World's largest nuclear fusion reactor comes online in Japan

JT-60SA produces largest volume of plasma ever made by humans, paves way for ITER

Japan's joint fusion reactor project with the European Union (EU), the JT-60SA, was inaugurated in Naka, Japan on Friday, marking the start of experimental operations for the world's biggest and most advanced tokamak.

Tokamak is an acronym from the Russian тороидальная камера с магнитными катушками which means "toroidal chamber with magnetic coils." When gaseous fuel is introduced into the chamber, the magnetic coils cause it to accelerate to very high speed, at which point the gas is ionized and becomes plasma.

The plasma is then heated to extraordinarily high temperatures (up to 300 million degrees Celsius) which is another reason for the magnetic coils – only powerful magnetic fields can contain plasma that hot.

A video of the event shows a countdown to activation of the tokamak at its inauguration. Upon activation, the plasma current hit one mega ampere. The discharge time was ten seconds and created around 140 cubic meters of plasma – the biggest volume of the super-hot star-like stuff humanity has yet created.

An announcement of the event reiterated that the EU and Japan supported operations and technical upgrades of JT-60SA so that it could continue research that informs the design of future fusion reactors.

The "SA" in the JT-60SA stands for "super advanced" – reflecting the fact it's an upgrade from the JT-60 – now with extra superconducting coils and other hardware.

Construction has been ongoing since 2013, with commencement delayed by a 2011 earthquake that saw a planned 2016 debut pushed back. A short circuit in 2021 required the rework of insulation on over 100 electrical connections and pushed things back even further.

In October 2023, JT-60SA became the largest operational superconducting tokamak in the world when it achieved first plasma.

The extremely high temperatures inside the tokamak could eventually be enough to force the hydrogen particles to overcome their natural electromagnetic resistance, and fuse together to create helium – releasing energy in the form of light and heat. It's a process that mimics the inner workings of the Sun.

Many – from scientists to climate change activists to energy industry professionals – have pinned hopes on using this process to fuel the world, as it is hoped to generate more energy than goes into producing it. Unlike nuclear fission, which splits atoms rather than fusing them, and produces dangerous waste products, fusion is considered clean.

"The generation of fusion energy does not produce carbon dioxide – making it an important technology in the path to net zero emissions. The fusion reaction is intrinsically safe: it stops when the fuel supply or power source is shut down. It generates no high-level long-lived radioactive waste," explained the European Commission's Directorate-General for Energy.

The JT-60SA is one of three fusion-related devices the EU and Japan are collaborating on, which complement the pair's work on the International Thermonuclear Experimental Reactor (ITER) project.

Meanwhile, ITER's main reactor and first plasma are scheduled for 2025. ITER, still under construction in France, will build on the knowledge scientists glean from tests on the JT-60SA. The six-storey tall JT-60SA is about half the planned height of ITER, but its plasmas are expected to closely resemble those produced by its successor. ®

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