RF heating is the family of radio-frequency and microwave techniques for heating 📝plasma and driving current.
The family's shared principle is resonance. A magnetized plasma rings at characteristic frequencies — the gyration of its ions, the gyration of its electrons, and hybrid resonances between them — and a wave launched at one of those frequencies transfers its energy to the matching particle population. Each resonance defines a member of the family: 📝ion cyclotron resonance heating (ICRH) at tens of megahertz, 📝lower hybrid current drive in the gigahertz range, and 📝electron cyclotron resonance heating (ECRH) at more than 100 gigahertz. The choice of frequency selects not just the hardware — antennas, waveguide grills, or 📝gyrotron-fed mirrors — but which particles get the power and where in the plasma it lands.
RF heating is one of the two great routes of auxiliary power, distinguished from 📝neutral beam injection (NBI) by its currency: waves rather than particles. Waves add no fuel, momentum, or fast particles of their own, couple through structures that can sit behind the 📝first wall, and can deposit power with surgical localization — which is why the same systems that heat a plasma also drive current, control instabilities, and assist startup. Nearly every magnetic confinement machine fields at least one RF system, and some, by design, rely on RF heating alone.