858 



THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1957 



400 



350 



300 



a 



z 

 o 

 o 

 iJJ 250 



a. 



o 



o 200 

 < 



z 



UJ 



a 



LU 



150 



100 



Z= 15.00", 0.100" DIA APERTURE, 

 OB READINGS NOT NORMALIZED. 



RIPPLE 

 WAVELENGTHS, 

 N = 4 



BELOW 08 



30 DB 

 BELOW DB 



CYCLOTRON 

 FREQUENCY 



N = 2 



40 DB 



, PLASMA 

 FREQUENCY 



40 60 80 too 



FOCUSING FIELD IN GAUSS 



20 



140 



Fig. 1 — Frequencies and amplitudes of several narrow-band UHF peaks 

 measured at a fixed probe position, about 16 inches from the gun anode. N is the 

 number of beam-ripple wave-lengths between anode and probe. Other peaks have 

 been observed at higher harmonics of the "proper" frequency (encircled points), 

 and at about half that frequenc}'. 



As shown by the encircled points in Fig. 1, these frequencies range be- 

 tween 1.03 and 1.06 times the calculated cj^clotron frequency, and have 

 amplitudes as high as 65 db above the background noise. The amplitudes 

 decrease with increasing ^V, falling off as the minus two-thirds power of 

 the frequency. 



