Studying fusion-born alpha particles in the ITER experiment

The ITER fusion experiment is scheduled to begin in the next few years, and when it does, the fusion reactions will need to be monitored and studied with dozens of diagnostic systems.

One of the most important parameters is the dynamics of the high-energy alpha particles born in the fusion plasma. The energy from these particles, redistributed to the rest of the plasma, sustains the fusion reaction and creates an energy surplus.

Korsholm et al. designed a Collective Thomson Scattering (CTS) diagnostic for the ITER plasma to detect these alpha particles. The diagnostic will work by scattering a gyrotron beam off fluctuations in the fusion plasma. It will be sensitive to alpha particles with energies between 300 keV and 3.5 MeV and other types of fast ions.

“We have designed, installed, and operated CTS diagnostics on a number of current fusion devices, but making an incarnation for ITER was a completely different story,” said author Søren Korsholm. “It requires solutions to challenges not seen in current fusion experiments.”

Because ITER is designed to be the largest tokamak reactor ever built, the plasma temperature, magnetic field strength, and neutron radiation are more intense.

For example, the CTS could have failure modes that are far more consequential for ITER than on smaller devices. The probe beam frequency is optimized for performance but has a resonance near the launch location that could cause component damage and stop ITER operations. To mitigate this, the authors used a split waveguide with electrically biased halves, so electrons will not accumulate and cause a damaging ionization cascade.

Now that the design is finalized, the researchers will support the ITER team as they construct and install their diagnostic.

Source: “ITER Collective Thomson Scattering - Preparing to diagnose fusion-born alpha particles,” by S. B. Korsholm, A. Chambon, B. Gonçalves, V. Infante, T. Jensen, M. Jessen, E. B. Klinkby, A. W. Larsen, R. Luís, Y. Nietiadi, E. Nonbøl, J. Rasmussen, D. Rechena, M. Salewski, A. Taormina, A. Vale, P. Varela, L. Sánchez-García, R. M. Ballester, V. Udintsev, and Y. Liu, Review of Scientific Instruments (2022). The article can be accessed at https://doi.org/10.1063/5.0101867 .

This paper is part of the Proceedings of the 24th Topical Conference on High-Temperature Plasma Diagnostics Collection, learn more here .