Work in full swing in assembling ITER’s giant superconducting magnets

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Japanese energy major Toshiba announced last month that it has completed the manufacture of the first of four toroidal field coils it is supplying to the International Thermonuclear Experimental Reactor (ITER), or the world’s largest nuclear fusion project, currently being assembled at Cadarache in France.  

The ITER machine, the assembly of which began in July last year, is designed to replicate the fusion power of the sun to enable generation of clean unlimited energy, and the first ultra-hot plasma is expected to be generated in late 2025. The world’s largest science project is intended to demonstrate that fusion power can be generated on a commercial scale. 

Toroidal field coils are giant superconducting magnets that will generate the magnetic cage to contain the ITER fusion reactor’s plasma. Nine of ITER’s 18 toroidal field coils are being manufactured in Europe, while the other nine are being made in Japan. Toshiba, which is fabricating four toroidal field coils, together with six coil cases, has now completed making the first coil, which is 16.5 metres (m) in height, 9 m in width and weighs around 300 tonnes. 

“Toshiba ESS will continue to contribute to ITER, which will initiate plasma experiments in 2025, by supplying toroidal field coils and cases, which require highly precise processing technology to produce”, Toshiba director and senior vice president at the company’s Power Systems Division, Shinya Fujitsuka, said in a statement.  

ITER is a partnership composed of the European Union, the UK, Switzerland, China, India, Japan, Korea, Russia and the US. Each partner contributes in-kind hardware to support their share of project construction while sharing all of the science and technology. 

Meanwhile, the first of six superconducting magnet modules for the ITER central solenoid left the General Atomics facility in the US last month for the ITER site in France, according to an ITER (also signifies “The Way” in Latin) statement. 

The central solenoid is at the heart of the ITER “tokamak” (derived from the Russian words for toroidal magnetic confinement). The tokamak, which will produce thermonuclear fusion power, relies on the magnet to propel and shape its plasma stream. It initiates plasma current, as well as drives and shapes the plasma during operation. 

Earlier this year, ITER also announced that the sixth poloidal field coil (PF6) was inserted into the fusion machine’s tokamak pit on April 21. It marked the start of the assembly of ITER’s magnet system. The PF6 coil, which was manufactured by the Institute of Plasma Physics of the Chinese Academy of Sciences, weighs 350 tonnes and has an external diameter of around 11.2 meters, making it the heaviest of ITER’s superconducting magnets. The PF6 lies at the lowest surface level of the six circular magnets surrounding ITER’s vacuum chamber and the first one to be inserted in the tokamak pit. 

Creating the magnetic fields in a tokamak requires three different groups of magnets. External coils around the ring of the tokamak produce the toroidal magnetic field, confining the plasma inside the vessel, while the poloidal coils that orbit the tokamak control the position and shape of the plasma. Instead, the central solenoid in the center of the tokamak uses a pulse of energy to generate a powerful toroidal current in the plasma that flows around the torus. The movement of ions with this current, in turn, creates a second poloidal magnetic field that improves the confinement of the plasma, as well as generating heat for fusion. 

The terms toroidal and poloidal refer to directions relative to a torus of reference. The poloidal direction follows a small circular ring around the surface, while the toroidal direction follows a large circular ring around the torus, encircling the central void. 

Instead, ITER’s smallest poloidal field magnet —PF1— has successfully undergone vacuum pressure resin impregnation at the Sredne-Nevsky Shipyard in St. Petersburg in Russia, according to the Russian state atomic energy corporation Rosatom. 

A Rosatom statement earlier this year said that the 200-tonne poloidal field coil 1 (PF1) is one of six poloidal field coils designed for plasma confinement in the ITER machine. Nine metres in diameter, the magnet is a complex system whose building blocks — 8 double pancakes wound from niobium-titanium cable-in-conduit conductor — have been stacked and joined electrically with over 6 kms of superconductor being used during winding of the PF1. 

ITER’s realising of a self-heating plasma is expected to generate 10 times more heat than is put in. Fusion provides clean, reliable energy without carbon emissions, with minute amounts of fuel and no physical possibility of an accident with meltdown. The fuel for fusion is found in seawater and lithium, while it is abundant enough to supply the world for millions of years. A football-sized amount of this fuel is equivalent to around 10,000 tons of coal. 

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