Talk-Polywell.org

Why is it that fusion is not always mentioned in discussions on alternative energy?

Fusion is not going to be affecting the electrical grid in 10 years, and most discussions focus on the very-near term. However, underfunding fusion becomes a self-fulfilling prophecy that keeps it always in the long term. Twenty years ago, we proposed building a small burning plasma experiment. It wasn’t built. If it had been, we could have shown by now how a burning plasma works, and not be waiting for results on ITER in the 2020s. Fifteen years ago we proposed building a long pulse superconducting tokamak, which can be operated for long periods of time to investigate the science of controlling plasmas. We would have had that data by now instead of waiting to see the results on such experiments now starting up in Asia.

One of the main challenges of fusion is finding the best way to surround a hundred million degree plasma with a material structure. So the main line approach to that is to surround it with a solid material, tungsten, which has been quite successful in present fusion experiments. However, there are many questions concerning its survivability in a fusion reactor. At PPPL, we are developing an alternative approach. We surround the plasma not by a solid but actually by a liquid, a liquid “wall.” This is an alternative approach to the plasma materials problem. If a solid gets bombarded by some particles streaming out of a hot plasma, it can break, it can sputter, it can erode. Liquids, however, don’t break. Liquids are automatically self-healing. So if we surround the plasma with a liquid, it could possibly erase a significant amount of the materials problems for fusion research. And if the liquid is flowing, the liquid can take the heat of the plasma. One particular liquid, liquid lithium, has a possibly remarkable effect on the plasma. Particles that hit it get absorbed very well, so when you surround a plasma by liquid lithium, it is like a sponge. Particles don’t come back. They get stuck. Why is that good? If you have a standard material, cold particles from the material get ejected into the plasma due to sputtering. That cools down the plasma edge, can make the plasma more turbulent, the plasma can cool further, and the fusion reaction rate is diminished. A liquid lithium wall doesn’t do that. The plasma stays hot. Plasma physicists predict that with the boundary condition of lithium, the plasma should be less turbulent. So liquid lithium is in the vision of plasma engineers because it is a material that won’t break, and in the vision of theoretical physicists because it improves the properties of the plasma. So this is a major research thrust at PPPL.

If a physicist who started the field went to sleep for 40 years and came back today, he or she would be amazed.

chrismb wrote:

If a physicist who started the field went to sleep for 40 years and came back today, he or she would be amazed.

That strikes me as very selective!

If a physicist who started the field went to sleep for 60 years and came back today, he or she would be surprised at the lack of progress [in what seemed then a straight-forward physics issue].

Skipjack wrote:Without having read the article. How do you make a "liquid wall"?
IMHO, you would have to enclose the liquid in something and that is then again going to suffer from the same problems as all the other proposed wall materials.

Perhaps not, might one create a "bundt cake pan" lithium fountain around the tokamak plasma torus?

They are using a sponge like material soaked with liquid lithium:
http://nstx.pppl.gov/DragNDrop/Scientif ... totler.pdf

rjaypeters wrote:Perhaps not, might one create a "bundt cake pan"

Skipjack wrote:Yeah, that is what I suspected. But how would that prevent outgassing that could contaminate the plasma at the temperatures and bombardement hitting the Lithium this would seem likely to happen? I would assume that having gaseous Lithium mix with the plasma would not really help, or am I wrong there?

chrismb wrote:

rjaypeters wrote:Perhaps not, might one create a "bundt cake pan"

I could do you a burned pan cake. Is that much the same?