Electron Resonance

netron so that the magnetic field is parallel with the axis of the cathode. The cathode is mounted in the center of the interaction space. The direction of an electric field is from the positive electrode to the negative electrode. The law governing the motion of an electron in an electric (E) field states that the force exerted by an electric field on an electron is proportional to the strength of the field. Electrons tend to move from a point of negative potential toward a positive potential. In other words, electrons tend to move against the E field. When an electron is being accelerated by an E field, energy is taken from the field by the electrons. The law of motion of an electron in a magnetic (H) field states that the force exerted on an electron in a magnetic field is at right angles to both the field and the path of the electron. The direction of the force is such that the electron trajectories are clockwise when viewed in the direction of the magnetic field. Magnetron oscillators are divided into two classes: negative resistance and electron resonance. . Negative Resistance: A negative resistance magnetron oscillator operates by a static negative resistance between its electrodes and has a frequency equal to the natural period of the tuned circuit con- nected to the tube. The split-anode negative resistance magnetron is a variation of the basic magnetron, which operates at a higher frequency and is capable of more output. . Electron Resonance: An electron resonance magnetron oscillator operates by the electron transit- time characteristics of an electron tube (the time it takes electrons to travel from the cathode to the plate). It is capable of generating very large peak-power out- puts at frequencies in the thousands of megahertz. The electron resonance magnetron is most widely used for microwave frequencies. Modern designs have a reasonably high efficiency and relatively high output. However, one disadvantage of the electron resonance magnetron is that its average power is limited by the cathode emission. Furthermore, the peak power is limited by the maximum voltage that it can withstand without damage. The operation, coupling methods, tuning, and seasoning of magnetrons are discussed in the fol- lowing subsections. Since this information is general in nature, the recommended times and PMS proce- dures in equipment technical manuals should be followed when baking-in a specific type of magne- tron. Figure 2-7 shows a magnetron. Figure 2-7.—Magnetron. 2-10