864 



THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1957 



(5) The patterns of microwave noise power resemble blurred envelopes 

 of the UHF traces. 



Some idea of the transverse distributions of UHF noise power and 

 electron-current density, in a region of strong proper-frequency exci- 

 tation, is given in Figs. 6 and 7. The measurements were taken by mov- 

 ing a small aperture in a broad arc through the probe centerline, just 

 in front of the probe aperture. In both illustrations, the relative noise 

 power has been "normalized" to compensate for variations in electron 

 current traversing the RF gap. 



The curves of Fig. 6 are typical of most such measurements. The beam- 

 current density varies smoothly through a single broad maximum, and 



50 



45 



40 



in 



_l 



UJ 



cj 



UJ 



a 



a. 



UJ 



o 



Q- 

 UJ 



35 



30 



25 



^ 20 

 < 



cc 

 o 



2 15 



1 



148.5 MCS POWER 



Z=17.10 INCHES 

 B = 51.30 GAUSS 

 Bc=-90 GAUSS 



0.250 



0.225 



0.200 



0.175 



0.150 



0.125 2 



0.100 



0.075 



0.050 



0.025 



0.05 0.10 0.15 0.20 0.25 0.30 0.35 



TRANSVERSE IRIS POSITION IN INCHES 



0.40 



Fig. 6 — Simultaneous point -by-point measurements of collector current and 

 relative noise power, obtained by moving an 0.013-inch diameter aperture in a 

 broad arc through the probe centerline. The probe is stationary, about 18 inches 

 from the gun anode, and the fields have been adjusted for maximum amplitude of 

 the proper frequency, 148.5 mc. The cyclotron frequency is 143.8 mc. 



