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How To Line a Thermonuclear Reactor
sciencehabit writes "One of the biggest question marks hanging over the ITER fusion reactor project — a giant international collaboration currently under construction in France — is over what material to use for coating its interior wall. After all, the reactor has to withstand temperatures of 100,000C and an intense particle bombardment. Researchers have now answered that question by refitting the current world's largest fusion device, the Joint European Torus (JET) near Oxford, U.K., with a lining akin to the one planned for ITER. JET's new 'ITER-like wall,' a combination of tungsten and beryllium, is eroding more slowly (PDF) and retaining less of the fuel than the lining used on earlier fusion reactors, the team reports."
This is known as the "first wall" problem in fusion reactors. It's good to hear there's been progress.
It's discouraging to hear how slow progress is on ITER.
Where are these temperatures of 100,000 C ? - Tungsten BOILS at 5660 C and Beryllium at 2970 C - Of course, that's at 1 atmosphere pressure. Something doesn't seem right to me unless the 100K is a good ways away from the walls or the pressure inside is incredibly high (doubtful).
Magnetic fields contain the plasma. That heat never reaches the walls.
I think the pressure inside is low, and the temperature is the temperature of the (low pressure) plasma. So think a smallish number of ions at really high velocity.
From what I understand, the plamsa is confined by a magnetic field, but not perfectly. So, when some plasma ions go astray, they've gotta hit a material that can take high temperature. The beryllium is probably converted into some useful atom by a nuclear process when this happens.
I might be really wrong about this, but it's my best guess.
"Nuclear" includes fusion. But consider this: Fusion has been "5 years away" for 40 years.
And it will continue to be "5 years away" for another 40 years. In the meantime, we should be building fission plants based on standard designs. And we should bring back breeder reactors, so we can make more fuel out of used fuel.
But that's not going to happen because of the politics of shrill earth-firsters and others who don't understand nuclear and who think that every nuclear plant is Fukushima or Chernobyl.
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BMO
Tungsten is used on the divertor, not the first wall, so the fact that it's a high-Z material is less relevant.
The confined plasma itself doesn't contact anything (and if it were to, it would cool down and fizzle out); the region of the interior where the magnetic field lines are closed never contact the first wall or divertor. The region outside the closed field lines, the 'scrape off layer', is drawn close to (and particles impinge on), the tungsten divertor strike plates. It's not the plasma per se; but there are still loads of hot, fast particles, and there's still the possibility of material being ejected from the strike plates. However, it will not get drawn in to the main ('confined') plasma, where the impurities can radiate energy away from the plasma. This is the beauty of the divertor configuration, as opposed to, say, limiters -- contaminants are kept out of the plasma, and ash is transported out through the scrape-off layer.