Bunching is formed in Magnetron :

• Bunching takes place in magnetron like Klystrons which is known as phase focusing effect. This effect is useful for the favored electron to maintain the phase . Since such electron are retarded at each interaction with RF field.
• Diagram shops the wheel spoke bunches in the cavity magnetron. These bunches rotates counter clockwise with the correct velocity to keep up with RF phase changes between adjoining anode poles.