Comment by __MatrixMan__ | Hacker News Reader

Comment by __MatrixMan__ | Hacker News Reader

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1. Yes, sorta, but it's more than just the magnetic field. You're also heating the fuel, so you have to offset that too. Plus there are pumps which circulate coolant to carry heat away from the plasma and towards a turbine, so you have to offset their power. Probably a few other things as well.

2. I don't think plasma == fusion. You can get plasma just by heating a gas beyond a certain point. Plasma cutters, for instance, operate on super heated air, no fusion anywhere nearby.

3. I think the wall of the reaction chamber heats up because they're being bombarded by radiation.

Most of the radiation incident on the reaction chamber walls is infrared, radiated from the hot plasma, but there are also more exotic things like stray neutrons also crash into the sides of the thing. These cause the metal to deteriorate over time (and become somewhat hazardous), but they also they impart additional heat energy.

So you have to have two cooling systems, one to keep the magnets actually cold so they they remain superconducting, and another to keep the housing below the point where it melts. It's this second one that let's you pull heat away from the hot metal donut that is a tokomak and use it to make electricity.

Between the magnet coolant and the chamber coolant and the reacting plasma you have some of the steepest thermal gradients anywhere in the known universe.

Thanks..right I know about plasma in general, I just assumed in this case it was caused by the fusion. Maybe not. But they have fusion right? Just not recovering any/enough energy to make up for power requirements.

The article is light on details. It doesn't mention an operating temperature or Q factor.

I would hazard to guess that no - they did not achieve fusion. They achieved plasma which is a precursor to fusion. Controlled plasma, at a high enough temperature, is an environment in which fusion can occur. All this article says is they created controlled plasma. Crucially, they did so with high temperature magnets which is fairly novel.

https://en.wikipedia.org/wiki/Fusion_energy_gain_factor You might also be interested in reading this. Q factor is what's used to discuss whether a fusion device is generating net positive energy.

No tokamak, even one intended to achieve fusion, would first be operated on D or DT. They'd first extensively test it with ordinary hydrogen.

I doubt they have achieved any fusion reactions. They don't state any numbers on density or temperature so it's impossible to know. But in general plasma is never "caused by" fusion. Creating a plasma is quite easy compared to getting it hot and dense enough to fuse.

They likely can have some fusion reactions (if they use fusible fuel, like D-D). Fusion is not that hard to achieve, you can do that on a table-top scale (Farnsworth Fusion).

I'm musing about the phrase:

> plasma is never "caused by" fusion

Which do you suppose comes first in a gravitational confinement scenario, plasma or fusion? It sorta seems like a chicken/egg scenario. I mean you gotta get those electrons out of the way, but where does he heat come from to do that, if not fusion?

Definitely plasma. Look at star formation in nebulae. Most of the hydrogen in them are in glow mode plasma. It takes a very small amount of energy to ionize plasma and a a huge amount to fuse it. So when stars are forming they might start as cold hydrogen, but they get progressively warmer and more dense until they ionize, then get even warmer and more dense, until they're burning.

https://en.wikipedia.org/wiki/Star_formation

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