The Magnetron

Author: J.B. Hoag

Fig. 38 D. A magnetron

Figure 38 D shows a magnetron tube. This consists of a cylindrical plate and axial filament in a highly evacuated tube, located between the poles of a strong magnet. The filament, the plate, and the magnetic lines of force are all in the same direction. In the absence of the magnetic field, electrons from the filament travel outward to the plate, radially like the spokes of a wheel. With a small magnetic field, the electron paths are curved. At a critical field strength, the electrons just miss the plate. At this point the plate current i suddenly drops to zero. This cutoff is indicated at H_c in Fig. 38 E.

Fig. 38 E. Plate current i of a magnetron as the magnetic field strength H is changed