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: Fittings/Gammas vs. Neuts
Date: Aug 10, 09:14 am
Poster: Richard Hull

On Aug 10, 09:14 am, Richard Hull wrote:

I have used a lot of different fittings.

The absolute best, cheapest and easiest to use are the QF or quick flange (also KF - Kwik Flange) fittings. These cost between $20 and $30 per connection (two flanges, one centering ring and one clamp). Common QF fittings go up to 3" diameter, but the fusorite will not need much large than QF16 or QF25. I use both, as needed.
See Kurt Lesker or Duniway catalogs.

They are fast to connect and disconnect and good all the way up to high vacuum levels (~10-5 torr). However, for those with Turbo pumps or other UHV systems, the only way to go is conflat fittings (CF). They are way more expensive, being in the area of 40-50 bucks per completed union, but are rated out to 10E-10 torr with bake out. Conflats are also not for experimental systems which need to be taken apart frequently as a lot of bolt torquing is the order of the day. (6 bolts of a small fitting and as many as 32 bolts on really large conflats!).

Conflats go by outer flange diameter and start at 1.33 inches and go up to 24", but most common CF fittings stop at 14" diameter. I use only one size and that is the ubiquitous 2.75" conflat.

I really mix and match to suit some good hamfest buys on valves. Valves will kill the average amateur vacuumist or fusorite. A cheapo HV valve is about $200.00 new and a good one is 375.00 new.
Hamfests often see valves in the $20.00 range, but you can't choose the fittings on the ends. Thus, I have a hodge-podge of valves and fitting to save money based on fortuitous valve purchases.

For those not hamfest savy, or starting from scratch and buying their way in with pure cash, I would recommend QF only in the QF25 area and buy valves to match. For $1000.00 you might expect to get two really good valves and enough hardware and unions to make about 10-15 junctions with maybe one "T" and one "X" fitting and a short SS flex hose. Money is chewed up rapidly in the world of deep vacuums.

For all gas lines You should use only Swagelock fittings and valves!! These work well and are re-usable, re-sealable, an are deep vacuum rated. Swagelock 1/8 or 1/4 fittings are recommended. I started with 1/8", but all the pros use only 1/4".

On radiation....

I have yet to record any Gamma rays and those are just not to be found in the fusor at all. I have not seen any real heavy X-radiation etiher and I measure with a broad range of radiation instruments. The thick SS walls in my system probably stops any such radiation.

I have measured only soft X-rays streaming through the observation port glass. I have reported extensively on this list with posts regarding this hazard, specifically, in a recent post about curious 90 degree radiation from the seals. The outer shell of the fusor is very radiation quiet during operation.

The proton thrown out of the tritium reaction carrys away about 3 mev of energy and this should indeed collide with the walls and can kick out photons. The energies should be moderate, but might penetrate and walls. A standard geiger detector might not see these and even an ionization chambered instrument might miss most, giving a deceptively low reading. I'll have to check this out with a special "gamma hunt" run of my fusor using modified techniques.

Richard Hull