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May 09, 2023

Advancing fusion energy: Researchers achieve record

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Nuclear fusion reactions generate large amounts of energy. An example of nuclear fusion is the reactions happening in the sun's core. Harnessing fusion energy has long been a goal of scientists and researchers as it produces no greenhouse gas emissions or long-lived radioactive waste.

However, there are several bottlenecks to producing fusion energy, such as the requirement of high temperatures and pressures, plasma instability, cost, scalability, and finding energy balance.

Despite these challenges, significant progress has been made in fusion energy research.

Tokamaks are a device used in magnetic confinement fusion. In these reactions, a powerful magnetic field is used to control and confine the hot plasma of the fusion fuel in the reactor core. The plasma is heated to high temperatures using neutral beam injection or radiofrequency heating. The main goal is to sustain a stable plasma state where the fusion reactions can occur continuously, providing a limitless energy source.

A recent study by researchers from Oak Ridge National Laboratory (ORNL), Princeton Plasma Physics Laboratory (PPPL), and Tokamak Energy Ltd shows a significant breakthrough in fusion energy research. The team has achieved temperatures of nearly 100 million degrees Celsius, required for fusion power plants to generate commercial energy.

Additionally, they achieved high temperatures in a compact tokamak, which has not been done before!

In this study, the researchers focused on refining the operating conditions of a high-field spherical tokamak (ST) device called the ST40. Compared to other fusion devices, the ST40 device stands out due to its smaller size and its spherical plasma.

The team used an approach similar to the one in the 1990s in the TFTR tokamak, which generated over 10 million watts of fusion power. ST40 was operated with a toroidal (doughnut-shaped) magnetic field at values slightly above 2 Tesla.

The team used 1.8 million watts of high-energy neutral particles to heat the plasma. Though the plasma discharge, or the period when the fusion reactions were actively taking place, was just 0.15 seconds, the ion temperatures in the core reached more than 100 million degrees Celsius.

The team used the TRANSP transport code developed at PPPL to measure the ion temperatures. This code is helpful because it takes into account the measured temperature profiles of the impurities and deuterium, the primary fuel used in fusion reactors.

They found that the temperature range for the impurities was higher than 8.6 keV (approximately 100 million degrees Celsius), whereas the temperature range for deuterium was around that value. This finding suggests that the heating method used in the experiment effectively achieved the desired high temperatures.

The results provide optimism for the future development of fusion power plants based on compact high-field spherical tokamaks. These advancements could lead to more efficient and economically viable fusion energy solutions, offering a promising avenue for sustainable and clean energy generation.

The study was published in the journal Nuclear Fusion.

Study abstract:

Ion temperatures of over 100 million degrees Kelvin (8.6 keV) have been produced in the ST40 compact high-field spherical tokamak (ST). Ion temperatures in excess of 5 keV have not previously been reached in any ST and have only been obtained in much larger devices with substantially more plasma heating power. The corresponding fusion triple product is calculated to be ni0Ti0τE≈6±2 x 1018 m-3 keVs. These results demonstrate for the first time that ion temperatures relevant for commercial magnetic confinement fusion can be obtained in a compact high-field ST and bode well for fusion power plants based on the high-field ST.