Floating Trains

World's Fastest Train

Several months ago, Tom Scott uploaded a video in which he rode the Chūō Shinkansen SCMaglev train in Japan.

How does he get this much funding...?

Anyway, this train holds a world speed record: it achieved a maximum speed of 603km/h back in 2015. Even the cruising speed is 500km/h! Japan has exported its maglev technology to the USA, so hopefully their transportation will stop being shit in the relatively near future.

Maglev trains aren't new. The SCMaglev system in particular has been in development for half a century. But the physics used makes it ten billion percent cooler than ordinary maglevs! (Both figuratively and literally. And there's a good reason for this.)

Superconductors

The SC part of SCMaglev stands for superconducting. A superconductor is a material whose properties change below a critical temperature, denoted by T_c. At normal temperatures, there is some electrical resistance from electrons bumping into atoms and each other, which makes them lose some energy as heat. (Their kinetic energy doesn't just disappear, after all—energy can't be created nor destroyed.) This train uses a niobium-titanium alloy.

But below its critical temperature, usually a few degrees above absolute zero, the electrons slide around smoothly thanks to some quantum effects causing the relatively long-distance pairing up of electrons. (That's in conventional superconductors at least—unconventional superconductors are still a mystery.) This means there's zero electrical resistance, and as a result, you can keep a circuit running indefinitely!

Since an electric current leads to a magnetic field, engineers have figured out that you can use superconductors to create a crazy efficient electromagnet. As long as it's kept cold, you only need to power it once.

How do they do it?

Two paragraphs ago, I mentioned a critical temperature, and that it's usually close to absolute zero. (High temperature superconductors—those that work above the boiling point of nitrogen—do exist, but they're still very cold, and the majority of them are brittle. The ones that can work near room temperature are only able to do so under even crazier pressures.) In the SCMaglev and elsewhere, these superconductors rely on liquid helium to keep them cool.

Once the liquid helium cools the magnets down, they power it up. The current then gets trapped, and it produces a powerful magnetic field, and you can manipulate the direction and speed by changing the polarity of regular electromagnets lined along the track.

Levitation, on the other hand, is achieved in a more practical way. Some unpowered figure-eight shaped coils are lined along the track, and in short, the superconducting magnets induce an electric current in those coils, giving them their own magnetic field. Its shape separates the field into one north and one south pole. These poles would normally cancel out, but if you offset the main SC magnet a little, you can create a net force that pushes the train upwards! It's a bit hard to explain without graphics, so here's a video: