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Wait, what? Tiny fusors? Not for me!

Posted: Mon Dec 18, 2017 7:09 pm
by Jim Kovalchick
So, it seems that the 2.75" tee fusor is the flavor of the day such that evem Richard is advocating them. Recently I had a chance to get a plus ultra grande chamber, and in spite of tiny fusors being in style, I am going it. I offer for your viewing pleasure the start of my next model fusor chamber complete with two 8" ports, four 6" ports, and four 2.75" ports. This ahows my progress so far. I'll post updates as I reach major milestones. Cheers, Jim K

Re: Wait, what? Tiny fusors? Not for me!

Posted: Mon Dec 18, 2017 11:37 pm
by John Futter
Jim
That seems to be entirely adequate

Re: Wait, what? Tiny fusors? Not for me!

Posted: Tue Dec 19, 2017 12:30 am
by Richard Hull
A fine catch on the surplus scene.

I'm not ditching my 6" spherical fusor IV either. The smaller systems might let the new guys save some money by purchasing smaller, less expensive crosses and Tee's. They still have to prove they have done fusion to the same standard as everyone else, of course.

For Spheres, a 6-8 inch system looks very impressive and will not waste a lot of gas as would a giant 12" sphere or giant cylinder.

Richard Hull

Re: Wait, what? Tiny fusors? Not for me!

Posted: Tue Dec 19, 2017 4:56 am
by Dennis P Brown
Small fusors appear to offer higher neutron rates for a given voltage and power; whether that is valid will, with more experiments posted, be proven one way or the other.

In any case, your chamber has a lot of gadgets attached - what are they?

Re: Wait, what? Tiny fusors? Not for me!

Posted: Tue Dec 19, 2017 7:59 am
by Jim Kovalchick
Dennis,
The Eye-Sys is a low pressure gage. It likely won't stay and will be replaced by a standard glass vacuum gage because it is of dubious heritage and may not work. The blue box is a mini convectron that I'm using only because it has a switch that I can use to trigger the Eye-Sys off when pressure gets into millitorr range. I'm keeping my fingers crossed for the Eye-Sys because I don't care to have glass hanging from my chamber.

My primary instrument will be an old, reliable baratron not seen in the picture.

The 2.75 port on upper left is a secondary view port. It will be looking down toward the poisser and will give better views of star mode than the primary view port that will be installed on the 8" port in the rear after a sacrificial pyrex disc is applied. The spacious vista of a 5 inch window will help me see a good bit of the chamber interior which will be useful for seeing any issues such as arcing and for just really nice video. It's x-rays will face the back wall, and the secondary view port will get a lead cap.

The feedthrough is still under construction and will attach to the left.

I haven't settled on a grid design yet. I've been begging my son to design me one...

This chamber is large, but it's only slightly larger than my son's original mixing bowl fusor that he got pretty good numbers from. My goal is to do some activation experiments. If this version doesnt meet my needs, I have a 6-sided 2.75 conflat I can try. :)

Jim K

Re: Wait, what? Tiny fusors? Not for me!

Posted: Tue Dec 19, 2017 8:58 am
by Jim Kovalchick
Some comments on the big vs small debate... I am skeptical of neutron numbers derived fron bubble detectors parked close to small chambers. You dont get accurate activity numbers from a detector parked right up next to radiation and then treat it like a point source. The geometry of the source and detector sizes just don't make sense to me. My nuke professors back in school would have given me no mercy if I did that.

I get that big chambers may waste deuterium, but that would seem to be something fixed by both design and operational considerations. Fixing a leak or outgassing issue by flushing more d with bigger in and out flow is not a size issue. Also, wasting current by using it for plasma production vs using an ion source is not a size issue.

Re: Wait, what? Tiny fusors? Not for me!

Posted: Tue Dec 19, 2017 11:57 am
by Dennis P Brown
Jim, I agree that more data is required - especially (and hopefully soon), Ag activation. If the flux is over a million neutrons/sec, activation will be strong and provable. That, I would think, will be the 'Au' standard for proof, maybe (lol.)

Don't know the voltage you are planing on using but a thick glass plate (or stack of thinner plates) can also shield for x-rays very well.

Re: Wait, what? Tiny fusors? Not for me!

Posted: Sun Dec 24, 2017 10:07 am
by Jim Kovalchick
Some status updates

I've added the view port you see in the front. I will turn the fusor to face the wall during operation. I added a 5 inch sacrificial pyrex plate to protect me and the view port. The plate is held in place with wedged aluminum foil.

I've also added the high volt feed through. It's fabricated from a 6" CF flange and a dual post insulator. The stalk is #6 all-thread.

Upon sealing his chamber my son always left a coin or two inside much like the coin ceremony during the building of old masted ships. In keeping with the tradition but with my own personal twist, I put a uranium marble in mine. I doubt it brings the chamber good luck, but maybe it will tell me something about the UV light output of the plasma.

Re: Wait, what? Tiny fusors? Not for me!

Posted: Sun Dec 24, 2017 10:47 am
by Dennis P Brown
Looks really good; also, might want to place a glass blank inside the chamber view port to shield your main window so as to keep it clean.

Re: Wait, what? Tiny fusors? Not for me!

Posted: Sun Dec 24, 2017 11:09 am
by Jim Kovalchick
Dennis, I put the pyrex plate inside the chamber. It will keep the view port clean, act as a sacrificial heat shield, and block a view x-rays. This is a technique I used on my last fusor, and it worked pretty well.

Re: Wait, what? Tiny fusors? Not for me!

Posted: Sun Dec 24, 2017 1:52 pm
by Richard Hull
That might be one of the best looking chambers to be presented here in years!! Keep us up to date on your progress. I am fairly sure that there is a significant UV component in a fusor. Vacuum UV can only be found in such systems. Any dangerous UV would never leave the system, of course, without a Quartz window.

All the best in getting this plus-ultra system on line.

Richard Hull

Re: Wait, what? Tiny fusors? Not for me!

Posted: Sun Dec 24, 2017 4:32 pm
by Silviu Tamasdan
Well _some_ UV is bound to escape, depending on intensity and wavelength. Glass is to UV what lead is to gammas, they get attenuated but not completely absorbed. That's the problem with photons, you can never get rid of them completely.

Re: Wait, what? Tiny fusors? Not for me!

Posted: Sun Dec 24, 2017 5:06 pm
by Dennis P Brown
Regular plate glass cuts off essentially all hard UV (UV-B) and one need not worry about that spectrum at all (say about 330 nm and shorter.) That said, do be aware that both UV-A even to Blue-Green ... say down to 450 nm can be harmful to the eyes (apparently, the new very white LED's street lights can damage the eyes); however, little of those wavelengths are usually produced via a plasma in a fusor. If one is using a Hg source, plate glass is rather effective cutting off most the harmful wavelengths.

Re: Wait, what? Tiny fusors? Not for me!

Posted: Sun Dec 24, 2017 9:46 pm
by Jim Kovalchick
Final holiday update
I used a helium leak detector to locate some CF torquing issues, but a fairly bad leak remained. I never thought to pass a little helium over a KF 40 bellows hose I was using to connect to my turbo. When I finally hit it, it was a huge hit on the leak detector. I have temporarily replaced it with hard pipe. I was able to remove the leak detector and roughed the chamber to less than 10 mllitorr in five minutes. Isolated, the chamber rises less than a milltorr a minute. This is all before any bake out. I think my chamber is ready for plasma.

Next steps after the holiday - clean up the construction mess to make the lab safe, get my power supply ready, and get some current and HV indicators attached.

Re: Wait, what? Tiny fusors? Not for me!

Posted: Mon Dec 25, 2017 7:21 am
by Dennis P Brown
Yes, bellows can be a tricky issue since they are easy to overlook; while sorry to hear that, still, I am glad you have a tight system now - the bake out will certainly and dramatically lower the out gassing rate. I use dry air to purge my accelerator to better enable it to get into the low vacuum range more quickly; that or argon might be useful for your chamber if you decide to go ultra high (below 10^-6 torr.)

Re: Wait, what? Tiny fusors? Not for me!

Posted: Mon Dec 25, 2017 1:16 pm
by Richard Hull
Great work and what a beauty. That is a system to be proud of. I'll bet it will kick butt and easily hit the mega mark with ease in the 35-45 kv range.

Richard Hull

Re: Wait, what? Tiny fusors? Not for me!

Posted: Tue Dec 26, 2017 12:39 pm
by Jim Kovalchick
First light for this chamber.

1. Started at -8 kV with air.

2. Walked voltage to - 17.8 kV holding about 8 mA.

3. Need to rework HV cable because I heard some ticking from the cable near tbe feed through at peak voltage. Probably dont have the shield stripped far enough back.

4. One of my grid wires shifted a little when it warmed, but otherwise there was only minor and brief arcing as I stepped voltage.

5. I don't think this is a surprise to anyone but the uranium glass marble did glow a little. The glow doesnt show up well in the photo.

Re: Wait, what? Tiny fusors? Not for me!

Posted: Tue Dec 26, 2017 2:07 pm
by Dennis P Brown
I discovered the hard way that 30 kV will go a long way along an insulated cable and reach the shielding strap (and I had carefully cleaned the cable after striping away the shielding); a good four inches was needed, so I ended up removing 8". In the HV cabinet, I even placed the cable end under oil for the ballast resistor connection to play it safe.

Re: Wait, what? Tiny fusors? Not for me!

Posted: Tue Dec 26, 2017 2:34 pm
by Jim Kovalchick
Dennis,
I just atripped back about 8 inches where there was only 4 before. This seemed to do the trick up to -40 kV. This is the highest voltage I've ever spent any time at. It made a nice tight spot of plasma.

Re: Wait, what? Tiny fusors? Not for me!

Posted: Tue Dec 26, 2017 10:38 pm
by ian_krase
Allegedly, folding back the shield, possibly over an O-ring or similar, rather than just cutting it can also help. That is what I did, and while I had corona I never had arcover at 50kV just from the end of my cable.

Re: Wait, what? Tiny fusors? Not for me!

Posted: Wed Dec 27, 2017 5:34 am
by Finn Hammer
When the voltage in a circuit exceeds 20 - 30kV, field control becomes a game changer, and the key word here is radius of curvature.
Why is that?
The object is to avoid flash over in the form of arcs, or discharges into the surrounding air in the form of corona.
These things appear in the reverse order, without corona, there are no arcs. So fight corona and you will contain your charge.

One good way to control the field gradient of an electrical connection is with the use of toroids, below is the way I suggest it should be done, at least it is how I intend to do it when I get so far.
Dual toroidal field controll
Dual toroidal field controll
Cheers, Finn Hammer

Re: Wait, what? Tiny fusors? Not for me!

Posted: Wed Dec 27, 2017 7:10 pm
by Richard Hull
Field control is the answer and I have written extensively on this in the past. I purchased a nice hand spun 4" diameter, copper toroid from John Freau at the 2012 HEAS. I purchased another aluminum 4" toroid from John at this past HEAS gathering in October. I currently use a 2" ball on fusor IV but will probably use the 4" toroid on fusor V, if it ever gets built. I kill corona at the 2.75: conflat bolts just below the insulator terminal with silicone HV putty wadded over the cap head screws. My past 1990's decade of Tesla coiling experience taught me all about "practical" field control.

See the image attached on how to not arc along a 12 tall coil with 50 kv at one end and 1.2 megavolts at the other....in air!!

Richard Hull

Re: Wait, what? Tiny fusors? Not for me!

Posted: Wed Dec 27, 2017 10:11 pm
by ian_krase
Can you tell me more about these balls? Is anything inside them? Do they enclose the connector, or get drilled for a banana plug?


Has anybody pulled off fully insulated HV connections?

Re: Wait, what? Tiny fusors? Not for me!

Posted: Wed Dec 27, 2017 11:45 pm
by Richard Hull
The ball on fusor IV is just a hollow chrome ball with an internal banana jack. My HV cable is not shielded at all but is a 50kv rated silicone HV wire with a banana plug on the end. This just pushes through a concaved hole in the ball and into the banana jack. No corona at 50kv. A ball is never as good as a toroid but 50kv is a rather low voltage and as long as there is no corona or sharp grounded components within 3 inches and the ball is kept meticulously clean of dust and grime, there is little chance of a DC arc.

There are many images of fusor IV in images du jour.

Richard Hull

Re: Wait, what? Tiny fusors? Not for me!

Posted: Thu Dec 28, 2017 6:00 am
by Dennis P Brown
When you ask:
Has anybody pulled off fully insulated HV connections?
I assume you mean a near zero corona, fully insulated connection? If so, I have done this for all internal connections for my fusor power supply by building all diodes and ballast resistors/connections under oil. Simple, cheap and easy. This method also eliminates humidity problems. A minor advantage - I can use normal wire and connectors to assemble some components since, when under oil, they are fully insulated. Saves me money and lost power from the x-former.

As for 'messy', I've had no issues in this regards because I allow these devices to drain overnight; if in a hurry, I just rinse with 90% alcohol and use lint free rags. The oil (synthetic motor oil; anti-corrosion additives improve the oils dielectric properties further so they are actually better) is very cheap (compared to most x-former oils) and easy to obtain just about anywhere. Do not use regular motor oil.

There is a link to the photo of the insides of my full wave diode bridge and return current resistor for the x-former system (oil not yet added to diodes.)

download/file.php?id=10789&mode=view

Here is the complete assembly, with oil and covered. The small oil pan item on the left is my main output ballast resistor with its main power cable connection all under its own oil bath:

download/file.php?id=10788&mode=view

This system has performed without issue for some time now. I get zero corona issues and no flash over problems (a good idea to prevent this from happening to your HV diodes. Also, really keeps diodes cool which is very important - esp. for the ballast resistor to dissipate heat during long and/or heavy current operation.)

For a large vertical insulator column, wouldn't be too difficult to add a cup for oil if one does not want to deal with machining or buying sphere's or other or shaped brass/copper adapters; and these metal items can still have issues on very humid days. Nor is dust then an issue. Also, provides a nice and almost fool proof physical reminder barrier to the HV terminal.

While I just bury my main fusor connector (just 32 kV) in a ceramic case, for really high voltage (over 50 kV), whenever I deal with those levels I always go with oil since, again, eliminates humidity and flash over problems and creates a safer system.