Mode Conversion (MC) heating and current drive using waves in the Ion Cyclotron Range of Frequencies (ICRF) have several attractive reactor-relevant applications. These include on-axis and off-axis electron heating and current drive [1,2], MHD activity control [2], sheared poloidal flow drive and synergism with lower hybrid waves for enhanced current drive [3,4]. They have motivated recent experiments on JET to study MC using the 3He minority ICRF heating scenario in D and 4He plasmas. In these experiments, the 3He concentration was increased systematically to investigate the transition from the 3He minority heating regime to the MC regime.