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Later, it was shown that the oscillation period is equal to the electron transit 

 time from the vicinity of the cathode to the vicinity of the anode and back. 

 This made it possible to calculate a value for the constant in the above 

 equation in good agreement with experiment.'" The oscillation frequency is 

 that of the rotational component of the electronic motion, that is, approxi- 

 mately the cyclotron frequency of equation (7). 



The mechanism must be explained in terms of electrons moving in the DC 

 radial electric and axial magnetic fields and the superposed RF radial elec- 

 tric field. This may be done as follows: An electron leaving the cathode 

 in such phase as to gain energy when moving from the cathode toward the 

 anode will also gain energy during its return, striking the cathode with more 

 energy than it had when it left. There, such an electron is stopped from 

 further motion during which it would continue to absorb energy from the 



Fig. 7. — An approximate orbit of an electron which gains energy from the RF field in 

 a cyclotron frequency or Type II magnetron oscillator, shown for the plane case. The 

 orbit is continued as a dashed line indicating how it would be traversed were it not stopped 

 by the cathode. The DC electric force on the electron is directed from cathode to anode. 



RF field at the expense of the oscillation. The electron will execute an 

 orbit something like that of Fig. 7 for the plane case. An electron leaving 

 the cathode in the opposite phase, on the other hand, loses energy when 

 moving toward the anode and again on its return toward the cathode. As 

 is shown in Fig. 8, it reverses its direction after the first trip without reaching 

 the cathode surface and starts over on a second loop of smaller amplitude, 

 remaining in the same phase and continuing to lose energy to the field. This 

 process continues until all the energy of the rotational component of the 

 electron's motion has been absorbed by the RF field. If the electron is not 

 removed at this stage, in its subsequent motion the rotational component 

 will build up, extracting energy from the RF oscillation. Means such as 

 tilting the magnetic field or placing electrodes at the ends of the tube have 

 been used to remove the electrons from the interaction space when all the 



" K. Okabe, Proc. I.R.E. 17, 652 (1970). 



