Designing Diagnostics for ITER: At the Crossroad between a Scientific Facility and a Fusion Power Plant
Abstract: Driven by an accelerating need for global energy decarbonisation, the technological development of fusion energy is poised to enter a new era. ITER is leading the way toward fusion energy production. As the world’s largest tokamak, the device is a major step up in scale and power from present fusion research facilities. ITER will ultimately achieve a tenfold energy gain in the plasma, resulting in 500 MW of fusion power sustained over long pulse durations of up to 500 s. ITER is a research facility; however, because of the significant fusion output, it is also the first tokamak constructed and managed as a nuclear fusion reactor under regulatory oversight. ITER’s scientific and technological research program will validate plasma scenarios and control schemes relevant to future fusion power plants in addition to numerous technologies, including an extensive set of diagnostics.
The diagnostic systems installed on ITER will deliver more than a hundred measurement parameters for physics, control, machine protection, and to ensure ITER compliance with nuclear regulatory requirements. Amongst these parameters are the plasma current and confinement, the electron density profile, radiated powers, impurities, fuelling ratios and neutron flux. The measurements must be highly reliable, in particular for those parameters with control and machine protection roles. As will be presented, this is addressed by having, as much as possible, a minimum of two complementary diagnostics for every measurement parameter.
Many diagnostic techniques on ITER have been successfully demonstrated and perfected on previous tokamaks; however, the implementation of each technique on ITER comes with added challenges due to the harsh nuclear environment. The overall integration of these systems into ITER’s 26 diagnostic ports must also be carefully coordinated in order to ensure safe access to the areas intended for hands-on maintenance and local operations. Near and inside the vacuum vessel, where human access will not be permitted, maintenance and inspection tasks will be performed remotely. For example, calibration of optical and neutron diagnostics will rely on a dedicated remote handling apparatus.
ITER is headed to initial nuclear operations in the early 2030s. Construction is already well in motion, with many diagnostic components installed with the design and manufacture of others strongly advancing. Operations will progressively ramp up from low fusion power D-D reactions before reaching 500 MW of D-T fusion power. Measurement and control of fusion power will be paramount to achieving high fusion performance, as well as machine protection and nuclear safety. For this, neutron diagnostics providing the fusion power measurements are designed to be sensitive to neutron emissions spanning multiple orders of magnitude. Ultimately, ITER will break into burning plasma regimes as yet unexplored in tokamaks where plasma heating is dominated by energetic alpha particles. Characterization of such conditions motivated a comprehensive set of diagnostics that will be outlined in the presentation.