Potential Tokamak Breakthrough

Point out news stories, on the net or in mainstream media, related to polywell fusion.

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jmc
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Potential Tokamak Breakthrough

Post by jmc »

Seeing as there is all this interest in inducing rotation through radiowaves (which is not a real breakthrough as smaller tokamaks today can have just as much rotation with low energy neutral beams, I see radio wave rotation more as damage control for ITER)

I thought I'd draw your attention to a real potential breakthrough in tokamak technology, the use of molten lithium to eliminate particle recyling and thus eliminate all temperature gradients which drive turbulence.

http://www.pppl.gov/lithiumtokamak.cfm

There have been some simulations done on the possible confinement times that could be expected if this was accomplished and they are long enough for tokamaks considerably smaller than JET to achieve ignition.

In my opinion as someone who works for tokamaks, this is the most promising new technology on the horizon, as it allows the construction of a comparaively low power tokamak, bypassing the material heatload issues. If this works we could see fusion within a decade.

MSimon
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Post by MSimon »

If this works ITER will need to be redesigned.

It is rather obvious that the boys behind ITER jumped the gun.
Engineering is the art of making what you want from what you can get at a profit.

Solo
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Post by Solo »

That's very interesting. I'm all for tokomaks if they can work.

kurt9
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Post by kurt9 »

MSimon wrote:If this works ITER will need to be redesigned.

It is rather obvious that the boys behind ITER jumped the gun.
Screw the ITER. Perhaps the Japanese or Chinese (or the Koreans who are not part of the ITER consortium) may choose to develop this technology as separate effort. Also, the U.S. reduced its commitment to ITER several years ago.

icarus
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Post by icarus »

Stabilising turbulence is a non-trivial problem, even in a non-conducting fluid where there are no EM effects.

Any toroidal flow is hydrodynamically unstable to the first order.

In the same way that a flow along pipe and river bends causes a secondary flow that rotates the slower moving particles nearer the center outward and the faster moving particles inwards. It is an inescapable fact of the simple Euler equations for fluids, as is the Coriolis acceleration in a rotating frame.

I found it unbelievable when I first looked at the Tokomak design that anybody had not seen this (or had seen it and underestimated it) when they were chosen as the "go to" option for fusion. It will be a gargantuan task to ever stabilise these flows.

A contained spherical blob has many simple internal flows that are inherently globally stable flow, i.e. sans turbulence. That's why Polywell has my interest.

Like Bussard said, "How many stars look like donuts?"

There is a deeper wisdom in this statement than the surface facetiousness allows.

hanelyp
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Post by hanelyp »

The toroid has the advantage of closed magnetic field lines. Thus losses depend on cross field diffusion and turbulence. But as mentioned, the tokomak has severe turbulence problems.

The polywell, it so far appears, has little turbulence in the plasma. But it uses an open field line magnetic configuration that leaks. This is remedied by an electric field structure to re-inject electrons and contain ions independent of the magnetic field. If a magnetic field configuration was found to deliver similar stability with closed magnetic field lines, it would be very promising, and probably not a simple sphere.

I still find the argument "stars are spherical, so should fusion reactors be spheres" very weak and lacking foundation. Stars are contained by monopole gravity. If primary containment is by magnetic field, lacking monopoles, I wouldn't expect a similar configuration.

jmc
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Post by jmc »

Regardless of donuts and stars, CDX-U has achieved confinement times 6 times above ITER scaling experimentally and I trust experiments more than any theory. LTX which is predicted to have even lower recycling should do even better. Increase the confinement time and you can build a smaller machine.

Reduce the volume of ITER by a factor of 10 and you've got yourself an economical fusion machine that can really work.

icarus
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Post by icarus »

Stabilising turbulence with temperature gradients seems like piling more complications onto an already complicated problem ...i.e. good luck with that.

The number of work-arounds, variations, add-ons and permutations on Tokomak designs is a manifestation of one thing only ... it is fundamentally flawed.

Each and every iteration is trying to make a square wheel roll.

No one wants to fart in fusion church and come out and say it unless the high priests should be offended and they may begin to vacate the cathedrals of fusion physics.

MSimon
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Post by MSimon »

hanelyp wrote:The toroid has the advantage of closed magnetic field lines. Thus losses depend on cross field diffusion and turbulence. But as mentioned, the tokomak has severe turbulence problems.

The polywell, it so far appears, has little turbulence in the plasma. But it uses an open field line magnetic configuration that leaks. This is remedied by an electric field structure to re-inject electrons and contain ions independent of the magnetic field. If a magnetic field configuration was found to deliver similar stability with closed magnetic field lines, it would be very promising, and probably not a simple sphere.
The funny thing is one of the proposed solutions for the Tokamak turbulence problem is to make it leaky.
Engineering is the art of making what you want from what you can get at a profit.

jmc
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Post by jmc »

icarus wrote: 1)Stabilising turbulence with temperature gradients seems like piling more complications onto an already complicated problem ...i.e. good luck with that.

2)The number of work-arounds, variations, add-ons and permutations on Tokomak designs is a manifestation of one thing only ... it is fundamentally flawed.

3)Each and every iteration is trying to make a square wheel roll.

No one wants to fart in fusion church and come out and say it unless the high priests should be offended and they may begin to vacate the cathedrals of fusion physics.
1)Removing temperature gradients makes the system simpler from a physics point of view. Achieving that is more complex from a technical point of view.

2)Add ons modifications and permutations are a pervasive part of all engineering, look at the steam engine, computers, aircraft. Even look a Bussards talk and you'll find the development of the Polywell filled with permutations and it still doesn't work! Permutions are how you develop complex systems and plasmas are in escapably complex. Live with it.

3)All this talk of stars, donuts, square wheels, churches and high priests has nothing to do with science and everything to do with taking sides. Getting electricity from fusion its what's important how we do it isn't.

jmc
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Post by jmc »

MSimon wrote:
hanelyp wrote:The toroid has the advantage of closed magnetic field lines. Thus losses depend on cross field diffusion and turbulence. But as mentioned, the tokomak has severe turbulence problems.

The polywell, it so far appears, has little turbulence in the plasma. But it uses an open field line magnetic configuration that leaks. This is remedied by an electric field structure to re-inject electrons and contain ions independent of the magnetic field. If a magnetic field configuration was found to deliver similar stability with closed magnetic field lines, it would be very promising, and probably not a simple sphere.
The funny thing is one of the proposed solutions for the Tokamak turbulence problem is to make it leaky.
Tokamak turbulence isn't a show stopper, its an aspect of the system, it means you have to build a bigger machine, but its not necessary to eliminate turbulence completely.

MSimon
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Post by MSimon »

Tokamak turbulence isn't a show stopper, its an aspect of the system, it means you have to build a bigger machine, but its not necessary to eliminate turbulence completely.
Bigger is not a show stopper for physics. However, for economics it could be a killer.
Engineering is the art of making what you want from what you can get at a profit.

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