40 years of ICRF Physics on the JET Tokamak: Highlights and Lessons Learned for Future Facilities

During its 40-year operational period (1983–2023), the Joint European Torus (JET) made significant contributions to the advancement of knowledge in the field of ion cyclotron range of frequencies (ICRF) physics in magnetically confined plasmas. The unique combination of large size, flexible auxiliary systems, and tritium-handling capabilities of JET provided an unparalleled environment for reactor-relevant investigations. The studies furthered the understanding of wave-particle interactions and fast ion dynamics. Furthermore, they explored the interplay between ICRF heating and key plasma phenomena, including current drive, rotation, and impurity transport. Notable achievements included the stabilisation of sawtooth oscillations, the characterisation of alpha-like fast ion behaviour, and the development of impurity control strategies. These achievements contributed to the validation of advanced ICRF heating schemes. Collectively, the results offer valuable lessons that directly inform the design and operation of ITER and other next-generation fusion devices.