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: Novice Questions
Date: Jan 28, 10:54 am
Poster: Richard Hull

On Jan 28, 10:54 am, Richard Hull wrote:

>So, questions:
>1. We've been reading about the electronic beam heating, and how it can even be a problem with steel vessels. Are we fooling ourselves with these Lucite viewports? Should we bite the bullet and buy glass?

Yes, buy glass. I hope those ports aren't too big. The proper view port in a steel chamber should be no larger than 3". limit yourself to only one port if possible. (blank off extra openings with SS plate.) I monitor with a camera and use a 1.5" port and on my next system with reduce that further to 3/4". In short use as little glass as possible in a neutron producing fusor. A demo unit (no neuts) can be assembled in a good pyrex belljar. RH
>2. We went to our friendly local welding shop to buy some hydrogen. We were told we couldn't buy it unless we had hydrogen rated fittings for the gas bottle. I haven't seen anyone mention hydrogen rated fittings on any postings (not that I've read all of these yet!), so I'm wondering if they were being straight with us. Comments?

Absolutely! hydrogen is rated for use with special fittings only!! Next, you don't want hydrogen at all! For neutrons you have to have deuterium! (isotope of hydrogen). Deuterium can be had at any go wleding supply house. It is supplied in free user throw away lecture bottles only. A small bottle 10-40 liter which should last for years and hundreds of different fusors will cost between $150 and $200. RH

If we should have hydrogen fittings, where can we get them? Bear in mind we need to connect both the vacuum pump and the gas fittings to the same flange connector on the chamber. Having a non-conducting vacuum hose also seems a very sensible idea.

The fitting on the Mathey deuterium cylinder is a CGA or GCA type 630 or something like that, fitting. Your welding supply house can help with an adapter to a common gas regulator assembly. Probably special order. Yes, you gotta' have a regulator. The adapter is brass and costs about $20.00. A really good gas or welding supply hose will have just the right guy who can fix you up.

I made up a copper 1/8" copper line adapter out of my regulator to carry the gas to the valve and chamber. From this point I used all swagelock valves and fittings. The needle valve set me back about $35.00 and the rest of the sage lock fittings were about the same price. I welded a swagelock 1/8" gas female fitting to the chamber and used a swagelock gas fitting for the 1/8" line to finalize the connection to the chamber.

Yes pure gum rubber hose is best from the pump to the chamber, thought the plastic stuff is OK too.
>3. The feedthrough seems a major question, particularly for a low budget project. Contemplating an $800-$1000 professional feedthrough encouraged me to seek alternatives. A friend suggested a sparkplug, which seems like it could work, if I'm prepared to use epoxy to seal it into place and modify it appropriately to create an electrode . Any thoughts? Is this crazy, and I should just pay the money?

Check the past postings here. I give complete data on using a spark plug provided you can do a little reworking. No need to spend money on a costly pro insulator. RH
>4. Mounting the feedthrough is not a trivial issue with stainless this thick. I'm certainly not going to try to tap it myself. We've hit on the idea of using the top viewport and either drilling the Lucite or getting a steel replacement. This has two additional advantage. If we have to replace the feedthrough after epoxying it into place, the plate is easily removable. If we mount from the top, then changing the inner grid becomes simpler and makes it less likely that we might impact the outer grid once it has become fragile.

Smart idea. Make the thing so repairs can be effected easily. RH
>5. What do you recommend for a stand for the outer grid? Before you build your first prototype, these small fabrication issues loom pretty large, particularly for those of us whose constructions have been mostly logical rather than physical.

I used the double end threaded alumina and porcelin standoffs which are often found in surplus electronic meets and stores. RH

>6. Is a vacuum gauge really necessary? It seems that we can pump for a reasonable time, then fire up the power supply until we have a glow, then pump until the glow is almost gone. (And therefore a non-conducting vacuum hose.) If we do need a gauge, does it really need to be the $800 ones?

A gauge is very handy and while not mandatory, you will ultimately get one anyway. Duniway Stockroom has some nice brand new TC gauges complete for as little as $239.00. Catch the cross talk on those in past posts. Shoot for the DV-6M. RH
>7. We were planning on buying a small spot welder for grid construction until we found there is no such animal. The posting on building a spot welder was very helpful. I've got several fair sized capacitors rated at 3000 ufd @ 50 VDC. It seems too simple to just get a 50 volt DC power supply and hook it up to the capacitor and the spot welding electrodes. It seems we could easily get a nasty burn from this setup if we're anything other than totally alert. What else are we not understanding here being novices?

Can't advise here other than to be ever cautious if jury rigging. I jury rig almost every thing and tend to be very cautious. RH

>Our plan is to start working with protium rather than deuterium, and then switch when the bugs are worked out.

NO NO NO use air only to work out bugs! Why fart with dangerous hydrogen if it won't do anything for you! That waw the entire idea behind a demo unit first. To allow the neophyte to get his or her "sea legs" and learn vital skills and technolgy with air and 2,000-6,000 volt supplies, poor vacuums, etc. There will be plenty of time to load up with explosive deuterium and impress 20-25,000 volts across the chamber. There is little danger of deuterium explosion with good swagelock fittings, pre-vacuuming all lines and chambers. Never open a valve to the D2 lines until they are pumped completely down to the fusor chamber pressure!!! It is the MIXTURE of air and deuterium which explode and not deuterium. RH

However, we've had several people express serious concern about even getting marginally detectable levels of neutrons, including a couple of physicists from local universities. Well, I'm not planning on taking a nap in full view of the fusor when running, but what is the real risk here? Directly and through secondary emission? Should we view the plasma only through a video camera and/or a mirror? Do we really need to filter the output of the vacuum pump and treat it as low level waste? This is supposed to be cool, I don't want my son getting leukemia in 20 years from it.

Forget that hooey. At the levels of performance of even my advanced fusor (best reported on the list thus far), the risk approaches zero. Be much more concerned about X-ray burns from these pesky little photons leaving large viewports. I would advise a camera for viewing as the eye is one of the most radiation sensitive organs. You will be extremely fortunate on a first pass shot at a fusor to make neuts at all. Technique pays off and that is learned over time. Check all past posts regarding all these topics. Yeah, I know it is a lot of reading, but it is also a lot of hard won, shared knowledge too! RH
>The more realistic danger I worry about is chemical: hydrogen explosion in the basement of our house. I expect to release and pump down such small amounts of hydrogen that as long as the vacuum pump is vented directly to the outside the amount of hydrogen that escapes into the basement atmosphere should be trivial, even considering the way the pesky little atoms migrate through just about anything. However, I am the cautious type, and I'm happy to pay for the hydrogen fittings to reduce this risk if it makes sense.

Smart fellow! Swagelock stuff is fine for D2 gas handling. Hydrogen doesn't migrate all that badly as it is diatomic. Helium is not and migrates rapidly.

Once pumped down, you will truly be using infintesimal amounts of D2 gas. (Thank goodness too, it is expensive.) The explosion hazard approaches zero provided good common sense is used in pumping out the lines, purging them properly with pure D2 and venting that first slug which might have a tiny amount of air in it. once hooked up and vacuumed down with all lines purged, avoid having to do it all over again by constant moving and disassembly of the gas lines. Have your needle valve real close to the chamber so the short chamber line to the valve can be disconnected, leaving the bulk of your gas line still under pure D2 pressure. I regulate the 750 psi in the D2 tank down to 2 PSI in the lines. reconnnecting and pumping the chamber will haul out the air and the gas lines can then be opened to admit pure D2 into the fully evacuated chamber.

Good luck, and do play with air only in demo mode before moving on to D2 and neutron production. You might find this alone will blow them away in a science fair as it is safer to demo and show the system with air and have the full knowledge that inserting D2 and uping the voltage will make fusion.

Richard Hull