Small fusion experiment hits temperatures hotter than the sun’s core

The researchers used an approach similar to past “supershots”.


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Future fusion power plants must reach 100 million degrees Celsius temperatures to produce commercial energy. To do so, the plasma must be controlled carefully. This work improved operating parameters for the ST40 tiny spherical tokamak device to reach the required temperatures.

Unlike other fusion devices, this one is distinct because it is smaller and has more spherical plasma. To arrive at these results, the researchers employed a strategy similar to previous “supershots” that generated more than 10 million watts of fusion power in the TFTR tokamak in the 1990s.

For the first time, a compact, high magnetic field, spherical tokamak, was used to demonstrate ion temperatures relevant to fusion. This proves that the spherical tokamak can meet one need for practical fusion energy production. These findings suggest similar fusion pilot plants may produce more compact and cost-effective fusion power sources than alternative arrangements.

Researchers from the Princeton Plasma Physics Laboratory (PPPL), Oak Ridge National Laboratory (ORNL), and Tokamak Energy Ltd. collaborated to create operational scenarios and analysis techniques under a groundbreaking Collaborative Research and Development Agreement (CRADA).

In a privately constructed experimental fusion facility, their experiments have shown that high ion temperatures important to fusion may be achieved. Researchers from PPPL and ORNL have actively contributed to the operation and data analysis of the ST40 device to reach the plasma temperatures necessary for commercial fusion energy.

In the study, ST40 plasmas were heated by 1.8 million watts of high-energy neutral particles while operating at toroidal magnetic field values of little over 2 Telsa—the ST40 plasma discharges produced ions with temperatures over 100 million degrees Celsius, lasting only 150 milliseconds.

The researchers used the TRANSP transport code created at PPPL to calculate the ion temperature of the primary species deuterium based on the ranges of impurity temperature profiles that were recorded. These profiles demonstrate that the impurity ion temperature range is far over 8.6 keV (100 million degrees Celsius) and that the deuterium temperature range is close to 8.6 keV (shown in magenta in the image above).

Journal References:

  1. McNamara, S.A.M., et al., Achievement of ion temperatures over 100 million degrees Kelvin in the compact high-field spherical tokamak ST40. Nuclear Fusion 63, 054002 (2023). [DOI: 10.1088/1741-4326/acbec8]
  2. Bell, M.G., et al., Overview of TFTR Results. Nuclear Fusion 35, 1429 (1995). [DOI 10.1088/0029-5515/35/12/I02]