Archived - Van de Graaff Fusion

Current images of fusor efforts, components, etc. Try to continuously update from your name, a current photo using edit function. Title post with your name once only. Change image and text as needed. See first posting for details.
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Frank Sanns
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Archived - Van de Graaff Fusion

Post by Frank Sanns » Wed Oct 14, 2009 2:08 am

There have been pros and cons of low current fusion but since I had a medium sized Van de Graaff generator I gave it a go.

The first picture is a photo of the VDG and my fusor.

The second picture is the half inch (1.25 cm) spark gap between the VDG and an inner grid electrode.

Last picuture is an electron beam at a pressure just before star mode. These are visible in the fusor albiet faint compared to a multi milliamp run, but still clearly visible. Small amounts of fluorescence of the pyrex bowls and the aluminum grid was faintly present. I will hold back quoting any neutron numbers since there is a chance that some noise from pulsing could affect the already paultry neutron numbers that I appeared to have been detecting.

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Jon Rosenstiel
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Re: Van de Graaff Fusion

Post by Jon Rosenstiel » Wed Oct 14, 2009 3:33 am

Way cool experiment Frank, you da’ man!

I have no experience with a Van de Graaff, but I’m guessing that the spark across your half-inch gap was continuous… is that correct?

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with one hand while pushing the on/off button with the other.

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Mike Beauford
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Re: Van de Graaff Fusion

Post by Mike Beauford » Wed Oct 14, 2009 3:46 am

I've got to second that. This is pretty freaking neat.
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Frank Sanns
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Re: Van de Graaff Fusion

Post by Frank Sanns » Wed Oct 14, 2009 4:10 am

It is high rep rate but not continuous. From the sounds and sights I would have guessed around 10 hz to 15 hz but I figured I had the evidence in the photo so below is photo number two from my first post blown up.

To my eye, I see four sparks. The shutter speed was 1/3 of a second so that is 12 hz. It was just one photo so the uncertainty is high for any one measurment but coupled with my observations I feel that the 10 hz -15 hz is a good number.

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John Futter
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Re: Van de Graaff Fusion

Post by John Futter » Wed Oct 14, 2009 5:47 am

Frank
I presume you are spaying electrons onto the belt to get negative charge on the terminal



if so ----Loose the spark gap and rely on the insulator to fusor for the breakdown ---throttle back the D2 gas until the insulator breaks down occasionly and re measure the neut output. Couch measurement indicates that your present voltage is 50 to 75 kV depending on the gap 3kV per mm ( my guess 20mm).

we have been doing a D2 run @ work today @ 1.4MeV for NRA measurement on light element contamination in a sample, rem ball 3.5 metres away from beam tube indicated 0.12 rem /hr @ 25nA beam current.



Volts are your friend here and at very small currents I suspect you will not see anything in the viewport

FWIW !!

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Steven Sesselmann
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Re: Van de Graaff Fusion

Post by Steven Sesselmann » Wed Oct 14, 2009 8:31 am

Frank,

This is a way to fusion which is more affordable and safer, and puts it within the acceptable limits of high school experiments.

Well done..

Steven
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Frank Sanns
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Re: Van de Graaff Fusion

Post by Frank Sanns » Wed Oct 14, 2009 12:26 pm

John,

You of course are correct. Much higher voltages is one of the big advantages of the VDG as well as the constant current when in continuous contact with the fusor terminal. I actually tried to operate that way for the reasons that you stated but my results were ZERO detectable neutrons.

I decided to use my handy dandy built in biological electrostatic volt meter to diagnose the problem. I used my hand to see how far the spark would jump at various spark gaps from zero to beyond an inch. At this point I HAVE to mention for the noob that this technique is NOT to be used with any other source of fusor power or would result in instant death to the one touching the HV terminal. Ideally, I should have used a small grounded sphere to determine the voltage but it was getting late and I needed data.

What I found was the lowest voltage on the terminal was when it was in contact with the VDG sphere. There now are many possibilities here but I think the most likely is leakage current of the entire system. HVDC can induce charges in other elements of the fusor and can distribute and disperse everywhere including ionization of of the air at the sharp radiuses on the terminal of the feedthrough. I think this is the cause for the low voltage when no spark gap is present.

When the spark gap IS present, the charge builds up on the VDG sphere and then discharges in a pulse of consolodated energy. Momentarily, the leakage of the system is overcome with the energy dump and results in momentary plasma and fusion. A larger or more capacitive VDG sphere/shape should help for pulsing. For coninuous HVDC, a higher VDG current (i.e. wider belt, spray more electrons, or run the motor faster) should help things. So would a sphere (as Richard uses on his fusor) on the HV feedthrough terminal.

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Frank Sanns
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Re: Van de Graaff Fusion

Post by Frank Sanns » Wed Oct 14, 2009 12:29 pm

Steven,

Definately a safer way to go. Neutron counts are very low though and detection for the noob may be an issue.

We do want to keep our noobs so they can become OFs (old farts) one day!

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Re: Van de Graaff Fusion

Post by myID » Wed Oct 14, 2009 1:02 pm

Hi-

had no time for calculation on this so just a quick thought:
Might be fusion happens- I guess for a very short moment (arc over- if you want to call this an arc)- the Voltage is high enough and you have a "high" current.
(Mostly depending on size of sphere on top of generator)
I think the "constant current" is much to low to sustain a discharge...(and goes well with your outcome of the"low voltage" when directly connected)
I guess what you interpret as "several 100 N/sec" could be noise from the spark?
Did you make a run without D2 to compare the outcome?
As Richard always says: bubbles would be nice to proof but I guess your "flux" is a little low here;-)

Independent of this- cool experiment and a nice fresh approach!

Greets
Roman

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Richard Hull
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Re: Van de Graaff Fusion

Post by Richard Hull » Wed Oct 14, 2009 4:34 pm

To do this thing right, the insulator needs to support the full VDG voltage. This is not a criterion that is met. Ideally, a larger VDG with a larger electrode and a short arc to the larger Fusor electrode could develop the voltage better. The salient point here is the ARC DROP in the fusor. This is an old vacuum tube term applied to thyratrons back in the day. (my day).

We see that in a working neutron producing fusor, this arc drop can be very high voltage indeed, but requires a delicately adjusted gas pressure of flowing D2.

With a VDG you can't find this point easily and would have to "poke around" in the dark on the optimum pressure.

I would have to count the neutrons myself before I would believe a VDG would be a good device for the fusor. The volts sound nice, but if there is any fusion only plus ultra (read expensive gear) would detect it. What you would save on the power supply you would have to spend X5 on the detector to affirm absolutely to a hyper critical audience that fusion has occurred. Even then, there would be little of it.

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