The toroidal field magnets surround the tokamak vacuum vessel. (Image Credit: ITER)
ITER is inching closer to going online. Its massive superconducting magnets, required for the reactor core construction, were recently transported to southern France. This concludes the 20-year reactor design process, which extended over three continents.
The ITER deposits hydrogen fuel into a torus (donut shape) to heat it and produce plasma, replicating the sun's conditions. A fusion reaction occurs when the reactor reaches 150 million degrees --- ten times hotter than the sun. Meanwhile, the superconducting magnets keep the plasma within the reactor's walls. Its tokamak uses niobium-tin and niobium-titanium-based magnets. Once electricity energizes the coils, the magnets cool to -516°F, making them superconducting.
These magnets are expected to deploy in three ways — all of which produce an invisible cage holding the plasma. First, 18 D-shaped toroidal magnets form the outer donut shape. The plasma's shape is controlled via a set of six magnets circling the tokamak. A central solenoid uses energy pulses to produce current in the plasma. The reactor's plasma current is expected to peak at 15 million A, setting a new tokamak record. And the magnetic energy of the magnetic field will reach 41 gigajoules.
All the toroidal magnets are 360 tons and measure 17m tall and 9m wide. Fusion for Energy, ITER's European wing, developed ten magnets, and the National Institute for Quantum Science and Technology (QST) in Japan fabricated eight of those coils along with a spare. The first step was manufacturing the conductor. This involved wounding a niobium-tin strand with copper strands, forming a rope-like structure. Then, that structure was placed inside a steel jacket with a central conduit that forced helium to flow.
The 19 toroidal magnets required conductors with over 54,000 miles of niobium-tin strands. Meanwhile, nearly 750m of the conductor had to be bent in a double spiral path and heated to 1,200°F to create the D-shaped magnet. That magnet was placed into a stainless steel D-shaped radial plate. Glass and Kapton tape insulated and wrapped the conductor, which was welded with cover plates, forming a double pancake structure that uses two conductor layers. Afterward, the structure became insulated, and the air pockets were eliminated and injected with resin to improve durability.
They built a winding pack made of seven double pancake structures and connected it, allowing electrical flow. The winding pack underwent insulation, heat treatment, and resin injection. It was placed in a 200-tonne stainless steel case that handles the forces of plasma movement and fusion energy production.
This fusion reactor will produce 500MW of thermal power (peak) and 200MW when connected to the grid.
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