Space Charge as Noise Generator

The oldest of a family of crossed-field microwave electron tubes wherein electrons, generated from a heated cathode, move under the combined force of a radial electric field and an axial magnetic field. By its structure a magnetron causes moving electrons to interact synchronously with travelling-wave components of a microwave standing-wave pattern in such a manner that electron potential energy is converted to microwave energy with high efficiency. Motion of the rotating swarm of electrons past the surface of the concentricanode microwave circuit induces a noise current in the copper circuit. This noise shock excites the resonators so that microwave fields build up at the resonant frequency. Space charge of either positive or negative sign can influence the paths of electrons. Space charge of positive sign is formed by electron beams passing through an imperfectly evacuated space. The beam electrons collide with gas atoms and ionize them. The heavy ions remain in the path of the electron beams for some time and prevent it from spreading. It is well known the spacecharge flow is closing itself inside crossed-field systems. Thus in closed space charge flows it can exist or excite electromagnetic oscillations. These oscillations don't connect with resonant structures of crossed-field systems. On the other hand the space charge flow may be described both Brillouin single stream state and two stream one. These states are instability and must transform to stability which consist of oscillation states. Such oscillation states have frequencies which don't connect with oscillations of resonant system and may be influence output or modulate base oscillations in crossed-field systems. Here we had studied both theoretically and experimentally the excitation of space-charge oscillations and their interactions with other oscillations in crossed-field systems. It is found both theoretically and experimentally radial and azimuth space-charge oscillations. These oscillations interacting with other oscillations existing in crossed-field devices (magnetrons, amplitrons etc.) such as ion oscillations and base oscillations were changed output spectrum. The space charge oscillations stretches from some dozen megahertzes to some gigahertzes.