mixed throughout. RH

> Could some type of deflection or sampling method be positioned near the apex of the ray. Since some appear to impinge on the Fusor outer shell, a sampling port located there would be a good place to put the MS...I am rashly ignoring all sort of practical issues such as magnetic shielding and etc., ...assuming they can be worked out Comments?



I prefer to avoid the apex of the rays with delicate stuff as they are really just pure, hot, and drill like, boring electron beams.

In the early fusor III, one beam intercepted the view port glass and created a flairing spot which eventually chiped off. I now align my inner grid to the view port such that looking in on it, I see a wire dead center in the viewport. The E beams blast out the electrostatic center (often the geometric center of the open, spherical triangular sections of the inner grid.

I might also note that should an E beam enter the exhaust port, you could outgas the hose on the other side of the nipple by E beam heating and have the devil's own time trying to keep the thing pumped! All this is crap which should be mechanically figured when assembling a system. Especially a neutron producing higher power system. Demo fusors in plastic desicators will never hit low vacuums and have high current opeartion at the same time for the above reasons.

Richard Hull