DarrellTaylor's Fusor Build Thread

[darrelltaylor]

I'm chuffed to bits! A good vacuum and some good pictures!

It is plasma isn't it?

[Richard Hull]

Darrell, I have placed your name in the Plasma Club listing.

Richard Hull

[darrelltaylor]

Does anyone have any advice on how to create a nice 'star mode'?

Also, how can I read the temperature in the plasma, what type of meter/ gauge would be most suitable?

[John Futter]

Darrell
The plasma temperature is worked out from the number of eV you have put into the plasma roughly 11,000 degrees kelvin per eV

so for a 20kv fusor the max temp of the plasma is 220,000,000 degrees kelvin
Plasma temperature is the equivalent temperature you would have to raise the gas to to equal what the electrical discharge is doing for you.
It is not real temperature as it refers to the electron temperature equivalent only

[Richard Hull]

Check on the FAQ on Temperature. You should have already consulted the FAQs in this forum.

viewtopic.php?f=24&t=9223

Richard Hull

[darrelltaylor]

Thanks for the info.

I'm actually curious as to the actual physical temperature of the plasma in the centre of the vacuum chamber. Its just for my curiosity really - but if I was to hypothetically stick a thermometer into the centre of the plasma, how hot would it be?

[Richard Hull]

That will not tell you the temperature of the plasma as a thermometer is a solid mass and the bombarding particles would heat it and it alone to real world temperatures and not the thin plasma particles relative kinetic energy equivalent temperture, which is in hundreds of millions of kelvins. Perhaps you still don't grasp the relationship in the plasma energy-temperature equivalences. Such actual glowing plasma measurements are often measured with an optical spectrometer looking at doppler broadening of deuterium wavelengths.

Even a demo fusor, not doing any fusion and running at 10kv, might be expected to have a high end plasma temperature of 100 million kelvins. But the bulk of the particles in the plasma will be on the order of 1-10 million kelvins or so.

Work is afoot here using a special infrared camera system to measure the bulk temperature of the plasma. Find that thread and you will understand, perhaps.

Richard Hull

[darrelltaylor]

Hi again.

I have a couple of questions after a few runs of the demo fusor.

Firstly there is a bright white glow at the exit point of the chamber where the vacuum hose is attached. What causes this? Is this ionisation of the brass vacuum fitting atoms? I have done a quick search and found nothing - but I will search some more on the forums because im sure im not the first to notice this.

This white glow slightly increases its size upto approx. 12kv at which point it jumps from the size it has reached to a smaller size and back to the 'fully grown' size, flickering like a lightbulb (so to speak).

I have attached a couple of photos of the glow that im referring to along with a close-up of the fitting from the outside:-

The other question that I had was about the colour of the plasma. The colour is very violet - although a friend described it as blue - I see more purple. The camera catches a more blue light. Either way, what dictates the colour? Is this directly related to the predominantly Nitrogen atoms in the vacuum?

Thanks in advance for any pointers or advice on finding the answers that you can give.

[Richard Hull]

Vacuum leaks where air is flowing into the chamber can create glows at those points. The whitish glow at the vacuum port can be oil/air mixtures ionizing at a circular sharp edged gradient point. I have seen glows moving into a transparent vacuum pump hose towards the pump, even! A really great pump never has these issues. Pumps that are struggling and back streaming oil after long operation periods are often the cause of these glows.

The color of all glows are a combination of visible colors emitted by various ionic recombination of elements. In a good pumped chamber, in theory, the glows are due to nitrogen and oxygen. If doing fusion and in a rather pure deuterium gas environment, the glow will be a ruby red.

Bluish, purple-violet is the norm for air.

Richard Hull

[Rich Feldman]

What happens to the upper glow when you connect a wire directly between fusor end plate and the vacuum pump?

[darrelltaylor]

Thanks for the replies......

I'm planning to upgrade the demo fusor because I want to achieve 'star mode' but I have in the back of my mind my plans to build a fusion fusor, so I want to try to update the demo fusor with parts that I can re-use for the fusion fusor if that makes sense.

To improve the vacuum performance and reach a deeper vacuum I was planning to add a foreline trap with a bellows value either side, and use solid pipe (as per the plans for a fusion fusor). Do you think this will improve the depth of vacuum that I draw or should I start directing these questions into the vacuum dedicated part of the forum?

Of course, I will also ditch the vacuum gauge in favour of something useful. I'm undecided if I should replace like-for-like with a range of 0-100 micron or change to a thermocouple. I think the thermocouple would be more appropriate for the fusion fusor but a like-for-like switch would fit the demo fusors design......

And thanks for the colour explanation - I found the same answer through further re-reading of the FAQ's last night too

Rich - im not sure I follow your logic. The chamber end plates are earthed (via the NST), and the vacuum pump is earthed through the standard UK 3-pin plug. I can happily connect a wire between the fusor chamber end and the vacuum pump and see what happens, im just not sure what it might do?

[Richard Hull]

I would get a thermocouple gauge ASAP so that you will be able to know your vacuum level. It can help find leaks, too.

The general rule is to ground all touchable metal objects in any system. Your system uses the end plates as a substitute for the outer grid normally placed in all demo systems. This is a less than perfect scenario. You have no real outer grid entirely surrounding your central grid. The pump, the chamber body or in this case, the end plates, etc., must be grounded. You are working from the "Make" article and not the recommended path shown to be the normal demo fusor here. "Make" magazine or their website does not do fusion or know much about it. We do.

Richard Hull

[Rich Feldman]

Rich - im not sure I follow your logic. The chamber end plates are earthed (via the NST), and the vacuum pump is earthed through the standard UK 3-pin plug. I can happily connect a wire between the fusor chamber end and the vacuum pump and see what happens, im just not sure what it might do?

Sounds like you got it right, Darrell, assuming a proper 3-pin plug on your NST.

I suggested the experiment because it's trivial to perform. Any change in the "top" plasma would show that your electrical connection between fusor and pump has room for meaningful improvement (in its DC or AC impedance).

Here's an alternate approach. Instead of adding a fat wire, you could start by measuring the DC and AC voltage between metal parts at the two ends of your vacuum hose. Should be less than 1 volt.

[darrelltaylor]

Rich - im not sure I follow your logic. The chamber end plates are earthed (via the NST), and the vacuum pump is earthed through the standard UK 3-pin plug. I can happily connect a wire between the fusor chamber end and the vacuum pump and see what happens, im just not sure what it might do?

Sounds like you got it right, Darrell, assuming a proper 3-pin plug on your NST.

I suggested the experiment because it's trivial to perform. Any change in the "top" plasma would show that your electrical connection between fusor and pump has room for meaningful improvement (in its DC or AC impedance).

Here's an alternate approach. Instead of adding a fat wire, you could start by measuring the DC and AC voltage between metal parts at the two ends of your vacuum hose. Should be less than 1 volt.

I see. The electrical connection is provably less than ideal. Thanks Rich, it gives me another direction to follow-up!