Confinement of an electron beam by oscillating electromagnetic fields

It has been shown theoretically that a charged particle can be bound in stable orbits about the axis of a circular wave guide by the fields of the TE 01 mode at cut-off (Weibel, 1959). This result was verified experimentally. The apparatus consists of a 20-cm long section of a circular wave guide - properly terminated - into which is fed radio-frequency power from a magnetron at f = 9.29 kMc/s in 2 μsec pulses. A uniform TE 01 field is excited over the entire 20-cm length of the guide. An electron beam which is injected axially at one end of the cavity diverges strongly due to coulomb repulsion if no radio-frequency power is applied. During the radio-frequency pulse, however, the beam is confined to the axis and 90 per cent of the current is collected by an axial probe of 0.3-cm diameter which is located at the other end of the guide. Between pulses when no radio frequency is applied, no measurable current reaches the probe. In its trajectory from the gun to the probe each electron spends about 170 radio-frequency periods in the focusing field.