Maglev

Maglev can also mean general magnetic levitation.

A magnetic levitation train, or maglev, is a type of train that is suspended in the air above a single track, and propelled using the repulsive and attractive forces of magnetism. Because of the lack of physical contact between the track and the vehicle, the only friction is that between the carriages and the air. Consequently maglev trains can potentially travel at very high speeds with reasonable energy consumption and noise levels (systems have been proposed that operate at up to 650 km/h (404 mph), which is far faster than is practical with conventional rail transport). Whilst the very high maximum speeds make maglev trains potential competitors to airliners on many routes, the high cost of the lines has limited their current commercial application to one line in Shanghai that takes people 30 km (18.6 miles) to the airport in just 7 minutes 20 seconds (top speed of 431 km/h or 268 mph, average speed 250 km/h or 150 mph). Other maglev applications worldwide are being investigated for feasibility.

Technology

There are three primary types of maglev technology: one that relies on superconducting magnets (electrodynamic suspension or EDS), one that relies on feedback controlled electromagnets (electromagnetic suspension or EMS), and a newer potentially more economical system that uses permanent magnets (Inductrack).

Japan and Germany are active in maglev research, producing several different approaches and designs. In one design, the train can be levitated by the repulsive force of like poles or the attractive force of opposite poles of magnets. The train can be propelled by a linear motor on the track or on the train, or both. Massive electrical induction coils are placed along the track in order to produce the magnetic field necessary to propel the train, leading some to speculate that the cost of constructing such tracks would be enormous.

Unmoving magnetic bearings using purely electromagnets or permanent magnets are unstable because of Earnshaw's theorem; on the other hand diamagnetic and superconducting magnets can support a maglev stably. Conventional maglev systems are stabilized with electromagnets that have electronic stabilization. The electromagnets and electronics tend to be large, power-hungry and expensive.

The weight of the large electromagnet is a major design issue. A very strong magnetic field is required to levitate a massive train, so conventional maglev research is using superconductor research for an efficient electromagnet.

The effect of a powerful magnetic field on the human body is largely unknown. For the safety of the passengers, shielding might be needed, which would add additional weight to the train. The concept is simple, but the engineering and design aspects are complex.

A newer, perhaps less-expensive, system is called "Inductrack". The technique has a load-carrying ability related to the speed of the vehicle, because it depends on currents induced in a passive electromagnetic array by permanent magnets. In the prototype, the permanent magnets are in a cart; horizontally to provide lift, and vertically to provide stability. The array of wire loops is in the track. The magnets and cart are unpowered, except by the speed of the cart. Inductrack was originally developed as a magnetic motor and bearing for a flywheel to store power. With only slight design changes, the bearings were unrolled into a linear track. Inductrack was developed by physicist Richard Post at Lawrence Livermore National Laboratory.

Inductrack uses Halbach arrays for stabilization. Halbach arrays are arrangements of permanent magnets that stabilize moving loops of wire without electronic stabilization. Halbach arrays were originally developed for beam guidance of particle accelerators. They also have a magnetic field on the track side only, thus reducing any potential effects on the passengers.

Currently, some space agencies, such as NASA, are researching the use of maglev systems to launch spacecraft. In order to do so, the space agency would have to get a maglev-launched spacecraft up to escape velocity, a task that would otherwise require elaborate timing of magnetic pulses (see coilgun) or a very fast, very powerful electric current (see railgun). Maglev-launching could also be used to make conventional launches more efficient: accelerating a craft up to mach 1 before firing the main engines can save 30% of the weight of the launch vehicle (Heller, 1998).

Pros and Cons of different technologies

Each implementation of the magnetic levitation principle for train-type travel involves advantages and disadvantages. Time will tell as to which principle, and whose implementation, wins out commercially.

Technology	Pros	Cons
EMS (Electromagnetic)	continuously suspended when power is provided; proven, commercially available technology	narrow gap between track and vehicle; not inherently fail-safe
Superconducting EDS (Electrodynamic) systems	large gap between track and vehicle	currently (2005) reliant upon low-temperature superconductors that must be refrigerated with liquid helium; vehicle must be wheeled for travel at low speeds
'Inductrack' system	failsafe; good suspension distance; no power required to be provided to the magnets	new technology still under development (2005)

Existing Maglev Systems

In Berlin, the M-Bahn was built in the 1980s: a driverless maglev system with a 1.6 km track connecting three U-Bahn (metro) stations. Testing in passenger traffic started in August 1989, and regular operation started in July 1991. Because of traffic changes after the fall of the Berlin Wall, deconstruction of the line began only two months later and was completed in February 1992. The line was replaced by a regular U-Bahn line.

The world's first commercial automated system was a low-speed maglev shuttle that ran from the airport terminal of Birmingham International Airport (UK) to the nearby Birmingham International railway station from 1984 to 1995. The length of the track was 600 m, and trains "flew" at an altitude of 15 mm. It was in operation for nearly eleven years, but obsolescence problems with the electronic systems made it unreliable in its later years and it has now been replaced with a cable-drawn system.

Transrapid, a German maglev company with a test track in Emsland, constructed the first operational high-speed conventional maglev railway in the world, the Shanghai Maglev Train from Shanghai, China to the new Shanghai airport at Pudong. It was inaugurated in 2002. The highest speed achieved on the Shanghai track has been 501 km/h (311 mph), over a track length of 30 km. Transrapid uses EMS technology.

Japan has a test track in Yamanashi prefecture where test trains have reached 581 km/h (363 mph), faster than wheeled trains. These trains use superconducting magnets which allow for a larger gap, and repulsive-type "Electro-Dynamic Suspension" (EDS). In comparison Transrapid uses conventional electromagnets and attractive-type "Electro-Magnetic Suspension" (EMS). These "Superconducting Maglev Shinkansen", developed by the Central Japan Railway Co. ("JR Central") and Kawasaki Heavy Industries, are currently the fastest trains in the world, achieving a record speed of 581 km/h on December 2, 2003. If a proposed Chuo Shinkansen is built, connecting Tokyo to Osaka by maglev, this test track would be part of the line.

The world's first commercial automated "Urban Maglev" system commenced operation in March 2005 in Japan. This is the nine-station 8.9 km-long Tobu-kyuryo Line Linimo, otherwise known as the Nagoya East Hill Line. The line has a minimum operating radius of 75 m and a maximum gradient of 6%. The linear-motor magnetic-levitated train has a top speed of 100 km/h. The line serves the local community as well as the Expo 2005 fair site. The trains were designed by the Chubu HSST Development Corporation, which also operates a test track in Nagoya. Urban-type maglev trains patterned after the HSST has been constructed and demonstrated in Korea, and a Korean commercial version is proposed by Rotem.

In the US, the Federal Transit Administration (FTA) Urban Maglev Technology Demonstration program has funded the design of several low-speed urban maglev demonstration projects. It has assessed HSST for the Maryland Department of Transportation and maglev technology for the Colorado Department of Transportation. The FTA has also funded work by General Atomics at California University of Pennsylvania to demonstrate new maglev designs, the MagneMotion M3 and of the Maglev2000 of Florida superconducting EDS system. Other US urban maglev demonstration projects of note are the LEVX in Washington State, the Massachusetts-based Magplane, and a design similar to HSST by American Maglev Technology of Florida at Old Dominion University in Virginia.

On December 31, 2000, the first crewed high-temperature superconducting maglev was tested successfully at Southwest Jiaotong University, Chengdu, China. This system is based on the principle that bulk high-temperature superconductors can be levitated or suspended stably above or below a permanent magnet. The load was over 530 kg and the levitation gap over 20 mm. The system uses liquid nitrogen, which is very cheap, to cool the superconductor.

The first patent for a magnetic levitation train propelled by linear motors was US patent 3,470,828, issued in October 1969 to James R. Powell and Gordon T. Danby. The technology underlying it was invented by Eric Laithwaite, and described by him in "Proceedings of the Institution of Electrical Engineers", vol. 112, 1965, pp. 2361-2375, under the title "Electromagnetic Levitation". Laithwaite patented the linear motor in 1948.

Proposals

UniModal is a proposed personal rapid transit system using Inductrack suspension to achieve average commute speeds of 160 km/h (100 mph) in the city.

China is reported to be considering maglev as a possible technology option for building a planned high-speed rail network to connect major cities, although the cost may make this impractical. A Shanghai-Hangzhou Maglev Train may be in the planning stages.

A maglev line has recently been proposed in the United Kingdom from London to Glasgow with several route options through the Midlands and Northeast, and is reported to be under favourable consideration by the government. [1] [2]

More exotic proposals include maglev lines through vacuum-filled tunnels, where the absence of air resistance would allow extremely high speeds, up to 6000-8000 km/h (4000-5000 mph) according to some sources. Theoretically, these tunnels could be built deep enough to pass under oceans or to use gravity to assist the trains' acceleration. This would likely be prohibitively costly without major advances in tunnelling technology.

References

Heller, Arnie (June 1998). "A New Approach for Magnetically Levitating Trains--and Rockets". {{cite news}}: Unknown parameter |org= ignored (help)

External links

Maglev train companies

These websites contain further information provided by companies building maglev trains (alphabetical order).

General Atomics (USA)
HSST (Japan)
Maglev2000 (USA)
Rotem (Korea)
Transrapid International (Germany)
Ultraspeed (UK; uses Transrapid technology)