RF stabilized plasma

[ravingdave]

Story.

http://www.livescience.com/technology/0 ... power.html




David

[Mike Holmes]

Does this mean that ITER just became a whole lot more feasible? What are the odds that MIT made a mistake here? After all, they don't have any explanation, apparently, for why it works. Can somebody technical look at the actual paper?

I mean... this sounds pretty huge. Any application for Polywell?

Mike

[joedead]

Yeah, what's up with this?

I would expect news like this to be earth-shattering in the physics community....?

[MSimon]

Another link:

http://www.sciencedaily.com/releases/20 ... 185016.htm

ScienceDaily (Dec. 3, 2008) — Research carried out at MIT's Alcator C-Mod fusion reactor may have brought the promise of fusion as a future power source a bit closer to reality, though scientists caution that a practical fusion powerplant is still decades away.

In other words they still have no clue and won't be able to decide if they have a clue for quite a while.

Also telling:

"That's very important," Marmar says, because presently used techniques to push the plasma will not work in future, higher-power reactors such as the planned ITER (International Thermonuclear Experimental Reactor) now under construction in France, and so new methods must be found.

In other words: we knew we couldn't make it work when we built it. We were hoping for Step 2 more commonly known as the Magic Step.

Here is the 3 step process:

1. Build it
2. Magic Step
3. It works!

[pstoller78]

Could these observed forces somehow be related to the POPS effect? I realize both are rf based, could this research along with the POPS research taken together tell us more about how rf fields interact with plasmas at a more fundamental level.

[Mike Holmes]

The way the article reads, this sounds in fact like it is a magic step. That is, that it solves one missing link in another process. Are you saying that it's not? Or that there are other missing links? Or that this particular process itself has a magic step that's being ignored?

Mike

[jmc]

Yeah, what's up with this?

I would expect news like this to be earth-shattering in the physics community....?

Not that Earth shattering. Plasmas can already be made to rotate with neutral beam injection. Its just that the bigger you make the plasma the faster you must inject the neutrals in order for them to be ionized close to the core and thus deposit their energy there. The faster you inject the neutral the less torque you apply to the plasma per unit heating power.

I'm pretty sure radio wave rotation won't eliminate all plasma instabilities and allow us to build tokamaks 10's of centimetres in diameter that can achieve break even. It'll just allow us to achieve the same results that have already been achieved with neutral beam on larger devices.

And it has absolutely nothing to do with POPS.

[Art Carlson]

I finally got time to look at the paper, so even though the mob has long ago moved I, I thought I should comment.

I wouldn't call it a breakthrough. It is another knob we can turn to optimize, or at least understand tokamaks. The progress in tokamaks (as in most technologies) in the past has mostly been the sum of many such small discoveries. That will continue to be true in the future. Whether such steps will ever add up to a practical technology is still unknown.

What I can say about the physics is this.

Neo-classical tearing modes are macroscopic MHD modes that are expected to be a big problem at reactor scales. One way to stabilize them is by rotating the plasma. Essentially, there is a field perturbation associated with the modes. If the mode is stationary, the perturbations slowly diffuse through the wall and allow the mode to grow. If the plasma is rotating, any piece of wall sees an AC field, which it can oppose with eddy currents.

Transport of energy and particles on the closed flux surfaces is thought to be dominated by drift wave turbulence. If you have not just a velocity, but a *shear* in the velocity ( d v_phi / d R > 0 ) then the plasma eddies associated with this instability get torn apart before they can develop their full destructive power. In particular, this is wha H-mode has better confinement than L-mode.

So there are good reasons to be interested in controlling the plasma flow, but like I said, there is still a long way to go before it helps you build a reactor.

[Skipjack]

Thanks for the feedback Art!
Always good to get your informed input to a discussion!