Fifty Years of Progress in ICRF, From First Experiments on the Model C Stellarator to the Design of an ICRF System for DEMO

We present a comprehensive overview of the use of ICRF (ion cyclotron range of frequency) scheme from its beginnings, with specific attention paid to the progress that has been achieved on the understanding of the interaction between the plasma edge and the ICRF heating. The developments and the progress made in overcoming the challenges faced are emphasized. We also describe, based on personal experiences, some of the dead-end roads, the sound deductions that sometimes were prematurely discarded or the intuitive conclusions that were later confirmed by more experimental data. We end with a vision for the future.