High pressure gas discharge fusion

[artis]

I thought to myself , have there any been any physical attempts or calculations in theory about the possibility of creating a net electrical gain of energy from a pulsed fusion approach where a high pressure/density gas mixture is prepared constantly within a container and a high current pulse is initiated through the gas (possibly by a high voltage ignition kick) where low voltage high current would hen ionize the plasma channel and cause sudden expansive heating and fusion.
I assume such an approach would be very inefficient with low gas pressures where most of the pulse current energy would be wasted and very little fusion would take place but how would this approach scale up with increasing gas pressures to the point where a sudden large burst of current could heat up a high pressure gas and cause rapid expansion etc?

Sort of like inertial confinement fusion only there they use lasers for examples to suddenly implode a small sphere.Tokamaks seem to use high current for both ohmic heating and plasma confinement, although their plasma is of very low pressure and the current heating reaches a limit where they have to help with additional methods.

Anyway a curious question of mine, thanks.

 

[DEvens]

I'm doubting it. The issue is one of energy density. To get fusion you need to have a certain density and temperature of plasma. That's what the Lawson criterion is about.

https://en.wikipedia.org/wiki/Lawson_criterion

You need to have a certain temperature at a certain density for long enough. Higher temperature or higher density can let you have less time.

I'm doubting you can get that temperature from electric currents. At least, not with ordinary electric currents from ordinary voltage sources. Say, capacitors and transformers and such. Arc welders, for example, top out at about 20,000 degrees C.

https://hypertextbook.com/facts/2003/EstherDorzin.shtml

You would need considerably hotter than that to get useful temperatures to produce fusion. Inertial confinement is targeting 100 million K.

https://lasers.llnl.gov/science/icf

So you would need something about 5000 times as hot as an arc welder. As I said, not with conventional capacitors and transformers and such. I don't know just how you might approach that. Whatever produces that kind of electric current is going to be very hard on things like electrical conductors, just for example. If it achieves 100 million K in plasma, what does it do to copper wire?

Now just barely possibly you could get some kind of "one shot" thing. Say you charge up a capacitor, hook it to your plasma cell, then explosively crush the capacitor. That *might* give you something useful. But I'm still thinking it will be way cold.

 

[artis]

thanks for stopping by this thread,
Well I am familiar with Lawson criteria that is why I wrote that the gas in the cylinder would need to be of very high pressure, since the "burn time" here is small and pulsated.

Well I am not thinking about arc welders or capacitors I have one other device in mind, a large faraday disc on steroids.
This is all ofcourse just me having a thought on a subject that I find interesting so take this with a grain of salt.
Magnetic confinement systems (tokamaks etc) all use a lot of copper and materials as well as energy (useful output energy from the reactor otherwise) just to keep the confinement fields and the cryogenic cooling etc, my thinking is this, throw away the cryogenics and all that confinement magnets etc , just imagine an arbitrary straight tube like structure fill it with a very high pressure gas mixture (as much as the walls can physically withstand) then have electrodes (large ones) at each end sort of like a classical tube fluorescent lamp,

now for the initiation of the plasma channel I would use a high voltage ignition source that can produce a spike necessary to create a plasma channel but then a low voltage very high current source is attached to the main electrodes at all times so whenever the plasma channel is created the main current should start running through the channel heating the plasma, ideally if all of this happens very rapidly the sudden heating should create an expansion shockwave further increasing the heating and fusion.a large homopolar generator given it's physics once spun up to speed can essentially just sit there and spin wasting only the energy lost in the bearings yet when a low enough resistance loop or path is given it can unleash a tremendous amount of current through it where literally the only limitation is that of the copper wires/busbars themselves.
Given the few that have been built for experiments I think achieving a couple million amps would be within modest limits with multiple in parallel probably capable of more than that.

So basically very high pressure gas , fast repetition pulses I wonder what this could do.
probably the device could be set up as a resonator because due to the low voltage high current as soon as the plasma channel would cool off the current would drop and so once it drops below a certain point new HV ignition occurs giving a new burst, the gas would have to be constantly recirculated and filtered out so that each shot can produce the most fusion.

The idea here is to forget about magnetic or otherwise confinement which takes up huge space and resources and instead just use high pressure (which magnetic confinement can't) and brute force the damn thing , then the heat that is produced in the walls can be taken off and used as is done elsewhere.

I am not sure but maybe the leftover charges from each burst can be collected on electrodes for direct conversion but this is just a guess.
PS. I wouldn't say "wire" size is the limiting factor , there is no problem of making the wires in the thickness of a train rail or thicker, I don't see that as the problem here , there might be other ones for sure.

 

[artis]

PS. a tokamak as I understand also uses current through plasma as it's first and main plasma heating source just that due to the very low plasma density/pressure this heating method only is capable of bringing the plasma to a certain temp. so further increase is done by other methods , yet here given we could use orders of magnitude (many i think) higher pressure maybe a huge current burst could do the trick to achieve the necessary temp all by itself, that is also the question I guess.

Quite frankly I was wondering hasn't something like this been tried or at least calculated already?

 

[DEvens]

Actually, there is one very insistent reason you can't make the conductors thicker. You need the current to be concentrated. You can't have the current being introduced into the plasma over 100 cm square areas, because that will diffuse the effect. You need it to be released in as tight a region as possible. So that's going to vaporize the end of your conductor. Probably long before you get any fusion-range useful temperatures in any kind of plasma. If it can make the plasma fusion hot, it's going to make the necessarily-narrow end of the conductor hot enough to ionize it.

 

[artis]

Ok I get your point, about the electrodes themselves, true, electrodes might be a problem, I guess they always are, even in high power vacuum tubes.

Well from what I hear ITER uses AC where the scope signal would look like stairs in order to achieve a ever increasing current through their plasma within each cycle or each plasma burn.
Although since they have to refill the toroid chamber after each burn then in theory Iter is also a pulsed machine.

As for the electrode area, ok let's suppose we have an electrode with adequate surface area to handle extreme pulsed currents, Surely we would like to have a bigger current through a thinner sheet of plasma but the plasma itself also limits the current density through a given cross section of given density plasma so while our electrode might be larger we can then increase maybe other parameters to give the same current/plasma density,

I wonder what would be the effect of having a strong static B field in the middle of the tube where the field lines run in the axial direction of the tube (plasma current direction) when the current burst is introduced this should create a bottleneck effect (like at the ends of a plasma mirror) when the charges would start to flow suddenly through the field the current and heating would tend to expand the plasma from center outwards while the B field would tend to compress this expansion. Although I assume there are no real ways of simulating any of this even if for fun?

 

[Rive]

I wonder what would be the effect of having a strong static B field in the middle of the tube where the field lines run in the axial direction of the tube (plasma current direction) when the current burst is introduced this should create a bottleneck effect (like at the ends of a plasma mirror) when the charges would start to flow suddenly through the field the current and heating would tend to expand the plasma from center outwards while the B field would tend to compress this expansion.

It was 20+ years ago that I read that book, so take it with some salt: one of the very first devices built for experimenting with plasma was more or less worked by the method you described. It was easy to build: you needed only a transformer with a BIG core (to store up as much energy as possible), then stop the DC current through the primary and watch what happens in the gas tube attached to the secondary...

The plasma channel worked ~ the way you described: the current trying to shrink the diameter, but the temperature tries to expand it. There was one additional feature to it, what made science abandoning this setup: the channel was not stable. The initial arc was 'blown up' to some random curve-like shape (just what you can see on any vid about long DC arcs: like here [moderator: link removed] at 9 min - what an ***** idiot...) really fast.

Apparently even the last real usage far predates the Internet, so it is hard to find relevant documents (or I'm lacking the necessary google-talent for this): I could not find anything useful. I'll try some more before giving up.

Ps.: for any Mentor: please feel free to remove the link if this level of unpreparedness and carelessness is not acceptable here - but it is hard to find a really good DC arc.

Ps2.: that book was from the unlucky side of the Cold War, and it was old even that time I read it. Nothing useful popped up from google. As of new sources, the closest to this direction would be about 'pinch', I think.

 

[anorlunda]

Ps.: for any Mentor: please feel free to remove the link if this level of unpreparedness and carelessness is not acceptable here - but it is hard to find a really good DC arc.

I really liked your post. Most informative. But yes, the antics in that video you linked were just too blatantly oblivious to safety. I removed the link.

But the instabilities you mention are also true for AC arcs, so maybe this picture will help make your point.

\

Edit: It also makes me think of rocket triggered lightning experiments that my company used to perform. In the picture below, the straight line arc was the wire. But subsequent re-strikes follow the plasma path remnants of earlier strikes, except that those plasma paths are displaced downwind. Note the kinky shape of those paths, incipient instabilities. The horizontal green streaks are vaporized remains of the wire.

 

[artis]

Well, I read some articles where scientists at Sandia labs and elsewhere have seemingly created some ways by which to minimize or eliminate the Birkeland current instabilities,(I would have posted the links but they did not explain precisely how they did it)
Speaking about the electrode area, in theory since the device is pulsed, maybe one could have wide ends like in the picture while a smaller diameter center, I believe some of the devices are or have been already made in such way.

@Rive by the "unlucky side" of cold war I suppose you mean the USSR?

I do wonder what is the effect of a strong axial E field during the current burst of such a plasma because the current drives the plasma hot as well as there are proton and electron axial velocity within the plasma at that moment which is what confines them as their motion through the field tends to push them towards the middle, although I would suppose that increasing their axial velocity their gyroradius while traveling along the field lines would become smaller and so maybe the confinement would be even better?

Because as I understand what one wants is a maximum current and plasma temperature but then once that is achieved also a maximum "squeezing" of the plasma and confining it to a thinner radius so that in order the current could have a better effect and the total fusion rate and confinement time in the pulse would increase?PS. I see these pinch devices can have both a solenoid type magnet which produces a field where field lines are in the axial direction and particles would follow the lines looping around them and there are devices that use axially shaped current carrying wires or a cylinder which creates a field seemingly perpendicular which then pushes the plasma current towards the center since two currents in the same direction repel one another, I wonder have these two field approaches have been combined in a single machine, I did not find any specific examples.