My fusor is only arcing and not creating the purple glow

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Luca Bob
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My fusor is only arcing and not creating the purple glow

Post by Luca Bob »

I have been building my demo fusor recently and I have turned it on for the first time. I started getting arcing from the two terminal inside the vacuum chamber. At first I thought this was normal as they were quite close and electricity can arc well in a vacuum (I think). So I started putting more and more insulation around one of the terminals but to no avail. It started getting weird when it looked as if the arc was quite literally crossing through the the rubber plate that makes up the floor of the vacuum chamber! Things got even stranger when if encased the whole terminal in a rubber tube and the arcs jumped out of the top of the terminal, went down the side of the rubber tube, then crossed the rubber floor then straight to the other terminal. Whats happening here? Can someone tell me wha I must do to fix this?

I’m using a 6KV 30 mA NST with two HV diodes, one on each output terminal connected to the center terminal for a negative voltage. The outer terminal is grounded to the NST ground, the NST ground is connected to a grounding rod. The system is being controlled using a variac. Keep in mind that this is just a demo fusor and does not contain any Deuterium.

Here is a video to show you what’s happening:

https://www.youtube.com/watch?v=40GwnkHYGhg

https://www.youtube.com/watch?v=v295wN7tMTg
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Dennis P Brown
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Re: My fusor is only arcing and not creating the purple glow

Post by Dennis P Brown »

Arcing cannot occur if the vacuum is low enough (not sure were the cut-off occurs); if your pressure is in a specific range (significant fraction of a torr) arcing will occur. So, what is the pressure (Pa or Torr) of the system?
Luca Bob
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Re: My fusor is only arcing and not creating the purple glow

Post by Luca Bob »

I dont have a vacuum gauge and so have no way of measuring it (Like I said this is just a demo fusor so its not necessary to have one for the operation of this.) This is the pump im using:

http://www.ebay.co.uk/itm/Industrial-Qu ... 7675.l2557

I asked someone if this pump will be sufficient and they said it would. The vacuum in my chamber is quite good. After the pump has been switched off it takes about 2 minutes before it re pressurises.
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Liam David
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Re: My fusor is only arcing and not creating the purple glow

Post by Liam David »

The pump is making the same noise my pump makes when there is a large leak. You want your pump to be making a deep lub-lub-lub sound. Also, that looks like a one stage pump, which can get you to glow mode in a sealed chamber, but not star or bugle jet mode.
You want a 2 stage pump capable of <15 microns. This pump is on the cheaper end of 2 stage ones http://www.ebay.com/itm/2-Stage-3CFM-1- ... 1c34ee5457 and happens to be the one I use. I'd be surprised if you are even reaching 10,000 microns.

Search around on the forums for ways to locate vacuum leaks.
-Liam David
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Dennis P Brown
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Re: My fusor is only arcing and not creating the purple glow

Post by Dennis P Brown »

That pump is enough to create a very poor vacuum that would allow a plasma to be created but hardly enough to create a high resistance gas for the plasma if the electrodes are too close together. While that pump might get a really leak free small chamber down enough for a glow discharge without arcing, your not getting there and without a vacuum gauge can't see how you can fix that issue. Since your pressure is too high and the amount of gas in that poor vacuum is acting like a conduction path for your power supply electrodes you are getting arcing not "plasma" glow discharge (like a neon sign tube.) To get a "glow discharge" you will either need a better pump or create a greater distance between electrodes. While I've run a laser supply at 10 - 15 torr and had an excellent plasma, the tube was fairly long - it appears your electrodes are too close together for that pressure .
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Dennis P Brown
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Re: My fusor is only arcing and not creating the purple glow

Post by Dennis P Brown »

Aside: I've got $1500+ two stage pumps that easily get down to a micron for under $70 (including shipping) on ebay; in fact, I have two and have seen many more on the site. They appear from time to time and are the basic item one MUST have to create a good vacuum system. A gauge for the micron range should also be a basic item one has and these can be found cheap on ebay all the time.
Luca Bob
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Re: My fusor is only arcing and not creating the purple glow

Post by Luca Bob »

Thanks. Will a 2.5CFM dual stage pump work instead of a 3CFM dual stage pump?
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Richard Hull
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Re: My fusor is only arcing and not creating the purple glow

Post by Richard Hull »

A total rubber floor is a no, no. Once a single fine arc connects, internally, it is conductive via carbon tracking. Your pressure is not low enough as well. Is the bell jar just sitting on a rubber pad? Many problems might exist here.

Richard Hull
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Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Liam David
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Re: My fusor is only arcing and not creating the purple glow

Post by Liam David »

It will just take a little longer to pump it down. What 2 stage pump are you thinking about?
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Dennis P Brown
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Re: My fusor is only arcing and not creating the purple glow

Post by Dennis P Brown »

Both Richard and Liam are making important points. First, your system is leaking badly if the pump sounds like that. Next, Richard is correct about a rubber end plate. You really should have a metal or glass end plate. A large O-ring can be cut to act as a vacuum seal between the bell jar and base plate. A metal plate is best because it becomes your common ground point - this is, in turn, is grounded to a known and proven ground.
Luca Bob
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Re: My fusor is only arcing and not creating the purple glow

Post by Luca Bob »

I was thinking of this one, it is 3CFM dual stage -

http://www.ebay.co.uk/itm/Rotary-Vane-V ... 2c8161b4ca

This is my set up. A large thick rubber pad is glued onto a thick plank of wood. drilled through this are the two terminals and the air outlet. The jar is not just resting on the rubber. In all four corners of the area there are wooden pillars going up. On the top is a wooden square as big as the jar. The jar has a flat top allowing to wood to rest on top of it. Bolts connect the wood to the pillars, when I screw the wing nuts connected to the bolts the wood square pushes down with a lot of force onto the glass jar which pushes it into the rubber. This creates a very good vacuum. The leak I believe is coming from the ground terminal as I have recently made the hole bigger to fit insulation around it and have not applied all of the things I have done to the other terminal to make it airtight.

If the pump you suggested ($70 including shipping) will work correctly with my fusor and that shipping price is correct for the UK then please send me the link to it.

Thanks for the help!
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Dennis P Brown
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Re: My fusor is only arcing and not creating the purple glow

Post by Dennis P Brown »

First off, getting a good pump (and shipping to UK is a very different matter) will work with any fusor but no pump should work with your design. You need to start over - a rubber base is worse than useless since as Richard said, it will short out your system for the very reasons he stated.
As for pumps, as I said, they appear from time to time on ebay - check ebay every day for a few months - you'll see one or more units at great prices - getting them shipped to UK is a matter you need to research. These types of vacuum pumps can handle a lot of sfm, and are high end two stage vacuum pumps that will handle the pumping needs of any diffusion or turbo pump you are likely to obtain on ebay. As for running a real fusor, no way will just a two stage pump alone do that - again, you'll need a DF or turbo with the two stage pump. In no case will any pump work on your system since it appears to be massively leaking - as I and others have posted.
Next, throw away your base plate and make a metal one that is properly grounded. That will require a proper feed through's for the high voltage lead. Also, get a vacuum gauge FIRST! No pump will work at all if your system is leaking (like yours appears to be) and the best method to determine if your system is leaking is to have a vacuum gauge! Get a unit (mechanical is fine) that will to cover atmosphere down to about a torr (or equivalent in Pa or milli=Pa.) Also, get another unit that measures microns (say from a 1000 microns (or Pa equiv) down to a micron (again, or Pa equiv.)) These units are cheap on ebay but only you know your needs, price range and types your wall power can handle.

Aside: if you are a young teen, I'll look over ebay and find a few items that you can reference (but not necessarily are good to buy! Again, only you can determine your exact needs.) Just say so and I'll do some clicking ... .
Luca Bob
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Re: My fusor is only arcing and not creating the purple glow

Post by Luca Bob »

Im a little dismayed that I will need to re make most of it. I like the idea of having the pillars and the wing nuts that will push down the jar into the rubber, is it ok if I keep that. I will make sure the rubber only covers the part where the jar comes into contact with the wood, not in the middle where the terminals are to prevent arcing. Whats the benefit of having the metal base, is it better than having the outer grid grounded? If I do decide to have the metal base shall I remove the outer grid? I'm not planning to run a real fusor any time soon btw. Also, is my power source sufficient? Thanks for all the help! I would like it if you could help me look for a few things on ebay such as a vacuum gauge that will work with a 1/4" flare fitting.
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Chris Bradley
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Re: My fusor is only arcing and not creating the purple glow

Post by Chris Bradley »

Dennis P Brown wrote:Aside: I've got $1500+ two stage pumps that easily get down to a micron for under $70 (including shipping) on ebay; in fact, I have two and have seen many more on the site. They appear from time to time and are the basic item one MUST have to create a good vacuum system. A gauge for the micron range should also be a basic item one has and these can be found cheap on ebay all the time.
A two stage pump to under a micron!? Sorry, I don't believe that. Please show me a gauge reading showing a sub-micron chamber pressure with just a two stage pump.
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Chris Bradley
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Re: My fusor is only arcing and not creating the purple glow

Post by Chris Bradley »

Luca Bob wrote:A large thick rubber pad is glued onto a thick plank of wood.
I've no idea how you think this will hold the vacuum. You might be forgetting that there is also sealing required around the feedthrough, in which case you have practically no vacuum at all.

The rubber is shockingly hard and will not be sufficiently compliant to form a vacuum seal.

I'd say you are around a few 10s to 100 torr pressure. Around 1/10th bar, and 'bar' is not a unit we tend to use when talking about a vacuum! About 3 to 4 oom out.

You need a hard flat surface for the chamber and gasket to sit on and the feedthrough needs to be vacuum capable.

Having worked with various home made rubber gaskets, they can present problems but there is no way to yet know what problems it'll cause you. You are far from knowing what problems a rubber sheet may cause you because you are way to high on pressure, presumably through a major leak.

You require a vacuum gauge to diagnose and fix your problems. I would recommend you need to replace your rubber with something much thinner and softer, and the wood plank needs to be replaced with a min 10mm aluminium sheet flat to a few 10's of microns max.
Luca Bob
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Re: My fusor is only arcing and not creating the purple glow

Post by Luca Bob »

Chris Bradley wrote:I've no idea how you think this will hold the vacuum. You might be forgetting that there is also sealing required around the feedthrough, in which case you have practically no vacuum at all.

The rubber is shockingly hard and will not be sufficiently compliant to form a vacuum seal.

I'd say you are around a few 10s to 100 torr pressure. Around 1/10th bar, and 'bar' is not a unit we tend to use when talking about a vacuum! About 3 to 4 oom out.

You need a hard flat surface for the chamber and gasket to sit on and the feedthrough needs to be vacuum capable.

Having worked with various home made rubber gaskets, they can present problems but there is no way to yet know what problems it'll cause you. You are far from knowing what problems a rubber sheet may cause you because you are way to high on pressure, presumably through a major leak.
There is excessive amounts of sealing on the feed throughs. I have utilized rubber gaskets, washers, plastic connectors and sealant. The jar and the rubber provides a very strong vacuum as it is impossible to remove it when the pump is on. This is even true when the wooden square above it that is used to press it down into the rubber is not present. The leakage i'm experiencing is because I have altered one of the feedthroughs and have not yet done the above to make it properly air tight.
Luca Bob
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Re: My fusor is only arcing and not creating the purple glow

Post by Luca Bob »

Ok im considering this pump:

http://www.ebay.co.uk/itm/2-Stages-1-3H ... 2a3bcf1581

On the basis that it has the correct power and frequency for the UK. It has 2 stages and only 2.5 CFM. As having a 2.5 CFM rating means that it will take longer to pump down its not really a problem to get this one instead of a 3 CFM one, am I right? I have notices that it has two outlets, im guessing I can attach the hose on one and a flare vacuum gauge on the other?

Thanks
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Dennis P Brown
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Re: My fusor is only arcing and not creating the purple glow

Post by Dennis P Brown »

First off, my pump gets down to about a micron (bewteen 1 - 2 microns on a calibrated vacuum gauge - also, I didn't say under a micron ... (through a similar sized two stage pump I have at work has no issues with getting to 1/3 micron and this is on a rather large glass bell jar. So, some can.)

Second, since this person is intent on using a wood and rubber base plate, and no amount of posting saying this isn't a good idea appears to matter, I do not think this poster wants any advise on their real problem but only their specific question about a specific pump. So, I'm giving up.

Best of luck pumping down a wood and rubber plate using any available small vacuum pump.
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Chris Bradley
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Re: My fusor is only arcing and not creating the purple glow

Post by Chris Bradley »

Dennis P Brown wrote:First off, my pump gets down to about a micron (bewteen 1 - 2 microns on a calibrated vacuum gauge - also, I didn't say under a micron ... (through a similar sized two stage pump I have at work has no issues with getting to 1/3 micron and this is on a rather large glass bell jar. So, some can.)
No issues? I'd be checking my pressure gauges at that point.

You tend to enter molecular flow regime when pulling a few microns through a pipe to a pump, which a rotary pump doesn't do very well.

Image

I'm no expert so maybe this sort of thing is possible with modern pumps, but it's news to me that you can get so low with a rotary pump.
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Chris Bradley
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Re: My fusor is only arcing and not creating the purple glow

Post by Chris Bradley »

Luca Bob wrote:There is excessive amounts of sealing on the feed throughs. I have utilized rubber gaskets, washers, plastic connectors and sealant. The jar and the rubber provides a very strong vacuum as it is impossible to remove it when the pump is on.
'A very strong vacuum'?

You would not notice the difference between a 1/10th atm vacuum and a micron vacuum. If this is the basis of your analysis of how good your vacuum is, you need to sit down and think about the whole thing again.

Both a 1/10th atm and a 1 micron vacuum will largely have the same mechanical characteristics, in that both will result in a differential with atm of around 14psi. A 1/10th atm vacuum in a chamber of a 100 sq in footprint will require a 1300lb force to separate it, whereas a one micron vacuum will be a 1450lb force. You think you can feel that much difference by pulling on it?? How strong are you that you can pull with a >1000lb force by hand?

Whatever sealing you think you've done, I'm telling you that it isn't working. There's nothing more to be said 'til you fix that.
Luca Bob
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Re: My fusor is only arcing and not creating the purple glow

Post by Luca Bob »

It was my understanding that rubber was a very good material to used to seal things to make them airtight and thats why I used it. Apparently it is not, so I will not use it. I also ask what is wrong with a wood surface? The base of the chamber will be metal but I am talking about having the whole setup on wood, how would that effect anything? I am not intent on using a wood and rubber base plate I was just asking whether I should keep it as I assumed that the jar would be more airtight if the rim of it was resting on rubber rather than wood or metal.

Secondly, I do want advice on my real problems, if i didn't then I would not be addressing the current problems that have been sent to me by people on this forum. The pump is one of the problems, that is why I am asking about it. If i did not ask the questions I asked in the previous post then it could lead to my fusor not working, I just want help picking my pump. I am being very thorough this time as I had asked on another forum weather the current bad pump im am using is ok for fusor operation and they said it would be fine, it isn't. Also please respect that I am new to working with pressure and pumps so I am likely to get things wrong.

Thanks for the help!
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Chris Bradley
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Re: My fusor is only arcing and not creating the purple glow

Post by Chris Bradley »

OK, so the main thing I was trying to encourage you to consider is that wood is no good as a material for a vacuum envelope. Effectively, you are using that stiff hard rubber as your vacuum envelope. Neither wood nor rubber are suitable materials for that purpose.

Consider, as the chamber pressure drops that hard rubber sheet will have to be taking the atmospheric load, because the wood is not fit to be a vacuum envelope so will bleed air in behind the rubber. This makes the rubber distort, and any hard effort you may or may not have made a good seal with will then be instantly undone because everything will flex and change shape.

Rubber is fit for making seals from, not for making vacuum chamber envelopes from. Also, you need to pick the right sort of rubber, as they come in all shapes and sizes, or to be specific in various material types, surface finishes and hardnesses. Yours is a very hard rubber and not the sort you'd choose for seals.

Also, not that this yet concerns you, but you can't really let polymerics get exposed to a plasma because the free ions will start reacting with the rubber and will outgas reaction products spectacularly, as well as change the physical properties of the rubber. The total surface area of rubber to the chamber volume should be kept to a minimum, and it is also worth while 'shadowing' any rubber with earthed metalwork where possible which reduces exposure to free ions/electrons. If you have an experimental setup where you can assure that the rubber is protected - for example you might create some metal box within the belljar that contains the plasma - then there are ways to accomplish that sort of thing. However, this is adding complexity when the most appropriate remedy might simply be to use a metal base plate.
Dan Tibbets
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Re: My fusor is only arcing and not creating the purple glow

Post by Dan Tibbets »

Your pump may be fine. At this stage don't worry about a better pump. The sound in the video is consistent with a large leak as mentioned. As you start pumping, the pump should sound like this, but the sound should quickly change to the mentioned "lub-Lub" sound. That it doesn't is a strong indicator of a major leak. You should have a valve between the pump and chamber. Close it, turn off the pump, then listen for hissing and try to localize. The gasket looks like it may be a open cell foam. It will never make a good seal if this is indeed the case. Even a closed cell or solid gasket may not seal well if the connecting edges are too broad. The atmospheric pressure pushing on the outside pushes the pieces together, but the resultant pressure needs to be concentrated to a small area. That is why narrow knife edge dimensions are used for the best seals.Remove the gasket and try some ointment (grease and rubber seals do not work well together in my limited experience). Petroleum jelly or hydrocortisone ointment (not cream) worked for me when I was playing around. Do not use a scented ointment like Vicks Vapor Rub.This ointment/ grease may make an adequate seal if your jar and base plate are smooth enough and nor warped relative to each other. The grease can seal small leaks, but not larger leaks. This is not a good sealing material but it may far exceed the dismal seal you presently have. A true vacuum grease works better but is also very much more expensive.

Also, keep in mind that you could have a leak anywhere anything penetrates the chamber. With the power off and disconnected (for safety) if you can hear a hiss, run your finger over the seal areas of the base, feed throughs, etc. If you hear a change in the hiss you have possibly located a localized major leak.

The arc is consistent with a mild vacuum. The pressure may be ~ 10,000 to 50,000 Microns. For a good glow discharge you will need to get below several thousand Microns, hopefully into the hundreds of Microns, and even lower for bugle, e- beam and star modes.

A gross test of your jar and base plate. Without a gasket, try to rock the bell jar on the base plate. If you can obtain a noticeable rocking motion, the matting surfaces are not flat and level enough. You might never get a good seal in this case. The solution is to machine the surfaces, possibly a major undertaking. An alternate flatter base plate may serve provided the glass base itself is not too uneven.

Dan Tibbets
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