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: HV Feed through
Date: Nov 21, 00:13 am
Poster: Joshua Resnick

On Nov 21, 00:13 am, Joshua Resnick wrote:

>Thanks for sharing this!!!! This is sage advice from a real designer of real world stuff and counts in the grand scheme of things. As a grizzled old engineer myself, info like this is appreciated and cherished.
>I gotta try this sometime soon.
>The nearly .6" hot electrode will help hold the coronal stresses way down as opposed to say a .125 diameter rod, especially at voltages over 20kv.
>The only problem I have with your design is the teflon. I have used it before and it does give some minor outgassing and with ion bombardment and the large surface area you have in chamber, it may refill the chamber with unwanted gases as fast as your pump tries to empty it. (unless you have a real monster pump like a Welch 1397.)


I was unaware of Teflon's out-gassing properties. I, however, did surmise that because it is a plastic, even though it has great temperature characteristics, it would release some *nasties* as those beautiful long molecular chains were broken. I used the Teflon only on the seal portion of the feed. The actual supporting stalk mates with this unit, and a thinner conductor continues through a machinable ceramic stalk to the electrode. I am considering glass-mica or just regular alumina, both are fine but I believe (Don't quote me on this) that glass-mica has a higher K.
As we all know, during operation, there is a faint ion glow throughout the chamber, this situation can only be exacerbated by the increase of voltage. While thinking about you last post, it seemed very reasonable to expect that this stray ion bombardment would cause out-gassing from the Teflon. Perhaps some grounded mesh type material (Al screening) could be placed at the base of the chamber on standoffs so that it is above the Teflon and surrounding the ceramic shaft with a hole rimmed by a toroidal conductor spaced away from the shaft. This would raise the ground plane up and, ions would form on it rather than on the base plane and would avoid the feed. In addition, My outer grid could be a solid sphere only with a mesh covered hole on top for line of sight from the observation window to the plasmoid. This would further isolate the discharge regions of the chamber.
Thanks again for your input, we all know what a design challenge these things are.

Joshua Resnick

My pump is very big.