[liftm]

I'm a physics layman, and I'm having some trouble with uniting the content of your comment with the fact that existing magnetic confinement experiments have reported maintaining a plasma at the right temperature for longer times (not with fusion, but with microwave heating, and with the power of those heaters in the 10MW range).

Have I understood the consequences of those reports wrong? Does the heat loss you talk about only occur with fusion? (And if so, is it even a problem if the conditions for fusion to occur can be created by external heating this "easily"?)

[adastra22]

In order to protect astronauts from decompression, the hull of a spacecraft has to be insanely good at stopping gas particles. Not 99.5% good, but like 99.9999999…% with 20 zeros! That’s very good.

But a thin metal sheet has no trouble doing this, as demonstrated by the Apollo lunar lander.

Some things are just not as hard as they sound. Magnetic confinement works very well. It easily achieves the necessary 9’s.

It’s just hard to keep it stable at millions of degrees, but that’s a different problem.

[matt123456789]

Wait til you guys hear about DNA transcription error rates!

[credit_guy]

I'm not sure, but we can try to figure out what is going on. And by the way I'm a physics layman too. I just read a lot of books about fission and a few about fusion too, it happens to be my hobby. When I'm bored, the bookmarks that I browse are [1] and [2].

So, when reports state that the a certain temperature was achieved and sustained for a certain period of time, what are they actually saying? We could go and find an article and get into some details, but I imagine they say that somewhere in the plasma that temperature was reached and sustained. But it is quite likely that that region is quite microscopic, maybe a very, very thin inner torus inside a larger torus. There is a gradient of temperature from the region where the announced temperature happens to the walls of the device. But one way or another that thin inner region can't have a surface area of anything close to 1 square meter. To get to 1 GW of power, you need 10^-12 square meters, and to get to 10 MW you need 10^-14 m2. That's about the surface area of a torus of (circular) length 3 m and diameter 1 femtometer. 1 femtometer is roughly the size of a nucleus of deuterium or tritium, so in principle this is the minimum diameter of a torus where you can talk about fusion.

[1] https://www.ncnr.nist.gov/resources/n-lengths/

[2] https://www.oecd-nea.org/janisweb/