Nuclear Fusion Breakthrough with a Tokamak: 17 Minutes

The only way to solve the world’s power problems

I’m a great supporter of the proposition that nuclear fusion energy should be a critical component of the world’s future power generation strategy. Recent advances bring the realisation closer.

There are several technical approaches to solving the huge problem of safely creating a plasma hotter than the core of the sun and harnessing the vast energy derived from fusing hydrogen atoms. It’s been called ‘taming the fusion bomb’ and that’s not very far from the reality.

Differing experimental approaches

Here’s a quick summary of the main experimental approaches:

• In December 2022, the US National Ignition Facility at the Lawrence Livermore Laboratory in Berkeley announced a huge step forward with a net energy gain in their set up. 192 synchronised high power lasers inject energy into a gold encased pellet of deuterium and tritium the size of a ball bearing held within a thimble-sized ‘hohlraum’. The set-up NIF produced 3.15 megajoules (MJ) of fusion energy output using 2.05 MJ of laser energy delivered to the target, demonstrating the fundamental science basis for inertial fusion energy. This ignition was over a very short period of time (milliseconds) and sustainability is a major challenge.

• Torus/Tokomak: There are several experimental constructions around the world, including JET in Europe, in the US, Russia and China. The Tokamak concept uses superconducting magnets to confine plasma in the shape of a torus. These magnets generate a strong magnetic field that keeps the plasma from touching the walls of the tokamak, allowing it to reach the high temperatures and pressures necessary for fusion.

There are other novel approaches as well, but on a much smaller (and less cash-demanding) scale, such as First Light Fusion in Oxford, UK, which I wrote about some months ago.

Major issues

The problem of maintaining a sustained reaction to enable realistic peaceful power generation is considerable.

The NIF hohlraum approach will require fuel replenishment cycles, something which the First Light approach addresses head on.

The EAST Tokomak experiment in China seems to be making great progress, having managed to sustain the plasma for 1000 seconds — that’s a huge 17 minutes.

These Tokomak constructs are ‘programmable’ in a broad sense and can be operated in several ‘modes’. It’s the discovery of the Super I-Mode that has generated a lot of scientific excitement.

Super I-mode Tokomak operation

The “super I-mode” was first discovered at the Hefei-based Experimental Advanced Superconducting Tokamak (EAST) reactor during a record-breaking 17-minute operation in December 2021, but it’s only now that the results have completed peer review and publication in Science Advances.

The EAST experiment

The above picture is an internal view. The whole chamber is about 2 metres in diameter, and when running the system consumes 7.5 MegaWatts, generating a plasma current of 1 MegaAmps. It’s very hot: 100 x 10⁶ Kelvin is required.

The super I-mode is a significant advancement in the field of magnetic confinement fusion because it has the potential to significantly increase the efficiency of the tokamak. The super I-mode is able to maintain high plasma pressure and temperature for longer periods of time, which could lead to higher rates of fusion reactions.

In order to achieve the super I-mode, the EAST team used a combination of advanced heating methods, such as neutral beam injection and radio frequency heating. They also optimised the shape of the plasma and the magnetic field to achieve the high confinement regime.

The EAST team also observed that the super I-mode is robust and can be sustained for long periods of time, even in the presence of disruptions. This is important because disruptions can cause the plasma to lose energy and cool down, which could lead to a loss of fusion reactions.

The EAST experiment has made significant progress in the field of magnetic confinement fusion and has demonstrated the feasibility of sustained nuclear fusion reactions. The observation of the super I-mode is a major achievement that has the potential to significantly increase the efficiency of tokamaks and bring us closer to the goal of practical fusion energy.

Conclusions

The realisation of peaceful nuclear fusion power has been fifty years away for the last eighty years. It’s still fifty years away, but I do believe that you will see it before 2075. Pity I’ll miss it — unless huge strides are also made in anti-aging medicine as well as nuclear fusion.

It’s clear to me that real advances have been made. Ten years ago the idea that a plasma could be maintained for 17 minutes was beyond belief.

I’m wondering now how many of the other Tokomak projects can be run in Super I-mode. It surely can’t be that simple can it?

The peer-reviewed paper is at Science Advances.

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Canonical link: this story was first published in Medium on 2 February 2023