Plasma at Last!

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.
Robert Dwyer
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Plasma at Last!

Post by Robert Dwyer » Fri Aug 11, 2017 1:06 am

Well, although my vacuum chamber was not pulling down anywhere close where I would have wanted it, I was overcome by a bit of impatience, and decided to pull out and old dc power supply I had for a HeNe laser I built a while back. After grounding the frame and chamber, attaching my high voltage probe, and setting up the power supply, I got my first light! I couldn't run the plasma for long, because once it ignited the pressure spiked up quick! I think this may be due to the plasma burning out water, oil, and other nasty vacuum-ruining stuff. It has been over a year since I began planning this project, and I finally have a plasma to show for it! Still just an air plasma at 650 volts and 1800 microns, but beautiful it is!
20170810_174917.jpg
650 Volt Plasma at 1800 Microns
20170810_170942.jpg
More of the Same Plasma
20170810_174922.jpg
A View of the Rest of the Chamber
Though this isn't as good as I would like, I would like to apply to the plasma club with this. Eventually once I fix the leaks in my chamber, and finish building my true fusor power supply, I am hoping to shoot for star mode here. A lot more to go, even more to learn, but I do consider this a big step in the right direction!
If we throw more money at it, it will have to work... right?

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Richard Hull
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Re: Plasma at Last!

Post by Richard Hull » Fri Aug 11, 2017 5:39 pm

I have placed you in the Plasma club. You haven't seen anything yet! Get down to 20 microns and below for the real show.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

Robert Dwyer
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Re: Plasma at Last!

Post by Robert Dwyer » Wed Sep 06, 2017 3:47 am

I have come bringing yet more pictures of plasma!

After fixing some leaks, and replacing the old chinesium forepump/diffusion pump combo with a really nice roughing pump, a bellows hose instead of the old pvc tubing, and all foreline flanges as KF, I tried my hand with making a plasma once again.

This time however, I was using a much more powerful power supply: my (hopefully) fusion capable XRT based PSU (post on that coming in the future).

The pressure in the chamber was 180 microns while the picture was taken. You can see how a beam forms from the glass viewport towards the center of the grid. I do not know whether that is an ion or electron beam, but either way, it is really cool! I overjoyed once I saw it. Another phenomenon I noticed was that when I was raising the voltage, the grid seemed to spark a bit. Perhaps there is material being burned off? It did not look like arching at all.
Plasma_180mTorr.jpg
Plasma at 180 Microns. Voltage measurements to come.
You may notice that the viewport is not shielded. I did too. After realizing that I was running higher voltages (estimating 20kv+), I immediately hit my HV off switch. I was used to running with my old 6kv max HeNe laser power supply that I didn't even think of X-Rays when I transitioned to the larger power supply. After doing another short run with myself away from the viewport and a radiation detector by the glass, I verified x-ray production. The viewport is positioned down now, and I working on a camera and display system so I can safely continue to work further with the fusor.
If we throw more money at it, it will have to work... right?

JoeBallantyne
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Re: Plasma at Last!

Post by JoeBallantyne » Wed Sep 06, 2017 5:05 am

You might consider inserting a sacrificial piece of glass in front of your viewport on the inside of the chamber. So that you can protect it from an electron or ion beam hitting it, and causing local heating and failure of the glass in the viewport. Viewports can get pricey, so protecting them is a good idea. The other thing you can do is put a fine metal screen in front of it on the inside of your chamber, and electrically connected to your chamber. That will also protect the viewport, but at the price of partially obscuring the view. Ion and electron beams are not kind to glass.

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Dennis P Brown
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Re: Plasma at Last!

Post by Dennis P Brown » Wed Sep 06, 2017 1:26 pm

Congratulations on joining the plasma club.

Getting only to 180 microns is a very poor level - either your pump isn't acceptable for fusor work or you still have very bad leaking. That issue will need to be your first priority before you deal with high voltage power supplies.

As for x-rays, in the low 20 kV range isn't too serious of a threat. I have a 32 kV high current system and have measured no x-ray radiation at all; my thin steel shell and my view port (1/2 inch glass), provides me more than enough shielding. Any Geiger counter (even the cheap surplus ones) can give you a decent (if not accurate) reading to provide information if you should be concerned - if one experiments with real fusor power supplies having one of those is an important safety device.

A quick aside: in that one picture with the red wire, I hope that isn't your ground wire? That ultra flimsy bead of solder holding that wire to a SS flange is a very bad idea - I assume the last picture is the latest and that the wire is soldered to a real electrical connector and properly bolted. Also use a real point of ground - like a threaded bolt! Floating that case to +20 kV with a real fusor supply is asking to be killed. Also, alligator clips can slip off easily (so, hopefully, that isn't being used to hold the ground wire in place.)

Robert Dwyer
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Re: Plasma at Last!

Post by Robert Dwyer » Thu Sep 07, 2017 3:06 am

Joe,

I had forgotten about the effects of the beam hitting the glass. Would putting a magnet on the side of the viewport help deter the beam?


Dennis,

I agree 180 microns is very poor! I believe the leak is in my HV feedthrough that I made. I believe it is in the end cap that I was using to seal the end of the ceramic. AS for the red wire, yes it was my ground for when I was using the HeNe supply. During the first 20kv+ run I secured it wiht the an alligator clip. I agree that this is not acceptable. So today I re-did my grounding scheme, and added multiple grounds to the fusor chamber, and case, to the variac ground pin where all of the electronics are also grounded.
20170906_201904.jpg
I ended up bringing out my ludlum 177 counter with pancake probe out to measure the radiation emitted from the fusor window. I pushed up the voltage to about 20kv and measured about 100,000 cpm. I am unsure of the accuracy of this measurement. Thankfully I no longer need to worry about it too much because the viewport is now aimed down towards the ground.
20170906_203510.jpg
Overall, although I am making progress, I still have much more to go. I still have yet to complete my gas delivery system, along with my neutron detection system, which I am not confident in. Luckily I am now in contact with Carl Willis, who lives in the same city as me, who, It looks like I may meet with this weekend to discuss my fusor, and nuclear engineering in general.
If we throw more money at it, it will have to work... right?

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Dennis P Brown
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Re: Plasma at Last!

Post by Dennis P Brown » Thu Sep 07, 2017 12:32 pm

I seriously doubt the Ludlum meter is really seeing that high an x-ray reading. A fusor can generate a lot of noise for a digital circuit; still, while no way 20 kV generated x-rays will go through the SS walls of that chamber avoiding the window might be a good idea, for now. I like the idea of placing a piece of glass inside the window to protect it from ions - it will also reduce any x-rays; consider a thick disk of glass (3/8 to 1/2.) In this way much of any x-ray threat is gone, as well.

As for the vacuum - you have checked the vacuum pump (vacuum gauge just connected to the inlet of the pump? If that does not mostly bottom out the micron gauge reading , then something is very wrong with the pump. If you suspect the HV feed, remove it and test the system. If the chamber gets to a few microns, then you know for sure the issue.

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Richard Hull
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Re: Plasma at Last!

Post by Richard Hull » Thu Sep 07, 2017 7:56 pm

Once you have x-ray voltage, (15kv+), the amount of x-radiation is purely a function of current delivered at that voltage. I am sure that far more than 100,000 cpm of x-rays were there. GM counters of the Ludlum type are pretty noise immune around a fusor. It is proportional tubes, (3He and BF3), and ion chambers that are hyper noise suseptable. X-rays out of a common glass view port are horrendous and dangerous. At only 20kv, the bulk of the x-rays are 10-15kv and are "flesh burners". I have written about pointing view ports and x-ray "easy escape paths" away from observers in a couple of FAQs and many postings in the past.

GM counters will only tell you that you have x-rays. They will tell you zero about how bad they are or supply any sort of quantitative info on them. Only an ion chamber should be used to give decent data on instantaneous x-ray does rates. Dosimeter pens will give OK data on long term, total absorbed dose. All radiation instruments tend to give data related solely on the exact loacation of the detector. Jamming a detector at the window will give an unusually high but correct rate for that point only and will tell you nothing about what you get 5 feet away.

If you are worried about personal safety, take measurements only at your obsever station....That will be what you are getting. Usually and hopefully, this is virtually unreadable.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

Robert Dwyer
Posts: 54
Joined: Sun Sep 04, 2016 9:34 pm
Real name: Robert Dwyer
Location: New Mexico

Re: Plasma at Last!

Post by Robert Dwyer » Sun Sep 10, 2017 4:14 am

Richard,

Thank you for your reply.
I moved the pancake probe to other points around the fusor (right by the chamber) and raised the voltage to approximately 25kv. Practically no x-rays were detected actually leaking from the fusor chamber. At one point in raising the voltage, I noticed that the plasma "flickered" a bit. When this happened the x-ray counts seemed to spike for a split second with the "flicker." Still this spike reads on the probe about 150cpm, something that doesn't really concern me considering it only did that twice. I also have a civil defense dosimeter pen that I hasnt gotten any readings outside of the fusor, but perhaps I will put in the path of the viewport that is pointed downwards to see better categorize the dose of x-rays coming from it.

As for my chamber's pressure, it turns out I had mistakenly used the wrong tube with that controller. I had attached a Hastings DV-3M tube instead of a DV-6M tube (which the controller is made for). Luckily I had a DV-6M tube, and now am able to get more accurate readings. It appears that my ultimate chamber pressure with that pump is about 8 microns. I think this is fairly good for just a roughing pump, and may be good for my initial tries at fusion which I am hoping to run at pressures of 30-50 microns of D2.
20170907_192753.jpg
Sorry for the blurry image. I am hoping to get videos of more runs with the plasma and post them here. Sadly I don't have a good camera/monitor setup yet, as I have just been using my phone to record. That will most likely be my next purchase after tubing for the gas system.

AS of right now I have not set up a way to measure current yet, and I have been using a high voltage probe to measure the voltage. A better HV measurement system is on its a way however, and once finished, I will make a post on the whole electrical setup in my fusor construction/operation forum post.
If we throw more money at it, it will have to work... right?

ian_krase
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Re: Plasma at Last!

Post by ian_krase » Sun Sep 10, 2017 9:28 am

Your civil defense pen is one of the (rare) sensitive ones, right? The common ones don't start reading until the beginning of nuclear war tier acute safety hazards and devolve from there.

Also, do you have good voltage instrumentation? The flickering of the plasma can come along with very large (order of magnitude) changes in voltage, at least in my very brief experience. (This I suspect is much worse with switching supplies)

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