PART II — THE UHF XOLSE SPECTRUM 



865 



the noise-power density is greatest at the rim of the beam so defined, 

 and least near its center. No evidence of azimuthal periodicity was 

 found. The curves of Fig. 7, which are less typical, indicate five distinct 

 peaks of RF power, despite a nearly symmetrical pattern of collector cur- 

 rent. At the time of this measurement, cathode emission may have been 

 uneven, due to coating damage by ion bombardment. 



In the rippled beam on which these measurements were made, the 

 ratio of flux encircled at the cathode, to that in the drift space, was 

 \er3^ small for most electrons. One would, therefore, expect the trans- 

 verse noise-power distribution in this beam to resemble that in a smooth 

 Brillouin beam.^ The noise power expected when a pinhole aperture 

 is located at the beam center can be compared with that when the aper- 



48 



44 



40 



36 



^ 32 

 (J 



UJ 



O 



28 - 



a. 



UJ 

 Q. 



N 



20 



< 



2 



q: 16 



O 



z 



12 



4- 



COLLECTOR CURRENT 

 0.020" DIA IRIS - 



Z = 15.00 INCHES 

 B = 54.8GAUSS 

 Bc=".4 GAUSS 



J_ 



J_ 



_L 



_L 



0.05 O.IO 0.15 0.20 0.25 0.30 035 

 TRANSVERSE IRIS POSITION IN INCHES 



0.24 



0.22 



0.20 



-0.18 



0.16 (o 



LU 



tr 



LU 

 Q. 



0.14 2 



< 



-0.06 



0.04 



0.02 



0.40 



Fig. 7 — Transverse distribution measurements similar to those of Fig. 6. 

 This pattern was obtained a week hiter than that of Fig. 6, and the cathode was 

 operated at a higher temperature. The cyclotron frequency would be 153.2 mc 

 for the field used. 



