How Japan's Maglev Train Works

Buried here, deep in a Japanese mountain pass, is one of the world's rarest technologies. A  43-kilometer-long magnetic levitation train track. Which will eventually become part of the  world's first inter-city Maglev train, connecting Tokyo and Osaka.

With the power of superconducting magnets,  these trains hover a mere 10 centimeters above their track, while pummeling along at a  mind-boggling speed of 500 kilometers per hour. With no physical contact required with  the track, they can operate in any weather conditions and have lower maintenance costs  due to reduced friction and fewer moving parts. Despite the advantages of Maglev trains  over traditional high-speed trains, The only commercial high-speed Maglev  line currently in operation is just 30 kilometers long.

Connecting  Shanghai Airport to it’s city. A journey the train makes in only 8 minutes,  but a track this short largely defeats the advantage of high speed maglev, by the time  the train gets up to speed, it needs to slow down again. A 30 kilometer journey in 8  minutes actually equates to an average speed of 225 kilometers per hour, slower than  the top speed of conventional high speed rail.

The planned future network of high-speed  maglev tracks, just 400 kilometers long, and it pales in comparison to the extensive  network of 60,000km of regular high-speed train tracks already in place around the world,  with an additional 50,000km under construction. Why is this gap so large? Let's  delve deeper into how Maglev trains work and explore the reasons  behind their restricted deployment.

We have two primary methods of levitating  a train. We can pull the train up using attractive forces or push the train  upward using repulsive forces. The pulling approach involves a combination  of a magnetic iron rail and an electromagnet that uses attractive forces to raise  the body of the train.

This is an active system where the gap between  the rail and the magnet is crucial as the strength of the attractive force  decreases with the square of the distance. Meaning, the train needs active  controls and feedback loops ensure that these gaps stay between 8 and  12 mm. If the train begins to drop, the magnetic force holding it up will quickly  weaken, causing it to fall even further.

It’s an unstable configuration. These types of  trains are referred to as Electromagnetic Suspension trains. This is the system the 30  kilometer line in Shanghai uses.

[1][REF_00] Japan opted to use a different  system, with a more significant gap of 10 centimeters between the track and train. 8 times greater than the gap for electromagnetic  suspension, while also providing a passively stable method of levitation. A vital property  to have in the earthquake prone region.

[2] In this approach, magnets onboard the train  interact with passive coils on the track. As the train moves over these coils, they  experience a changing magnetic field, which generates the opposing  field that lifts the train upward. If the train is stationary on top of  the coils, there is no change in the magnetic field.

So this dynamic system only  works when the train is already going fast. The trains have wheels that drop  down when the train is slowing down, but flip into the carriage  when they reach 100 km/h. [1] In order to achieve a stable position on  the track, the north and south poles are arranged vertically on the sides of the track. 

The magnets are formed from coils of wire, arranged in a figure 8 pattern. A  south pole points upwards on one side, while the north pole points up on the other. If the train were to drop slightly or  move sideways, the magnets on the train induce currents on the opposite coils,  generating a stronger magnetic field, which pushes the train back to the  midpoint of the figure 8 shapes.

[3] This dynamic system is forgiving, with  the 10 centimeter gaps between the track and the train naturally maintained with  no need for complex control inputs. [1] However, the Japanese Maglev train, called L0,  will be the first of its kind. These trains, known as SCmaglevs, need superconducting  coils to generate the extremely powerful permanent magnetic field on the train. 

These are the coils that induce the changing magnetic field and allow the train  to levitate in a stable configuration. These coils, located on each side of the  carriage, must be maintained below their critical temperature to ensure their current flows  without resistance. The niobium-titanium coils are cooled using liquid helium and placed inside  a container that is cooled by liquid nitrogen.

The coils are cooled using a Pulse Tube Refrigerator [4]. Which uses  sound waves to cool the helium. The same type of refrigeration cycle that the  James Webb telescope is using to keep its infrared sensors cold enough to detect even the faintest  infrared heat radiation from the distant past.

A sound wave is just a pressure wave and  pressure and temperature are directly proportional. Higher pressure  will cause higher temperature. We can take advantage of this by creating a  standing wave, where the peaks and troughs of the wave are stationary.

We can do this in a  closed tube where the resonant frequency of the tube is determined by the tube's length. Here  the sound wave will bounce off the closed end and create a region of compression and high  pressure, and therefore high temperature. We can now place a stack that spans this  hot region at the end of the tube to the cold region at the centre.

Now if we place  a heat exchangeron either end of the stack, we can now transfer the heat to a  radiator and the cold side will conduct heat away from the superconducting  coils. Keeping them cold. [REF] [5] There are eight of these coils  per car, with four on each side.

However, having a magnetic field strength  of this magnitude right next to passengers, and traveling by at half the speed of sound,  could cause some serious problems. Ferrous objects aren’t allowed anywhere near MRI  machines. The engineers needed to find a way to ensure the magnetic field did not extend into  the passenger cabins, or far away from the train.

We can’t block magnetic fields,  but we can redirect them, in the same way we can conduct electricity  to where we want it to go using copper wires. Where we measure the ease of passage  for an electric current with resistance, we measure the ease of passage for a  magnetic field with reluctance. Where copper has a low resistance,  Iron has a low reluctance.

We can use electric steel shielding to divert the  magnetic field away from the cabin and stations. Electric steel contains 3% silicon and is  post-processed to produce large crystal grains aligned in a specific direction, which is  controlled by a cold rolling process. The grain oriented electrical steel can carry about  30% more magnetic flux in this direction, allowing engineers to direct the magnetic  flux in the desired direction.

[6] However, this shield is heavy, so we want  to use as little of it as possible. Luckily, we can also tailor the magnetic field shape  through careful design of the magnets themselves. If we placed two parallel magnets like  this, north poles aligned horizontally, the magnetic flux lines would run parallel  to the magnets and be densers between the magnets.

However, if we flip one of them,  the magnetic flux lines connect up and create a kind of bubble in the between them. The  magnetic field will be weaker in this location. This is how we arrange the coils on either  side of the cabin.

There are 4 sets of coils on each side. So we also need to flip the  magnets so the north and south poles face each other. This creates a low magnetic  field bubble through the corridors.

[7] With the use of shielding, the field  strength is reduced to only 0. 5mT, almost equivalent to Earth's  the magnetic field. [7] Of course, near the magnets the field's  strength is unavoidably high, and this prevents us from using certain materials  in these areas.

The tracks for example need to be constructed from low-magnetic  steel, or fibre reinforced composites. [8] But how does a levitating train propel  itself if it’s not touching the ground? For conventional rail we just apply a torque to  the wheels that will push off against the ground.

Wheels are actually a bit of a middleman in the development of torque. Many trains use  electric motors to turn their wheels. The electric motors use electromagnetic force to turn a shaft.

What if we could  take the same motor and unwrap it. This is called a linear motor.  Where alternating coils attract and repel the train with precise timing.

[2] To brake the trains can use this system in  reverse, this is regenerative braking. Since electrodynamic systems don’t work at low speed,  they also have brakes for their wheels. The trains also feature an air brake that can slow  the train down very effectively at top speeds.

There is one other challenge when  dealing with contactless trains, how do they get electricity? For lower-speed  Maglev systems they use a low friction third rail, common in metro systems, to bring  electricity to the trains. [REF][2] But as speeds get higher this isn't  practical [REF][REF_00] as it defeats the purpose of reducing friction from  the rails.

Some early versions of the Japanese style electrodynamic system  actually had a gas turbine onboard to provide power. But it now uses a linear  induction coil to collect power from the changing magnetic field from the guiding  coils. [REF][REF] [9].

This does create a magnetic drag force, but it’s more effective  than carrying a large generator on board. The Japanese Line is set to be the first  long-distance high-speed Maglev train. Its first phase, covering 285 km, will connect  Tokyo to Nagoya and is scheduled to open by 2027.

The second phase, which will  complete the remaining 438 km to Osaka, is expected to be completed a decade later. So why is Japan pursuing this futuristic  technology? Japan has long been at the forefront of train technology.

After opening their Tokyo to  Osaka Shinkansen line in 1964, the world's first high speed train, they immediately began exploring  ways to reduce the 4 journey to under 1 hour. Starting in the 1970s, Japan Airways and the  Japanese Central Rail Station constructed a 7km testing track here in. Miyazaki They began with  prototypes of trains that could reach speeds of 60 km/h in 1972, and by 1995, they had developed  trains capable of reaching up to 411 km/h.

As the Miyazaki test track became too short,  the Yamanashi test track began construction in 1990. This 20km test track was conveniently  located between the cities of Tokyo and Nagoya, along the route of the upcoming new Maglev line.  Here, they transformed the design from a prototype to a fully functional train capable of carrying  700 passengers in 12 cars at speeds of 500 km/h.

But, high-speed Maglev trains are more  than just a science experiment. They are an efficient and super fast way to move  people. But, building these trains is more than just an engineering challenge,  they are also an economic challenge where they have to compete against cars,  planes, and other types of trains.

Whenever Maglevs are brought up in the US, the  idea of traveling between New York and LA in 7 hours is often used as a statement of its  potential. It’s the very first line on the US Department of Energy's own website. But a track  of this length makes little economic sense.

[10] If we plot the travel time for trains,  planes, and cars between say San Francisco and LA. Two large population centers  within a reasonable driving distance, this is what it looks like. Trains  are outright the best option.

Even though planes are faster, airports  are usually located far outside the city, and security wait times increase the length  of the journey. A high speed train will save passengers time, and in turn make an economy  more productive. A reduction of travel time of 2 hours for 900 passengers equates  to 1800 hours.

Equivalent to 75 days. Faster trains simply extend the range at  which trains are competitive to airlines. Large cities between 200 and 800 kilometers apart are perfect contenders for high speed  rail.

DC to New York in just 60 minutes. This map shows the potential economically viable  high speed rail connections in the US. [11] Unfortunately, as it stands, the US is  not investing much in high speed rail, and Maglev systems are even harder to build. 

They require completely new tracks that require electromagnetic coils along the entire length  and specialized materials that are not affected by the incredibly strong magnetic fields passing  by them at 500 kilometers per hour. The Japanese line that connects Tokyo to Nagoya recently  had a price increase to 13. 7 billion dollars.

Maglevs are between 10 and 50 times more expensive  than high speed rail. The incredibly successful French high speed rail, the TGV built in  the 80s and 90s cost 2 million dollars per kilometer [12]. The first stage of the Japanese  line is set to cost 77 million dollars per km [1] Even when compared to the same route  from Tokyo to Osaka via High-speed rail, the maglev system will cost 11.

3 times  more per kilometer. That is a large price to pay to reduce the travel time by 1 hour. The Tokyo-Nagoya line is taking a more  direct route through mountainous terrain, a staggering 86% of the track  would be underground.

[13] Tunneling over 200 km significantly increases  costs. Interestingly, this also leads to increased operational expenses. When the train  travels in the open air at speeds of 500 km/h, the unobstructed air simply moves aside.

However,  when traveling through a tunnel, the air has no escape route, this creates additional drag which  in turn increases the force required to propel the train forward. [14] The energy usage of the new line will  30% higher compared to the existing Tokyo-Osaka line . [14] But that’s  still vastly better than flying .

[15] For now, I don't see Maglev technology being  used beyond some special projects like this. The radical increase in costs simply do not  justify the increases in top speed over high speed rail. And it’s beyond imagination for  the US, we are struggling to get regular rail service even in places uniquely  suited to it like the Texas triangle.

4 high population cities located in a triangle, with only the hellscape of  interstate highways connecting them. With the recent speculation about  the potential of room temperature superconductors, a technology that would  make maglev trains vastly easier to build, interest online in superconductor  technologies is higher than ever. But a lot of it is unintuitive, and  actually understanding how magnetic fields work is a fantastic tool in an  engineer's arsenal.

So many of our most important technologies depend on this physical  phenomenon. But, you don't have to pay for a whole university level course to understand  the fundamentals. There's a free way you can learn about magnetism and electricity,  with this fantastic course on Brilliant.

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