Saturday, June 10, 2006

Train flying in flying colours! പറക്കും വണ്ടി പറവണ്ടി!

Yes, that is magnetically levitated train. These trains are literally flying. At very high speeds, these trains are “flying” approximately 10cm above the ground level. There is no contact between the train and the ground at high speeds!

What is magnetic levitation?

The meaning of levitation is “To rise or cause to rise into the air and float in apparent defiance of gravity”. We can levitate a ball by keeping it near the output pipe of a vacuum pump. If we levitate an object using magnetism, then we are magnetically levitating that object. But ordinary magnets may not do the trick. We need very strong magnets, especially if we need to levitate a heavy object like train. You can see a live frog levitating in a magnetic field here in this video

How can we achieve levitation?

One of the methods is superconductivity. The magnetically levitated trains (or in short, maglev) in Japan use superconductivity for levitation. The advantage of levitation is that there is no friction between the wheel and the track compared to ordinary trains because there is no contact between the train and the ground. The result is that it can “fly” in high speeds. The highest speed achieved by a maglev all over the world is 581 km/hour by the maglev train in Japan! The high speed bullet trains in Japan are now running at a speed of 250-270 km/hour.

What is superconductivity?

When certain metals (like tin, aluminum) and metallic alloys are cooled below a specific temperature, their electric resistance vanishes. This phenomenon is known as superconductivity. No electrical resistance means there is any electric loss. Once current is applied to a coil in a superconducting state (which can then be called as superconducting coil), this current continues to flow permanently without any loss, even without any applied voltage. Experiments have demonstrated that currents in superconducting coils can persist without applied voltage for at least 100,000 years without any measurable loss. We all know that electricity can generate magnetic field. If we run an electric current through a wire (by connecting the wire between the positive and negative terminals of a battery), electricity will be generated and at the same time, a small magnetic field will also be generated in the wire. If we pass a large amount of current through the wire and at the same time, there is no electrical loss in the wire (say, due to superconductivity), the magnetic field generated will be tremendous. Superconductivity was discovered in 1911 by Heike Kamerlingh Onnes, who was studying the resistivity of solid mercury at very low temperatures using a refrigerant. At the temperature of -269 degree Celsius, he observed that the resistivity abruptly disappeared. For this discovery, he was awarded the Nobel Prize in Physics in 1913. Why we need to cool the metals for superconductivity is a question not easy to answer in simple terms. It all related to vibration of electrons and their movement.

Thus, one of the major difficulties associated with the application of superconductivity for commercial use is the fact that the metal needs to be cooled to a very low temperature (of the order of -180 to -270 degree Celsius). Even in Antarctica, the lowest temperature attained was around -90 degree Celsius! We need special materials like liquid nitrogen or liquid helium to achieve such a low temperature. We might have seen superconductivity at room temperature in movies like Terminator. But such superconductivity is only in movies and science fictions so far!

We have seen that superconductive metals are highly magnetic. Therefore, if we can place a superconductor over a strong magnet, it will float above the magnet because of the repulsive forces between the two objects (the magnetic is having strong magnetic fields and the superconductor is also having strong magnetic fields). This phenomenon is called magnetic levitation. This is the principle behind magnetically levitated trains. Levitation of a superconductor in a magnetic field is displayed here. You can also read more about superconductivity there.

It should be noted that superconductivity is one among the many techniques available for magnetic levitation. There are magnetically levitated trains which use other methods for levitation as explained here. However maglev trains in Japan are the only magnetically levitated trains which use superconductivity for levitation.

How are these superconducting maglev trains flying?

There are superconductive magnets in the train. They will be cooled to a very low temperature and electricity will be passed through them so that strong magnetic fields are generated in them. Also electrical coils are placed on the two sides of the track. Electricity at high voltage will be passed through these coils so that strong magnetic fields are generated in them also. We know that the magnetic fields can attract and repel. This attraction and repulsion of the magnetic fields cause levitation (due to repulsion) and forward movement (due to attraction) of the maglev trains.

The superconductive magnets in the train and the electric coils on the sides of the tracks is together is called motor of the train. These are called motors because their purpose is just like any other motor-to move the train. Conventional motors are cylindrical in shape. However the motors here (superconducting magnets in the train and the electric coils in the track) are linear in shape (just imagine that a cylindrical motor is unrolled and made flat). Therefore, the motor of maglev train is called linear motor. The superconducting maglev trains run at ultra-high speeds after being levitated by 10 cm as a result of the magnetic force that lies between the superconducting magnets in the train and the electric coils on the sides of the train track.

You will get more information on how these trains “flying” by clicking here and here. Some details are given here too. You can see a Wikipaedia article on maglev trains here which also explains the different means for levitation.

Maglev starts moving by using the wheels rolling over the ground. As it gains speed, it will slowly raise above the ground. Before stopping also it will land on the ground. These trains can be operated unmanned using a centralized control system. No driver is needed!

Japan is not the first country to experiment on maglev trains. There were maglev trains in Britain and Germany. One maglev train is making its commercial runs in Shanghai, China. It is alleged that China had copied Germany’s maglev technology to build their maglev trains. USA is also planning maglev trains for commercial applications.

Will it be realistic?

Not sure. Japan has already spent a lot of money for the development of maglev trains and they are in an advanced state also. The estimated cost for building an operational maglev line between Tokyo and Osaka in Japan is around US$ 82 billion. The operational cost is expected to be 20% higher than that of the existing bullet train. However the running time between Tokyo and Osaka can be reduced from 2.5 hours to 1 hour if maglev is used. It is expected that the time advantage may attract more passengers to maglev.

There is a health concern also for such trains. It is not sure whether people with cardiac pacemakers can use maglev because of the presence of superconducting magnets in the train. Studies are also being conducted to analyze the effect of maglev running through highly populated areas because high speed may cause vibrations in houses and related problems. Also when a high speed maglev train enters a tunnel, there can be problems associated with high pressure air acting between the tunnel and the train (or vacuum? I am not sure).

In Tokyo, the test run of the maglev train is taking place in Yamanashi prefecture. With prior booking one can participate in the trial run and experience the 581 km/hour “flying”. You can see how these trains are flying by clicking here.

ആംഗലേയ ബ്ലോഗില്‍ ഫ്ലൈയിംഗ് ട്രെയിന്‍ ഇന്‍ ഫ്ലൈയിംഗ് കളേഴ്‌സ്!

സമര്‍പ്പണം- അതുല്ല്യേച്ചിയുടെ അപ്പുവിന്