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This is really another form of hot fusion, they're claiming that as the bubbles collapse they reach high enough temperatures for fusion
There have been some advances in conventional fusion lately - this is from new scientist -
(http://archive.newscientist.com/archive.jsp?id=23294300 - you have to log in so I've posted a big chunk)
Creating 100-million °C plasma is one thing; keeping it hot is another. Turbulence within the super-hot plasma has a nasty habit of transporting the heat out as fast as colossal electric currents and particle beams can shovel it in. But if you can create a region of low turbulence within the plasma, it acts like a scarf around a hot-water pipe-and the heat stops pouring out of the machine.
The existence of such heat transport barriers came as a complete surprise to fusion physicists. "No one predicted them," says Cowley. "But we're certainly all glad that they exist."
The first transport barrier to reveal itself is known as the "high-confinement mode", or H-mode, which traps heat at the edge of the plasma. Experiments at various fusion laboratories have shown that when the amount of power trapped in the plasma exceeds a threshold, a region of low turbulence suddenly appears around the edge of the plasma. Exactly why H-mode occurs is still not fully understood, but its effect is dramatic, doubling the amount of time the machine can sustain fusion temperatures.
Recent experiments at JET have shown that H-mode isn't stable, but repeatedly collapses, zapping the walls of the machine with huge heat loads. It's not all bad news, though: these sudden releases of energy also allow impurities, including fusion-killing helium "ash", to escape.
The trick to keeping fusion alive lies in a balancing act, using H-modes to keep the heat in while allowing their collapse to clean up the plasma. Researchers at JET have now perfected the trick by "tickling" the plasma with judicious amounts of magnetic and radio-frequency energy. They have also come up with a way to combat the heat-load problem, using squirts of inert gas that spread the energy trapped in the edge of the plasma over a wider area, reducing wear and tear on the machine walls.
But this is not the only good news to come the way of the long-suffering fusion community. At October's meeting of the American Physical Society, Joelle Mailloux, one of the researchers at JET, presented the best evidence yet for even more powerful heat-trapping effects-and ones that occur in the bulk of the plasma, not just at the edge: internal transport barriers.
These ITBs are now expected to play a crucial role in the success of any future power-producing reactors. By carefully controlling conditions inside the machine, it's possible to put a twist in the magnetic field that dramatically cuts the rate of heat loss. "That gives higher temperatures and plasma densities even than H- mode," says Mailloux. "And that should lead to smaller and cheaper reactors."
At the APS meeting, Mailloux and her team unveiled the spectacular improvement in JET's performance made possible by ITBs. Their heat-sealing effect raised the temperature at the centre of the plasma to over 300 million °C, well over double the level needed to trigger sustained fusion. It also increased tenfold the volume of plasma at or above fusion-level temperatures-a breathtaking improvement in performance.
But ITBs are more than just supercharged versions of H-mode. "Their real advantage over H-mode is that they produce a large amount of the current in the plasma," says Mailloux, "That means much less current has to be supplied from outside to keep the plasma confined."
Huge temperatures, bigger plasmas, lower power demands-is nature finally giving fusion scientists a break? It sounds too good to be true, and Mailloux is the first to admit that it's hardly plain sailing from here. "ITBs are fragile, and they need a large initial input of power," she says. "We don't yet have scaling laws for them either." |
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