After clearing things out with the viral temperature "record", I will continue where I have stopped. The last article was about the fourth state of matter - plasma, but after reading it you might wonder - HOW THE HELL CAN WE CONTAIN SOMETHING THAT HOT?!
And really, if you know some basic physics, you might know that tungsten has the highest melting point at 3687 K. That is about 0.32 eV, while we need 15 keV for a fusion power plant. So again - HOW TO ENCLOSE SUCH HOT PLASMA?
Short answer - we do not let it touch any wall B-)
How Sun does it?
Luckily for Sun, it does not need to be contained in a container, as it levitates in space. But the temperature of the Sun is not all equal across its volume. Sun surface and surroundings have a temperature of several hundreds of thousands of Kelvins, while temperature under surface is less than 10 000 K! The 15 million Kelvin (1.5 keV) is reached gradually towards the core. And the core is where the nuclear fusion reactions happen.
Sun keeps particles in its core in extremely dense condition due to the gravity! And all surrounding layers simply serve as isolation of super-hot Sun core from the cold Universe.
How can we do it?
As you can imagine, we cannot make the super-hot, super-heavy, levitating ball on Earth to produce electricity for us. So we have to be cleverer than the Sun.
As already mentioned, we need plasma to about 15 keV to make fusion here on Earth. So temperature is fixed. If you remember from my last post, I mention that plasma density and energy confinement are as important as the temperature.
As it is usually in life - we cannot have both parameters large. Henceforth, one can either focus to have a large density or large confinement time. The former approach is known as magnetic confinement fusion, while the latter one is named inertial confinement fusion.
Inertial Confinement
This principle uses fast compression of the plasma usually with lasers. The plasma is produced by compression of a small tablet (size of a pill) that is centered in the large box/container (size of a house). In such way, plasma cools down until it reaches the wall. The compression makes plasma so dense, that it is about a hundred times larger than that of the lead! However, the confinement time is quite short - a billionth of the second, due to the pulsed nature of the process.
I do not plan to write too much about inertial confinement, as I did not study it. Besides my lack of information, I also think that commercial nuclear fusion power plant will not work based on the pure inertial confinement principle. Presently, it seems as very non-economical approach. If you wonder why do people still invest billions of dollars/euros in its research, the answer is simple: equations governing plasma implosion due to the lasers are very similar to those of nuclear (fusion) hydrogen bomb. So military invests in this approach.
Magnetic confinement
Here, plasma is significantly larger (size of a house) than for inertial confinement and chamber is more filled with plasma. But plasma is guided by the magnetic field along the chamber in such manner that plasma does not touch the wall (i.e. as less as possible). The density of magnetically confined plasma is relatively rare, like 1 million times smaller than the air that we breathe in. The low density is compensated with relatively large confinement time at the order of 1 second. In theory, this approach can work continuously, but such operation was not achieved yet.
In the upcoming weeks, I will explain both principles in more details, and going deeper with the machine design.
Please feel free to ask anything in the comments. I will either try to answer you in the comment or even make the new post.