Japanese Maglev Line: Chuo Shinkansen

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Japanese Maglev Line: Chuo Shinkansen

Postby lpetrich » Wed Dec 24, 2014 2:34 am

JR Central starts construction on Chuo maglev | International Railway Journal
JR Central hosted ceremonies at Shinagawa station in Tokyo and at Nagoya station on December 17 to mark the start of construction on the Yen 5.5 trillion ($US 46.45bn) Chuo maglev line between the two cities.

Work starts on Chuo maglev - Railway Gazette
According to JR Central, construction work on the 286 km between Tokyo and Nagoya will get underway in earnest in early 2015, and take about 10 years; around 85% of the line is expected to run in tunnel. Revenue operation is due to start ‘by 2027’. The second phase from Nagoya to Osaka would not be completed until 2045.

The reason for this leisurely schedule is because its builders don't want to incur an excessively large debt from building it.

They are expecting a travel speed of 500 km/h, and a Tokyo-Nagoya time of about 40 minutes.

Chūō Shinkansen has more detail. Also Maglev, Electromagnetic suspension, Electrodynamic suspension, Linear motor, SCMaglev (all Wikipedia)

The Chuo Shinkansen will use Japan's SCMaglev system, which uses electrodynamic suspension and a linear-motor system. On the sides of the track are a series of coils in figure-8 configuration. The train has superconducting magnets that make eddy currents in the side coils as the train travels. These eddy currents make magnetic fields that interact with the train's magnets to pull it up and away from the sides. The train has rubber-tired wheels so it can travel when it is too slow to levitate itself.

The trains are propelled by additional magnets on the sides of the track; the train-track system forms a linear motor.

Some other maglev systems use electromagnetic suspension: magnets below the track pull the train up to it. That's Transrapid's system, the system used in Shanghai. This kind of maglev requires some rather tight tolerances: about 1 cm of separation. It also requires continual adjustment of the suspension magnets, since it is in an unstable configuration. Electrodynamic suspension, however, is stable.


Superconductivity is worth a bit of discussion to indicate the engineering challenges of using it. Some metals become perfect electricity conductors when chilled below a certain temperature. This critical temperature is usually about a few K (List of superconductors, Superconductivity), often around the boiling point of helium (4 K) but seldom above the boiling point of hydrogen (20 K). That's why high-Tc superconductors have been so interesting. However, it's been hard to make good superconducting magnets out of them.

An interesting feature of superconductivity is that ordinary conductivity and superconductivity are more-or-less inversely related. Highly-conductive metals like copper don't become superconducting, while the best superconductors are poor ordinary conductors. For that reason, many superconducting magnets are designed with their superconducting wires having copper cladding. If the wires get overheated, then the superconductivity gets quenched, but the current can get conducted through the copper. This comes about through the mechanism of superconductivity: Cooper pairing. As metals' conduction electrons travel, they make the ion cores wiggle, and the cores then push and pull on their neighbors. Thus, electrons can interact with each other, and become loosely-associated pairs, the Cooper pairs. This is a very weak pairing, and it is easily broken up, thus explaining superconductors' low critical temperatures. But when they are present, then pairings can get correlated with each other, making a superfluid of pairings. Thus, supeconductivity. I say superfluid because helium superfluidity involves similar effects. This also explains why ordinary conductivity and superconductivity are inversely correlated -- poor ordinary conductivity is from electrons having lots of obstacles, and thus lots of opportunities to interact with each other, thus making good superconductivity.

Superconductivity can also be destroyed by magnetism, and superconducting materials are either Type I or Type II. A Type I's critical magnetic field is typically a few hundred gauss or a few hundredths of a tesla. A Type II's one is more complicated. It has a Type-I-like one, but above that one's critical field, the field pokes holes in the superconductivity, holes that it goes through. This effect also has a critical field, but that field can be as high as several tesla. Superconducting magnets are thus usually made from Type II superconductors.

There's also a balance between critical temperature and critical field; to have a high critical field, one needs low temperature, and vice versa. That's why it's necessary to use liquid helium to cool superconducting magnets.
lpetrich
 
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