the forward travelling wave being utilised

Full Title

Transit-time tubes, e.g. Klystrons, travelling-wave tubes, magnetrons > Travelling-wave tubes; Tubes in which a travelling wave is simulated at spaced gaps > Tubes in which an electron stream interacts with a wave travelling along a delay line or equivalent sequence of impedance elements, and with a magnet system producing an H-field crossing the E-field > the forward travelling wave being utilised