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

Posted: Wed Dec 27, 2017 10:34 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.
IMG_20171227_111933.jpg
Dual toroidal field controll
Cheers, Finn Hammer

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

Posted: Thu Dec 28, 2017 12:10 am
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: Thu Dec 28, 2017 3:11 am
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: Thu Dec 28, 2017 4:45 am
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 11:00 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.

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

Posted: Thu Dec 28, 2017 12:44 pm
by Jim Kovalchick
As far as the ticking I was experiencing, it went away after I peeled the shielding on my hv x-ray machine cabling a few more inches back. I also rewrapped my insulation tighter and thicker with polyimide tape. I use polyimide on all my exposed conductor points. I have tested this on my new fusor under load to 40 kV with no corona hiss to speak of.

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

Posted: Mon Jan 01, 2018 7:55 pm
by Jim Kovalchick
A few updates for my fusor:

1. I did some runs with deuterium, but even at elevated voltage the neutron numbers were dubious at best.
2. With deuterium versus air in addition to neutrons I was expecting a plasma color change from air and higher pressure Paschen points. For a given voltage the Paschen point was only a few milltorr higher than air. The color was more blue than the pink I was hoping for.
3. All of the observations pointed toward an air leak polluting my plasma. Reluctantly, I broke vacuum and connected my helium leak detector. My home made feedthrough has developed a leak at the stem. My guess is that heating impacted the stem seal. I will need to make a repair.
4. I've been using the neutron detector I demo'd at HEAS. I had it tuned for the SK-1 clicker such that it would only sound on neutrons. Here in my lab I have it connected to NIM components, and I have the ability to adjust its threshold. I noticed that my detector, which uses the LiI element out of a NeutronRAE, easily sees x-rays above 28 kV. So for folks using NeutronRAEs for neutron detection you will need to demonstrate x-ray discrimination before claiming fusion. I am using the 59 keV gammas out of Am 241 to set my threshold.

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

Posted: Mon Jan 01, 2018 11:17 pm
by Richard Hull
Jim, Thanks for passing on the x-ray issue with the neutronRAE detection system. Fortunately the detections of same can be discriminated out of the data

Richard Hull

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

Posted: Sat Jan 06, 2018 6:23 pm
by Jim Kovalchick
I'm still having trouble getting neutrons out of my fusor. I'm troubleshooting my detector, but I decided to also do a little glow cleaning. Here is a pretty picture of some liow voltage deuterium plasma 4000 V and 10 mA.

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

Posted: Sat Jan 06, 2018 8:43 pm
by Richard Hull
Just from what I see, you are basically clean and it is just a matter of a bit more operation and hitting the higher voltages of 30kv with a pressure as low as 5-6 microns and 8ma and you had better be counting. The real rock and roll will be obvious at that pink glow with 35kv or more at 10 microns and 10ma. (kind of a 500k n/s zone). All the best in moving upward. To hit the mega mark on fusor IV, I must be over 40kv applied, 12+ microns, 12 + ma. At this point, most the rays are gone or very faint.

Richard Hull