Radio Frequency Heating of Plasmas Using Compressional Alfvén Waves

Two factors favor the use of relatively low frequencies (below a few megahertz) for heating large fusion plasmas. The first is that supplying the necessary few hundred megawatts of radio frequency power is already within current technological possibilities. The second is the exploitation of well-separated resonances of Alfvén waves inside the plasma-filled reactor cavity to greatly simplify the antenna structure. The large minor radius and high plasma density in TFTR-class and reactor tokamaks will accommodate fast-wave toroidal eigenmodes at frequencies which are well below all the cyclotron frequencies of ions of the fuel gas and of most impurities (carbon, oxygen, iron). Electron transit-time magnetic pumping and Landau damping provide adequate absorption mechanisms, but care is necessary to achieve RF power deposition deep inside the plasma.