Pinch plasmas

It may be difficult to separate "theory" from "application," but let''s see if this helps facilitate the discussion.
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ngawel
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Pinch plasmas

Post by ngawel »

I'm sure this topic has been beaten to death by the fusion veterans, but I'd like to learn a little more about pinch. I've read up on the basic types, as well as how Z-pinch favors confinement and the theta pinch is more stable. Those two properties, of course, seem mutually exclusive.

So I guess my questions are:

1) Does anyone have a good source that talks about what types of experiments they've tried with plasma pinch?

2) Would this be an experiment I would want to pursue, say, in my garage? or are there issues with regulations? (Thinking about EM emissions and FCC type stuff) Would there even be any benefit to this?
joedtitus
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Re: Pinch plasmas

Post by joedtitus »

i have been interested into this subject my self could u enlighten me about it i have only read about it so far. I am staring my fusion fusor in Decemeber some time.
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Re: Pinch plasmas

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Chris Bradley
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Re: Pinch plasmas

Post by Chris Bradley »

1) Have a good internet search - there is plenty - one as just posted, try wiki, and I believe Uni Wisconsin is still trying out various pinch projects.

2) What kind of experiment do you want to try out? Fusion? You need a few million amperes to get a pinch going at fusion temperatures. See 'Bennetts' relationship (it is eqn. '12A9' in falstaff's link). If you just want to compress a plasma then that is probably do-able. Javier Lopez has been trying and posting on this forum, though it is difficult to see the actual progress he's been making as his work doesn't appear to be well instrumented.

Various can-crusher enthusiasts can dump megawatts into their kit from capacitor stacks (I don't know what that translates to in amps, but it's all good fun). But this will be the limit of experimentation for z-pinch for the amateur, I think.
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Mark Rowley
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Re: Pinch plasmas

Post by Mark Rowley »

Wow ! This post is highly ironic. For the past week I have been experimenting with the Z-Pinch concept. In fact, I was working on a related Youtube video when I decided to take a break and check in with the fusor forum. I have posted a couple of quick pics below and will post a link to the video when I am finished.

The first picture is of a full discharge and the second is of a more moderate plasma which shows some of the pinch effect. Currently and as pictured, the coils are set up in the traditional magnetic mirror approach.

This evening I will be making better coils that (hopefully) will resist deformation. My discharge is about 7 kv from a fully charged 11.25 uF cap. The tube is 2.5 " in diameter and 13 inches long.

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Mark Rowley
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Re: Pinch plasmas

Post by Mark Rowley »

Here is the accompanying youtube video.

http://www.youtube.com/watch?v=EVOiTcRRmDY

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Richard Hull
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Re: Pinch plasmas

Post by Richard Hull »

Any neutrons or fusion detected? Electronic detection seems out on this one. Only the bubble detectors will tell the story.

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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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Chris Bradley
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Re: Pinch plasmas

Post by Chris Bradley »

When you say 'discharge' I presume that this is just your discharge through the gas you are referring to.

But what is your current discharge through the coil? What is the field you are generating? It's a good practical show and there is a small pinch going on there, but it doesn't look to be much of a pinch.

best regards,

Chris MB.
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Mark Rowley
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Re: Pinch plasmas

Post by Mark Rowley »

Sorry Chris, dont have the equipment at this time to answer your questions. As I stated, this is just a simple demonstrator. By no means am I trying to reinvent the wheel or make any outrageous claims. This was just a fun project based upon several books I had aquired some time ago.

Regarding the visual aspects of the pinch, I can be fairly confident that the visual "pinches" are either on the early rise or on the downward fall of the current pulse. The peak current is more likely during the bright flash which renders my digital camera useless for any usable photo aquisition. Maybe this weekend (time allowing) I will attempt a photo run with a very dark filter. Who knows, this may give some better photos of a much brighter and narrow plasma. Fun none-the-less.

Mark Rowley
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Re: Pinch plasmas

Post by Frank Sanns »

Hi Mark,

Nice to see your progress. It looks good.

Are your pinch coil and tube electrodes in series so the discharge powers both the flash and the pinch?

You might try using your camera on manual with a high f number and a
couple of second exposure in a dark room. When the unit fires, it will
record the image during the time lapse. You will need to use a tripod
of course.

Also, what was the music? I was familiar. Was is from the soundtrack
from the movie ca. 1980 THE FINAL COUNTDOWN?

Frank Sanns
Achiever's madness; when enough is still not enough. ---FS
We have to stop looking at the world through our physical eyes. The universe is NOT what we see. It is the quantum world that is real. The rest is just an electron illusion. ---FS
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Chris Bradley
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Re: Pinch plasmas

Post by Chris Bradley »

Sure. I see that. It's a nice demonstrator effort, but I'm just wondering if you're able to put more current discharge through the coil. Or are you running that with a constant DC current? I'm just thinking that if you are not already doing so, can you trigger an HV discharge through the discharge tube, and a high current/low DC discharge through the coil simultaneously?
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Mark Rowley
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Re: Pinch plasmas

Post by Mark Rowley »

"I'm just thinking that if you are not already doing so, can you trigger an HV discharge through the discharge tube, and a high current/low DC discharge through the coil simultaneously?"

As presented, that is exactly how the circuit is arranged.

"......but I'm just wondering if you're able to put more current discharge through the coil."

I would really like to do this, but am cautious as I dont want my coil to explode and damage the tube. I cannibalized a small percentage of my quarter-shrinker capacitor bank for this experiment so I have the capability for several larger tests. This would necessitate the construction of an improved coil design both in deformation resistance and flux placement.

Any ideas for a more rigid coil?

Hi Frank, you guessed it...The Final Countdown

Mark Rowley
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Doug Coulter
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Re: Pinch plasmas

Post by Doug Coulter »

Way back in the day (early '70s) I was a grad student running a pinch experiment for a professor. In this case we had no interest in fusion, but the idea has stuck with me since, because the results were so good for what we WERE trying to do. Our apparatus was quite simple, but very effective at getting pinches down to the 1u size region. As I have no drawing right now, I'll attempt to describe this, and soon will be posting on a new test I plan to make, now that I have all the pieces other than hours in the days to get it done quickly.

Imagine a piece of large coax, with a spark gap in the center conductor a little back from one end (which is shorted). That's about it, except we did this bit with a 3" OD brass tubing as the outer conductor, and a 1/4" tungsten rod as the inner conductor, using a piece of pyrex glass as the insulator inside the big brass pipe (length about 5"). The other center conductor at the "shorted" end was a piece of about 1" diameter copper with a hole drilled through the middle for a small trigger spark gap electrode, also copper. We used a large capacitor (call it 8" by 20" by 30" tall) at around 15kv discharged into this via 10 pieces of RG-8 in parallel. I found out the hard way that you need at least 10 or they explode from magnetic repulsion at the peak currents we had -- in the 100kA region. We were using perhaps (my memory...) 15kV and about 100 uF Maxwell capacitor for this.
It was one designed for very low series L and R, center bolt and case ground. We built a special plate and ring connector for the top of this to keep inductance low and provide for all the coax pieces to connect.

Procedure was to get the best vacuum possible (our setup was a diff pump, no cold trap), then charge the cap and fire the trigger gap via a small coupling cap and an auto spark coil. There was a 1/4" hole in the side of the tube(s) with a Be window to let the Xrays out, and indeed there were plenty of X-rays far higher in energy than the kV we were using. After taking spectra with this setup for my advisor using a salt (NaCl) crystal and the film about 4 ft away, which took about 20 shots to expose the film, we looked at the thing as a point source for Xray microscopy, and indeed it was very good for that -- the pinch was calculated to be down to about 1 micron in size. Just put your sample close, and the film far, and you have a nice camera with plenty of high resolution magnification.

I of course plan to try this with other materials that might do fusion in these conditions, we saw Xrays up to the 100kV region from this. That's one heck of a compression ratio considering we had perhaps several cc's of plasma to squish down to that size in the pinch. I've managed to acquire the vac system (very nice new Pfeiffer turbo etc etc) and the capacitors -- Maxwell 120uF @ 10kV, rated at 100kA per shot at 10^5 shot life, and I have 3 of them (eg two spare if anyone is interested).

Warning to anyone trying this -- the magnetic field in the coax leadin at the 100kA level is very serious and makes the coax want to explode. I spent one day picking untold thousands of pieces of braid out of my hide when we found that 7-8 pieces in parallel weren't enough. I was young then, wouldn't want to repeat that experience and only have my eyes because I was looking the other way at the time..

My new setup will use 12 pieces of RG213 about 3 ft long apiece, and I am taking serious measures in the connections and blast shielding and to equalize the currents in the coaxes...This lashup could also duplicate the focus fusion experiments with the right stuff at the vacuum end, which I also plan to do. But I think this does a better job, I don't hear him claiming under 1u concentration sizes...

Also you should know that despite "heroic" measures in shielding there is going to be enough EMP when you do this to fry any PC or other electronics within perhaps 30 ft. We even fried tube type stuff (including a Tektronix 555 scope) and had to build a 6'x6' Faraday cage for the operator and test gear to make measurements. There was no more than one inch of exposed non-coax conductor in this lashup, everything else was totally shielded...

In the pictures, see one of my caps with the coax connector I machined for this. There will be heat shrink on the conductors, and a blast shield cap on top of this, as the coax tends to blow right were it has to be stripped and separated for the connection. 100kA will be hard to get with only 12 pieces of coax, but possible, with a sadly slow risetime due to the impedance mismatch.
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Re: Pinch plasmas

Post by Andrew Haynes »

Mark, hows the z pinch going. Is 7kv 11uf enough for fusion.
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