2. Magnetrons

2.1 Operating principle

• Magnetrons are an old invention (in 1922, Albert W. Hull, an engineer at General Electric), which became established towards the end of the 1930s with the development of the first radars, notably in Great Britain. Hull started with a ring-shaped diode, with the cathode in the center. Between cathode and anode, a voltage V _k created by an electrostatic field E generates a radial current of electrons. Hull applied a homogeneous magnetic field B perpendicular to the plane of the diode in the zone separating cathode and anode: in its presence, electrons adopt a circular motion. Above a certain value B _hull , they are prevented from reaching the anode...